Gryphon CAST Episode 11 Transcript

Speakers: Amanda Reside, Michael Lim and Chris Caruso

Amanda Reside

From oxygen, food and medicine to shade and interior decoration. Plants provide us with many benefits, despite how intertwined they are with our well-being. Many people don't actively interact with plants daily. Often we think of them as ornamental, relatively stationary and slow to change beings. However, they can adapt to change quicker than you think. Open your ears and mind and let's look closer at the dynamic nature of plants. Welcome to Gryphon CAST, a podcast where we casually chat about science coming out of the College of Biological Science at the University of Guelph and how that work can affect lives around the world. I'm your host, Amanda Reside. With me today is co-host Michael Lim and special guest Dr. Chris Caruso. We'll be chatting about Dr. Caruso's recently published study, looking at how plants can change their physiology in order to respond to declines in pollinator population. To start, how would you describe your research in general and the work that's done in your lab?

Chris Caruso

Yeah, so I call myself a plant evolutionary ecologist, which is a little bit of a mouthful, but it really just means that I study how plants evolve in response to their environments.

Michael Lim

So, it kind of building off of that. Why did you decide to focus on this specific topic? Was there a moment where you decided to go into this work?

Chris Caruso

Yeah, so I actually started graduate school wanting to study seed dispersal by birds in the tropics. And that was a career choice that was inspired by my high school ecology teacher, who is an ornithologist. But after about a year in my program, I basically realized that I wasn't nearly as interested in being either an ornithologist or a tropical biologist as I had originally thought. But during that year, I did take a field course in Costa Rica and I did a small project where I was looking at basically manipulating the floral displays of a tropical plant and looking at how that affected the hummingbirds that came to pollinate them. And that was actually the start of what I do now. Although, of course at the time, I had no idea that that was where I was going to head. So yeah, so I started out on a pretty different path.

Michael Lim

So, you recently published a study titled "Plasticity in floral longevity and sex-phase duration of Lobelia siphilitica in response to simulated pollinator declines". So, to begin with, I'm curious about your research interest in flowering plant physiology that all stem from that study with hummingbirds. And how those interests change have been affected by pollen declines over the years?

Chris Caruso

Yes, so I actually have a pretty long history of studying how floral traits of plants evolve in response to pollinators. So for my PhD, for example, I studied floral evolution in hummingbird pollinated plants out in the Rocky Mountains. But actually, until pretty recently I wasn't paying a whole lot of attention to work that was being done on pollinator decline. And that is in part because pollinator decline research has primarily focused on agricultural plants for good reasons, for food security reasons. But, you know, my research interests are more in wild plants. And also, pollinator decline research has really focused more on measuring how pollinator populations have changed. Whereas I'm actually more interested in studying on, you know, things from the plant perspective and so how plants are responding to changes in their environment.

Amanda Reside

So, for this study in particular, you focused on two aspects of plasticity. So that would be floral longevity and sex phase duration for the audience. Can you briefly describe what plasticity itself means and these two aspects that you focused on.

Chris Caruso

To understand plasticity? I think probably one of the easiest ways to do it is imagine that you take plants that carry the same genes, so maybe siblings or clones potentially, and you put them out in different environments. So, if they produce different traits in different environments, despite having the same genes, that is what we would call plasticity. And you can see plasticity in all different kinds of traits. You can do it in floral traits and leaf traits in, you know, biochemical traits. There's all kinds of possibilities there. Interestingly, a lot of floral traits are actually not very plastic. And this is why we can use floral traits to identify plants, right? Because they don't change a lot based on the environment. Yeah. It's kind of obvious what you think about it., right? But it turns out that floral longevity, which is just the amount of time that a flower is open to pollinator visitation and also sex days duration, which is just the amount of time that a flower is either shedding pollen, which are the male (the male gametes) that's the equivalent really of sperm that plants produce or that the amount of time that they're able to receive pollen that can be used to fertilize their ovules, which are what we would call the female gametes. Those traits can actually be the plastic. Those are some floral traits that can be. And so that's why we focused on floral longevity and on the length of the male and female phase, rather than traits that are less plastic like flower size or flower colour.

Michael Lim

So, in the introduction of your study, you mentioned that previous work had focused on evolutionary changes in flower traits across generations, usually multiple. So why do you think it's important to study changes within a generation instead of this longer timescale?

