Coevolution occurs when two (or more) species influence each other’s evolution. In this session, we look at coevolution in several diverse systems. Dr. McFall-Ngai begins with an overview of different types of symbiosis, including the important interactions between hosts and their beneficial microbes. Dr. Estes studies the coevolution of sea otters, sea urchins and kelp. Using historic records, he has been able to show the impact of human over-hunting of otters on an entire ecosystem. In the last video, Dr. Baldwin describes the amazingly intertwined lives of the Nicotiana attenuata plant and the Manduca sexta moth. In a fascinating twist, defensive toxins produced by the plant to prevent predation by the M. sexta caterpillar, may in fact protect the caterpillar from predation by a spider.
All Course Materials for this Session (Educators only)
00:00:08.00 My name is Margaret McFall-Ngai
00:00:09.14 and I'm a professor
00:00:11.14 and the Director of the Pacific Biosciences Research Center,
00:00:13.14 School of Ocean and Earth Science and Technology,
00:00:16.07 the University of Hawaii at Manoa.
00:00:18.12 I'd like to start my lecture here
00:00:19.28 with thanking the iBiology team
00:00:21.22 for this opportunity to speak to you today
00:00:24.24 about the field of symbiosis.
00:00:27.12 So, the field of symbiosis is about living together
00:00:29.22 -- it's host-microbial interactions
00:00:32.15 that I will be talking about specifically today.
00:00:34.27 And there's a bit of a revolution in biology.
00:00:38.23 Symbiosis and host-microbial interactions
00:00:41.09 are taking center stage in biology.
00:00:46.11 And I'm going to talk to you today about why this is happening now
00:00:49.04 and exactly why we're sort of in the center of a revolution.
00:00:52.09 So, I'm going to start by talking about
00:00:54.20 the words that we use to describe symbiosis.
00:00:57.11 So, this person right here is
00:00:59.29 Heinrich Anton de Bary
00:01:02.16 and this particular person
00:01:04.25 lived in the 19th century,
00:01:07.04 and at the end of the 19th century
00:01:08.15 he coined the term symbiosis.
00:01:11.21 And the definition that he gave to this term
00:01:13.24 was the living together of unlike organisms.
00:01:16.23 And this particular definition of symbiosis
00:01:21.00 has remained with the field
00:01:22.19 until the present day
00:01:24.20 -- it's a very, very, very general way,
00:01:27.18 but very useful way
00:01:29.24 to think about this particular phenomenon in biology.
00:01:34.00 So, that said,
00:01:37.07 symbiosis is a bit of a catch-all term
00:01:39.05 with no information
00:01:40.19 concerning the effect of fitness.
00:01:42.22 So, what I'm showing up here is
00:01:45.06 I'm showing a very classic symbiosis
00:01:46.21 that a lot of people know of
00:01:49.28 and a lot of people think about,
00:01:51.18 and this is the symbiosis between
00:01:53.09 a clownfish and an anemone,
00:01:55.08 and they live together, persistently,
00:01:57.19 for much of their lives,
00:01:59.07 and it's a classic symbiosis
00:02:01.27 that you can think about.
00:02:03.00 But like I said, the word itself
00:02:05.05 confers no... no...
00:02:09.22 it's a catch-all word with no information
00:02:11.22 concerning the effect on the fitness
00:02:13.19 of either partner.
00:02:14.28 And so first I want to describe
00:02:17.18 what fitness means.
00:02:18.20 So, fitness is an individual's reproductive success,
00:02:23.10 and that is the number of offspring
00:02:25.10 that an individual leaves to the next generation.
00:02:28.06 And so let's think about this idea
00:02:32.14 in terms of symbiosis.
00:02:33.23 So, when we talk about fitness,
00:02:35.23 when we're talking about symbiosis,
00:02:37.14 I think there are...
00:02:39.02 I'm going to consider that there are two partners
00:02:41.03 -- there's symbiont #1 and symbiont #2 --
00:02:42.17 and in a mutualism,
00:02:44.25 which is one of the types of symbiosis,
00:02:46.17 both partners will benefit,
00:02:49.12 and what that means is that both partners
00:02:51.07 will have more in the successive generations
00:02:57.02 from being a partner with the other.
00:02:58.11 And so in the case of the clownfish
00:03:00.17 and the anemone,
00:03:02.03 the clownfish gets a very safe place to live,
00:03:04.07 because the tentacles of the anemone
00:03:06.03 are harmful to other animals;
00:03:07.20 the fish, the clownfish,
00:03:10.28 has learned ways to avoid the danger
00:03:13.08 of living in the tentacles of this anemone;
00:03:15.23 and the anemone gains from having the fish there
00:03:20.25 because the fish releases ammonia
00:03:22.17 that is taken up by the anemone
00:03:24.16 and it's used in the energy production
00:03:28.01 of the anemone.
00:03:30.27 So, this is a true mutualism.
00:03:32.24 The next type of symbiosis I'm going to consider is commensalism.
00:03:36.13 In a commensalism,
00:03:38.14 one partner benefits and one partner is unharmed
00:03:41.19 -- there's no change in the fitness,
00:03:43.25 no change in the reproductive fitness.
00:03:46.29 So, what I'm showing here
00:03:48.25 is another example and this example, here,
00:03:51.05 is the shark/pilot fish example,
00:03:54.21 and in this particular case
00:03:58.15 what happens is is
00:04:01.25 the shark is a messy eater
00:04:03.21 and he eats fish and all sorts of various things
00:04:07.11 and food is released around him
00:04:10.20 and the pilot fish that are associating with the shark
00:04:14.24 take advantage of the fact that the shark is a messy eater.
00:04:18.22 In this case, the pilot fish
00:04:22.01 gained from living with the shark,
00:04:23.12 but it seems to have no effect on the shark.
00:04:26.02 And so in this case, it's very likely that
00:04:28.07 the pilot fish will leave more to the next generation
00:04:30.07 from living with the shark,
00:04:32.10 but the shark...
00:04:34.05 it won't affect the shark's fitness whatsoever.
00:04:36.05 The third example that I'm going to give
00:04:38.28 is the example of parasitism.
00:04:40.26 So, these are the three major types of symbiosis,
00:04:42.27 and in parasitism what happens is
00:04:46.15 one partner benefits and one partner is harmed.
00:04:48.22 So, I'm showing down here a tree,
00:04:51.10 and this particular tree trunk
00:04:53.28 has a large gall on it,
00:04:56.07 and the large gall is present
00:04:59.19 because there is a pathogen that is living,
00:05:05.00 a microbial pathogen is living inside this gall
00:05:06.04 and has created this large gall on this tree.
00:05:11.00 Now, the pathogen, that microorganism that's living in that gall,
00:05:14.06 benefits from living...
00:05:15.23 from parasitizing this tree.
00:05:17.29 The tree on the other hand
00:05:19.25 is harmed by this association,
00:05:21.10 so this is a classic parasitism.
00:05:23.24 So, one of the things I should mention is that
00:05:26.05 as the field has grown,
00:05:27.26 there's a little bit of misuse of these terms,
00:05:32.04 and this is one of the reasons
00:05:34.11 why I wanted to bring this up.
00:05:35.25 The term commensalism
00:05:38.22 is often used by the biomedical community,
00:05:40.13 in my mind and the mind of a lot of people who study symbiosis,
00:05:45.07 And what they'll say is that
00:05:48.29 the microbes in your gut,
00:05:50.14 which I'm going to talk about a little bit...
00:05:51.24 the microbes in your gut are commensal,
00:05:54.11 and what this means is that
00:05:56.19 they have no effect on the host
00:05:58.24 -- they're benefiting but have no effect on the host.
00:06:01.14 But now we know that
00:06:03.29 they have a tremendous effect on the host
00:06:05.22 and are very often very important for our health,
00:06:10.01 and beneficial.
00:06:11.14 There are some in there that are likely commensal,
00:06:12.25 there are some in there that are likely
00:06:15.01 budding pathogens,
00:06:16.17 there are some in there that are likely,
00:06:18.00 or many in there, that are likely mutualists,
00:06:19.25 but we really can't categorize them,
00:06:22.14 so the very best thing to do in the instance
00:06:25.04 where you really don't understand
00:06:27.07 what type of symbiosis it is
00:06:29.19 is to just call it a symbiosis
00:06:31.19 and to call the partners a symbiont.
00:06:34.11 So, let's consider for a second
00:06:37.13 host-microbe symbioses.
00:06:38.29 So, what we're talking about is we're talking about
00:06:41.11 viruses, bacteria, protists
00:06:43.13 -- or single-celled eukaryotic cells --
00:06:45.02 and fungi, living with animals and plants, basically.
00:06:48.18 So, the question is,
00:06:51.02 is this a rarity?
00:06:52.21 And I have to say that when I started my career
00:06:54.09 working in this field,
00:06:56.23 back in the early 1980s,
00:06:58.12 this was considered a very unusual feature of symbiosis...
00:07:02.20 symbiosis was considered an unusual feature
00:07:04.19 in the biological world.
00:07:06.16 And in fact, if you look at a textbook,
00:07:09.03 even today,
00:07:11.00 you will see that symbiosis is covered,
00:07:13.16 but it's covered in only a few pages
00:07:15.10 of a 1200-page textbook.
00:07:17.13 It was and is today still considered a rarity,
00:07:20.15 but I hope you convince you that
00:07:23.00 it's not a rarity at all.
00:07:24.26 But why was it considered a rarity?
00:07:26.26 Well, we would find it...
00:07:28.29 historically, we were looking at
00:07:31.01 unusual situations in things like
00:07:34.14 the hydrothermal vent symbioses in the deep sea.
00:07:38.10 Down at 2000 meters, you know,
00:07:39.21 you see these smokers down at 2000 meters,
00:07:42.01 and these particular smokers
00:07:44.11 would have associated with them
00:07:46.16 these very large tube worms,
00:07:49.00 and these large tube worms
00:07:51.01 had in association with them,
00:07:53.29 bacteria, and these bacteria
00:07:55.28 allowed these particular tube worms
00:07:57.27 to live on the chemical energy
00:08:00.12 that was provided.
00:08:02.02 So that was a true symbiosis
00:08:04.16 that's been studied by lots and lots of people.
00:08:10.01 Bioluminescence is another kind of symbiosis
00:08:14.13 and very many organisms who are bioluminescent,
00:08:17.16 not all, but many organisms that are bioluminescent,
00:08:20.05 are bioluminescent because they harbor
00:08:22.18 luminous bacteria in association with the organism.
00:08:27.04 So, in the case of this anglerfish,
00:08:28.12 up here in the angle
00:08:30.15 is a pure culture of a particular bacterial species,
00:08:33.26 and that allows the anglerfish
00:08:36.21 to use that light in its predation.
00:08:40.09 And then, lastly,
00:08:42.10 I'm going to give the example of coral reefs.
00:08:44.24 Coral reefs would not form
00:08:47.04 if they did not have a very...
00:08:49.17 a mutualistic symbiosis
00:08:51.04 with a unicellular organism called
00:08:55.06 And these zooxanthellae live inside of the cells of corals
00:08:58.03 and they provide them with the photosynthate.
