47 Briana Ezray – Mullerian mimicry and why telling bumble bee species apart by color can be hard.


Speaker 1: From the Oregon State University Extension Service, this is Pollination, a podcast that tells the stories of researchers, land managers, and concerned citizens making bold strides to improve the health of pollinators.

I'm your host, Dr. Adoni Melopoulos, assistant professor in pollinator health in the Department of Horticulture. Many of us in the US and Canada are seeing our first bumblebees of the year fly. If you look a little closely, you'll notice that not all the bumblebees have the same color pattern. In fact, you can use the color patterns on bumblebees to tell them apart.

But my next guest explains, when it comes to bumblebees, you can't always judge a book by its cover. Brianna Ezrae is doing her PhD in entomology at Penn State University in Dr. Heather Hines' lab. And she's looking at the question of why bumblebees over evolutionary time tend to look a lot more similar through a process known as Mularian mimicry. And what's really cool is that she's piecing together these evolutionary processes, looking at bees that are found right here in Oregon. So it's a really great episode to learn about these fascinating evolutionary processes, bumblebee biology, and just some of the very interesting bees that we have here in the state of Oregon. Hope you enjoy the episode. Brianna, welcome to PolyNation.

Thank you for having me. Okay, so right across the continent, bumblebee queens are popping out. They're flying around. Can you tell us a little bit about where they've emerged from and what they're going to be doing over the next month?

Speaker 2: Yes. So the queens you're seeing right now have recently emerged from hibernation. So over the winter they hibernate underground. And actually right now they are both searching for nests and getting some resources, so eating some food pretty much. So they previously made it in the fall, and so now they can begin to establish their nests.

Speaker 1: So they've been, some of them might have been underground for a while, and so they're just popping out and they must be really hungry.

Speaker 2: Exactly, exactly. So you'll see them kind of visiting some flowers and also starting to collect resources to feed their first workers. So they're going to lay their eggs and begin to develop worker bees.

Speaker 1: And so where are these nests going to be? Where are they looking for nests?

Speaker 2: Yes, so most bumblebee nests are actually underground. So they find like old rodent holes or small holes under the ground.

Speaker 1: Okay, so they're searching for them and they may at this point have a little bit of pollen and some brood down there. Exactly. You know, one thing I've always wondered about is when they go in there, do they, and I know in the diagrams I've seen, they make a little wax cup and they fill it with nectar. Do they kind of stay there after they provision the initial nest?

Speaker 2: Yes, so once the workers have established, the queens actually will never leave the nest again.

Speaker 1: Oh, really? Yes. Okay.

Speaker 2: So you'll only see queens early in the spring.

Speaker 1: And that explains why sometimes people often ask me, why do the bumblebees get, you know, so big in the spring? It's because that's the only time you see the queens.

Speaker 2: Exactly. Except the end of the season. Exactly. At the end of the season, you will see the future queens that are looking to mate and then they'll actually be the ones that go underground.

Speaker 1: Okay, thanks for that basic biology. I know lots of people are curious about what's going on and this kind of lays the foundation for all of us. Thank you. Of course. So now I know one of the reasons why people really love bumblebees, apart from their cute and their biology is really interesting, is that unlike some of the other species where it's taxonomically really difficult to tell species apart, you've got these really handy color patterns. Can you tell us a little bit about what that color is and what are some of the species in western Oregon that are really common?

Speaker 2: Of course. So the color on bumblebees is actually from their hairs. So the hairs are what have the colors and they can range from red, black, brown, white, yellow, and bumblebees are actually, yeah. So across the world, there's actually approximately 400 different color patterns for bumblebees.

Speaker 1: You're joking. Wow. Okay. All right. Cool.

Speaker 2: Fascinating. And in western Oregon, there's actually quite a few species. The most common one is really fairly easy to identify. It's called bombus falsnesenskii and it's the yellow-faced bumblebee. And so it has a yellow face and then demand it's black, except for a small yellow stripe near its stinger. But another easy one to identify out west is bombus melanopagus because it's the only one in Oregon, in western Oregon that has red hair on its abdomen. Okay.

Speaker 1: All right. And I remember when we talked previously, the one thing you warned me about, and I remember talking with Elaine Evans when we had our episode with Elaine last year, she said, oh, Minnesota is a lot easier to tell the bumblebees apart because in Oregon, you have a lot of bees that might look like bosnesenskii, for example. Exactly.