Chris Caruso

Well, human mediated environmental change is happening quite quickly, you know, compared to the pace of environmental change that's happened in the past. I mean, environments have always been changing, but not necessarily this quickly. And so given that people who study evolutionary ecology of all different kinds of organisms think that these very short term responses within a generation. So, instead of looking across generations, across longer timescales, that these sorts of responses could prevent populations from going extinct before they have a chance to evolve traits that could help adapt them to their new environment. In this case, you know, we're really interested in, you know, how they could - can they stick around long enough to adapt to a world with fewer pollinators?

Michael Lim

Out of curiosity, I'm sure it varies a lot between different plants but what is the typical, I guess, lifespan or the time it takes from germination all the way up to being a fairly mature Lobelia siphilitica?

Chris Caruso

The study species that I used for the study Lobelia siphilitica is we generally consider it to be a short-lived perennial. So you know, it's going to flower a year or two after it germinates. It's going to flower pretty quickly and it will hang on for a few years potentially and continue flowering.

Amanda Reside

But when we're talking about floral longevity, we're talking about like within a season, right?

Chris Caruso

Yes, we're talking about very short-term changes. Exactly, within a season.

Amanda Reside

You chose to study plasticity in both early and late season flowers among the same species, Lobelia siphilitica, and you found different results for the two groups, which is interesting. So I was wondering, you know, what is the purpose of differentiating early and late season? And did you have any idea of how they would differ? Or is it just sort of, you know, good practice?

Chris Caruso

So honestly, the dirty little secret here is that studying both early and late season flowers was in many ways a decision we made to manage the workload for this experiment. The lead author on this project was actually an undergrad at the University of Guelph. She did this for her undergraduate thesis and there were only so many flowers she could follow at a time. And it's not hard work, but you have to visit the flowers every day until they, senesce (till they die). And so, you know, it's a commitment. And we were not necessarily - we didn't have any idea in advance about why early and late season flowers might be different. However, one thing that I would say and this we thought about this once we looked at the results is that flowers that are produced later in the season may have fewer resources available to them because the plant has already produced a bunch of flowers and is putting resources then into making seeds. And so that could affect the responses that we see later. But at the same time, the pollinator community could also be differing over the course of the season. We currently actually have a follow up study going like right now actually in the U of G Arboretum. That is going to, I think, help us figure out perhaps why early and late season flowers responded differently to simulated pollinator decline.

Amanda Reside

So that's something I'm hoping we'll know more, a little more about by I don't know next spring maybe spring 2023. [Crosstalk] So that's, you'll have to do a follow up episode. I know that's another undergraduate thesis project that's on the go right now. Cool.

Michael Lim

So in your study, you focus on a plant called obviously Lobelia siphilitica, but why did you choose to work with that particular species? Were they particularly affected by pollinator decline?

Chris Caruso

That's a great question. It's a species that I know how to work with. I know how to grow it. I know I know how it works. I know what it will do and what will work easily and what sorts of projects won't work and all of that. So, it's convenient in that sense. But it turns out that Lobelia siphilitica is particularly interesting to study from a pollinator decline perspective because it can't produce seeds in the absence of pollinators the way the flower is constructed. If it doesn't get visited by a pollinator, it doesn't make any seeds. And so, it should be particularly vulnerable to pollinator decline. And that is one reason why it turns out to be a pretty great species for studying responses to pollinator decline.

Michael Lim

Are many other flowering plants also able to pollinate on their own without pollinators or would that mean a vast majority them are like Lobelia where they can't do it on their own?

Chris Caruso

So, Lobelia isn't unique. About one third of plant species are unable to produce seeds in the absence of pollinators. But then that leaves the other two thirds that actually can. And we are studying those different, different studies system on different study. You know, maybe when some of that comes out, we can talk some more. But, you know, about one third of flowering plants are completely dependent on pollinators to produce seed. And so that's a lot of species.

Amanda Reside

So, your study is also unique in that you experimentally reduced pollinator access to the plants but you didn't eliminate it entirely. So why did you choose this approach instead of just eliminating it entirely? And why is that relevant to plants in the natural environment?

Chris Caruso

Yeah. So, it would actually be much, much, much easier to just completely eliminate pollinators. That's actually a really easy thing to do. But it wouldn't be representative of what most plant species are experiencing as pollinators decline. Which is not no pollinators, but fewer pollinator visits. And, you know, that was what we you know, we really wanted to simulate here. And, you know, when you do experiments, that's one thing you really have to try to do is, you know, as close as possible sort of simulate the environmental change that you're trying to study. So, I wish we could just get rid of all of them. It would be so much easier.

