University Place

Alternate Lifestyles: Plants that Eat Animals

[Carol Shirk, Dodge County Master Gardener Association]

My name is Carol Shirk, and I’m with the Dodge County Master Gardener Association.

Thank you for coming.

Tonight, we have with us Erica Young. She is an associate professor in the Department of Biological Sciences at UW in Milwaukee. Tonight, she’s gonna present a profile of plants that not only capture insects, prey, to supplement their nutrient intake, but she’s also going to present with us animals that farm a range of invertebrates and bacteria to support their nutrient requirements in order to thrive on a nutrient poor wetland ecosystem. So, we’re gonna talk about farmer plants tonight.

Erica grew up in Western Australia, where there is a wide diversity of plants. She also lived in Sweden, she lived in Ireland, but now she resides in beautiful Wisconsin.

So please join me in welcoming Erica.

[applause]

[Erica Young, Assistant Professor of Biological Sciences, University of Wisconsin-Milwaukee]
Thank you very much, and thanks for being here tonight. So yes, I’m gonna give you a little bit of a profile of some of the carnivorous plants that I’ve gotten to know over the years and give you a little bit of information about the research we’re also doing on these plants.

So, my outline of my talk. I’m gonna tell you a little bit about, what what are carnivorous plants, and why are they – have they become carnivorous? Where you’re gonna find carnivorous plants. Which plants are carnivorous? Which types? I’m gonna take you through a profile of a few plants that are carnivorous. And then I’m gonna finish with some of our work on pitcher plants, bugs, and bacteria I’m gonna call this, talking a little bit about our research.

So, what are carnivorous plants? So, I did a Google hit a Google search on carnivorous plants. Last time I gave this talk, it was around 990,000. It’s now over a million hits for carnivorous plants. There’s a huge interest in carnivorous plants, but there’s also a lot of maybe misinformation or maybe sensationalized information about carnivorous plants.

So, I’m gonna tell you – start by telling you what carnivorous plants are NOT. So, they are NOT parasitic. This plant in the middle there is a a a parasitic orchid. We also have the parasitic Rafflesia here. We have a number of orchids that are parasitic, and mistletoe here.

They’re also not any large plant that gives off some kind of an odor to attract insects. So, this is – these are not carnivorous plants. We’re not talking about any of these type of plants, although these are fascinating in other ways.

So, just to remind you, how do plants get their nutrients? Of course, you’re familiar with how they can – they need light. They take CO2 up from the atmosphere to do photosynthesis. They’re also getting water and nutrients like phosphorous, nitrogen, potassium, and those things that you’re used to putting – helping supplement the soil to allow that plant to grow well.

So, carnivorous plants also do all of these things. They just – they started out as normal plants, but then they evolved additional characteristics.

So, why did they do this? Why are they carnivorous? They’re carnivorous because they grow in a lot of ecosystems that don’t have a lot of nutrients in the soil. So, you know as gardeners that you often need to add nutrients to the soil. You add fertilizer. You add compost and such. But out in the world, here in boreal ecosystems, in sandy ecosystems, in bog wetland ecosystems, there’s often not enough nutrients in those ecosystems to support good growth of plants.

So, carnivorous plants tend to do well in these type of ecosystems because they have this way of getting extra nutrients that they can’t get from the soil. So, most carnivorous plants that you come across live in fens and bogs.

So, they typically, in a review in 1984, Tom Givnish said that they typically grow in sunny, wet environments where the soil conditions provide inadequate mineral nutrients. They’re getting enough sunshine here, but they can’t get enough nitrogen, phosphorous, and potassium from the soil.

So, what are they? What are we talking about, these types of plants? There’s a few examples here. But carnivorous plants are plants that as well as doing all those things that normal plants do, they also can absorb nutrients from dead animals, typically insects, and through this, they gain increased growth, it improves their survival, or they can reproduce faster or better because of that capacity to be carnivorous.

So, this comes through a range of adaptations that allow them to attract and capture and then of course digest those insect prey to extract the nutrients out of them.