00:09:00.29 So, these zooxanthellae
00:09:06.03 are capable of photosynthesis
00:09:08.00 and they translocate the photosynthate to the host.
00:09:10.26 And so the zooxanthellae get a place to live
00:09:14.02 and the host coral is given the photosynthate,
00:09:18.27 and so they both benefit.
00:09:20.07 So, in all the cases I'm showing on this slide,
00:09:22.13 these are mutualistic symbioses,
00:09:24.26 and they're ones that have been
00:09:28.05 studied for over 100 years...
00:09:31.18 actually, not this one,
00:09:33.00 this one they discovered in the late 1970s,
00:09:34.10 but the many, many symbioses
00:09:36.07 that are mutualistic like this,
00:09:38.05 and kind of unusual,
00:09:39.21 have been studied for decades.
00:09:41.12 But now we're finding out that
00:09:43.13 nearly all animals and plants
00:09:45.20 are likely to have beneficial symbioses.
00:09:47.28 So, this is a whole new area,
00:09:51.27 this is a whole new finding,
00:09:53.17 and this new information
00:09:56.23 is from the last two decades of work.
00:09:58.29 And so I'm just showing
00:10:01.25 a whole array of animals
00:10:04.00 that are now known to have
00:10:05.27 beneficial symbioses with microbes.
00:10:10.29 So, I want to just take one minute
00:10:13.10 to pay tribute to what I...
00:10:15.22 the person who I consider
00:10:17.23 the mother of the field of symbiosis,
00:10:19.22 and this is Lynn Margulis.
00:10:21.07 And Lynn Margulis lived 1938-2011,
00:10:23.27 and she was the person
00:10:26.12 who felt that symbiosis was a major driver
00:10:28.17 in the evolution of animals and plants,
00:10:30.19 and she was always way ahead of her time.
00:10:33.20 She became famous f
00:10:35.19 or the endosymbiotic theory
00:10:38.11 of the origin of the eukaryotic cell,
00:10:39.17 and that is to say that bacteria
00:10:41.05 became symbiotic with other bacteria
00:10:43.03 and made a more complex cell.
00:10:45.14 And she showed that at the end of the 1970s,
00:10:50.06 it was very, very controversial,
00:10:52.00 she was way ahead of her time and always was,
00:10:54.09 but she is actually the person
00:10:57.07 who had the vision to say
00:11:00.19 exactly what we're seeing today,
00:11:02.04 and that is that symbiosis
00:11:04.02 is a major thing in biology
00:11:05.16 and has likely been over evolutionary history.
00:11:10.01 So, like I said, nearly all animals and plants
00:11:13.01 are likely to have beneficial symbiosis
00:11:16.05 and this is new information
00:11:18.12 from the last two decades of work.
00:11:20.12 And so what I'm showing here
00:11:22.27 is I'm showing a person,
00:11:24.09 and this person in this artistic rendering
00:11:27.18 is completely covered by microbes.
00:11:30.09 And we are, from the minute we're born,
00:11:34.00 through our life,
00:11:36.25 we associate very intimately with the microbial world.
00:11:39.06 And so we know now that you have as many, if not more,
00:11:42.25 microbial cells than human cells in your body.
00:11:45.04 So, you have about 10^13 human cells
00:11:47.08 and somewhere between 10^13 and 10^14 bacteria
00:11:50.00 that live with you, persistently,
00:11:52.26 your whole life and confer health.
00:11:57.06 So, the question is,
00:11:58.15 why didn't we know about this?
00:12:00.16 Why wasn't this more obvious?
00:12:03.07 Well, it turns out that there was
00:12:05.19 a huge technical problem
00:12:07.06 that we've been able to overcome.
00:12:09.05 And so, the technical problem
00:12:11.02 was a difficulty in identifying
00:12:14.15 and classifying the microorganisms,
00:12:15.17 and why we couldn't do that
00:12:17.15 was because most of these organisms
00:12:19.19 were unculturable under laboratory conditions,
00:12:22.19 and so they're called viable but nonculturable.
00:12:26.00 In other words, they live,
00:12:27.22 but we just can't bring them into the lab
00:12:29.28 and study them the way that we
00:12:33.13 would want to.
00:12:34.18 So, it's about less than 1% of the bacteria
00:12:38.15 that live in association with animals are culturable,
00:12:40.22 so this was a huge technical problem.
00:12:43.12 And so... because
00:12:45.17 we just couldn't know who they were.
00:12:47.10 The other thing was that...
00:12:50.15 another technical problem was that
00:12:53.12 they are relatively featureless.
00:12:55.12 So, what I'm showing here
00:12:57.17 is I'm showing a set of
00:13:00.12 different types of shapes and so on and so forth
00:13:02.27 that you might see
00:13:04.19 in different kinds of bacteria.
00:13:06.00 And so you might compare and contrast that
00:13:10.15 with the morphologies that you see of
00:13:13.09 very, very many plants and animals.
00:13:15.28 I mean, you can really, very well,
00:13:19.12 tell the differences between plants and animals;
00:13:21.21 with microbes, it's not so easy.
00:13:23.25 So, they weren't culturable
00:13:26.08 and you couldn't... they didn't...
00:13:27.26 they were pretty well featureless,
00:13:29.11 so these were big problems.
00:13:31.12 So, even though they're featureless,
00:13:33.06 we began to visualize microorganisms
00:13:36.03 back with Anton van Leeuwenhoek.
00:13:38.06 So, this is Anton van Leeuwenhoek
00:13:40.11 with, you know, several hundred years ago,
00:13:42.08 but he was a guy who
00:13:44.23 developed the very first microscopes,
00:13:47.06 and so he was the first person
00:13:49.26 who allowed us to visualize microorganisms.
00:13:51.16 And what Anton van Leeuwenhoek did was
00:13:54.15 he took a swab
00:13:56.19 and swabbed the inside of his cheek
00:13:58.10 and then he applied that to his microscope,
00:14:01.16 and he was able to see, for the first time,
00:14:06.23 So, not only was he the first person to see microorganisms,
00:14:08.21 but he was the first person to see microorganisms
00:14:10.26 that associate with humans,
00:14:12.08 and those were the microorganisms
00:14:14.16 inside of his own mouth.
00:14:17.07 So, then we fast-forward
00:14:19.29 to the electron microscope,
00:14:21.27 and the electron microscope
00:14:23.21 was invented several hundred years later,
00:14:25.21 in the late 1960s,
00:14:27.28 and the invention of the electron microscope
00:14:31.02 allowed us to see much more detail in microorganisms.
00:14:34.17 And this was actually the microscope
00:14:37.10 that allowed Lynn Margolis,
00:14:39.22 who I spoke about earlier,
00:14:41.06 to visualize the complexity of the eukaryotic cell
00:14:44.04 and to resolve the fact that,
00:14:46.12 in fact, the eukaryotic cell
00:14:49.07 was the result of a symbiotic association
00:14:51.22 between microorganisms,
00:14:54.22 or among microorganisms.
00:14:57.02 So, then fast-forward a little bit more...
00:15:01.22 so, these two characters,
00:15:04.26 Carl Woese and Norm Pace.
00:15:06.27 So, Carl and Norm were doing molecular biology
00:15:10.05 of microorganisms
00:15:11.20 at the University of Illinois...
00:15:13.22 well, Carl was at the University of Illinois
00:15:15.15 and he working with Norm Pace,
00:15:17.08 and they introduced the use of gene sequences
00:15:20.01 to determine relationships in the biological world.
00:15:22.08 So, notice that this is 1977,
00:15:25.04 so it's around the same sort of time that people
00:15:27.25 are beginning to think about using the microscope,
00:15:29.20 the electron microscope,
00:15:31.11 as a mechanism by which to classify the biological world,
00:15:34.26 but this was a new instrument
00:15:36.22 that Carl Woese and Norm Pace
00:15:38.24 introduced to the community of biologists.
00:15:42.08 So, the instrument was the 16S ribosomal RNA gene.
00:15:46.02 It's a highly conserved marker gene,
00:15:48.19 and the reason why this gene could be used
00:15:50.17 was because it's conserved throughout evolutionary history
00:15:53.12 and so it gives you an idea of
00:15:56.24 changes that are very, very old,
00:15:58.12 and would allow you to
00:16:00.21 classify all of the biosphere by molecular methods.
00:16:04.22 And this is the phylogenetic tree
00:16:07.26 that came as a result of the analysis
00:16:10.14 of the biological world.
00:16:12.07 And so what you'll see is you'll see that
00:16:16.15 there are the bacteria...
00:16:17.25 there are three domains of life
00:16:19.09 -- the bacteria, the archaea, and the eukaryea --
00:16:21.26 and the eukaryea contain
00:16:25.12 the animals, plants, and fungi.
00:16:27.09 And so, look at... the animals, plants, and fungi
00:16:30.12 are just these three twigs
00:16:32.03 at the very top of the tree of eukaryea,
00:16:35.21 which is, you know, is showing us that
00:16:39.02 the vast diversity of the biological world
00:16:41.13 is invested in the archaea and the bacteria.
00:16:44.27 So this was a huge change in our world view.
00:16:49.03 So, how big was this change?
00:16:51.20 Well, let's go all the way back to Aristotle.
00:16:56.07 So, Aristotle was one of the first people
00:16:58.08 to classify the biological world,
00:16:59.28 and what Aristotle did was
00:17:01.25 he classified it based on what he could see.
00:17:04.01 So it's animals and plants, basically.
00:17:08.18 So then, you know, fast-forward, as I mentioned,
00:17:11.09 to Anton van Leeuwenhoek,
00:17:13.03 who saw animals, plants, and what he called animalcules.
00:17:16.15 And then, in the 1970s,
00:17:20.20 there was a worker named...
00:17:24.24 who used the electron microscope,
00:17:26.14 his name was Thomas Whittaker,
00:17:27.23 and he developed something called the five kingdom model,
00:17:30.07 and so the five kingdom model
00:17:32.15 had sort of the featureless bacteria and archaea,
00:17:34.22 down here at the base,
00:17:36.11 the protists above that,
00:17:38.07 and those are the eukaryotic cells,
00:17:40.07 and then up at the top he had
00:17:42.24 the fungi, animals, and plants.
00:17:47.20 So, Carl Woese and Pace,
00:17:50.07 looking at this in context with their sequencing,
00:17:54.10 what they had was these three domains.
00:17:57.23 And remember that all, all of this,
00:18:02.05 up here at the top,
00:18:03.24 all of this stuff up here at the top
00:18:05.13 is now invested in this group here.
00:18:09.23 So, it's a huge change
00:18:11.23 in the way we see the biological world.
00:18:13.17 So, what have we done?
00:18:15.12 We have moved from having visual analysis...
00:18:19.02 for a couple thousand years,
00:18:21.22 we looked at the biological world
00:18:23.20 and we classified it based on what we could see,
00:18:27.00 and now what Carl Woese and Norm Pace did
00:18:30.27 was they gave us molecular analysis.
00:18:34.26 And molecular analysis is the... are the genes,
00:18:37.15 and that allowed us to very correctly
00:18:40.12 organize the biological world
00:18:43.23 as it actually exists.
