The Making of a Parasitic Plant: Parasitism as a Life Strategy • iBiology

00:00:06:16 Hi, I'm Dr. Caitlin Conn,
00:00:08:22 and I'm an assistant professor of biology
00:00:11:12 at Berry College in Georgia.
00:00:13:16 And today I'm going to introduce you
00:00:15:22 to some amazing plants that I've been studying
00:00:19:01 since I was in graduate school.
00:00:21:14 These plants are amazing because they're parasitic.
00:00:24:23 So they steal resources from other plants.
00:00:28:13 And here, you can see three examples of parasitic plants
00:00:32:05 but you'll soon be familiar with many more.
00:00:36:02 Throughout today's lecture,
00:00:37:11 we'll focus on three different learning objectives.
00:00:40:18 The first is to explore parasitic plants
00:00:43:20 within the broad context of parasitism.
00:00:47:00 Next, we'll identify common adaptations
00:00:50:16 among different groups of parasitic plants.
00:00:53:10 And then we'll discuss the range of host dependence
00:00:56:20 that we observe among different parasitic plants.
00:01:00:16 And we'll also have three key concepts today.
00:01:03:24 So the first is symbiotic relationships
00:01:06:24 or long-term interactions
00:01:09:04 between members of different species.
00:01:12:05 The second key concept is convergent evolution,
00:01:15:21 which happens when similarities evolve independently
00:01:19:22 in different groups of organisms.
00:01:22:10 And the third key concept is trait reduction,
00:01:25:22 which is the loss of genes, processes,
00:01:29:12 or structures that we commonly observe among parasites.
00:01:34:08 So let's dive in to that first key concept right away.
00:01:39:08 As you just heard, symbiotic relationships
00:01:41:28 are long-term interactions
00:01:43:25 between members of different species,
00:01:46:02 and these interactions persist across generations.
00:01:50:15 These symbiotic relationships can have different outcomes
00:01:54:05 for the organisms involved,
00:01:56:08 depending on the type of relationship
00:01:58:17 that we're talking about.
00:02:00:08 So here we have an example of a symbiotic relationship
00:02:04:18 that's beneficial for both members.
00:02:07:23 We have a plant, specifically a legume,
00:02:10:27 and we're looking at its roots.
00:02:12:20 And if you look where the white arrow is pointing,
00:02:15:13 you'll see a nodule and you can see other nodules
00:02:18:22 in the roots here as well.
00:02:20:10 And inside these nodules, there are bacteria
00:02:24:14 that take nitrogen from the atmosphere
00:02:27:10 and convert it into a form that the plants can use.
00:02:31:06 And in exchange for this service,
00:02:33:10 the bacteria get resources from the plant.
00:02:36:27 So again, this is a symbiotic relationship
00:02:39:27 in which both members benefit.
00:02:43:04 In some symbiotic relationships, one partner benefits
00:02:46:27 while the other may be neither helped nor harmed.
00:02:50:20 And a commonly cited example of this
00:02:53:07 is the relationship between bromeliads and frogs.
00:02:57:14 Bromeliads are mostly tropical plants
00:03:00:14 and they often hold water among their leaves.
00:03:03:28 And some frogs will lay their eggs
00:03:06:20 in the water held by bromeliads
00:03:08:28 and their tadpoles will hatch and mature there.
00:03:12:06 And it's often thought that this symbiosis
00:03:15:02 is beneficial for the frogs
00:03:17:16 but it doesn't really have an impact on the bromeliads.
00:03:22:06 And still other symbiotic relationships can be beneficial
00:03:26:05 for one member and harmful to the other.
00:03:29:14 So consider mistletoe.
00:03:31:14 In this picture, mistletoe looks like the clusters of green
00:03:35:09 up in the branches of the tree.
00:03:37:16 Mistletoe lives in trees and it physically attaches itself
00:03:42:00 to the trees and it steals resources.
00:03:45:10 So mistletoe is indeed a parasitic plant.
00:03:49:00 Mistletoe doesn't usually kill its hosts
00:03:51:28 but heavy infestation can be harmful to the health
00:03:55:16 and development of a tree.
00:03:58:14 So these three examples of symbiosis
00:04:01:06 that we just discussed fall into three different categories.
00:04:05:14 With mutualism, both partners benefit.
00:04:08:15 With commensalism, one partner benefits
00:04:11:11 and the other isn't impacted.
00:04:13:26 And with parasitism, one member benefits
00:04:16:25 at the expense of another.