So, types of carnivorous plants. This shows you essentially a family tree of plants. We’ve got monocots up here, we’ve got a range of different dicot groups down here, and a whole range of different names. You can’t probably see them so well, but the ones with colors here are the ones that in green, this whole group, this family, the Droseraceae are carnivorous. Up here, we have Bromeliaceae. Some of -some the bromeliads are carnivorous. And then there’s a few that are, hmm, maybe carnivorous. We haven’t done enough work to really decide whether they are or not.

So, the thing that you can take away from this is, there’s over 600 species of carnivorous plants known, and these have evolved multiple times. These guys here are not related to these ones down here. And so, they’ve come up with this strategy to use insects, capture insects, and become carnivorous because it’s a really, really good idea, and it’s what we might call convergent evolution. This group here has a similar characteristic or adaptation to a group down here.

Okay. So, what do they manage to catch? So, what I’ve done with my colleagues Ellison and Gotelli here showed a profile of a whole range of different types of carnivorous plants, and then said: “Well, exactly what are they catching?” So, I’ll take you through this diagram here. This shows a range of different groups of insects and spiders and springtails the Venus flytrap is catching. The red there mostly is Formicaceae, which is ants. The green here is spiders. The sundews are also catching Diptera, which are the flies. Pinguicula also catches lots of flies. The pitcher plants here, the Nepenthes and the Sarracenia, are also catching lots of ants. And this group down here also catch mostly ants. Whereas Triphyophyllum is catching ants, flies, as well as spiders.

So, sticky surfaces tend to catch flies, whereas pitchers catch ants that, kind of, tumble in and then can’t get out again. Traps can catch things that crawl around, like spiders and flies. You might notice there’s not many butterflies, there’s Lepidoptera down here in this purple. Only a few of those are caught. But many more in the other – other groups. So, not many butterflies, not many moths, not many bees or wasps.

And this might be important, because these carnivorous plants are also flowering plants, so they need pollinators. You see this is a flower from Sarracenia. This is a sundew with a flower on it. A whole range of other plants here. Beautiful flowers, and including the – the examples that I brought, which I hope you can come up and have a look at after the talk, with some beautiful flowers on them. So, there’s this, sort of, contrast between wanting to capture insects and then needing them to do the pollination that’s essential for reproduction for these plants. So, it seems that they use different groups of insects to – to – essentially to eat versus to use as pollinators.

Okay. So how good are they at actually catching stuff? So, these guys here with the big sticky surface, they tend to be fairly good at capturing, but pitcher plans here, they’re capturing less than five percent of the insects that visit, tumble in. It’s not a really good capture rate. It’s a good thing they’re not relying that to- to get their dinner. They’re only relying on it just to, kind of, help to supplement that nutrient intake.

So, prey capture and retention, keeping those insects in there, is relatively rare.

So, in this beautiful watercolor of Nepenthes here, you see the leaf and then the beautiful pitchers that result on the end. You can see this – it costs a lot of energy to make these pitchers. If youre a plant that’s only making leaves, you’re gonna have a lot more energy available to make more leaves than if you have to make these huge, elaborate pitchers. So, this will only pay off for the plant if they gain a benefit by having those pitchers. So, it only pays off one, when there’s high light, so there’s a lot of energy coming in they can use for photosynthesis, but also when there’s not – not much nutrients and so there’s a real incentive to be able to make those structures.

[advances one slide too far]

Oops.

So, that occurs in these ecosystems like this bog where you’ve got bright sunlight, lots of energy, but low nutrients.

So, how much does this really help? So, there have been some studies to try and work out how much these plants are actually benefiting from the nutrients that are coming in from insects. So, this has been investigated – investigated using natural isotopes of nitrogen. There’s two different types of nitrogen that are slightly different. You can measure that on a mass spectrometer and then work out how much of the nitrogen are they getting from the soil versus how much are they getting from the insects that fall in and are digested.