00:18:45.23 So, what we found, of course,
00:18:47.06 is that the biological world
00:18:50.09 is mainly microbial,
00:18:52.11 and the animals, plants, and fungi
00:18:54.02 are but a small patina
00:18:57.07 on the top of the microbial world.
00:18:59.21 So, what did this revolution mean for symbiosis?
00:19:04.21 So, what it meant was that we could identify microbes
00:19:10.09 and determine their relationships,
00:19:12.21 among them and between them,
00:19:14.06 even those that we not culturable.
00:19:15.15 We could extract the DNA from them and say,
00:19:18.04 what is the DNA telling us about who they are and what they are doing?
00:19:21.13 But at first, with Carl Woese in the very, very beginning,
00:19:25.14 sequencing was excruciatingly slow and expensive.
00:19:29.20 And then, around 2006,
00:19:32.10 something called next-generation sequencing
00:19:35.05 came onto the scene,
00:19:36.21 and this has been
00:19:38.22 the most important thing of the whole revolution.
00:19:42.21 And imagine... this was only 10 years ago.
00:19:45.19 So, what happened at this point
00:19:47.29 was that there was a technology-enabled transformation
00:19:51.24 in our ability to sequence quickly and cheaply.
00:19:55.01 So, what I'm showing in this graph
00:19:57.05 is I'm showing the cost of sequencing per megabase...
00:20:02.18 so, you see, in 2001,
00:20:04.14 it was up at about 6000 dollars a megabase,
00:20:07.23 and it followed Moore's Law
00:20:10.03 -- the doubling in computer power every two years --
00:20:15.09 it followed Moore's Law for...
00:20:17.05 until about 2006, down here...
00:20:19.16 until about 2006,
00:20:21.25 and then next-gen sequencing was invented.
00:20:25.25 And look at what happened.
00:20:28.01 It went down from...
00:20:30.01 the cost went down from 600 dollars a megabase
00:20:32.06 to 35 cents in less than 10 years,
00:20:35.19 and now it's down to 3.5 cents.
00:20:38.13 And so this was incredibly enabling
00:20:41.05 to the community of biologists.
00:20:43.05 In other words, lots and lots and lots of people
00:20:45.23 had the resources
00:20:47.17 to be able to characterize the microbial world,
00:20:49.25 and so people have gone all around the world
00:20:53.18 characterizing the microbial world.
00:20:56.10 So, a whole frontier opens...
00:20:58.05 a whole frontier.
00:21:00.10 We can learn, who are the microbial partners
00:21:02.25 of animals and plants?
00:21:04.28 What are they doing?
00:21:06.11 How are they doing it?
00:21:07.18 And what is there importance to health and disease?
00:21:10.18 And so when you're thinking about a symbiosis
00:21:12.28 you think that many...
00:21:15.07 most of them are established new each generation.
00:21:17.19 Not all kinds are,
00:21:19.17 some of them the symbionts are passed
00:21:21.17 in or on the egg,
00:21:22.25 but most of them are established anew each generation,
00:21:25.14 just after birth.
00:21:27.02 And so when a baby is born,
00:21:28.27 what happens is at soon as
00:21:32.01 it goes through the mother's birth canal
00:21:34.12 it begins to acquire its microorganisms.
00:21:36.17 Then there's a development,
00:21:38.08 a trajectory that's not unlike
00:21:41.10 what goes on in the maturation of a forest
00:21:43.22 -- there's a succession of organisms --
00:21:46.05 and in humans you get
00:21:49.09 a mature set of microorganisms
00:21:51.01 somewhere between the ages of two and four.
00:21:53.26 And then what happens is you become a stable association,
00:21:55.29 that changes some over life
00:21:59.22 with various changes and aging and so on,
00:22:02.22 but it's a fairly stable population.
00:22:06.19 So there's a trajectory
00:22:08.00 and we're learning a great deal
00:22:10.16 about how all of this works at this point,
00:22:14.04 but it's new data...
00:22:15.23 I mean, it's just the beginning of the field.
00:22:18.01 What have we learned so far?
00:22:19.28 What we have learned so far is that
00:22:23.01 for many, many, many animals, including humans,
00:22:25.26 the complexity is absolutely daunting.
00:22:28.22 And what do I mean by that?
00:22:30.17 So, let's take humans for example.
00:22:32.12 So, what I'm showing here is I'm showing
00:22:34.11 my favorite comedian, Woody Allen,
00:22:36.09 and I've been very generous with him
00:22:39.25 -- I'm making him 6 feet tall
00:22:42.05 or a little bit over --
00:22:44.03 and so... but his,
00:22:46.14 if you compare the ratio is his size to a microbe's size,
00:22:48.26 2 meters to 2 microns,
00:22:50.22 so he's a lot bigger than a microorganism.
00:22:53.24 However, if you look at the number of genes
00:22:57.21 that Woody Allen has
00:23:00.19 compared to the number of genes that the microbes
00:23:02.18 associated with his body have,
00:23:04.05 the ratio is about 1:1.
00:23:07.18 If you look at cell number,
00:23:09.11 it's thought to be somewhere between 1:1 and 1:10.
00:23:13.11 In other words, there are about 10 times as many
00:23:15.29 microbes associated with you,
00:23:17.12 and that number has just this last year
00:23:20.11 become a little bit controversial,
00:23:21.24 so it's somewhere between here and here,
00:23:24.00 but that is to say that there are
00:23:26.25 just as many microbes associated with you
00:23:28.12 as you have human cells.
00:23:30.01 Then, if you look at gene diversity,
00:23:32.25 because instead of just...
00:23:34.09 so, you know, all of your eukaryotic...
00:23:36.14 all the human cells are of a single genome,
00:23:39.04 but the microbial cells are of
00:23:42.01 thousands, or hundreds if not thousands, of genomes.
00:23:46.07 The difference in gene diversity is thought...
00:23:48.22 for every single human gene
00:23:50.09 there are 200 genes of microbes,
00:23:53.11 so the gene diversity of microorganisms
00:23:55.09 is very much greater.
00:23:57.18 So at this point Woody Allen
00:23:59.22 feels pretty insignificant.
00:24:01.28 What I'm showing here is I'm showing the power of animal model systems
00:24:04.06 for the study of complex characters,
00:24:06.01 and the example that I'm using
00:24:08.07 is developmental biology.
00:24:09.23 And in development biology,
00:24:11.18 what I'm showing here is I'm showing
00:24:13.11 a fertilized egg,
00:24:15.22 and that fertilized egg goes from 1 cell to 10^13 cells
00:24:18.23 and produces something like
00:24:21.02 the miracle of George Clooney, my favorite actor.
00:24:23.14 So, this has been, this has been...
00:24:28.13 this approach has been extremely successful
00:24:30.18 to understand developmental biology.
00:24:34.10 So, what we've been able to do
00:24:36.29 is to take model systems,
00:24:38.15 you know, experiments that evolution has done,
00:24:40.14 and ask how, in this simple model system,
00:24:43.14 a particular developmental phenomenon
00:24:47.11 has been solved.
00:24:49.09 And so what I'm showing is
00:24:51.16 I'm showing an array of model systems
00:24:53.12 and I'm showing ones in which
00:24:55.27 Nobel Prizes have been awarded,
00:24:57.16 and it turns out that 6 Nobel Prizes
00:24:59.28 in developmental biology
00:25:01.14 have been awarded since 1995 and 2007,
00:25:04.06 and all 6 of them went to
00:25:07.24 individuals working on models.
00:25:09.09 So models have been an extremely valuable way
00:25:12.28 to study very complex characters.
00:25:15.09 So, because symbiosis
00:25:17.23 is such a complex character,
00:25:19.18 we feel, those of us in the field
00:25:22.03 who study models,
00:25:23.27 feel that it's a really good way to try to understand symbiotic associations.
00:25:28.10 So, we are developing,
00:25:30.02 the field is developing some models for symbiosis,
00:25:32.17 we're exploiting nature's toolkit
00:25:34.18 and, as I said,
00:25:36.22 evolution has done some enlightening experiments.
00:25:39.17 So what I'm showing here is I'm showing
00:25:41.27 a variety of them,
00:25:43.06 and so there are
00:25:45.05 various nematode symbioses
00:25:47.01 and various other invertebrate symbioses,
00:25:51.19 and we even have, over at UC Berkeley,
00:25:54.19 Nicole King studying the choanoflagellate symbioses,
00:25:58.13 at the base...
00:26:00.05 thought to be the base of the animal kingdom.
00:26:02.26 And then up here some vertebrate models.
00:26:06.05 Now, the vertebrates,
00:26:07.24 all the vertebrates have complex associations,
00:26:09.29 they have large consortia associated with them,
00:26:13.10 and so these people studying over here
00:26:15.10 are really interested in studying germ-free animals,
00:26:18.17 and so I sort of look at them as
00:26:20.21 engineered models.
00:26:22.10 Over here, many of them are studying
00:26:24.19 natural models
00:26:26.16 and these, the invertebrates are
00:26:28.21 naturally very simple associations,
00:26:33.01 and so they lend themselves to looking at a natural situation
00:26:35.12 and how that...
00:26:37.12 how the bacterium and the host animal get together
00:26:40.22 and maintain a stable association.
00:26:43.22 So, I...
00:26:46.17 my lab works on this beautiful animal, here,
00:26:48.24 the bob tail squid.
00:26:51.14 This is not a giant's hand, this is my technician's hand.
00:26:54.08 A very small squid that's indigenous
00:26:56.21 to the Hawaiian archipelago,
00:26:58.25 and this is the symbiosis that I've been working on
00:27:02.10 and that I would like to tell you about
00:27:04.10 in my next lecture.
00:27:07.02 Thank you very much.
00:00:07.25 I'm Jared Leadbetter
00:00:09.08 and I'm at the California Institute of Technology.
00:00:12.07 And, for some 24 years now,
00:00:14.14 my research has sought to clarify the relationship
00:00:16.26 between termites and their hindgut microbes.
00:00:19.21 Now, of particular interest to me
00:00:22.22 is the metabolism of hydrogen
00:00:24.20 that is generated during this fermentation of wood,
00:00:27.11 but today I want to give you a broad overview
00:00:30.17 on microbial diversity
00:00:33.08 and on some of the essentials
00:00:35.22 of termite hindgut microbiology.
00:00:38.26 So, I want to talk about
00:00:41.07 biological diversity in general,
00:00:43.14 because many who are interested in biology
00:00:45.17 are missing, actually, some of the
00:00:48.21 full diversity that we see in the microbial world.
00:00:52.01 And, then I also want to comment about
00:00:54.15 how some of this diversity is surprisingly abundant
00:00:56.28 in certain areas of the world,
00:00:58.23 and that we must understand
00:01:01.11 what that diversity does and how it functions.
00:01:03.03 So, this will bring me to termites
00:01:05.17 and the symbiosis they form with their hindgut microbes,
00:01:08.14 and I want to introduce you to several major groups
00:01:11.10 of termite hindgut microbes,
00:01:13.17 the cellulose decomposing protozoa,
00:01:17.01 methane producing archaea,
00:01:18.27 and a group of abundant and unusual bacterial
00:01:21.27 called spirochetes.