00:04:19:26 Now, throughout this lecture,
00:04:21:15 there will be some questions written in blue.
00:04:24:22 And whenever you see one, I encourage you
00:04:27:10 to pause your video and take a few minutes
00:04:30:06 to consider the answer.
00:04:32:10 So the first question is this,
00:04:34:10 besides these three examples of symbiosis
00:04:37:28 that we just discussed, what other examples
00:04:41:00 can you think of of mutualism, commensalism and parasitism?
00:04:51:25 Now, let's move on to learning objective one,
00:04:54:22 which is to explore parasitic plants
00:04:57:20 within the broad context of parasitism.
00:05:00:28 Parasitism is found across the tree of life.
00:05:04:08 So bacteria are parasitic if they take resources from a host
00:05:09:19 and a well-known example is listeria monocytogenes,
00:05:13:19 which can cause illness in humans who ingest food
00:05:17:18 that's contaminated by it.
00:05:19:24 Animals can be parasitic.
00:05:21:18 So think of the worms that live
00:05:23:22 inside the gastrointestinal system of humans,
00:05:27:04 pets and farm animals.
00:05:29:14 There are many well-known examples of parasitic protists.
00:05:33:10 And one is leishmania, which is transmitted
00:05:36:21 by biting sandflies and can make people pretty sick.
00:05:41:09 Parasitic fungi include the smut fungus,
00:05:44:20 which uses important crops
00:05:46:23 namely grasses and sedges as a host.
00:05:50:12 And as you know by now, plants can be parasitic.
00:05:53:20 The parasitic plant that you see here
00:05:55:28 is called Triphysaria versicolor,
00:05:58:04 and it doesn't look that unusual for a plant,
00:06:01:22 but underground, it attaches itself to host plants
00:06:05:14 and steals resources.
00:06:08:12 So now let's focus specifically on parasites
00:06:11:24 in the plant kingdom, and let's discuss
00:06:14:02 a few remarkable examples of parasitic plants.
00:06:18:11 This parasitic plant is one of my favorites
00:06:20:25 and it's commonly called the Australian Christmas tree
00:06:23:28 because it produces these beautiful orange blooms
00:06:27:12 around December.
00:06:29:02 It attaches to host plants underground
00:06:31:14 using specialized invasive structures.
00:06:34:05 And sometimes those invasive structures
00:06:37:03 mistake inanimate objects for host plants.
00:06:40:24 For example, this parasitic tree
00:06:43:03 has been found attached to underground power cables.
00:06:48:25 Our next remarkable parasitic plant is Rafflesia arnoldii
00:06:52:21 or corpse flower and it produces
00:06:55:05 the largest flower of any plant species.
00:06:58:20 It's beautiful, but it's called corpse flower
00:07:01:12 because it smells like a rotting corpse.
00:07:04:03 And this smell attracts insect pollinators.
00:07:07:24 This huge flower doesn't last long.
00:07:10:03 And in fact, the corpse flower plant
00:07:12:22 spends most of its life inside of a host.
00:07:15:28 And when it finally emerges,
00:07:17:25 it lacks many of the structures that we typically associate
00:07:21:11 with plants like stems, leaves, and roots.
00:07:25:21 And the final remarkable parasitic plant
00:07:28:05 that we'll discuss here is unfortunately remarkable
00:07:31:26 in its negative impact on agriculture.
00:07:35:04 This is Striga hermonthica or witch weed.
00:07:38:07 And in this picture, it's the plant
00:07:40:12 with the pink flowers.
00:07:42:11 Striga species parasitize grass crops usually
00:07:46:20 like corn, which is what's shown in this picture,
00:07:49:24 or rice. And Striga species cause billions
00:07:53:12 of dollars of yield losses every year.
00:07:56:15 Striga outbreaks are very difficult to control
00:07:59:18 for a number of different reasons.
00:08:01:18 First, a single Striga plant
00:08:03:25 can produce tens of thousands of tiny,
00:08:06:12 easily dispersible seeds.
00:08:08:12 And those seeds can remain dormant in the soil
00:08:11:08 for years if necessary.
00:08:13:10 And they only germinate when they detect a nearby host.
00:08:17:25 Shortly after germination, they attach to that host,
00:08:21:09 and by the time they become visible above the soil surface,
00:08:25:14 damage has already been done.
00:08:27:27 Now, we call parasitic plants that attack crops
00:08:31:08 or other plants cultivated by humans, parasitic weeds.
00:08:35:24 And Striga species are some of the most destructive
00:08:39:03 parasitic weeds in the world.