So, we’ve got the Nepenthes pitcher plant. Up to 70% of the nitrogen that is inside that plant here is coming from insects, whereas something like Sarracenia is only around 15%. And there’s a range of other plants. The Dionea, the Venus flytrap, also up to 80% of the nitrogen that’s inside the plant has come from insects that – that’s caught and digested.

So, these – this group are what we call passive traps as opposed to the Venus flytrap that has a more active mechanism.

So, let’s have a look at some of those strategies. This is a range of Sarracenia, a type of Sarracenia. You can see it growing in a pot there, and it has really unusual pitchers that if you slice them lengthwise, you can see the opening here, and then a narrowing tube, and it’s got all of these downward pointing hairs. Now, can you imagine if you’re an insect crawling in there, you get a little ways in, it’s gonna be very difficult to fight your way back out again.

There’s another organism, another carnivorous plant called Genlisea that has, this is what the plant looks like. It’s actually an aquatic plant. So, this part here is above the water in the sunshine, and these what look like roots are actually dangling down in the water. And this is what they look like in cross section, and you can see once again all these, sort of, hairs pointing down. So, if there’s a little springtail or something that comes in from the water, it can get stuck, and it can’t make its way back out again. So, they – they call these sometimes lobster trap – lobster pot trap structures.

We also have passive pitfall traps, like the pitcher plants, that just have an opening here that if an insect is crawling around on the plant, it can often tumble in and then it can’t get out again. So, this one here is Cephalotus. This is a pitcher plant that’s found actually in Western Australia. So, here is Australia, and this is a blow up of just the western part of Australia, and this is where I was born here in Perth, and then these plants are found along on the southern coast. And that’s the only place they’re found in the whole world.

Darlingtonia is another pitcher plant that comes a little closer to home but that also is found in California here. You can see these beautiful structures that the light shines through. They almost look like flowers. And in some ways, that’s what they’re trying to look like, because the insects are attracted to them. They fly in. There’s also nectar in here, so they’re attracted to the nectar, and they tumble in, down into the tube here and drown and are caught. So, you can see them growing in a wetland here. Once again, nutrient poor ecosystem.

Heliamphora is a beautiful pitcher plant with quite a different sort of structure. You can see these the big – the opening here. And that’s only found in high altitude areas of Venezuela, which is, once again, a very narrow distribution of these plants.

And Nepenthes you may be a little more familiar with. This is a Southeast Asian plant that actually Charles Darwin worked on. And you can see the beautiful leaves here, and then the pitchers hang off the leaves. And there’s a range of different genera – species that have slightly different pitcher structures. Nepenthes are all found within Southeast Asia here, all through Indonesia, Saba, Malaysia, and also a little bit in Madagascar and in Northern Australia.

Sarracenia is the one that you probably, if you have seen carnivorous plants, that’s the one that you have seen. I have a pot over there from a population that we keep in the greenhouse, but we also have a, working with those out in the field in the Cedarburg Bog. So, there’s a number of species. This is the local one, one that’s flowering here, and a range of other species. You can see the eastern part of the US and well up into boreal regions of Canada.

It’s interesting when you look at distribution maps of something like Sarracenia, you can see their somewhat spotty distribution. And of course, Sarracenia will only be found in wetlands. So, within that blob here, it’s the wetlands in that area that it’ll be found. I was trying to find how close to here you would find Sarracenia purpurea. Thats – and on the U.S.D.A. database, it’s definitely found in Dodge County. I tried to find information about where it’s found in Horicon Marsh, but I couldn’t – couldnt find it. Maybe some of you know whether it’s found in Horicon.

So, adaptations. What is it about these plants that allows them to attract prey? So, this is a photo I took of a – a Sarracenia purpurea in the Cedarburg Bog. You can see this vein structure that is supposedly supposed to look a little bit like flesh or rotting flesh, and this might attract insects. Of course, this is all speculation. We can’t in the side – inside the head of a mosquito to know what it’s thinking. But there’s also this structure along here. It’s called the nectar roll. And underneath that roll, there is a number of glands that secrete nectar, and so obviously that’s really attractive to insects as a food source. So, they come along here and then tumble inside.