00:01:24.12 I'm going to then touch on
00:01:26.26 how we can study different termites
00:01:29.06 and learn about different events that may have occurred
00:01:31.19 during this symbiosis in the past,
00:01:33.22 and then I'll give you some conclusions.
00:01:39.02 I wonder how many people who are watching this
00:01:41.11 have grown up thinking about three kingdoms.
00:01:45.10 Up until the 1960s,
00:01:47.01 I think most people grew up thinking
00:01:50.17 that there were animals, plants, and fungi,
00:01:52.24 and that maybe, depending on their education,
00:01:55.27 even up through current years,
00:01:59.22 most enthusiasts of biology
00:02:02.11 understood there to be between three and five kingdoms.
00:02:05.07 Maybe you had the bacteria as a fourth
00:02:08.29 and the protists as a fifth,
00:02:13.04 But, starting in the 1960s we had a revolution
00:02:16.25 in the study of the relationships between different organisms,
00:02:19.10 and started to realize that many things that we were seeing,
00:02:22.06 and also not seeing,
00:02:24.13 are very, very different from these three major groups.
00:02:27.12 So, for example, if you look at a key gene
00:02:30.10 that is present in all known organisms,
00:02:33.00 you can make comparisons between this gene
00:02:36.13 and from that infer
00:02:38.24 how those organisms are related to each other.
00:02:41.16 The thing I want to point out on this slide
00:02:44.13 is that you have the fungi
00:02:46.02 and the animals
00:02:48.02 and the plants,
00:02:50.16 and those are just three twigs on a branch
00:02:53.27 that has many other twigs.
00:02:58.10 If those three twigs and the length of those lines
00:03:01.11 denote evolutionary relationships,
00:03:04.27 then there are more than three kingdoms.
00:03:07.25 There are easily a half-dozen.
00:03:10.20 The other thing I want to point out here
00:03:13.04 is that if you think about "plant metabolism"
00:03:16.11 there are some organisms on this tree
00:03:19.14 which also carry out photosynthesis,
00:03:23.13 let's say the kelp or the red seaweed,
00:03:28.09 but those branches are actually
00:03:31.11 very different from the plants.
00:03:32.28 They are as distantly related to plants
00:03:35.08 as you and I are from plants,
00:03:37.15 and I think that's very important.
00:03:39.12 Also, when we talk about single-celled eukaryotes, like protozoa,
00:03:43.11 we realize, oh,
00:03:46.17 Paramecium and the protozoan Babesia
00:03:49.08 are actually two very different organisms,
00:03:51.21 again, as distantly related to each other
00:03:54.14 as we are from let's say the yeast
00:03:57.01 that you use to make beer and bread.
00:04:03.11 So, the number of kingdoms
00:04:08.16 or major divisions of life
00:04:11.01 already gets more complex than those three that we know.
00:04:15.13 The truth is actually much more complex than that,
00:04:17.22 because this is now just a snippet
00:04:20.27 of a branch of a much more complex tree.
00:04:23.19 You'll see that I have just blown up
00:04:26.14 this section of a much larger tree.
00:04:29.27 One of the things I want to point out on this slide
00:04:32.18 is that there are many, many branches on this,
00:04:34.22 easily 100
00:04:37.18 which are more distant from each other
00:04:40.22 than the distance between corn and animals,
00:04:44.12 and what that suggests, then,
00:04:46.13 is that we have a lot to learn about
00:04:51.24 the differences between these different groups.
00:04:53.28 So, for instance, everything
00:04:56.12 that is lying outside of this circle is a microbe,
00:05:00.02 the single-celled organisms
00:05:01.19 which are smaller than you can see with your naked eye.
00:05:04.11 So, for as much as we can appreciate biological diversity
00:05:06.19 that you can see,
00:05:08.17 the true diversity of life
00:05:10.22 is beyond the resolution of the human eye
00:05:12.12 and we have to use other methods to really
00:05:14.02 understand how it works.
00:05:16.14 The second thing I want to point out
00:05:18.23 is how different the way of living is
00:05:22.15 for corn, or a plant,
00:05:24.20 and ourselves,
00:05:27.05 or from a yeast that's used to make bread and beer.
00:05:29.28 If the length of those lines,
00:05:31.25 which is comparatively short,
00:05:33.28 and the differences of these organisms is so great,
00:05:38.06 imagine the possible differences
00:05:41.13 in the ways that these organisms live.
00:05:44.08 So, we are potentially really missing out,
00:05:46.28 not just on the diversity
00:05:49.17 in terms of how things are related,
00:05:51.16 but also missing out on the diversity
00:05:53.25 of what organisms are actually doing in the environment.
00:05:56.10 And so, if we're to understand the environment,
00:05:58.16 we really have to learn more about
00:06:00.22 what these other organisms are doing.
00:06:04.27 Let's come back to this tree.
00:06:07.06 Let's come back to this organism kelp.
00:06:09.23 I want to illustrate another point:
00:06:11.25 it's not just that there are many, many organisms out there
00:06:14.25 which are different from the organisms we're most familiar with,
00:06:17.04 but in some environments those organisms are present
00:06:21.15 and very, very abundant.
00:06:23.14 Take the kelp -
00:06:25.29 you can find kelp forests off the coast of California,
00:06:29.02 and those kelp are performing
00:06:31.21 what we might call "plant metabolism".
00:06:33.25 So, they are the primary producers in those environments,
00:06:36.06 but, keep in mind, they're not plants.
00:06:39.03 So, the story of these coastal ecosystems
00:06:43.03 is in a large part driven
00:06:45.12 by an organism that's very different from a plant,
00:06:47.20 and so if we want to understand those coastal ecosystems
00:06:50.10 part of the story is understanding
00:06:53.02 the biology of kelp
00:06:54.20 and understanding in what ways they are similar
00:06:57.03 and different to the terrestrial,
00:06:59.05 or land plants that we study.
00:07:03.24 Now, I want to shift from the oceans
00:07:06.02 to my own research, which is study on
00:07:08.25 termites and their hindgut microbes,
00:07:11.00 and I want to point out that the termite hindgut
00:07:14.02 is an environment.
00:07:16.02 It happens to be an environment that lives
00:07:18.17 in a small insect,
00:07:20.15 but we can compare and contrast that environment
00:07:22.16 with, for instance,
00:07:24.24 a very rich marine environment like the Sargasso Sea.
00:07:28.03 There are certain reasons why
00:07:30.16 you might want to study a small environment
00:07:31.14 like in a termite.
00:07:33.00 The Sargasso Sea is a wonderful and amazing place,
00:07:34.28 and very important to study, but it's a thousand kilometers across,
00:07:38.07 and there's only one of the them.
00:07:41.03 The termite hindgut is only about one cubic millimeter in volume,
00:07:46.01 and yet it contains hundreds and hundreds
00:07:48.13 of microbes that you find no where else in nature.
00:07:51.08 Just if you were to take the top millimeter
00:07:53.14 of the Sargasso Sea,
00:07:55.22 the volume of that across those thousands of kilometers
00:07:59.19 is 19 orders of magnitude greater
00:08:01.27 than the volume of that one termite.
00:08:03.21 So, we can actually bring a termite into the laboratory
00:08:05.28 and be able to study an entire environment.
00:08:09.25 The hindgut... it's tiny yet complex...
00:08:12.18 many hundreds of species
00:08:14.20 and some of those species are yet unstudied,
00:08:17.13 so it is still bewildering complex,
00:08:20.11 and it's well-bounded.
00:08:22.12 We know that the gut lining
00:08:23.00 and the outside of the termite
00:08:24.27 are where you might define the boundaries of that system.
00:08:27.26 The Sargasso Sea is wonderful,
00:08:29.25 but there's only one of them,
00:08:31.29 and its boundaries are a little bit user-defined.
00:08:34.03 We think that it's, you know,
00:08:35.23 the currents that are intersecting here and there
00:08:37.25 are what bound that region,
00:08:39.13 whereas in the insect it's very well-bounded.
00:08:42.00 And, of course, the termite is available
00:08:44.09 in large number of replicates,
00:08:46.04 so we can, in a laboratory,
00:08:48.22 have that one environment that's tiny and well-bounded
00:08:51.10 replicated in termite, after termite, after termite.
00:08:54.13 So, we can start to do some comparative studies
00:08:56.08 and perturbation studies
00:08:58.07 which are just not possible with a large environment
00:09:00.25 like the Sargasso Sea,
00:09:02.13 for which there's only one.
00:09:07.06 So, I study a very particular termite
00:09:09.14 that we find in ponderosa pine
00:09:11.18 that's fallen in the Angeles National Forest
00:09:14.02 of southern California,
00:09:15.19 and here is one of these ponderosa pines
00:09:18.10 and two of my former students,
00:09:20.25 who have peeled off some of the bark from this log,
00:09:22.28 which has been on the ground for probably five or ten years,
00:09:25.15 and if you look a little bit more closely
00:09:27.24 you can see that just on the underside of that bark
00:09:29.18 are a number of termites
00:09:31.19 of different, what we call, morphological castes.
00:09:34.02 These ones with the dark mandibles are actually soldiers.
00:09:36.29 Rather than eating wood,
00:09:38.21 they have big mandibles that they can use to attack,
00:09:41.01 for instance, another termite or an invading ant.
00:09:45.22 So, this is termite that we study, for the most part,
00:09:49.01 in my laboratory.
00:09:50.18 It's the Dampwood Termite, Zootermopsis nevadensis,
00:09:54.17 and it's about a centimeter in length.
00:09:56.09 It's one of the larger termites that you'll find on Earth.
00:09:58.27 Now, this is what we call a worker,
00:10:02.24 and from another specimen I've extracted the hindgut tract,
00:10:07.29 and that is shown here.
00:10:10.18 And, what you'll observe is that
00:10:13.17 there is a long tubular region,
00:10:15.18 which is somewhat analogous to our small intestine,
00:10:18.24 and then you have this hindgut paunch,
00:10:22.10 which is somewhat analogous
00:10:25.07 to our large intestine,
00:10:27.02 and it's in this paunch
00:10:29.22 that really you find a lot of things that excite microbiologists.
00:10:33.04 You find a density of microbes
00:10:35.08 you find nowhere else in nature,
00:10:37.12 and they represent all three domains of life.
00:10:40.04 Earlier on that slide,
00:10:42.06 I'd shown you that the tree of life,
00:10:44.16 where you actually have three major subgroups,
00:10:47.05 and those are the archaea,
00:10:49.00 the bacteria,
00:10:50.19 and the eukaryotes.
00:10:52.09 You find single-celled relatives of all three of those groups,
00:10:56.06 comprising hundreds of species,
00:10:58.07 in this hindgut paunch.
00:11:00.19 So, before I tell you about termite gut microbes,
00:11:03.04 I want to tell you a little bit more about termites.
00:11:05.17 There are about 3000 species of termites on Earth.
00:11:10.24 Termites are related to cockroaches
00:11:13.24 and to the mantids, like the praying mantis,
00:11:15.19 and they're actually, although insects,
00:11:18.05 quite distantly related to ants, wasps, and bees,
00:11:22.02 which are also social.
00:11:24.06 So, this is an example of where
00:11:27.06 society, or sociality in insects,
00:11:29.12 has arisen in two different groups of insects
00:11:31.08 which are very different from each other.