00:08:42:20 Different groups of parasitic plants
00:08:44:26 have evolved different ways to attach to a host.
00:08:48:09 Most of the parasites that we'll talk about today
00:08:50:26 attach directly to a host.
00:08:53:13 But mycoheterotrophs are different
00:08:55:23 because they go through a fungal intermediate.
00:08:59:10 So mycoheterotrophs connect themselves
00:09:02:03 to a mycorrhizal fungus that's usually in a mutualism
00:09:06:20 with a non-parasitic plant.
00:09:08:28 So the fungus becomes an unwitting middleman,
00:09:12:05 involuntarily shuttling resources
00:09:14:22 from its mutualistic, non-parasitic plant partner
00:09:18:22 to the parasite.
00:09:20:10 The mycoheterotrophs shown here are all orchid species.
00:09:24:02 And in fact, many orchids and many other plant species
00:09:27:29 as well are mycoheterotrophic at some point in life.
00:09:33:10 But most of the parasites we'll talk about
00:09:35:16 connect directly to a host.
00:09:37:18 They're called haustorial parasites.
00:09:39:25 And that's because the specialized invasive structure
00:09:43:15 that they use to get inside of a host
00:09:46:01 is called a haustorium.
00:09:48:15 And haustorial plants are quite diverse.
00:09:51:20 They include the familiar mistletoe,
00:09:54:10 the bizarre looking plant in the middle,
00:09:56:24 known as jackal food, and the parasitic weeds
00:10:00:19 and their less destructive relatives,
00:10:03:03 one of which is shown on the right.
00:10:06:24 Now, here we have a phylogeny of angiosperms
00:10:10:16 or flowering plants.
00:10:11:29 And this phylogeny comes from Professor Dan Nickrent
00:10:15:16 who maintains The Parasitic Plant Connection website.
00:10:19:11 Check it out for more information on
00:10:21:28 and great photos of parasitic plants.
00:10:25:20 So in this phylogeny, we're seeing a tree-like structure
00:10:29:26 that shows us the evolutionary history
00:10:32:23 of the plant groups labeled on it.
00:10:35:14 And any plant groups labeled in red
00:10:38:07 include haustorial parasites.
00:10:41:04 You'll notice that some of these red groups
00:10:43:22 are not that closely related to other red groups.
00:10:47:18 So it's pretty intuitive
00:10:49:09 that in those distantly related groups of parasites,
00:10:52:29 parasitism would have evolved independently.
00:10:56:18 But in some other cases, these red groups
00:10:59:18 are pretty closely related to other red groups.
00:11:02:07 And it's a little harder to tell whether parasitism
00:11:05:19 evolved independently in those groups
00:11:08:02 or whether it was inherited from a common ancestor.
00:11:12:02 But scientists have taken a closer look
00:11:14:16 at each of the groups labeled in red
00:11:16:25 and determine that parasitism
00:11:19:05 did indeed evolve independently in each of those groups.
00:11:23:18 And when a similarity or a trait like parasitism
00:11:27:14 evolves independently in different groups,
00:11:30:14 that's called convergent evolution.
00:11:32:28 And that's our second key concept in this lecture.
00:11:37:20 But why has parasitism evolved so many times among plants?
00:11:42:13 Well, to start to address this question,
00:11:44:29 think about the community of plants
00:11:46:27 that you would typically find in a forest.
00:11:50:01 Most of them are in competition
00:11:52:07 with one another for access to resources.
00:11:56:05 So parasitic plants may have an advantage
00:11:59:11 because instead of battling it out with other plants,
00:12:03:01 they can just steal from somebody
00:12:05:02 who has already obtained resources.
00:12:07:24 So in that sense, at least for parasitic plants,
00:12:11:06 cheating is an alternative to competing.
00:12:15:00 So pause and ask yourself this question.
00:12:17:26 What are some of the resources
00:12:19:24 that plants are typically competing for?
00:12:24:02 And now focus on the parasitic plant
00:12:26:13 on the right side of this slide.
00:12:28:11 This is called Conopholis americana, and it's a small plant.
00:12:32:07 It stands less than a foot tall, but its hosts are huge.
00:12:36:22 They're oak trees.
00:12:38:11 So relative to non-parasitic understory plants,
00:12:42:19 what advantage might Conopholis gain
00:12:45:22 by parasitizing large hosts like oak trees?
00:12:51:11 Now, an answer to the question
00:12:53:10 of why parasitism has evolved so many times among plants
00:12:57:20 may be found in the ecological principle