So, they actually did some work with experiments looking at the colored veins and how – how useful they were to attract insects. And they discovered that the nectar production is actually much more important than those visual cues that we see.

And you can see here in a different type of Sarracenia, the mouth, the opening. The peristome there is where the nectar is produced.

Okay. So, carnivorous – other types of carnivorous strategies, the more active traps. This leads us to a term called thigmotropism, thigmo meaning touch. So, the sensitive plant displays thigmotropism in that it will move through a tropism in response to touch. And these plants also do that, the Venus flytrap, of course, being the most famous one. We also have a number of other carnivorous plants that also use these active traps.

So, and also, we have active surfaces. The Pinguicula, I have an example of it here with the pink flower on. You can come and see afterwards. You can see the sticky surface has a whole lot of insects that are just caught here. If we look up close in the, kind of, cartoon, this is the leaf here. It has these stalks and secretory cells that produce a whole lot of really sticky mucilage that the insect might wonder down nearby, not realize that it’s a trap – its sticky, and it gets stuck there, and you can see all of these insects that are stuck and they can’t get away.

So, a lesser known fact, a rather unusual fact that I found out when I lived in Sweden, in Sweden they have a kind of yogurt called fil mjolk, which is essentially a slightly fermented milk, and they use the extract from the surface of these leaves as the culture for fermenting the milk. Who knew? I don’t know how they ever discovered that, but it’s quite – its quite – quite a nice – nice product anyway.

So of course, the Venus flytrap, you’re all very familiar with that. And I have, although it’s probably the most widely distributed carnivorous plant in the world in terms of in captivity or in people’s gardens or in – in their homes, it’s actually native only to a very small – small part of the Carolinas, once again, wetlands in those Carolinas.

And I have a brief video that I’m gonna show you about the trapping mechanism. So, you can see the – this is the – the, kind of, prongs here, and inside that trap, you have these hairs. These hairs are the sensitive parts that need to be – when they’re touched, they trigger the mechanism to close. So have a look here.

And that’s in real time.

[replay of video]

So, this trapping mechanism and the – the speed at which that trap can close is actually based on a mechanism which is somewhat similar to our nerve responses. In animals, these nerve responses are way, way, way faster, on the – the order of microseconds, whereas this is on the order of milliseconds. You have rapid fluxes of potassium ions, which are involved in our movement across cell membranes to – to get our nerve responses to allow me to move my arm around. So, this is what we call action potentials, and it’s based on a similar mechanism here, except it creates turgor pressure, or water pressure, on the outside of those trap, forcing that trap shut. And it’s an energy demanding process. There has to be cellular energy involved in doing that. And after the trap closes, it can take a while for it to recover and open again.

Now, if it’s successfully caught an insect, it’s also gonna be digesting that insect. But if you’ve been mean and nasty and gone and tried to make it close the trap when you’re not an insect, it’s gonna have to put extra energy into getting – getting that trap open again and ready to accept another insect.

There’s another plant here called Aldrovanda, the water wheel plant, which is found in a range of different parts of the world, although not in the Americas. We see cross section of this stem here. It’s an aquatic plant. It grows underwater. And it’s got these little, kind of, whorls along a central axis. This is just one whorl here, and you can see it seems to have caught something in these traps.

And in fact, this picture here is from a book published by Charles Darwin on insectivorous plants. He published that in 1875, and here’s his drawing of what the Aldrovanda looks like and the open trap opened up so he can see what that looks like.

He didn’t have high speed videos to be able to show us what the mechanism looks like, but you can see here the trap is open, and then the trap shuts again. And you can see a trap here that’s caught some sort of a aquatic insect or a little copepod in there, and it will slowly digest that and extract the nutrients from it.

