*Featured image photo credit: Laura Bizzarri

In this episode, Laura Bizzarri (PhD candidate, Garcia-Robledo lab) chats with us about her new paper, Bizzarri et al. 2022: ‘DNA Barcoding Reveals Generalization and Host Overlap in Hummingbird Flower Mites: Implications for the Mating Rendezvous Hypothesis.’ We talk about her meticulous fieldwork studying these tiny hummingbirds transporting even tinier flower mites, the ecology that might explain the lack of specialization among mite species, and how the time is ripe to revisit classic hypotheses in our field with modern genetic tools. Listen to our conversation and then read Laura’s full paper here!

Craving more context? Email Laura at laura.bizzarri@uconn.edu.

NATURALIST SELECTIONS IS AN INTERVIEW SERIES PRODUCED BY THE AMERICAN SOCIETY OF NATURALISTS GRADUATE COUNCIL. WE SHOWCASE GRADUATE STUDENT AND POSTDOC AUTHORED WORK IN THE AMERICAN NATURALIST, A PREMIER PEER-REVIEWED JOURNAL FOR ECOLOGY, EVOLUTION, AND ANIMAL BEHAVIOR RESEARCH. CATCH UP ON EXCITING NEW PAPERS YOU MAY HAVE MISSED FROM THE JOURNAL, AND MEET SOME TRULY BRILLIANT EARLY CAREER NATURALISTS!

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Credits

Featured Guest: Laura Bizzarri, University of Connecticut, US

Host, Editor, Producer: Sarah McPeek, University of Virginia, US

Original Music: Daniel Nondorf, University of Virginia, US

Transcript:

You’re listening to Naturalist Selections, a science podcast featuring graduate student and postdoc-authored work in The American Naturalist, produced by the American Society of Naturalists Graduate Council. I’m grad council rep Sarah McPeek and today I’m talking with graduate student first-author Laura Bizzarri! Laura is currently a PhD candidate with Carlos Garcia-Robledo at the University of Connecticut, US. Her April Am Nat paper is called: “DNA Barcoding Reveals Generalization and Host Overlap in Hummingbird Flower Mites: Implications for the Mating Rendezvous Hypothesis.” Hummingbird flower mites are tiny nectar-feeding arachnids that live in the flowers of tropical hummingbird-pollinated plant species. They hitch rides on the faces of unwitting hummingbirds to disperse among flowers. For a long time, researchers hypothesized that mite species would evolve to each specialize on a single flower species because specialization would maximize their chances of encountering a mate via hummingbird taxi among flowers of the same species. Laura set out to test whether hummingbird flower mites truly follow this ‘mating rendezvous hypothesis’ at La Selva Biological Station in Costa Rica. She used DNA barcoding analyses to examine the diversity of the mite communities found on 14 flower species. Her phylogenetic work reveals 18 distinct mite species and a much more complicated story than previous morphology-based species identifications could resolve. While a couple of the mites can be classified as flower specialists, most of the species she identified are generalists that feed on multiple flower species. This suggests that other ecological pressures such as resource competition may mediate mite flower-use more than sexual selection. In our conversation, Laura tells me about the fascinating natural history that may contribute to flower mite generalization at La Selva and reflects on the importance of revisiting classic hypotheses in our field with the tools of 21^st century science.

Sarah

As I was reading, my imagination was really running wild about what your field work must be like in La Selva. So can you tell me a little bit about just what it’s like to be out there in the field working on these flowers, watching these hummingbirds?

Laura

Yeah, definitely. It can be hectic. So a lot of it depends on the weather and that sort of thing. Luckily, the flowers are sort of always there, and it’s easy to just go out. So I would go out, try and find the plant species that I was looking for, and then just collect as many open flowers as I could and then bring them back to the labs. So La Selva was really nice because they have labs both, like, ambient labs and actual research facilities, and then just dissect the flowers under the microscope to extract all of the mites. It’s really hard, really, when you’re in the field, like, in the jungle, to actually start counting mites, especially because they start running out and they’re really fast and it’s a mess. It’s a lot easier to come than when they’re in ethanol under the microscope.

Sarah

That makes a lot of sense. You can actually see them in the field, but it’s just really hard to keep track of. I also have mites on the plants that I work on, and they move incredibly fast.

Laura

Yeah. Especially when they sense any motions like you simply touching the flower. They can probably sense that already. And so I don’t know if it’s like a defense mechanism. They start running around out of the flower. And so the idea is to just go in, pick off the flower as fast as possible, and put it in a tube with ethanol for preservation.

Sarah

Makes sense. Have you ever seen the mites on hummingbirds themselves? Because that’s how they get transported between flowers?

Laura

I actually have at least one video. So part of my research, I also recorded interaction between hummingbirds and their host plants using cameras. Right and in one of the videos, we could actually see mites running up and down the beak of the hummingbird.