00:11:33.19 So, termites, and those 3,000 species of them,
00:11:37.07 can be subgrouped into several different families,
00:11:41.11 and their closest relative in the insect world
00:11:45.04 is what we call the Wood Roach,
00:11:47.04 which is a non-social but wood-feeing insect
00:11:49.22 that you find in the Carolinas
00:11:52.19 and the Pacific Northwest
00:11:54.22 and in parts of China.
00:11:56.26 And, many of the microbiology...
00:12:00.02 the features of the microbiology in the Wood Roach
00:12:02.22 are actually shared with the termites,
00:12:06.13 and so it's thought that many of the
00:12:09.07 microbial processes that arose
00:12:11.28 arose in the last common ancestor of this roach and termites.
00:12:16.08 Now, the termite that I study, Zootermopsis,
00:12:19.07 belongs to this one groups in the Termopsidae.
00:12:21.22 So, over time, we can start to ask,
00:12:24.12 are any of the patterns that we see here
00:12:27.18 present in some of these other groups?
00:12:31.09 Now, if you extract the gut from Zootermopsis,
00:12:34.03 or another termite,
00:12:36.08 and you take a cross-section through that gut,
00:12:38.20 what you'll see is that the insect tissue itself
00:12:40.25 is actually very, very thin.
00:12:43.05 It's only about 10 microns in diameter,
00:12:46.05 so 1% of a millimeter in thickness.
00:12:49.14 The bulk volume of that is comprised by the gut contents,
00:12:53.10 and what you see here, these larger objects,
00:12:56.05 are single-celled eukaryotes called protozoa.
00:12:59.20 Now, historically, until the mid-1990s,
00:13:03.01 this region, this environment
00:13:05.17 was thought to be completely anoxic,
00:13:07.23 so, devoid of oxygen.
00:13:09.20 Many of the microbes that you find
00:13:11.18 in the core regions of this gut are poisoned by oxygen.
00:13:16.21 Here you have this insect,
00:13:18.08 which is living in the aerobic world
00:13:20.09 and wandering around on its six legs
00:13:23.00 in a piece of wood or on a piece of wood,
00:13:27.15 containing microbes which are poisoned by oxygen.
00:13:31.09 The story is actually even more complex,
00:13:33.13 because it turns out,
00:13:35.13 through studies that were performed
00:13:37.05 by Andreas Brune and John Breznak in the mid-1990s,
00:13:40.19 the oxygen actually diffuses across the insect gut wall
00:13:45.03 and then is consumed by biological processes
00:13:48.07 in the periphery of that hindgut,
00:13:50.28 and it's those biological processes in the periphery
00:13:54.07 which lead to the lack of oxygen in the core,
00:13:56.20 which protects some of those oxygen-sensitive microorganisms.
00:14:00.29 So, not only do you find organisms
00:14:03.03 which are unique to the termite gut habitat,
00:14:06.01 that you find nowhere else on Earth,
00:14:07.28 but many of these are poisoned by oxygen
00:14:10.04 and are very sensitive to desiccation.
00:14:12.29 So, their life outside the termite is very, very limited.
00:14:18.20 So, what you have
00:14:22.01 are microbes that are very dependent on their host
00:14:24.14 and, because of their processes,
00:14:26.10 which allow the host to derive nutrition from wood,
00:14:29.10 makes the host very dependent on their microbes.
00:14:33.25 And, when a termite emerges from its egg,
00:14:37.01 it doesn't have these microbes in its gut.
00:14:39.01 It's fed those microbes by other of its littermates
00:14:43.02 or by its parents,
00:14:45.06 and if those microbes don't take hold
00:14:48.04 that termite will fail,
00:14:51.21 and if that termite fails
00:14:54.25 those microbes will also fail.
00:14:57.15 So, when we look at one termite
00:14:59.14 that's walking around on a piece of wood today,
00:15:02.05 we are looking at over 100 million years
00:15:04.26 of having this microbial community
00:15:07.16 passed from one termite to the next termite to the next termite,
00:15:11.14 generation to generation to generation.
00:15:14.04 It's quite a remarkable story
00:15:17.04 of a journey that's been taken
00:15:19.04 between many, many organisms together.
00:15:22.26 So, if we go and look at a little bit of a higher magnification
00:15:26.08 of what's inside the gut,
00:15:29.13 this is what we call a DIC image
00:15:34.04 using a microscope
00:15:36.02 of some of the larger protozoal cells.
00:15:37.29 These are about 60 microns in length,
00:15:40.23 so roughly 20 of these laid end to end to end
00:15:43.27 would be a millimeter of length,
00:15:46.05 and some of these are the primary agents
00:15:48.08 of wood degradation in this termite.
00:15:50.02 You also see some smaller cells
00:15:52.26 which are also protozoa.
00:15:55.13 So, these are single-celled eukaryotes,
00:15:58.26 of which there are about a dozen
00:16:00.27 in this one termite
00:16:02.23 that you find nowhere else in nature,
00:16:04.14 and their closest relatives are in other termites.
00:16:08.04 There are some interesting associations
00:16:10.03 that you find between these protozoa and certain bacteria.
00:16:13.23 For instance, if you look at the surface of one of these,
00:16:16.15 at higher magnification,
00:16:18.11 you'll see that those protozoa
00:16:19.28 are covered with long lines of grooves,
00:16:23.03 and in those grooves you see these little black objects?
00:16:26.15 Those are bacteria.
00:16:29.09 So, the surface of that single cell of eukaryote
00:16:32.23 is arrayed with a very regular group
00:16:36.16 of a very specific bacterium
00:16:39.19 and, without knowing much more about,
00:16:42.07 the notion you might have is that
00:16:44.19 there is something that that protozoan
00:16:47.01 is getting from that bacterium and vice versa.
00:16:50.22 So, there are associations between the microbes
00:16:52.29 that live in the gut,
00:16:54.23 and there are associations with those microbes and their host.
00:16:58.04 So, there are many levels of biological interactions
00:17:00.06 which are occurring in this environment.
00:17:03.03 Another example of a protozoan that has a bacterial association
00:17:10.16 is this organism, which is called Streblomastix strix.
00:17:13.22 The eukaryote, the single-celled protozoan,
00:17:17.10 is actually very, very slender
00:17:19.04 and running through the center of this.
00:17:21.06 That protozoan is covered with a blanket, or a coat,
00:17:25.06 of long, thin bacterial cells
00:17:28.07 that are creating those ridges that you see.
00:17:31.05 We know very little about the interaction
00:17:33.06 between this protozoan and the bacteria
00:17:35.09 and what they're doing for each other,
00:17:37.22 but clearly it's a very specific and interesting interaction.
00:17:42.06 There are many cases of protozoa
00:17:44.27 and the bacteria that occur in these environments,
00:17:47.11 of which we have much more to learn in the future.
00:17:52.04 Now, there's an opening line to a book
00:17:54.26 by the biophysicist Howard Berg.
00:17:57.20 His book is called "Random Walks in Biology",
00:18:00.23 and the opening lines
00:18:03.11 are that biology is wet and dynamic.
00:18:06.10 What does that mean?
00:18:08.01 I've just showed you these still pictures,
00:18:10.02 but I think that the still pictures
00:18:12.12 don't do this environment justice.
00:18:14.25 Really, when you're looking at this environment live,
00:18:17.24 this is now some of that gut fluid
00:18:19.23 which has been diluted.
00:18:21.19 It's even more densely packed than this inside the termite,
00:18:24.02 but if you dilute that fluid and put it on a microscope slide
00:18:26.22 you see some of these protozoa
00:18:29.15 and coursing unamongst them,
00:18:31.15 lots of bacteria which are moving so quickly
00:18:33.22 you can barely focus on them.
00:18:36.12 I can just look at this forever,
00:18:38.26 and you can look at it using different types of microscopy
00:18:43.02 to show different details on some of these cells.
00:18:46.02 The point here is that
00:18:48.11 when I go to work every morning
00:18:50.04 I go to work in what I call a miniature Alice in Wonderland.
00:18:52.23 That it is, just from a naturalist's standpoint,
00:18:55.13 a very wonderful and diverse place
00:18:58.00 that begs lots of questions.
00:19:01.27 So, what is the interaction
00:19:03.29 that termites have with their gut microbes?
00:19:07.10 I want to give you an overview
00:19:09.08 of some of the major things
00:19:11.15 that we've learned over about the last 100 years
00:19:14.00 on the association between
00:19:16.19 the insect and its gut microbes.
00:19:19.00 Now, microbes have a huge challenge in life.
00:19:21.26 The challenge is, how do you eat something
00:19:24.02 larger than your head?
00:19:26.06 If you are the size of
00:19:29.18 one thousandths of a millimeter,
00:19:32.02 how do you gain access to nutrients
00:19:34.19 in a 2x4 or in a big log?
00:19:37.12 So, you have a really wonderful association
00:19:40.01 with an insect that has jaws and grinding mandibles,
00:19:43.12 which are very, very hard,
00:19:45.01 that can then take a large block of wood
00:19:47.09 and grind it into really small particles,
00:19:50.07 and then bring them into the gut
00:19:52.03 in a very controlled and wonderful environment
00:19:54.08 in which these microbes can thrive.
00:19:56.22 Now, in the hindgut, these protozoa that I showed you
00:20:01.03 have enzymes of their own,
00:20:03.02 and enzymes that they recruit from the insect,
00:20:05.14 to start breaking down the polysaccharides in wood...
00:20:08.18 the cellulose and another component
00:20:10.23 which we call xylan or the hemicellulose...
00:20:14.18 and these protozoa perform a very unusual fermentation.
00:20:17.22 It's a fermentation that differs
00:20:20.00 from the one that you use to make sauerkraut
00:20:22.02 or that you use to make beer and wine.
00:20:25.00 What those protozoa do
00:20:27.02 is they break down the hexoses in cellulose,
00:20:29.28 primarily to acetate,
00:20:32.00 so, neutralized vinegar,
00:20:35.05 and that acetate builds up in the hindgut of the termite
00:20:37.22 and is absorbed by the insect.
00:20:39.29 So, the insect is actually absorbing the acetate
00:20:43.21 and using it as its biofuel.
00:20:46.01 It is the source of carbon for the insect
00:20:48.19 and the source of energy for the insect.
00:20:53.00 Now, those protozoa
00:20:55.07 also produce hydrogen gas,
00:20:57.21 so think the 1930s,
00:20:59.27 this classic picture of the Hindenburg blimp
00:21:01.26 over New Jersey, blowing up in fire.
00:21:04.10 It was filled with hydrogen.
00:21:06.01 There's a lot of energy in hydrogen.
00:21:07.21 It's not just combustible;
00:21:09.24 it's an energy source that can be used by different microorganisms.
00:21:13.04 So, in the termite,
00:21:15.10 and in many environments which are non-marine
00:21:17.16 and devoid of oxygen,
00:21:19.17 hydrogen and CO2 is converted into methane
00:21:23.08 by a group of organisms called methanogenic archaea,
00:21:26.29 and this methane is emitted by the insect.
00:21:30.00 It is sort of lost calories.