Utricularia is another aquatic plant that has the traps underwater, but it also has leaves on the surface to capture light for photosynthesis. And of course, the flower is up in the air where the insects or pollinators can find it. You can see a number of brown colored traps there on the structure, and up close here, you can almost see the individual cells here. And then here it’s managed to catch some sort of an insect underwater.

This is a little video showing something coming in. It’s got this little trap door here. This is under negative pressure, and so like a vacuum in here, and so when something touches here, it kinda gets [sucking sound] sucked into that trap, gets digested, and slowly then that trap will recover.

I also have another quick video showing you a rather ambitious Utricularia who thought he was gonna catch a tadpole. And you can see the end of the tadpole’s tail is stuck in the trap here. He’s trying to get away. I don’t quite know how this is gonna end, but

Okay. So, then we come to the Droseraceae, which is probably the most diverse and certainly the most cosmopolitan of the carnivorous plants. You can see it’s found in all of the continents in large parts of the world. So, we’ve got a number of examples here. These are otherwise known as sundews. You may be familiar with that. Have those sticky surfaces with the hairs with the blobs of mucilage on the end which are really good at capturing especially fine insects.

And in fact, a colleague just sent me information about a new Drosera that’s just been discovered here on a Brazilian mountaintop. It only grows in this one place in the world on this Brazilian mountaintop. And it’s also believed to be the only plant that was discovered through someone posting photographs on Facebook. And presumably, somebody looked at it and said: “I’ve not seen that before,” and they investigated it, and they were able to find it and describe it, and they named it Drosera magnifica. And of course, because it’s found in such a small area, it’s also critically endangered. If you look in the background here, it looks like they’re clearing areas of this rainforest.

So, here is another type of Drosera that has a – a long stem with these hairs and these drops of mucilage on it. And you can see an ant that’s got caught here, and another insect that’s got caught here, and it’s curling over to trap the insect and supply it with lots of digestive enzymes from this mucilage that will slowly break it down so it can take up those nutrients.

So, this mosquito has got caught, and by struggling, it stimulates the Drosera to start curling these hairs over and to start moving the – moving its tentacles, and in a moment, it will start curling up.

Whee.

[laughter]

And as those drops of mucilage attach to the – touch the insect, they spread the enzymes, digestive enzymes, on it, and pretty much its history for that insect.

So, you’ve just seen that, and I heard a few gasps. Apparently, Charles Darwin had a dear friend called Lady Ellen Lubbock, and she said: “I never trusted Drosera since I saw it with my friend. I saw its horrid tentacles beginning all to bend.”

So, this leads me to Charles Darwin, who is one of the first scientists, you think – you might think of Charles Darwin for his work on the Theory of Evolution by Natural Selection, but he was a – he was a wonderful botanist, and he spend a lot of time working with Droseras, in particular. Here’s a – a few pictures not taken by Charles Darwin. Actually, the National Geographic had a fantastic series a few years ago with these high impact photos of carnivorous plants, particularly Droseras. Just beautiful, beautiful photos.

So, Charles Darwin, apparently, he was getting a lot of flak for his natural selection theory, and he retreated to his laboratory and said: “At the present, I care more about Drosera than the origin of any other species in the world.” He wanted to be done with that because he – he really enjoyed working with carnivorous plants. He would not have called them carnivorous plants. He called insectivorous plants, which is somewhat more gentle, you might say, and I’ll come back to that.

So, he did a lot of work. His – this 1875 publication, Insectivorous Plants, had a whole range of images of drawings that he – he did himself showing you the mechanisms. He described them as: “Ordinary plants procure the requisite inorganic elements from the soil by means of their roots, but, “There’s a class of plants which digest and afterwards absorb the animal matter.” So, he did a lot of work on the early natural history and also did active experiments to try and understand how these plants worked and – and why.

So, we have, coming up to Halloween here, his interest in carnivorous plants, and that, kind of, macabre, murderous plants, it kind of fed right into, kind of, the Victorian Gothic thing that was going on at the time his – of his life. There’s a review that tries to make this case. So, I just thought I’d put together some images for you here with Charles Darwin in – in Halloween drag.