Sarah

Oh, my gosh.

Laura

So that’s the closest I’ve gotten to see it happen in its natural setting. Right. But then for another part of the project, I also collected mites from the hummingbird beaks. So I was mist netting hummingbird, and so there obviously, when I collected the mites I could see them.

Sarah

So do they kind of stay right in the facial area so that they’re primed and ready to jump back off onto the next flower?

Laura

Yeah so what they do is that they will climb up the beak and then they usually hide in the nares, the nose of the Hummingbird. Right.

Sarah

That makes me itchy.

Laura

Yes. Then they just hide in there and then wait around basically until the hummingbird gets to a flower that somehow they might think is the right flower to get off.

Sarah

Do you know if the hummingbirds are aware that the mites are there, or are they so small that they don’t even feel them?

Laura

That’s a really good question. And I wonder that a lot in general, we say they’re not parasitic mites, so they don’t harm the hummingbirds. But I have wondered if it is itchy for the hummingbird to have tiny critters just running around in the noses. Yeah.

Sarah

It’s a really exciting and unique system. I’m also curious about why you decided to test the mating rendezvous theory in your work? What got you really interested in examining this old idea that we thought about the system for a long time using these new genetic tools that we now have?

Laura

So it was a bit of a combination of multiple things. So I think my first main goal was to just survey, like, mite species, Hummingbird mite species at this location at La Selva to at least have an idea of how many species there are, what host plants they use, what hummingbirds they use, and start figuring out the interactions. And then obviously doing all the background research, I read a lot about this Mating Rendezvous hypothesis, and so kind of went hand in hand with trying to survey the mites because then at that point, I had the data to actually test this hypothesis to see if this really high degree of specialization is actually what is happening. And then the DNA bar coding component came in, so that is something that my advisor had experience with in the research that he had done previously. And then it’s something that we started talking about. And I thought it was a really cool tool and also fairly feasible and accessible. I thought it would be a really good way of conducting this survey and potentially testing this Mating Rendezvous hypothesis.

Sarah

When you were initially going into that investigation, were you expecting to support the hypothesis or were you thinking that it might be totally wrong that the same mites would stay on the same flower species?

Laura

I guess I went a bit back and forth. I did have, you know, partially in mind that there must be something more going on, right, then this high degree of specialization, especially if you consider that again, we’re in a lowland tropical rainforest. Right. Tropics like super high biodiversity. We know it for the plants, we know for the hummingbirds. And then looking at even how many host plants there are, to me it made sense that I would have been able maybe to find more than one species of mite.

Sarah

And it seems like your results definitely show that meeting rendezvous hypothesis isn’t really supported in the system. There’s a lot more might diversity on an individual flower than would be expected under the tenets of that theory. So it sounds like you weren’t totally surprised by that. But what is your reaction to basically debunking this theory that we’ve held about the system for a long time? Was their nerves or hesitation associated with that?

Laura

Yeah. At the very beginning when I got my results, there was a moment of surprise and it was definitely like a positive surprise because I was very excited and I was like, this is really novel and it’s really cool and it happened using all these newer techniques. And then definitely there was some hesitation as well, especially because it has become a very important hypothesis, not just for the system but also for talking about evolution and reproductive isolation and that sort of thing. And it was hypothesized by a very well established researcher as well. I think as an early career researcher, it’s definitely somewhat normal to be at first a bit maybe scared. What just happened? Did I do it wrong? So there was a lot of double checking to make sure that everything actually was correct.

Sarah

I’m sure.

Laura

But yeah, and then obviously all of that once I actually double, triple checked it turned into a lot of excitement because then this opens up a whole lot of avenues for future research and answering more and more questions with the system.

Sarah

Yeah. That was actually the next thing I was really curious about is there are some aspects of the natural history of the system that you mentioned in the discussion that could be playing into why you’re seeing an opposite pattern in this system than we have. Because a lot of times when we’ve done DNA bar coding, we found generalist species are actually subclasses of specialists, but here we see the total opposite of that. So if you were going to speculate, what do you think might be contributing to the evolution of this pattern in the mites compared to these other systems?

Laura

Well, I think part of it is not necessarily related to their natural history. It’s more the methodology of how these species were identified. Right. Because both in the studies were specially species or generally species where it turned out to be specialist species. And in my study as well, I think the main point is that all of those previous identifications were based on morphology. Right. Which can be particularly difficult, especially with invertebrates. Right. And I think then DNA came in, and so that was like a very different way of looking at what a species is. Right.

Sarah

Yeah.