00:13:00:18 of competitive exclusion.
00:13:02:21 And this principle tells us that two species
00:13:05:28 cannot coexist in the long run
00:13:08:20 if they have the exact same ecological niche.
00:13:12:07 So they have to evolve different ways
00:13:15:01 to interact with their environment,
00:13:17:04 different ways to obtain and utilize resources
00:13:20:26 if they're going to coexist in the long run.
00:13:24:09 So if parasitic plants are using a host
00:13:28:05 to get their resources and non parasitic plants
00:13:31:10 are getting resources for themselves,
00:13:33:22 then those species have indeed evolved different
00:13:36:21 ecological niches and can persist together
00:13:40:12 over the long run.
00:13:46:04 So we've talked about one major example
00:13:48:28 of convergent evolution,
00:13:50:21 and that's the evolution of parasitism
00:13:53:04 across the tree of life and in the plant kingdom.
00:13:56:20 And now let's talk about some common adaptations
00:14:00:08 that have evolved convergently
00:14:02:13 among different groups of parasitic plants.
00:14:05:14 This is our second learning objective.
00:14:08:05 So here, you see two images
00:14:10:11 and they represent parasitic plants
00:14:12:21 from groups that independently
00:14:14:27 or convergently evolved parasitism.
00:14:18:06 And one adaptation that has evolved convergently
00:14:21:24 in these groups is a way to sense a host.
00:14:24:28 So at the top we have a parasite called dodder
00:14:28:01 and it picks up on nearby hosts when it detects metabolites
00:14:32:20 that those hosts are releasing into the air.
00:14:36:03 At the bottom, we have a parasitic plant
00:14:38:20 from the Orobanchaceae family.
00:14:40:27 And for some parasites in this family,
00:14:43:14 host detection has to happen before seed germination.
00:14:47:09 So it's usually happening underground
00:14:50:03 when those parasites seeds pick up on hormones
00:14:53:08 released by host plants.
00:14:55:17 So these hosts detection mechanisms are different
00:14:58:24 in the two groups of parasites shown here
00:15:01:18 but they serve a similar purpose,
00:15:03:21 which is to connect the parasitic plant with its host.
00:15:08:24 And of course, if haustorial parasitism
00:15:11:13 has evolved independently among plants,
00:15:14:09 then haustoria themselves
00:15:16:05 have evolved independently as well.
00:15:18:25 So on the top, you see haustoria from dodder
00:15:22:02 and they are penetrating the stems of a host plant.
00:15:26:02 In the Orobanchaceae, the haustoria
00:15:28:20 connect the parasites to a host's roots.
00:15:32:04 So again, the haustoria are different
00:15:34:13 in these two groups but have evolved convergently.
00:15:39:09 So now let's take a look at an amazing video
00:15:42:13 of one of those parasites, dodder,
00:15:44:25 as it goes through its life cycle.
00:15:47:18 This video comes from the lab of Dr. Jim Westwood,
00:15:51:09 who is a professor at Virginia Tech.
00:15:54:04 And you'll see a time lapse
00:15:56:09 of dodder's entire life cycle, really.
00:15:59:18 So here, it's germinating and the parasite seedlings
00:16:04:13 are growing up above the surface of the soil.
00:16:09:10 Pretty soon, you'll see them seeking out a host.
00:16:12:21 And remember that for dodder,
00:16:15:04 host detection happens when the parasite picks up
00:16:18:13 on those metabolites that the host plant
00:16:21:00 is releasing into the air.
00:16:23:24 So once dodder finds a host, it's going to coil itself
00:16:28:08 around that host plant.
00:16:30:04 You can see that up close right here.
00:16:33:25 The host plant in this video is tomato.
00:16:36:27 So dodder is wrapping itself around the tomato
00:16:41:28 and now you can see it forming haustoria.
00:16:44:22 They look like swellings that are growing inward
00:16:47:17 from the dodder toward the stem of that tomato host.
00:16:51:03 And those haustoria will indeed invade
00:16:54:15 the host plant's tissues,
00:16:56:07 and set up the connection so that the dodder
00:16:59:03 can steal resources.
00:17:02:21 The dodder continues growing on its tomato host.
00:17:08:13 And pretty soon we're gonna zoom out
00:17:10:05 for a bigger picture view of dodder interacting
00:17:13:29 with its host.
00:17:17:16 So here we have the dodder plant,
00:17:19:22 seeking out more of its tomato host.
00:17:28:11 And by the end of the video,