[laughter]

So, of course, this leads to these, sort of, popular notions of carnivorous plants. And you see lots of pictures like this, you know, these bloodthirsty plants. Here they seem to have confused the flower with the traps. Here are these great big fangs and teeth. And this person has actually made a live – a huge size model of a Cephalotus. And here once again, this bloodthirsty, kind of, you can almost see the blood dripping off him. But this really is a bit silly. It’s really quite ridiculous. And I’ll explain to you a little bit about, and of course, the most famous carnivorous plant, of course, is Audrey from The Little Shop of Horrors.

And I have to admit, I have come under attack from carnivorous plants. Here you can see the flower of a Sarracenia here. It’s sucking me – trying to suck me down into the – into the bog – the Cedarburg Bog

[laughter]

when we’re doing research, so, you know, you do – you can’t be too careful.

But this is the – the plant that we work with, Sarracenia purpurea, nestled here in the Sphagnum in the Cedarburg Bog and a nearby other bog called the Sapa bog, which has slightly different characteristics.

So, our earlier work on that. We noticed that they have different shapes. The plants, depending on where they grow, can look quite different. So, the ones in Sapa bog have these long, elongated leaves, flattened. There’s only a little bit of it that’s a pitcher. Whereas the ones in Cedarburg Bog have these upright pitchers, lots of – capturing lots of water. And there seemed to be some ideas out there that there’s a tradeoff between how well can they do photosynthesis versus how well can they capture insects? So, we set out to try and understand whether that was what was playing in between these two populations that were growing just about a mile apart but in a different type of bog.

So, the Cedarburg Bog. A typical plant in this fen ecosystem these upright. And that has a medium pH, a neutral pH, low nitrate, and then phosphate, the – the nitrogen and phosphorous nutrient further needed. Whereas nearby in the Sapa Bog, this is a true bog. It’s acidic soil characteristics, higher nitrate, higher phosphate available for the plant. So, maybe that means that they don’t need to do as much carnivory here and they need to do more photosynthesis. So, anyway, so in order to – to investigate this, we did some transplants. Now, you as gardeners all know that if you pick up a plant from one part of your garden and you transport it and transplant it somewhere else, it can start to look different after a couple of seasons. It’s got a different light environment. The soil might be different.

So, we transplanted some plants. We took 10 plants from Sapa and put them into Cedarburg Bog and vice versa. And then we transplanted 10 within the bog just to see whether the – the transplantation itself caused the changes. And then we had 10 plants that we didn’t move at all. And then we followed these plants, did measurements on their – the number of leaves, the diameter of the plant, the – the shape of the pitcher by characterizing the distance, the – the – the widths, the widths of the keel, the widths of the whole leaf, the pitcher aperture, all of these different characteristics over two years in these plants. And then we put all that data together. And what did we find?

We found that the different wetlands did actually provide very different growing conditions. As gardeners, I’m sure you understand this. If you were going to grow something even a county away or down the street but has different soil, you’re gonna get a different type of garden. The pitcher shape changed in response to those different conditions. With less nutrients in the soil, the pitchers became better shaped for insect capture. So, it supported this idea that there’s this tradeoff between photosynthesis and – and insect capture.

But we also found that despite carnivory, the pitcher plants growing with more nitrogen were still nitrogen limited. So out there in the natural ecosystems, many of these plants are, kind of, you know, struggling along. They’re doing okay, but they’re probably not growing as – growing optimally.

Okay. So, since then, we became more interested in what’s going inside the pitchers, because there’s actually a whole ecosystem in there. And part of my training is in aquatic ecosystems, and so I was now applying that idea to these tiny little cups of water, where you have a whole food web of organisms. So, you get the insect tumbles in, and it manages to feed all of these insect – organisms that live in that pitcher plant. You’ve got dead insects and a living population of invertebrates.