Amanda Reside

That makes sense. And you blocked off access by using mesh bags around the plants. Do you think that restricted access to different sizes, let's say a really small insect could get through the mesh compared to a hummingbird? Do you think this potentially differential access would make a difference and why would that be if so?

Chris Caruso

Yeah, so that's a great question. You know, Lobelia siphilitica is primarily bumblebee pollinated. They don't have the most diverse pollinator assemblage out there. But there are a lot of native plant species that have much more diverse pollinator assemblages where, you know, for example, they're visited by, you know, kind of both bumblebees, but also smaller native bees and maybe both specialists and generalists. And those are the kinds of study systems where it would be really interesting. And people have done this not quite in the same context as us, but, you know, in a related context, they have actually used different mesh sizes to eliminate maybe, you know, led in both the large and the small bees. But then maybe restrict the large bees, but still let the small bees in. And in the right study system, that would be really interesting to study because not all pollinators are declining in the same way some groups of pollinators are declining more than others. So, the overall assemblage in some cases is changing in addition to just there being fewer pollinators. And, you know, different sizes of pollinators can differ in their effectiveness. Some pollinators may visit and just not be very effective. They just don't transfer much pollen and others can be far more effective. So that's something I've been thinking about. But I would need a different study species to try to tackle that. I think it would be interesting.

Amanda Reside

Yeah, it would be interesting to attempt to restrict access to small pollinators while allowing the large ones in and I don't know how you do that?

Chris Caruso

That would be the trickiest one. You know, I have some colleagues who've done work where they actually sit there and they'll shoo away basically certain pollinators. I saw a talk at a meeting just about a month ago in Cleveland where someone did that. Now, there are some limits to how long you could do that for and with how many plants. But yeah, I mean, it's kind of funny, I imagine trying to explain that to someone who came by to see your experiment, like, what are you doing here? [laughter] So, yeah, I'm not the person to do that work, but I have colleagues who know a lot more about the bees than I do who, who have done those kinds of studies.

Michael Lim

In the end, your study concluded that floral traits like longevity and sex day duration can respond plastically to pollinator declines. But other traits like display size were unaffected. And you kind of hinted at this earlier that some traits were more likely to change than others. So why do you think in general the reason for this is, and under what conditions you might see some of those other traits like display size changing?

Chris Caruso

Yeah. So, you know, floral display size is an interesting trait because it's just the number of open flowers on a plant on any given day and it's determined by how long flowers stay open, so floral longevity. But also by the rate at which flowers open in the first place. So when the bud actually opens up and you have a flower that can be that's open and can be visited doing what we did, simulating pollinator decline if it increases floral longevity. And we did find evidence for that, but it decreases the rate at which the flowers open. Then those two things are going to balance each other out and display size is not going to be affected. Even though floral longevity like the flowers are staying open longer. And so that's our best guess now. And so, the next step is really to look at the effect of pollinator decline on the rate at which flowers are opening.

Amanda Reside

Based on the conclusions of your study, how has your perspective on the dangers of pollinator decline changed, if at all? And is this plasticity in methods of adaptation? Are these an indication that plants may actually have a fighting chance against the threat of pollinator decline?

Chris Caruso

Yeah. So, you know, I do think that this study is a hopeful one for, you know, the basically the fate of plants as pollinators decline. And, you know, plants may be rooted to the ground but they aren't passive which I think is something that, you know, I guess maybe a lot of us don't think about. They can respond to their environment including responding to pollinator decline and they can do it quite quickly. Right. I mean these responses were happening pretty much immediately after we simulated pollinator decline. So, you know, I think I think people should see it as a very hopeful thing that plants can respond to changes in their environment. They have evolved over billions of years the capacity to do that. But we tend to underestimate it because they're rooted to the ground, right? They don't they don't move around and they don't have what maybe we think of as behaviour. But I would argue that, you know, keeping your flowers open longer, you could think of that as behaviour. Right. I mean, it's a response to your environment.

Michael Lim

Ultimately, how you look at it.

Chris Caruso

It does, exactly.

Amanda Reside

If you've ever seen a timelapse of like a sunflower turning to face the sun. Yep. You know, the plants have, you know, mobility. Yeah. Maybe not as quickly or as obviously as we might think of it, but definitely they're changing.