Laura

And so for those studies, it went from generalist species to a lot of these cryptic species complexes of specialists. And in my case, that same we can call it issue led to the opposite pattern. Right. And then as far as their natural history, I think something that has been a lot on my mind is thinking about maybe competition among these different species of mites and potentially also competition between mites and hummingbirds as a mechanism that we’re talking about, like macroevolutionary processes. So over evolutionary time could have led to more generalist species instead of specialists, which can be counter intuitive. And it’s not necessarily what most studies find. Right. Because in general, when there’s a lot of competition, you expect a lot of specialist species. Right. Because then everybody is sort of dividing up their niches so that they can coexist. But if you sort of think about it, the opposite can be true as well, where they become generalists to sort of not have to rely on only one resource where they might have to compete with very closely related species. And so they can do these, like partial host switching where they might be able to use different hosts, which if one host species, one individual of that host species, is not available because there are other species on it, then they could just switch to a different one where they might not have competition rate.

Sarah

Yeah. I think that’s a really interesting idea. The idea that by generalizing, your almost relaxing competition for any one resource. Right. Any one plant species. And so competition is less because it’s dispersed over all of these different host resource feces. Yeah. That’s really interesting. Do you have any ideas for how you might test that?

Laura

So that’s actually something that I am looking into more with, looking at competition between this group of mite species and the Hummingbird species, which I think is sort of really interesting because there is a few different types of interactions going on. Right. They’re theoretically communalistic in the sense that they use these hummingbirds for transportation, but they’re also at the same time competing for the same food. Right. Which is nectar. And so I think a very interesting question to ask is how much does this competition for the nectar actually matter in terms of resource use of the mites?

Sarah

How much nectar are the mites consuming compared to how much the hummingbirds consume? Mites are much smaller than hummingbirds, but I’ve also seen mites completely drain flowers before.

Laura

Yeah. And I think I remember there’s one specific study that I read where they were actually specifically looking at whether mites can deplete nectar. And they actually can, which sounds sort of crazy because, again, they’re tiny. But in some flowers, I found hundreds of mites in one single flower. And so I don’t think it’s that crazy to think that they might actually deplete the nectar. But then the other thing is also that hummingbirds we know that nectar is not their only food resource because they also rely on insects and other types of arthropods to supplement their diets, whereas maybe for mites it is more their main food resource, even though even for mites, there have been some observations of them consuming like pollen and other sort of products of the flowers.

Sarah

Yeah. Oh a lot of interesting natural history to explore! Thinking a little more generally, do you have any advice for early career researchers who are thinking about, say, testing these old stories that we have about systems with new molecular tools?

Laura

Yeah. So I guess the first part would be to do your background research. Right. Because you really want to know the system and want to know what do we already know? Yeah. And what has been done already in the system to sort of start asking your own questions and then sort of related to that, also being creative and thinking outside of the box with building on the previous knowledge and coming up with your own sets of questions based on your interest and that sort of thing. And then that can also help you sort of address what are potentially maybe shortcomings or like gaps in the previous knowledge or in the previous studies. And then the other component, which I guess connects back to what we were talking about earlier as well, is to not let the fact that these might be well established theories or ideas necessarily stop you from testing them. Because I feel like especially for early career scientists, it can be very intimidating to make your own imprint on past work or in a system that has a lot of previous research because there’s always that fear of what if I did something wrong? And then that whatever person doesn’t like what I’m doing. I always just think that obviously double check everything. But also then don’t let the fact that it’s a well established idea sort of keep you from exploring all these new questions because that’s sort of the point of science is that as we learn about new methods and do more, we can find out new things. We can find out that things we thought were a certain way aren’t that way. And I mean, being stuck on one idea because somebody many years ago said that it was that way is sort of defeating the purpose of doing science and doing research, I think.

Sarah

Yeah, absolutely. And it seems like now we’re poised with all these new technologies to really go back and look at these old stories that we’ve told for a long time and really hold their feet to the fire and say is this still what we think based on the new evidence that we’re able to collect that just wouldn’t have been possible.

Laura

I think a lot of times people get stuck on this idea that if you look back at something that was established before with new methods and you find that that’s not necessarily correct, then that discredits that old hypothesis, which I don’t think it’s true at all because you wouldn’t have been able to do any of the new research if you hadn’t the preestablished knowledge and I think the change in the fact that we can sort of update these ideas as new technology comes in is something that’s really cool and really valuable.

Sarah

Yeah, absolutely right. All of these hypotheses are amazing jumping off points for lots of new questions both about the natural history of different systems and about these more general patterns in biology. So yeah, absolutely, give yourself context for the work that you’re doing now.

Laura

Yes, definitely. Background knowledge.

Sarah

Well, it’s a really beautiful paper. It tells a great story. It’s kind of a bit of a detective puzzle which is always fun. I really enjoyed reading it and it gave me a lot to think about in this really cool natural history system that I haven’t heard a lot about before, and also just about the way that we bring these ideas with us into the 21st century in science and how we can continue to give them credit and continue to work with them moving forward!

Laura

Thank you very much.