00:21:31.24 So, as we know, we can burn methane,
00:21:33.24 we use it as a fuel,
00:21:35.24 and that methane which is emitted by the insect, then,
00:21:38.22 is a fuel, a potential energy source,
00:21:40.21 which is lost from the system.
00:21:43.07 So, we can use a form of microscopy
00:21:46.07 to observe these methanogenic archaea in the termite.
00:21:50.07 Several years ago, I was trying to find out,
00:21:54.07 where are those archaea present in the system?
00:21:56.09 And what I learned is that
00:21:59.06 they are colonizing the gut wall of many...
00:22:03.21 inside the gut wall of many termites.
00:22:05.18 So, if you dissect out the gut,
00:22:07.29 you cut open the gut, you wash away all the contents,
00:22:11.05 and you sort of open that up
00:22:13.00 and look at the internal surface of it,
00:22:15.09 you can look for a type of fluorescence
00:22:19.08 called F420 fluorescence.
00:22:21.20 These organisms that make methane contain a vitamin,
00:22:24.04 and when you shine UV light on that vitamin
00:22:26.13 the vitamin turns blue.
00:22:28.16 And so, with a proper microscope,
00:22:30.29 you can start to see a number of different cell types,
00:22:33.18 which are blue,
00:22:35.18 that live on the inside of this gut wall.
00:22:38.12 And, in this image you see that there are
00:22:40.13 three different morphologies of organisms.
00:22:42.10 Now, I'm somebody who likes food,
00:22:43.28 so I like to say that this one long one
00:22:45.29 looks like long, blue spaghetti,
00:22:47.25 the curves rods look like basmati rice,
00:22:49.28 and some of these straight rods look like regular rice.
00:22:53.06 Now, termites emit up to 4% of global methane every year.
00:22:57.03 So, by studying these organisms in their environment,
00:23:00.00 and also culturing them and bringing them into the lab,
00:23:02.18 we can put a face on the process,
00:23:06.00 at a single microbial cell level,
00:23:08.19 for actually a very significant source of global methane...
00:23:12.17 not the most significant source of global methane,
00:23:15.25 but a small but significant source.
00:23:19.28 I like to show this slide,
00:23:23.01 of a paper mache cow,
00:23:25.01 because I knew that when I first got to Caltech
00:23:27.00 I was having some impact on undergraduate life there,
00:23:30.02 because when I talked about termites
00:23:32.22 and processes that occur in a cow
00:23:34.22 the next Caltech Ditch Day,
00:23:36.26 that occurs every spring,
00:23:39.06 the students had made this large paper mache cow
00:23:41.17 and filled it with chocolate pudding,
00:23:44.08 Easter grass, oatmeal,
00:23:47.06 and Easter eggs that were filled with clues
00:23:49.12 on where the students should go to their next puzzle.
00:23:53.21 And, you can see here,
00:23:55.23 the students trying to find those eggs.
00:23:57.28 The point I want to make here is that
00:24:01.11 cows lose about 20% of their electrons in their food
00:24:05.05 as methane.
00:24:07.06 It's a huge waste of energy.
00:24:09.09 And, although termites contain methanogens,
00:24:11.19 and emit methane,
00:24:13.25 it's only a very small amount of this hydrogen and CO2
00:24:16.25 that is lost to the system as methane.
00:24:19.11 On a global scale, it's significant,
00:24:21.22 but, actually, on a global scale,
00:24:23.22 the methane emission by termites
00:24:25.09 would be much more significant
00:24:28.03 if this hydrogen and CO2 was not being consumed
00:24:30.21 by a different group of organisms
00:24:33.14 which we call CO2-reducing homoacetogens.
00:24:36.17 So, many termites contain microbes
00:24:38.28 that completely push these methane organisms
00:24:41.19 out of the picture,
00:24:43.22 or push 90% of them out of the picture.
00:24:47.11 So, many termites will take...
00:24:49.20 have microbes that convert hydrogen and CO2 into acetate,
00:24:52.19 and this acetate then goes into that pool in the gut
00:24:56.05 and is absorbed by the insect.
00:24:58.10 So, up to a third to a fifth
00:25:01.01 of the acetate which is used as the biofuel
00:25:03.22 by these insects
00:25:05.27 is derived from carbon dioxide and hydrogen
00:25:09.02 by way of the activity of those protozoa,
00:25:11.11 and by way of the activity
00:25:14.00 of these organisms here.
00:25:16.02 So, I have long been interested
00:25:18.00 in the interaction between organisms competing
00:25:20.24 for this hydrogen and CO2
00:25:22.26 that make acetate and that make methane
00:25:25.26 from those...
00:25:28.02 to understand how they compete with each other,
00:25:30.01 how has this process come to pass in termites,
00:25:33.25 why doesn't it occur in the cow rumen,
00:25:35.29 and how do these hydrogen consumers
00:25:38.06 interact with the organisms which are producing the hydrogen,
00:25:40.18 the protozoa.
00:25:44.16 So, CO2-reductive acetogenesis
00:25:47.20 is a bacterial activity.
00:25:51.27 The process involves
00:25:54.13 the fixation of two molecules of carbon dioxide...
00:25:58.11 one, two...
00:26:00.26 with four molecules of hydrogen...
00:26:03.20 one, two, three, four...
00:26:08.09 and in the process, those two carbons are joined
00:26:11.07 and reduced to form the acetate,
00:26:13.15 and this metabolism
00:26:15.28 actually yields energy for the bacteria
00:26:17.24 which are performing it,
00:26:19.22 in addition to yielding the acetate
00:26:21.10 which can be used by the insect.
00:26:22.10 So, it's a mutually beneficial metabolism
00:26:26.08 that takes hydrogen produced during this fermentation,
00:26:28.18 turns it into additional fuel for the insect,
00:26:30.25 meanwhile supporting the activity of the bacteria that perform it.
00:26:35.22 But, for years,
00:26:37.19 we did not have a very good understanding
00:26:40.03 about what bacteria in the termite
00:26:42.19 are actually catalyzing this process.
00:26:44.09 We had some ideas, but, over the years,
00:26:47.06 we've been trying to learn more.
00:26:49.10 Now, if you look in the hindguts of termites
00:26:51.23 you'll even see, on some of these protozoa,
00:26:55.05 that there are very abundant spiral-shaped organisms,
00:26:57.24 which can be attached to the protozoa
00:26:59.28 and that can also be seen
00:27:03.10 living and swimming amongst the protozoa,
00:27:06.03 and in most termites these organisms we call spirochetes
00:27:09.10 are some of the more abundant bacteria
00:27:11.11 that you'll see swimming in and amongst these protozoa.
00:27:14.28 If you go to another portion of the gut,
00:27:17.09 maybe you'll see that there are even more
00:27:19.14 of these spiral-shaped organisms.
00:27:21.13 So, starting in the 1990s,
00:27:23.17 scientists at Michigan State and in Germany
00:27:27.02 discovered that these spirochetes
00:27:29.19 are actually very closely related to Treponema pallidum.
00:27:33.28 That's one of the most famous organisms in microbiology.
00:27:37.03 It's what causes syphilis.
00:27:39.11 Actually, all these bacteria in the termite
00:27:42.16 are species that belong to the same genus
00:27:46.13 as the agent of syphilis,
00:27:48.13 and yet you always find these organisms
00:27:51.12 present in happy and healthy termites.
00:27:53.28 But we didn't know what they did because, like syphilis,
00:27:57.13 they had never been cultured in vitro.
00:27:59.28 First observed in the 1860s,
00:28:01.21 over a century went by
00:28:03.26 before we had actually learned about what any of these do,
00:28:06.07 and I would still argue that we are still in our infancy
00:28:09.04 of understanding what the full breadth of the different roles
00:28:11.25 of the hundred or more species of spirochetes
00:28:14.12 that you can see in an individual termite hindgut.
00:28:18.21 But, a number of years ago,
00:28:20.27 I really endeavored for a very long period of time
00:28:23.04 to try to coax one or two of these species
00:28:26.11 into laboratory culture so that we could ask what they do,
00:28:29.12 and I had an idea:
00:28:31.19 maybe some of these are these acetogens
00:28:33.12 that can take hydrogen and CO2
00:28:35.07 and make acetate.
00:28:37.01 The problem with that is that activity
00:28:39.05 was not known to occur in any spirochete,
00:28:42.08 and none of these spirochetes from the termite
00:28:44.07 had been cultured.
00:28:46.01 So, it's an idea, but what you really need to do
00:28:47.24 is get one of these into the laboratory and ask it,
00:28:50.22 are you capable of doing that?
00:28:52.08 And, if not, what do you do?
00:28:55.20 So, what is a spirochete?
00:28:57.25 This is a political cartoon from the early 70s,
00:29:00.29 and will sort of shoot right over the heads
00:29:04.02 of almost all of us,
00:29:05.27 but I still include it because it's a little bit
00:29:08.21 of American history that Richard Nixon's first vice president,
00:29:11.23 Spiro T. Agnew,
00:29:14.15 sort of had to leave office for some misdealings that he had,
00:29:19.16 and this was before even the Watergate scandal blew up.
00:29:22.25 So, when I say spirochete,
00:29:24.26 I'm not talking about a spirochete,
00:29:27.21 but a different organism,
00:29:30.15 and these are bacteria
00:29:33.17 that have a very unusual body plan.
00:29:35.28 So, many bacteria can swim
00:29:38.04 and they have flagella that extend into the extracellular milieu
00:29:42.10 and act like propellers,
00:29:44.25 but spirochetes have flagella
00:29:46.17 that extend not out of the cell,
00:29:49.14 but out past the first membrane,
00:29:52.21 but lie in between the inner and the outer membrane
00:29:55.03 of the bacterial cell,
00:29:58.27 and actually will wrap around the cell, okay?
00:30:02.12 If you look at a cross-section, you can see what I mean.
00:30:05.24 These are the flagella that lie
00:30:08.06 in between the inner and the outer membrane,
00:30:10.04 and when those flagella turn
00:30:12.05 the entire cell becomes a propeller,
00:30:14.12 as opposed to being attached to the propeller,
00:30:17.01 and spirochetes are known to be able to move
00:30:19.11 into very thick, viscous environments,
00:30:22.02 and are sort of the world record holders in the microbial world
00:30:25.07 for being able to wiggle into really thick and tight places.
00:30:29.12 And, all the organisms that have this body plan
00:30:31.10 are also related to each other,
00:30:33.09 so it's both a related group
00:30:35.19 by genetics and by their body plan.
00:30:40.01 So, these are microscopic images
00:30:42.06 of the first termite gut spirochete that was isolated.
00:30:45.29 We call this organism Treponema primitia,
00:30:49.01 and the first thing we wanted to ask
00:30:51.21 was whether it was really a spirochete,
00:30:54.06 and what I want to point out here is that
00:30:56.09 if you look at it with a whole-cell negative stain
00:30:58.05 by transmission electron microscopy,
00:31:00.05 or a thin section,
00:31:02.02 it has these hallmark flagella
00:31:05.18 that are lying in between the inner and the outer membrane.
00:31:08.23 Now, the second thing we learned about Treponema primitia
00:31:11.28 is that it is actually a hydrogen+CO2 acetogen.