00:17:30:02 you'll see that those potted tomato plants
00:17:32:23 are completely covered by the dodder.
00:17:36:29 So clearly the dodder has been quite successful
00:17:39:25 in its host seeking
00:17:41:15 and its attachment to and parasitism of the tomato hosts.
00:17:47:26 Now we've started to address this question already
00:17:50:15 but pause your video for a minute
00:17:52:06 and ask yourself what traits parasitic plants share?
00:17:56:23 Besides the ones we've discussed already,
00:17:58:29 can you make hypotheses about other traits
00:18:01:29 that parasitic plants might have in common?
00:18:06:24 Well, we've already talked about the invasive haustorium
00:18:10:16 and it turns out that parasitic plants
00:18:13:01 from different groups have, in some cases,
00:18:16:10 convergently evolved reduced or absent structures
00:18:20:10 like leaves and roots
00:18:21:26 and have convergently lost photosynthesis.
00:18:26:03 Let's look at the haustoria again, first.
00:18:28:19 So here we have the haustoria
00:18:30:10 from dodder going into the stem of a host plant.
00:18:34:03 And now we have mistletoe in the middle,
00:18:36:24 and a parasitic vine on the right side of this slide.
00:18:40:14 And the haustoria are marked with white arrows
00:18:43:11 and you can clearly see how those haustoria
00:18:46:17 are connecting the parasitic plant to its host.
00:18:51:25 Now, let's talk about structural reduction.
00:18:54:09 So take a look again at Conopholis americana.
00:18:58:08 So this is that small understory plant that uses oak hosts.
00:19:03:01 The cream colored projections
00:19:04:28 coming off of this plant are the flowers,
00:19:07:10 and the leaves aren't so easy to see
00:19:10:10 because they've been reduced to scales.
00:19:12:22 They're present underneath the flowers.
00:19:16:24 Other parasitic plants from different groups
00:19:19:05 have also lost structures like leaves.
00:19:21:23 So on the left, we have a parasitic plant
00:19:24:09 called jackal food, you've seen it before,
00:19:26:25 and it doesn't have leaves either
00:19:28:27 although jackal food and Conopholis
00:19:31:04 do have roots and they use them to connect to a host plant.
00:19:35:14 And on the right, we have dodder,
00:19:37:18 and dodder also doesn't have apparent leaves
00:19:40:10 because its leaves have been reduced to scales.
00:19:43:21 And once dodder gets established on a host plant,
00:19:47:06 its roots will rot away
00:19:49:02 because it doesn't need them anymore.
00:19:50:25 It's fully reliant upon a host.
00:19:54:08 Photosynthesis has also convergently been reduced
00:19:58:04 or lost by parasitic plants from these different groups.
00:20:01:28 And that's why you don't see green tissue
00:20:05:00 on these parasitic plants.
00:20:12:14 So that brings us to our third and final learning objective,
00:20:16:16 and that's to discuss the range of host dependence
00:20:19:17 that we observe among parasitic plants.
00:20:22:16 So the parasitic plants that can photosynthesize
00:20:25:21 for themselves are known as hemiparasites.
00:20:29:16 Some can live with or without a host,
00:20:31:29 those are facultative hemiparasites,
00:20:34:11 but some photosynthetic hemiparasites
00:20:37:09 do need a host to complete their life cycle,
00:20:40:07 and they're called obligate hemiparasites.
00:20:43:14 The parasites that have lost photosynthetic ability
00:20:46:20 are fully reliant upon a host
00:20:49:09 to get through their life cycle.
00:20:50:26 So they're called obligate holoparasites.
00:20:54:12 So pause for a minute and ask yourself this,
00:20:57:26 why would parasitic plants lose the ability
00:21:01:12 to carry out photosynthesis?
00:21:04:00 Photosynthesis generates sugars for the plant,
00:21:06:24 so wouldn't it be really bad
00:21:08:22 to lose the ability to photosynthesize?
00:21:12:27 And as a followup question,
00:21:14:24 what are some of the consequences of losing that ability
00:21:18:15 to carry out photosynthesis?
00:21:22:22 Well, it turns out that this loss of photosynthesis
00:21:26:05 and this reduction or loss of certain structures
00:21:29:19 fall into a phenomenon known as trait reduction.
00:21:33:17 And trait reduction happens in parasites
00:21:36:26 because if parasites can either carry out
00:21:40:18 physiological processes and obtain resources for themselves
00:21:45:20 or they can rely on a host's physiological processes,