So, we’ve now done some genetic analysis. We’ve extracted the DNA and we’ve sequenced that to say: “Well, who is there?” We found, of course, insects. We found a range of crustaceans. We found green algae, including these ones here that grow red when they’re under nitrogen limitation. We found some ciliates. We found fungi. We found rotifers. All of these things are living in this tiny little pitcher of 20 to 30 mils of water.

But we’re also been interested in what happens to the break down. So, in the Drosera here, each one of these blobs of mucilage has enzymes in it which break down the insect. But in the pitcher plant, we know that pitcher plants don’t actually produce enzymes themselves. It’s one of the unusual things about these as carnivorous plants. So, the enzymes that break down the prey, the hydrolytic enzymes, come from bacteria and the invertebrates that live inside those pitchers in the – in the rainwater that collects in here.

So, we also did some scanning electron microscopy right deep down here in the pitcher surface. You can see the wall of the pitcher here, and these are all a range of different sorts of bacteria. You’ve got cocci. You’ve got rods. So, there’s a whole range of bacteria living in there, as well, and we think that they are doing much of the work of breaking down the – the nutrients.

So, the enzymes, one of the enzymes we’ve looked at are chitinases. Chitinases break down chitin that you find in insect exoskeletons. So, you can imagine in order to get at the juicy bits inside this fly, you’re gonna have to break down its exoskeleton to get inside. So, chitinases release nitrogen and organic carbon and good stuff for the – the ecosystem by breaking down the exoskeleton.

So, we did a range of greenhouse experiments where we added flies, a source of chitin, and then we measured the enzyme activity in the fluid.

So, we found that chitinase, the activity of this enzyme, is related to bacteria. So, I’ll take you through this briefly. We’ve got day zero is in red, day one is in orange, and day six is in that kind of yellowy color. This is chitinase activity up here. So, in the control over those three days, we didn’t add anything. No real change. Then we added flies here, and you can see between day zero and day one, a huge increase in that chitinase activity. So clearly, they were producing more of that enzyme to break down the -the flies. When we added antibiotics, which of course act against bacteria, stop bacteria growing, we didn’t see that increase. So, this led us to think that the chitinase activity is due to the bacteria that are growing in there.

So, what exactly are the bacteria? How do they fit into this ecosystem? We’re starting to – to tease this apart. We’ve done some genetic analysis and found a whole range of different bacteria that you would find in a typical aquatic ecosystem out in Lake Michigan or out in the stream out here. We found bacteria that are useful for nitrogen fixation. We found ones that are parasites on – on insects. We found some bacteria that are specialists in degrading chitin. We’ve also found some bacteria that are anaerobic, so they don’t need any oxygen. They might be growing right down at the base. We’re not sure yet.

So, this is really kind of like the plant’s microbiome. I’m sure you’ve thought about – youve heard this idea that we have a microbiome. We’ve got bacteria all within our gut that help us actually to digest and keep us healthy. These plants also have a microbiome.

So, we’ve done a range of different analyses using genetic tools to look at, what is the microbiome of each individual pitcher? So, each one of these is a different pitcher, and you can see each of these colors is a different type of bacteria. So, you can see some of them, these two here, look pretty similar, but many of them are very different. So, each individual pitcher, even on the same plant, has a unique community of these different bacteria. They’re presumably doing maybe slightly different things.

So, let’s go back to this idea of these carnivorous plants being deadly and carnivorous and nasty and coming to eat you. Really, this is really very silly. They’re not hunters. They’re not going out and hunting things. They’re farmers.

[laughter]

These carnivorous pitcher plants are farmers. And to leave you with a really, really bad limerick that I wrote: A young pitcher plant carnivore found taking up nutrients a bore. Making leaves into jugs, traps digests lots of bugs, farming bacteria to do the chore.

Thank you.

And I’d also like to thank Paul Engelvold, who helps me with the greenhouse and maintaining these plants, my students, Terry Bot and Jacob Grothjan, who have done a lot of the work, and a range of other collaborators that I’ve worked with over the years on carnivorous plants.

Thank you.

[applause]