Speaker 2: So actually, Oregon is one of those places where there's a lot of species that look like each other. So bumblebees can be extremely difficult to tell apart in certain geographic regions because they actually, the bumblebee species are kind of matching or mimicking each other's color patterns in those areas. And this is thought to be due to a mullerian mimicry.

Speaker 1: Mullerian. Yes. That's a funny word.

Speaker 2: It is named after a man named Mueller. Okay. And so this type of mimicry is they believe that species that have some sort of either poison or danger, so like a sting, will mimic each other so that it's kind of group defense almost in that if a bird eats one bumblebee and gets stung, it'll remember what that looks like and try and avoid that type of bee again.

Speaker 1: Even if it's of a different species, because it knows a yellow stripe with a little yellow on the shoulder is a bad dude. Dude at, sorry. Exactly. Okay. All right. So this is Mueller mimicry. So over time, the bumblebees, I guess, would tend to look more like the species tend to come together. Right.

Speaker 2: So in the United States, for instance, we actually are believed to have approximately three mimicry complexes. So in the Eastern United States, they all somewhat look like each other. So they kind of have a yellow stripe at the top of their abdomen and then black. In the Rocky Mountain region is where you find most of the bees that have that red on the abdomen.

And then in the Pacific region, so where Oregon is, you have the bees that look like bossa senseki eyes. So with the black and then a yellow band near the tail.

Speaker 1: I guess it raises the question of are those like fixed? Does the species have just that color? Right.

Speaker 2: So some species are monomorphic, meaning they have one color pattern and match that mimicry complex. However, there are some bumblebee species, actually quite a few in Oregon that are polymorphic. So they have more than one color pattern and actually cross between two different mimicry complexes. So one pattern will match that Rocky Mountain region, so that red and the other will actually typically match that Pacific region. So that black and yellow form.

Speaker 1: So they have the same species, but it has, it can have a range of colors. Exactly. Oh, well, this is getting more harder.

Speaker 2: Much harder. And depending on where you are, you might have the same species with completely different color patterns. And this is actually fairly common in Oregon. Okay.

Speaker 1: So I remember we talked before, we talked a little while ago, and you mentioned that these zones, there are actual kind of regions where the hybridization is more pronounced.

Speaker 2: Right. So actually, so for those monomorphic species, there's kind of a standard hybrid zone that comes kind of between, if you made like a diagonal line between Idaho and Arizona. That's where you're going to meet up between this red and this black form.

Speaker 1: Okay. So you got a species that kind of have a little bit of red or black depending on when you're in the further away from that line, you get the more fixed they become. Right.

Speaker 2: So there's some species, for instance, there's the polymorphic species bombast bifarius, which it actually has a black form, a red form and an intermediate form. And so that's in its hybrid zone is actually though shifted away from that standard hybrid zone towards the east. And then there's other species like bombast melanopagus, which has its hybrid zone oddly shifted west in the border between Northern California and Southern Oregon. And it only has two color patterns, so a red or a black. And in that hybrid zone, you can find both of those patterns.

Speaker 1: Oh, how? Okay. So why that's a little bit weirder because it's not following that line. What's exactly.

Speaker 2: So that's what my research is trying to describe. What is causing one? Where are these mimicry complexes? So that standard, as well as why are there some species such as bombast bifarius and bombast melanopagus that are shifted away from that standard zone?

So what could be driving that? And bombast melanopagus is especially interesting because it is actually the only red species in Western Oregon. So it's not matching the mimicry complex, that Pacific black, yellow pattern at all.

And what does that suggest to you? So we're trying to see if could that be due to some sort of climate, like climatic condition or historical biogeography. And we're leaning towards probably some sort of historical biogeography. So what that would mean is like, maybe that red form is the ancestral state. And now that black form is kind of moving up into that region to match that mimicry complex.

Speaker 1: All right. Well, let's take, I want to take a break and come back to that. But before we do that is imagine, like when you pick up a bumblebee identification book, it's frustrating because it has all the color morphs. And I guess it would be, it would be possible to have a guide to your region where it would be a little bit more, you kind of filter out all those weird things.

Speaker 2: Yes, you definitely could. So there's some Oregon would be a little bit complicated because it typically can have both of a lot of these species. But you could have, especially with my research where we're kind of getting the fine scale detail of where are these different. We can say if you are in this part of Oregon, you're likely only going to get this color form.

Speaker 1: That'd be so awesome. OK, well, let's take a quick break and I want to circle back and hear more about the mimicry and specifically your research. Sounds great. OK, so let's come back to these color patterns and you're studying these weird, these oddities.