00:21:49:19 and steal resources from the host,
00:21:52:10 well, then, natural selection often stops maintaining
00:21:56:18 those processes and structures in the parasite
00:22:00:09 if it can rely on a host to meet its needs.
00:22:04:01 And of course the consequence of this
00:22:06:05 is complete dependence upon a host.
00:22:08:28 And we see this in diverse parasites
00:22:11:24 from across the tree of life.
00:22:13:16 So for example, on the left, we have a chlamydia bacterium.
00:22:18:10 And these parasitic chlamydia bacteria
00:22:21:14 cause the sexually transmitted infection known as chlamydia.
00:22:25:11 And their genome, their entire collection of DNA
00:22:29:05 has likely been reduced by 3/4 or more,
00:22:32:19 relative to non-parasitic ancestors.
00:22:36:00 In the middle, we have a eukaryotic parasite
00:22:39:09 known as microsporidium,
00:22:41:14 and it has undergone genomic, structural,
00:22:44:24 and metabolic reduction.
00:22:47:06 And on the right, we have our familiar dodder plant.
00:22:51:00 Let's take a closer look at dodder.
00:22:53:03 And this time, it's just at the seedling stage.
00:22:57:17 So this dodder plant is emerging from a seed
00:23:00:20 and it lacks some of the structures that we typically see
00:23:04:06 in photosynthetic plants as they germinate.
00:23:07:14 So on the right, we have a cartoon of the germination
00:23:11:06 of a photosynthetic plant, and we can usually see
00:23:14:08 a root and embryonic leaves called cotyledons emerging.
00:23:19:14 But in dodder, those cotyledons are absent
00:23:22:12 and the root may be absent as well.
00:23:25:05 And remember that once dodder gets established
00:23:28:02 on a host plant, its root rots away.
00:23:33:01 So these parasites that are fully reliant upon a host
00:23:36:16 have to adapt to that host.
00:23:38:21 And the host can adapt in response.
00:23:42:08 Now, some obligate parasitic plants
00:23:44:24 like Striga on the left,
00:23:47:11 use hosts that are typically only around for a short time.
00:23:51:20 So Striga parasitizes corn or maize.
00:23:54:23 And it's usually only around for a single growing season.
00:23:58:23 But other obligate parasitic plants like Conopholis,
00:24:02:08 on the right, parasitize long-lived hosts like oak trees.
00:24:07:19 So what adaptations do you think a parasite of annual
00:24:12:11 or short-lived hosts would have?
00:24:14:16 And what adaptations do you think a parasite
00:24:17:12 of longer lived hosts might have?
00:24:20:04 Pause for a moment and consider that question.
00:24:24:22 With that, we'll wrap up this lecture
00:24:27:05 and we'll go through a quick recap
00:24:29:04 of everything we discussed.
00:24:30:29 So first of all, we got acquainted
00:24:33:17 with parasitic plants and we saw diverse
00:24:36:17 and amazing examples of parasitism in plants
00:24:40:16 in groups that independently evolved to be parasitic.
00:24:45:16 Then, we saw some different cases of convergent evolution.
00:24:49:23 Parasitism convergently evolved
00:24:52:01 across the tree of life and in plants.
00:24:54:21 And then we saw some adaptations
00:24:56:15 that convergently evolved among parasitic plants as well.
00:25:01:02 Then, we discussed the range of host dependence
00:25:03:26 that we see in parasitic plants.
00:25:05:24 And we noted that some have to have a host
00:25:08:26 to complete their life cycle.
00:25:10:28 So before we end this, I have three final questions
00:25:14:09 for you to consider.
00:25:16:08 First of all, what environmental conditions
00:25:19:04 might favor the evolution of parasitism in plants?
00:25:23:16 Think about things like climate, resource availability
00:25:27:04 and the other plants and non-plant members
00:25:30:04 of a particular community.
00:25:33:03 Next, what unique challenges might parasitic plants face?
00:25:37:23 Stealing from a host might seem
00:25:39:23 like an easy way to get through life,
00:25:41:25 but what are some of the difficulties
00:25:44:04 that are associated with this lifestyle?
00:25:47:15 And finally, what traits are parasites unlikely to lose?
00:25:52:05 Another way to think about this is what traits
00:25:55:08 could a host not compensate for
00:25:58:00 if a parasite were to lose them?
00:26:00:23 So that's it for today's lecture.
00:26:02:17 Thank you for tuning in.
00:26:03:27 And I hope that you enjoyed this exploration
00:26:06:25 of parasitism in plants.