Chris Caruso

No, that's 100% true.

Michael Lim

So in general, I think when people hear about pollinator declines, they're praying immediately to it being a, "Oh, no, save the bees type of issue" and you can't do that before that. Most people focus on the pollinators anymore, about the plants. So, is there anything you wish that people knew more about the plant perspective?

Chris Caruso

Yeah, I think there are two things that I wish people would think about more when they think about pollinator decline. And one is something I just mentioned, which is that, again, plants are not a passive partner in this plant-pollinator interaction. They can respond to pollinator decline on both short and long-term scales. And these are things we can study, right? We can study them. We have the tools to do that. We can make predictions about how plants may respond and maybe which plants are going to be quite vulnerable to pollinator decline and which are going to be able to actually adapt quite well. And second, I would like people to realize that it's important to understand how native or wild plant populations respond to pollinator decline. You know, although most of the research on pollinator decline has focused on agricultural species, most pollinators that visit agricultural species also visit wild plants for at least part of their life cycle. Agricultural food systems can't be decoupled from the native plant populations that surround them. So, you know, in addition to studying agricultural systems, which I would never say isn't important, I think it's very important. It's really important to understand how the natural systems and wild plant populations will respond to pollinator decline because that does have the potential to feed back and affect on agricultural systems and our food security that's related to pollination services.

Michael Lim

Right. I think it always links back to things are more interconnected than you think. So, a random plant that you've never heard of before could be really important to understanding and how could affect, you know, not just that plant but also the human ecosystem as well as the food chain and supply.

Amanda Reside

A little bit more of a personal question. What was your favorite part of working on this research project or what was the undergraduate student who worked on this stuff? What do you think her favorite part would have been?

Chris Caruso

Yeah, I do think pretty hard about my answer to this question. I actually I mean, personally, my favorite part was actually mentoring Kiana while she did this project for her undergraduate thesis especially because this was a project that we did on summer 2020. So, it was at the very start of the pandemic. And, you know, it feels like ancient history now. But I think we can all look back and remember how uncertain that all was. And so helping Kiana do this kind of despite everything else going on was really rewarding. Like, I mean, mentoring everyone is rewarding. But, you know, folks that managed to do kind of really interesting research like this in the middle of a global pandemic, it just it's really impressive. And, you know, it was such a great experience to be able to help someone do that despite everything. I mean, because we really had to improvise, you know, we couldn't use the area where we normally would pot plants in the greenhouse because there were all these restrictions on access to campus. So, we actually brought all the plants to my driveway and I repotted them there and then we moved them out to the arboretum for the experiment. So, it was a very memorable ... this whole project was very memorable because we really did have to just improvise. So yeah. So, I think overall, [crosstalk] yes, it is in more than one way. Yeah, hopefully in many ways, yes, we can do interesting science even in the face of a global pandemic. So, there you go.

Michael Lim

So, we kind of been all over this question and answer throughout this chat we've had so far, but what are the next steps for this work or I guess, going even beyond the things that you're currently working on and hoping to publish?

Chris Caruso

So I mean, the next immediate step is to test whether flowers that stay open longer that have this greater floral longevity, whether they actually do produce more seeds. That is what we would predict, because the longer you stay open, the greater the chance you have to be visited by a pollinator, even if you're no kind of more attractive than any other flower. You have more probability of being visited if you're sitting there with your flower still open. And so that's something that we are actually testing this summer to see whether that's the case. So in the very short run, that's really what I want to know is we know they we know they can keep their flowers open longer in response to simulated pollinator decline. But do they actually produce more seeds? You know, either way would be interesting, but that's the next thing we want to know. And I would say the longer term, what I think is going to be really interesting is to basically try to bring together this work where we're looking at very short term responses to pollinator decline and look and see how that then relates to longer term changes across generations. So really what we would call, you know, evolution like change across generations and you know, looking to see how these sort of short term changes - do they have any affect then on the longer term evolution of flora longevity, but also have other floral traits?

Amanda Reside

All right. So, we'll move on to our social media questions. Michael, would you like to ask the first one?

Michael Lim

Sure. So, for our first question, as an individual household, is there anything I can do to help fight against the effects of pollinator decline?