Speaker 2: Exactly. So I have, I'm looking at one where are monomorphic species, so that one color pattern species, trying to figure out where are our mimicry complexes in the Western United States. And then on top of that, looking at these polymorphic species, the ones with more than one and seeing are they matching with this? Are they varying? And if they are varying, why?

Speaker 1: And so you talked about it. There's one species you're studying. You have multiple species that have some kind of odd distribution. that doesn't follow this classic Rocky Mountain line.

Speaker 2: Right, so my main species I'm focusing on are bombus myelopagus and bombus bifarius. So each of these have these hybrid zones that are shifted away from that line. So bombus myelopagus is actually shifted west and bombus bifarius is shifted east. And so we're trying to do some work to figure out what is driving those to be where they are.

Speaker 1: It must be really complicated because this has taken place over evolutionary time. You can't just run an experiment in the laboratory. You have to piece together something that occurred a long time ago. How do you do that?

Speaker 2: Yes, so to start looking at this, I actually visited eight different natural history museums, including Oregon State's Museum, which has been extremely beneficial. So in each of these museums, I actually took kind of a template or coloring diagram of a bumblebee. And I looked at thousands of specimens, so museum specimens, and colored what their color pattern looks like, as well as took the information, museum special specimens are super helpful because they have their locality information so that geographic latitude, longitude, and year and collector, et cetera. So I can match the year that they were collected, where they were collected with their color pattern.

Speaker 1: I just want to quickly jump in here because we have all, I think we have about 120 volunteers around the state who are serving for bees. And when we did our training courses, we were emphasizing the importance of these, at the very minimum, you don't have to have the beautiful species but have that location information on there. It doesn't be spread the wings out, but get that ID.

Speaker 2: Exactly, it's so important. It's allowed me to actually do this kind of research to see, one, where are they? Two, is it shifting over time? So like, I have specimens all the way back to like the 1900s, two specimens that we've now collected currently.

Speaker 1: Okay, all right, so you got this intricate wave. It must be hard to color. How do you record these subtle shifts in color?

Speaker 2: Yes, so I actually, it's really, you have to be really focused in detail. So I take specimens and I look at them under a microscope because you have to see, especially with older specimens, the hairs, which is where that color is, can sometimes be bleach. So have too much light kind of on them and the color fades. So you have to look down to the hairs right at the base, figure out what segment they're on, and also get the fine details. So some specimens might have like a yellow arch mixed in with the red hair and others don't. Just trying to understand all the fine details of these color patterns.

Speaker 1: Sorry, what was the last thing you said? A yellow arch?

Speaker 2: So some species on the second segment have kind of a yellow pattern that in the middle, that kind of makes like a U shape. And sometimes it can be big, sometimes it can be small, and it can be difficult to see. So trying to see, does that vary geographically? What's happening?

Speaker 1: Oh, so your one grid may be like half yellow, half black or something. Exactly. I got you. Okay, all right. Okay, so you go through these museum specimens, you get these patterns and you get an idea of, I guess, the time dimension. You have some sense of time because some of these specimens go back.

Speaker 2: Right, so we have the time dimension, we have the patterns, so then we can map those and see that as well as we're actually also to try and understand ancestry as well as what might have happened over evolutionary time. We have done some barcoding, so genetic sequencing of the co-1 gene to see what is that ancestral state, is there any population structure, and what could be happening?

Speaker 1: Cause that- Oh, cause you could have bees with the same color pattern that are not that closely related, so it gives you one conclusion, but if they're all genetically similar. Right. Gotcha, okay.

Speaker 2: Yes, so those are the kinds of things we're doing to analyze this as well as to look at the climate, we're trying to use niche modeling. So we're taking climatic variables and seeing do the different colors kind of vary in what their climatic conditions that their sustained best are.

Speaker 1: Okay, so what would that tell you? So let's say you find like a more orangey one that's with a separate, what does that tell you?

Speaker 2: How does that- So what we're trying to see is could it potentially, and we have no idea, could it be that with like climatic change, this black form maybe is better adapted and moving north, for instance, from Elinopagus. So maybe it would be that in the future in Oregon, rather than having that red form there, it's gonna end up shifting to have black there and have the red actually shift over towards that Rocky Mountain region. We have no idea, so that's why we're trying to test this to understand climatic conditions as well.

Speaker 1: Is there an alternate hypothesis? Is there a reason why, because there's strong trends towards malaria and mimicry and bees becoming similar, is there a reason why a bee might wanna look different? Yes. It's so strong that everybody over time will settle out or?