00:31:15.11 Hydrogen stimulated its growth
00:31:18.01 and it consumed hydrogen and made acetate
00:31:21.18 in the expected four hydrogen to one acetate stoichiometry.
00:31:25.26 You could also grow this organism
00:31:27.27 under radioactive carbon dioxide,
00:31:29.29 and when you do that
00:31:32.07 it generates radioactive acetate,
00:31:34.21 so it's fixing CO2 into organic carbon,
00:31:39.02 and when you ask,
00:31:41.19 are both carbon positions of acetate labeled?
00:31:44.14 They were.
00:31:46.10 And lastly, there are enzymes associated with this pathway,
00:31:49.17 and this organism exhibits them all.
00:31:52.03 So, it is a bonafide hydrogen/CO2 acetogen
00:31:55.12 and, although a close relative
00:31:57.07 of the organism that causes syphilis,
00:31:59.08 this organism actually plays a key role
00:32:01.17 in the fermentation of food in the termite,
00:32:04.03 and in taking some nutritional value of that wood
00:32:07.04 and passing it back on to the termite.
00:32:10.06 Now, we have been studying this organism
00:32:12.22 for almost 20 years now,
00:32:14.21 and one of the things that we've done
00:32:16.28 is really looked at its genes for this pathway,
00:32:19.10 and used our study of these genes, in red,
00:32:23.15 to do comparative studies in other termites
00:32:26.07 and also in this particular termite and ask,
00:32:29.29 can we learn if this is the only acetogen,
00:32:33.18 or if there are other species,
00:32:35.13 and who are those other species?
00:32:37.25 So, we can take an approach, now,
00:32:39.28 where we can take a look at the diversity
00:32:42.16 of these genes for this pathway in this one termite,
00:32:45.23 but also in members of these two other major subgroups
00:32:48.29 of the termite line of descent,
00:32:51.11 and also in the Wood Roach.
00:32:53.11 And so, we've been learning a lot
00:32:55.16 about the diversity of organisms
00:32:57.18 that can carry out that metabolism
00:32:59.24 in a diversity of different species
00:33:02.25 and actually major subgroupings of insects that eat wood.
00:33:07.25 Now, we've also been able
00:33:11.29 to isolate a second spirochete from Zootermopsis.
00:33:15.04 This one we call Treponema azotonutricium.
00:33:18.28 Now, this organism
00:33:21.06 plays a very different role in the symbiosis
00:33:23.08 with the termite and its hindgut microbes.
00:33:26.01 So, if you think about it,
00:33:28.02 wood is not only tough to eat,
00:33:30.23 it's not a very good source of protein.
00:33:33.10 You know, at best, it's like a potato, right?
00:33:36.29 It's got a lot of polysaccharide,
00:33:38.23 a lot of carbs,
00:33:40.25 but not a lot of nitrogen.
00:33:43.00 So, you can be degrading that wood
00:33:45.06 and providing the calories to the host,
00:33:48.01 but that's only one of the hosts major problems in life.
00:33:50.26 The other problem is to make protein,
00:33:54.04 and so if you ask what's going to
00:33:56.08 limit the ability of this insect that's eating a block of wood,
00:33:58.27 or your home,
00:34:00.25 what's going to limit its proliferation,
00:34:03.15 part of the story is on protein.
00:34:06.10 So, it turns out that some 35 years ago
00:34:10.06 John Breznak, at Michigan State University,
00:34:13.10 discovered that termites contain microbes
00:34:15.25 that can take atmospheric nitrogen,
00:34:17.25 which is bathing all of us in the atmosphere all around us,
00:34:21.01 and can take that and turn it into protein,
00:34:24.09 that can then be fed to the insect.
00:34:27.18 And, this particular spirochete,
00:34:29.26 when we got it into culture in the laboratory,
00:34:32.19 we could show can do that same activity.
00:34:35.28 So, this is one of the organisms that we say
00:34:38.17 can exhibit diazotrophic growth.
00:34:40.18 It can grow with N2 gas
00:34:43.11 as its sole source of eventual protein,
00:34:46.08 and it shows several activities
00:34:48.17 which are associated with that activity,
00:34:51.04 and therefore it's playing a role
00:34:53.13 in taking a very abundant but unusable source of nitrogen
00:34:56.01 around the insect
00:34:57.25 and actually feeding the insect protein-level nitrogen.
00:35:01.29 I'll mention too that this particular organism
00:35:04.29 is unlike the first.
00:35:06.24 It's not an organism that can consume hydrogen
00:35:10.20 and fix CO2 into acetate.
00:35:13.07 It actually degrades sugars
00:35:15.14 and produces hydrogen that it can feed to the other spirochete.
00:35:18.19 So, it plays different roles in this symbiosis.
00:35:23.05 So, I've talked to you about some protozoa,
00:35:28.13 about some methanogenic archaea,
00:35:32.20 and about just some of the many, many bacteria
00:35:35.09 that you can find in a termite.
00:35:38.02 There are many other stories I could tell you,
00:35:40.05 but I want to leave off with my talk
00:35:41.27 by just pointing out that
00:35:46.06 we've talked about these three major groups in this environment.
00:35:49.15 That environment is dominated
00:35:51.11 by members of diverse groups
00:35:53.11 which are very different from the host itself.
00:35:55.28 So, just like the kelp forests,
00:35:57.23 these are environments
00:35:59.28 which are dominated by genetic groups
00:36:02.01 and groups performing physiologies
00:36:03.26 which are very different from sort of the paradigms of biology,
00:36:07.01 and that we learn a lot by studying them.
00:36:09.27 So, I think with that,
00:36:11.15 I'll close this introductory talk
00:36:14.08 on termite gut microbiology.
00:36:16.15 There are many, many general aspects
00:36:18.14 that we could discuss,
00:36:20.00 and of course can go into many other aspects
00:36:22.08 in great detail.
00:36:23.20 And so, I'd like to point out that
00:36:25.28 there have been many research groups and scientists
00:36:28.07 that have been working on termites for well over a century,
00:36:30.25 and I've tried to encapsulate some of their findings,
00:36:33.00 as well as the findings of my own laboratory,
00:36:35.21 into the presentation that I have given you today.
00:36:38.16 Thank you very much.
00:07.0 My name is Jim Estes.
00:08.2 I am a professor of ecology and evolutionary biology
00:12.2 at the University of California in Santa Cruz,
00:15.0 and I'm delighted to be here today to be able to
00:17.1 tell you about some of the things that my colleagues and I
00:21.0 have learned over the last few decades
00:22.3 about the ecological function of apex predators in nature.
00:28.2 If you look around you in the world,
00:30.0 wherever you're living,
00:31.2 you're going to see a species that we would call an apex predator,
00:33.1 and an apex predator is nothing but a large animal
00:37.2 that feeds on other species
00:40.1 that exists at what we call the top of the food web,
00:43.1 that is, there are no other species above it that feed on it.
00:46.2 These are some pictures of apex predators
00:49.2 that are part of our recent world, but are now extinct.
00:53.0 Some of them you'll recognize.
00:55.1 In the upper-left-hand corner is a picture of a species
00:57.2 that went extinct about 10000 years ago,
01:00.1 the dire wolf.
01:02.0 In the middle you'll see a big bear.
01:06.1 That's a short-faced bear.
01:07.2 That also went extinct not too long ago.
01:09.2 And toward the bottom of the illustration
01:12.0 are some species of things that we would call apex predators
01:15.0 that were around many, many hundreds of millions of years ago.
01:20.3 So, let's take a look at the history of the Earth.
01:23.1 Let's go back four and a half billion years
01:25.2 to the beginning of the Earth
01:27.2 and look at the history of life and when these creatures
01:30.1 that we call apex predators showed up.
01:32.3 Well, life started not long after the Earth was created,
01:35.2 maybe a billion years or so,
01:37.0 things that we refer to or we recognize as life appeared.
01:42.0 But it wasn't until about half a billion years ago that
01:47.1 a major event happened in the evolution of life
01:49.2 that was very important and that was called
01:52.2 the Cambrian Explosion.
01:54.2 The Cambrian Explosion was a very important time
01:57.0 in the history of the evolution of life
01:59.0 because all of the major life forms,
02:00.3 as we currently know them,
02:03.0 either from existing species or from the fossil record,
02:06.3 appeared right at that time,
02:09.2 including apex predators.
02:11.2 So, apex predators have been part of nature
02:14.0 for the last half a billion years.
02:17.1 They've been all around us.
02:19.1 So, this leads to two questions.
02:21.1 One is the question of why,
02:24.2 and that is a question for evolutionary biology,
02:26.2 why being,
02:28.1 why is it that all of a sudden, half a billion years ago,
02:31.1 all of these large apex predators
02:34.2 appeared on the Earth.
02:36.0 The other question is the question of,
02:38.3 do they really matter?
02:40.1 Would the Earth be a different place
02:42.1 had these animals not appeared in our fauna?
02:45.2 And that's a question for ecology
02:47.1 and that's going to be the focus of my lecture today.
02:51.0 So, I'm going to divide this lecture into three parts.
02:55.1 The first part, which I'm in the middle of,
02:57.1 or at the beginning of right now,
02:59.2 is going to be a focus on approach.
03:02.0 How do we answer these questions?
03:03.3 Part II is going to... the second module...
03:08.0 Part II is going to focus on one particular species and ecosystem,
03:11.1 and that is sea otters and kelp forests,
03:13.3 and the reason that I'm doing this is because
03:16.0 that's what my laboratory has been focused on
03:18.2 for the last half-century.
03:20.3 And then in Part III I'm going to look beyond sea otters and kelp forests
03:22.2 to other species and ecosystems
03:24.3 and ask the question:
03:27.1 to what degree are the things that we have learned
03:29.2 about sea otters and their ecosystems
03:32.1 applicable to other species and other systems around the world?
03:40.1 So, for Part I of the lecture,
03:42.1 there are really two major issues that I'd like to discuss.
03:45.2 One is that I need to provide you with
03:48.2 a conceptual template of what it is
03:50.2 that we're looking at.
03:52.0 We need some notion of both the
03:54.0 structure and function of nature
03:55.2 before we can ask questions about how nature works.
03:58.2 And the second is,
04:01.0 how do we actually go about testing hypotheses
04:03.2 that pertain to these purported functional relationships
04:06.1 that involve large predatory animals
04:09.1 or large apex predators?
04:11.2 So, first, the conceptual template,
04:14.1 and the conceptual template has two pieces.
04:16.0 One is what we call structure --
04:18.1 how is nature put together? --
04:20.2 and the second is what we call process --
04:23.1 and that is, how do these pieces that form nature
04:25.1 work when they're all together?
04:28.1 So this is a problem.
04:29.3 Uhhh... structure...
04:32.2 we use what we call a food web
04:34.3 to conceptualize the structure of nature,
04:37.0 and on the left of this slide you'll see
04:39.1 one of the world's simplest food webs.
04:41.1 This is a food web that was put together
04:46.1 for the cod system in the northwestern Atlantic,
04:48.1 and what you'll see in this particular illustration,
04:51.1 if you kind of squint your eyes and look at it,
04:53.0 because there's a lot of material there,
04:54.2 are what we call nodes and then linkages between those nodes.