Chris Caruso

Yes. I mean, our research doesn't speak directly to this but I would say that planting pollinator friendly plant species is always a good idea. You know, for every region, there's always information out there that you can get on, you know, for your region what are the pollinator friendly kind of native plant species?

Amanda Reside

Are there any plants in particular that, you know, come to the top of your head when you think about plants that are particularly affected, that maybe would be good choices for planting?

Chris Caruso

You know, I brought this up and I should have expected this follow up. That's a great question, actually. I mean, I think one obvious species that it's actually pretty straightforward to grow are milkweeds. I mean, not only common milkweed, but also butterfly weed, which, as it sounds is visited by butterflies but also other species. I would say certainly in southern Ontario, those are a couple of, you know, obvious ones that a lot of things will visit those flowers and find those resources. But also, if you have a sort of weedy area that has some native plants flowering in it, let them flower. Right. You don't have to make it look all manicured and beautiful. And that I mean, that would certainly help to in addition to kind of doing kind of dedicated pollinator garden planting.

Amanda Reside

Have you noticed many changes in the issue of pollinator decline over the years? And at this point, maybe with your hopeful study, are you noticing any improvements or solutions that might get us back to quote unquote, regular levels?

Chris Caruso

So, in terms of how the issue of pollinator decline has changed over the years, I do think that there's the realization that pollinator decline is complex. Like I think initially there was a lot of "It's the pollinator apocalypse, everything is disappearing!" saying, you know, the world's coming to an end. But it's actually a lot more complex than that. And that's the thing we've touched on, right? Some species are declining in some regions. Others are not. You know, for example, there's some evidence that in higher elevations, pollinator populations may actually be going up and that may be related to those areas actually being warmer. That may be a side effect of global warming.Is that high elevation areas that previously were difficult for some pollinator species to just even be warm enough for them to fly and and collect pollen are now more amenable. So, you know, there's a lot more nuance than we originally thought and I do think that's a big change and a good one. Right. Because I don't really see how running around saying there's a pollinator apocalypse is particularly helpful to anyone. Certainly it's not going to maybe help us solve anything. And so in terms of the second part of the question: Do we think things are improving or they will recover to regular levels? I mean, I do think that plants will adapt over time.

And in that sense, things will become I don't want to say more regular, but I guess for lack of a better word, more regular. They will adapt to a world with fewer pollinators. And in terms of the pollinator populations, you know, we should have more tools in terms of taking steps that are going to have a real material effect in terms of stabilizing pollinator populations. And whether that's having to do with regulating some of the chemicals, the pesticides, that can hit pollinator populations or whether it has to do with changing some of our practices in terms of when we work when you consider an agricultural system. We can get the evidence to figure out whether some of these concrete steps might make a difference in the pollinator populations.

Amanda Reside

So just to finish up here, I'd like to open the floor to any final comments that you might have about your work. And if our listeners only take one thing away from our chat today, what do you hope that it would be?

Chris Caruso

Got it. So, I think this won't surprise you, given some of my comments today. But again, I hope people remember that plants may be rooted to the ground, but they aren't passive. They have the potential to respond to pollinator decline and other changes in their environment. And so I think in that sense, it's important not to succumb to sort of fatalism that everything is awful and, you know, the whole system is going to collapse and all of that. But that doesn't mean to say that bad things can't happen. But plants do have the ability to respond to these changes in their environment. They've evolved that ability over millions and millions of years. And so that's a real, you know, a real reason for hope.

Amanda Reside

I love that, I love a message of hope when talking about environmental issues.

Chris Caruso

I think it's important to keep that in mind. You know, we have the tools to study these things we do and to understand and again, that doesn't mean that plants can do everything. There will be limits on their abilities to respond. But again, we can understand what those limits might be. Right. We have the ability to do that. And I think that should make us feel good. I mean, we have we have the ability to do that as scientists.

Michael Lim

And so with that, that brings us to the end of today's podcast. A big thanks again to our guest, Dr. Chris Caruso for joining us today. Gryphon CAST is brought to you by your host, Amanda Reside, and me Michael Lim with editing assistance from Ian Smith. If you're hoping to learn about different science topics, please check out SCRIBE Research Highlights. That's S-C-R-I-B-E Research Highlights on the University of Guelph website at uoguelph.ca, or you can follow us on social media @UofGCBS. You can find us on Instagram, Twitter and Facebook. Music in the podcast comes from uppbeat.io. There'll be details in the show notes as always. Until next time, please stay curious.