Speaker 2: So malaria and mimicry is a pretty strong force of natural selection. So that's why looking at these polymorphic species is interesting, because it's letting you see natural selection in action. However, there are a lot of other hypotheses, such as krypsis, so it could be that they're trying to camouflage with background or thermal regulation. So how they can handle different climatic conditions has been a hypothesis that's thrown out.

So there's a lot of different variables to look at. And like I said, it could be ancestry and historical biogeography. So it could be that that's where these species were. Historically, maybe got isolated during an ice age or something, and then this is where they are now and things are shifting since.

Speaker 1: Okay, so I wanna ask you about, for some reason I learned it, Molyneupigus, but Molynaupigus. Melanopigus, yes. Melanopigus. So tell us where that range shift is in Oregon. So when we've got people down in Ashland, we've got people up in Corvallis. Where can we see these different color morphs?

Speaker 2: Yes, so for Melanopigus, what you'll actually find is in California, black band on its abdomen, and in most of Oregon and Washington.

Speaker 1: So the orange band disappears completely and you've just where the orange was is black. Exactly. Okay, cool.

Speaker 2: And then in Oregon and Washington, it's kind of that orange-red band. However, in Southern Oregon and Northern California, you can actually find both color forms. And so this kind of ranges from, it's mostly on the coast, however, Ashland is an area where you can find both. And then it's kind of up to Florence on the coast and down to maybe kind of into some parts of the redwoods in Northern California.

Speaker 1: I was wondering about that because I was down south of Florence just this weekend and I thought I saw a black form and I was like, huh. Yes. Okay, cool. That's really great. Okay, so depending where you are, and so is there a hybrid or is it just black or red?

Speaker 2: So for melanopagus, it's just black or red because it's actually a Mendelian gene that's been created with either one or the other. However, not all polymorphic species are like that. So like I said, for bifurias, you actually can get the red form, black form in an intermediate.

Speaker 1: That is so cool. This is so cool. Your research is so awesome. It's gonna be great. This is like evolution in action.

Speaker 2: Exactly. I'm very excited about it. Okay.

Speaker 1: Is there anything else you want? We should know about mimicry. Is there something that we sort of missed?

Speaker 2: I think we covered most of it.

Speaker 1: Okay, this is really cool and this is really helpful for all of our, and it also motivates a lot of our collectors in getting specimens in far out places to kind of assemble these patterns.

Speaker 2: Exactly. The more we know, the better. So we can figure out what's where.

Speaker 1: Okay, let's take a quick break and then we're gonna come back and I'm gonna ask you a couple of questions. We ask all our guests. Sounds great. Great. All right, we are back and we've got three questions.

We ask all our guests. The first question is, is there a book recommendation? Is there a book that you find really inspiring or you really want people to know about?

Speaker 2: Yes. So my favorite book is called Bumblebee's Behavior, Ecology, and Conservation by Dave Goulson. Oh, great. I like this book. Because I think it's fairly easy read and you can learn everything you could ever want to know about Bumblebee's.

Speaker 1: And it's not that long. It's not like a tome.

Speaker 2: No, and it's not too complicated either. So I think that really anybody interested in bees can read it and learn a lot.

Speaker 1: I was recently reading Bill Stevens book, his Great Pacific Northwest. It's jam-packed, but it's hard to read. Exactly.

Speaker 2: That's one where I feel like you need to kind of have a basic understanding before you jump in. Whereas this one, I don't think you do.

Speaker 1: No, it's really great. It has all the aspects of life history and it's not long. It's easy to read. It's a great recommendation. Thank you. OK, so our next question is, there are a go-to tool for the kind of work that you do. Is there a tool that you couldn't do your work with? Yes.

Speaker 2: So I actually really enjoy using dichotomous keys. And that sounds a little strange, but especially working with these bee sheaths that can look exactly like you need a way to be able to tell them accurately apart.

Speaker 1: So for listeners who don't know what that is, they're probably picturing like a key to a door. What is a dichotomous key?

Speaker 2: So it is actually kind of a document where you get, like, if it's like this, go to this section, or if it's like this, go to this. And you kind of discover your way, almost like a detective, to find what the species is based off of a bunch of different characters.

Speaker 1: And there is a good dichotomous key for the bumblebees of North America.

Speaker 2: There are quite a few. So there's actually the book.

Speaker 1: I'll see you some more. Yeah, yeah.