04:59.2 The nodes are species
05:01.2 and the linkages are the interactions between species,
05:03.2 and in this particular case
05:05.1 what we call predator-prey or consumer-prey interactions.
05:09.0 Species feed on other species
05:11.3 and this is the way nature is put together.
05:14.2 And a simple look, or a quick look,
05:16.2 at this simple food web
05:19.0 will immediately emphasize the problem
05:21.2 of understanding these systems
05:23.1 and that is that they are monstrously complicated.
05:26.1 So these are difficult systems to work in
05:29.1 simply because of their complexity.
05:31.0 So, as ecologists, one of the things that we do
05:33.1 is we try to simplify this complexity.
05:35.1 We need to, what I call, modularize the system
05:37.2 or, that is, pick out the species and linkages
05:41.1 that really matter to study.
05:43.0 You can't study them all, there's just too many,
05:44.2 so modularization is one of the tricks
05:46.3 to understanding these systems.
05:49.2 The next point that I want to make
05:53.2 that falls into this conceptual template
05:55.1 is the nature of the interactions
05:57.3 between consumers and prey.
06:00.1 The interactions between consumers and prey
06:02.2 can be either what we call direct,
06:04.2 in which case there are no intervening species
06:06.3 -- a prey is eaten by a consumer --
06:09.1 or indirect,
06:11.1 in which case there are one or more interceding species.
06:14.2 So, for example,
06:16.2 a wolf might eat an elk
06:18.3 and an elk might eat plants,
06:20.1 and therefore the wolf might be having effects on those plants,
06:23.0 indirectly, by way of elk.
06:25.2 And you can easily imagine that
06:28.0 there are lots of potentially very complex
06:30.3 indirect interactions in nature.
06:32.3 So keep that in mind as we go forward.
06:37.2 As we think about these interactions,
06:40.0 the next point that is important to conceptualize
06:44.1 is that the strength of those interactions
06:46.2 might vary tremendously,
06:47.3 and I've tried to illustrate that in this illustration
06:50.1 between two directly interacting species, A and B
06:57.0 A might be wolves, B might be elk,
06:59.1 A might be sea otters, B might be sea urchins...
07:02.1 and that interaction can either be what we call
07:04.3 a strong interaction or a weak interaction
07:08.1 -- and I've tried to indicate that by simply
07:11.1 the variation in the weights of the lines
07:13.1 between these two particular cartoon illustrations
07:16.0 of the linkages.
07:17.1 A strong interaction is one where
07:20.1 the interaction has a big effect --
07:22.1 A might have a very strong effect on B
07:24.1 or B might have a very strong effect on A.
07:26.1 A weak interaction would be structurally the same
07:29.0 but the interaction consequences would be lesser.
07:33.0 Focusing now on process,
07:35.1 how do we understand the consequences
07:38.1 and the strengths of these linkages
07:40.1 between two interacting species, a predator and a prey?
07:42.3 The way that we do that is by perturbing the system.
07:45.2 It's the only way that we can really see into this
07:49.1 complex milieu of interactions among species.
07:52.2 So we would either add a species
07:54.2 or we would take a species away,
07:56.1 and we would look at how the consumer-prey interactions changed
07:59.2 and how the food web in general responded
08:02.1 to that change in direct interactions
08:04.3 through the various indirect interactions that might follow.
08:10.0 I'd like to raise two further details
08:12.1 that are important to our thinking
08:14.1 about the nature of food web dynamics.
08:16.0 One is what we call the directionality of forcing
08:18.1 and the other is what I would call
08:20.3 functional relationships.
08:22.1 So, firstly, directionality of forcing.
08:25.2 If we imagine a consumer and a prey,
08:27.2 and that consumer might be an elk and the prey might be a plant,
08:31.0 the consumer might be a wolf and the prey might be an elk,
08:34.3 the consumer might be a sea otter and the prey might be a sea urchin,
08:39.2 or the consumer might be a sea urchin and the prey might be a plant...
08:47.0 these two species can interact with each other
08:48.3 in two fundamentally different ways
08:50.2 in terms of the consequence of those interactions.
08:52.3 One is what we call bottom-up forcing.
08:55.1 In the case of bottom-up forcing,
08:57.2 it is the prey that really is
08:59.3 controlling the abundance and behavior of the consumer,
09:02.2 so changes in prey availability and prey abundance
09:05.0 are going to impact the consumer in a similar way.
09:10.1 The other is what we call top-down forcing.
09:12.1 In top-down forcing,
09:14.3 the consumer is having an impact on its prey
09:17.0 by the very fact that it eats it, alright?
09:19.3 Now, in nature, the interactions between consumers and prey
09:24.2 involve both of these forcing processes --
09:27.1 bottom-up and top-down.
09:29.1 When we look at nature
09:31.1 with the question in mind of the importance of apex predators,
09:33.2 we're really interested in top-down forcing,
09:35.2 and so much of what I'm going to be telling you about subsequently
09:39.1 is going to focus on this dimension to consumer-prey interactions.
09:43.2 The last piece of this is
09:46.1 what I would call functional relationships,
09:47.3 and that is, how is it that
09:50.1 a species that is affected by one other species,
09:52.2 let's say species A and B again, here,
09:55.3 let's say we're talking about elk and wolves,
09:58.2 how does the abundance and the functional importance of elk
10:01.3 in a system change
10:03.3 as the abundance of its predator
10:06.0 goes from being absent to very high?
10:08.1 So, that might be a linear change,
10:09.3 so there would be a gradual change in the abundance of elk
10:12.3 as the abundance of wolves changed.
10:15.1 It might be a nonlinear change,
10:18.1 so for example in the bottom-left panel here,
10:21.0 we can see a situation where
10:23.2 there's really a changing abundance of species B,
10:26.2 which in this case we're going to call the wolf,
10:33.1 that there would be really relatively little effect on the food web
10:37.1 until we reach some particular critical point,
10:39.1 and then we would have what we call a phase shift,
10:41.2 a very strong nonlinear transition.
10:45.2 The third dimension to this is
10:48.1 the process that we call hysteresis,
10:50.0 and hysteresis occurs when these functional relationships
10:53.2 that are strongly nonlinear
10:56.0 track along different lines
10:58.1 depending upon whether directionality of forcing,
11:00.0 that is, rather species B is becoming more abundant or less abundant,
11:05.0 is on the increase or on the wane.
11:07.2 So, when we have these functional relationships
11:09.2 that track along different functional relationships
11:12.2 depending upon the directionality of change,
11:15.1 we have a system that is characterized by hysteresis.
11:19.1 Obviously, nonlinear relationships and hysteresis
11:22.2 make our task of understanding species interactions,
11:26.1 and thus the importance of apex predators in nature,
11:28.3 more challenging.
11:30.1 So, in Part I of the talk,
11:32.1 I've gone through really the conceptual foundations
11:34.1 of what it is that I want to get across to you today.
11:36.3 We've talked about large-bodied predators
11:39.1 and that they have been part of our living world
11:42.3 for the last half a billion years.
11:45.1 I've talked about the concept of a food web,
11:47.2 a food web being the way in which species
11:50.2 interact with one another
11:52.1 through consumer-prey interactions,
11:54.0 and the food web being really
11:56.1 nothing more than a roadmap
11:58.1 of who is eaten by whom in nature.
12:00.1 I've told you that to understand and study these complex food webs,
12:03.3 it's often necessary to modularize or simplify them,
12:06.1 that is, to pick a series of species or processes
12:08.2 that we can manage and deal with,
12:10.2 because of the tremendous complexity
12:12.2 of virtually all food webs in nature.
12:15.0 I've told you a little bit about the nature of species interactions
12:18.1 and I've dichotomized
12:21.0 the way in which these processes work
12:22.2 between what I call bottom-up forcing and top-down forcing.
12:27.0 I've told you about two different ways
12:29.0 of thinking about species interactions,
12:30.2 that is, direct interactions
12:33.0 in which there are no interceding species
12:34.2 and indirect interactions
12:36.0 where a species might have an effect on some other species
12:39.0 by way of one or more intervening species.
12:42.2 I have argued that the way in which we understand this dynamic process,
12:48.1 and the only way that we can really see this in nature,
12:50.3 is by perturbing species.
12:53.2 By perturbing species,
12:55.1 we see the consequences of species interactions
12:57.1 that are simply not possible to see otherwise.
12:59.2 And at the end I told you
13:02.3 a little bit about some of the complexities of understanding
13:04.2 the functional relationships between
13:07.1 the abundance of a species and its effect on nature,
13:09.2 and we have discussed situations
13:12.1 where that might vary linearly,
13:13.2 we talked about the possibility that these things vary nonlinearly,
13:17.3 where we have what we call very abrupt phase shifts,
13:19.2 where we see virtually no effect over varying ranges
13:22.3 of particular species abundance
13:24.2 and then a very strong effect,
13:26.1 and we've talked about hysteresis,
13:28.1 which is the notion that the directionality or form...
13:31.2 or the form of these functional relationships
13:34.0 varies with directionality.
13:35.2 So, that gives you a conceptual foundation
13:38.0 for where I'm going to be going for the rest of this talk.
13:40.2 In Part II, I'll be talking about
13:43.2 the work that my lab has done on sea otters and kelp forests
13:45.3 over the last several decades,
13:47.2 and in Part III I'll be expanding the perspective
13:52.0 to other species and systems in nature.
13:54.1 Thanks very much for your attention
13:55.3 and I look forward to rejoining you for Part II of the talk.
13:58.3 Thank you.
- Duration: 41:42
- Margaret McFall-Ngai iBioSeminar: Living together: The Symbiosis of Host-Microbial Interactions
- Jared Leadbetter iBioSeminar: Termites and Their Symbiotic Gut Microbes
- James Estes: The Ecological Function of Apex Predators
- Ian Baldwin iBioSeminar: Studying a Plant’s Ecological Interactions in the Genomics era: the Story of Nicotiana Attenuata
Dr. Ian Baldwin is a professor and director of the Max Planck Institute for Chemical Ecology where he studies the Nicotiana attenuata as a model organism to understand how plants solve ecological problems. Baldwin received his AB in Chemistry and Biology from Dartmouth College in 1981 and started his graduate studies at Cornell University where… Continue Reading
Dr. James Estes is a Professor of Ecology and Evolutionary Biology at the University of California Santa Cruz. He completed his undergraduate degree in zoology at the University of Minnesota, a M.S. in biology at Washington State University, and a PhD in biology and statistics at the University of Arizona. Estes is known for his… Continue Reading
Jared Leadbetter was an undergraduate biology student at Goucher College when he attended a summer course on microbial diversity at the Marine Biological Laboratory in Woods Hole, Massachusetts. It was here that he first became fascinated with the amazing environment of the termite gut. Leadbetter went on to study termite gut microbes for his PhD… Continue Reading
Dr. Margaret McFall-Ngai is a Professor and Director of the Pacific Biosciences Research Center at the University of Hawaii Manao. Her laboratory studies the symbiotic relationship between hosts and microorganisms. She uses the Hawaiian bobtail squid as a model organism and studies its symbiotic relationship with the bacteria Vibrio fischeri. McFall-Ngai uses this binary symbiosis… Continue Reading