This Talk

Speaker: Caitlin Conn

Audience:

General Public
Educators of H. School / Intro Undergrad
Student
Educators

Recorded: June 2020

Educator Resources for this Talk

Talk Overview

In this active learning lecture, the following learning objectives are addressed:

Explore parasitic plants within the broad context of parasitism
Identify common adaptations among parasitic plants
Discuss the range of host dependence among parasitic plants

Parasitic plants are important in natural ecosystems and in agriculture. Parasitism is a successful life strategy that has convergently evolved in all kingdoms of life. Some parasitic plants indirectly steal nutrients from other plants by tapping into a fungal intermediate, while others form direct connections to hosts with a specialized invasive structure called a haustorium. Haustorial parasitism has convergently evolved multiple times among flowering plants, and stealing nutrients likely gives parasites a competitive advantage. To succeed as parasites, plants need mechanisms for host detection and for nutrient acquisition. Thus, similar traits have convergently evolved in plants with independent origins of parasitism. Finally, host dependence varies among parasitic plants.

This video is designed to accompany the Teaching Tools in Plant Biology resource “It’s not easy being not green – the making of a parasitic plant.” developed by Dr. Caitlin Conn and Dr. David Nelson.

Speaker Bio

Caitlin Conn

Caitlin Conn

Caitlin Conn received her PhD in genetics from the University of Georgia, where she investigated how the seeds of parasitic plants perceive nearby hosts. After completing two postdoctoral fellowships at Spelman College and Emory University, she started her own research program as an assistant professor at Berry College in Rome, GA. At Berry, the Conn… Continue Reading