Speaker 2: Yes, Bill Stevens has his good one, though some things, some of the species have changed since then. For Western United States, there's a really good one that's called bumblebees of the Western United States. And it's free as a PDF online. Excellent.

Speaker 1: And I remember once somebody showing me, I can never get it to run again. Paul Williams had this really great. Yes. But it's got some strange old JavaScript and I can't run it anymore.

Speaker 2: Right. So there's also, it can be a little bit more difficult. There's online Discover Life, Oh yeah. where you can kind of input what you found in your specimen and it'll bring up different options. So that's another online one that can work well.

Speaker 1: And so what are some of the key features that you look at at a bumblebee? You don't look at the color patterns often. Right.

Speaker 2: So you can usually kind of start with color patterns, but then at least for the males, a key trait is usually the genitalia. So actually, the genitalia can tell you one species over another. Other characters that they look at are kind of like cheek length in the bee, so whether it's like a long cheek or short cheek or some of the main ones.

Speaker 1: Here's a question. When it comes to some of our mimics, those characters can be pretty different or they are usually closely related.

Speaker 2: It varies. So usually they can be fairly different. So a lot of the mimics actually aren't always closely related. So you can find it that way. Okay.

Speaker 1: Excellent. The last question we have for you is there a species that you see that you really love?

Speaker 2: I'm biased and I really like bombus melanophagus. My research kind of focuses and I think that it has really pretty, especially in Oregon, that red color pattern is beautiful.

Speaker 1: Tell us a little bit about its natural history. Is there anything kind of peculiar about it in terms of the bumblebees of Oregon?

Speaker 2: Yeah. So it actually is one of the first bees to emerge. So when spring bees start to emerge, it's the first one that you'll see. So it usually emerges in around February. Wow. Probably already saw it.

Speaker 1: You know, I was talking with Rich Hatfield from the Xerces Society a while back and he mentioned that their nest can be some of the first to finish.

Speaker 2: That's also true. You'll see the workers could already be out and the males soon after. Okay.

Speaker 1: Very fast lifecycle. Okay. Great. Well, that it's been really, this is a really timely episode. Thanks for taking time out from all the way in Pennsylvania. And it's always, it's always, I think it's really exciting a lot to all of us in Oregon that, you know, Oregon bees are the center of focus of research elsewhere in the US.

Speaker 2: They are. They're very cool.

Speaker 1: Thank you so much and good luck with your research. Perfect. Thank you for having me. Thanks so much for listening. Show notes with information discussed in each episode can be found at pollinationpodcast.oregonstate.edu. We'd also love to hear from you and there are several ways to connect. For one, you can visit our website to post an episode specific comment, suggest a future guest or topic, or ask a question that could be featured in a future episode. You can also email us at [email protected]. Finally, you can tweet questions or comments or join our Facebook or Instagram communities. Just look us up at OSU Pollinator Health. If you like the show, consider letting iTunes know by leaving us a review or rating.

It makes us more visible, which helps others discover pollination. See you next week.

Briana Ezray received her BA in biology from Willamette University and worked for the Oregon Department of Agriculture on a survey of native bees pollinating crops. She began her PhD in 
Entomology at the Pennsylvania State University in Dr. Heather Hines Lab. Overall, her research involves topics such as bumble bee biogeography and mimicry, bee community disease ecology, and conservation biology. Specifically, her research examines two different directions which allow her to understand spatial, historical, and seasonal dynamics in bumble bees. First, she is working to better describe and understand the evolutionary and ecological processes driving why bumble bees mimic or match each other’s color patterns in certain geographic regions. Second, she is exploring seasonal patterns of disease prevalence and transmission in bee communities.

Listen in to this episode to learn more about Mullerian mimicry, it’s role in the evolution of bumblebees, and why it is the subject of Briana’s research.

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“Species that have some sort of poison or danger like a sting will mimic each other so that it’s a kind of group defense.“ – Briana Ezray

Show Notes:

  • What bumblebees are usually doing right after hibernation
  • What gives the bumblebees their color
  • How to identify the most common types of bumblebees in Western Oregon
  • What is Mullerian mimicry and how it affects how similar some bumblebees look
  • Why certain visual traits are localized to certain areas
  • What the “standard hybrid zone” is and how it affects the coloring of bumblebee species
  • What Briana is trying to accomplish in researching these coloring complexities
  • How Briana was able to study the evolution of the bee coloring
  • When a bee would avoid Mullerian mimicry to stand out from other species

“Oregon is one of those places that has a lot of species [of bumblebee] that look like each other.“ – Briana Ezray

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