66 Dr. Sarah Lawson – The small carpenter bee and their Cinderella daughters (in English)

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. I am so excited to be starting a new series here on Pollination to expand our understanding of the amazing diversity of bees we have here in the Pacific Northwest. This week we're focusing on the small carpenter bee from the genus Seratina, and we're doing it with the help of Dr. Sarah Lawson, who's a lecturer in the Department of Biology at Sacred Heart University in Connecticut. Dr. Lawson is going to be talking this episode about research she did with Dr. Sandra Rian at the University of New Hampshire on the evolution of social behavior in bees using Seratina, the small carpenter bees, as a model. In this episode, we're going to learn all about the fascinating life cycle of Seratina, how easy they are for anybody to study in their backyard, and its peculiar strategy of turning the firstborn female into this underfed dwarf female who acts as this kind of nursemaid to the other bees in the nest.

In other words, she's a Cinderella daughter. It's a really fun episode. Sarah knows a lot about Seratina. I hope you enjoy this episode about our first bee genus on Pollination. Okay, well, welcome to Pollination.

Speaker 2: Thank you so much. I'm really happy to be here. I love what you guys are doing. Thanks so much.

Speaker 1: Sarah, we're really excited to have you on the show because I think a lot of our guests are recording in the summer have seen the small carpenter bees, and often people mistake them for ants. They're such curious bees. I've never had anybody talk about them. Maybe you can tell us a little bit about Seratina. What do they look like and their natural history? Tell us a little bit about this genus.

Speaker 2: Yeah, they're a very interesting bee. They're found worldwide. There are about 21 subgenres in the world, and they're found on every continent except Antarctica, so they're super common. In the U.S., we have about 26 species, and actually, 21 of them are west of the Rocky Mountains, so most of them are over there with you guys. Yay. Yeah, you guys got all the Seratina diversity over there. They're really cute. They're very small.

We're talking the size of maybe a couple of centimeters, and they come in beautiful iridescent metallic colors from greens and blues and into the purple range. They're really beautiful bees, and they're pretty easy to find. If you just watch a flower for maybe five minutes, I guarantee you'll see one of those guys walking around. My other favorite part about it is their nests are really easy to find. Any small, bushy plants such as Sumac, any of the berries like raspberries, blueberries, blackberries, or roses, if you go into those and see any of the cut stems, you'll see a perfect little hole in the middle of the stem, and that's those guys just digging a little nest.

Speaker 1: So it would be, if you looked at a regular stem, it would have the pith or still in there, but if you find, if you're walking by and you see a perfect hole in it, you may have found a nest.

Speaker 2: Exactly, yes. So they're really fun to open up. They can't sting you, so you can look at them and they're kind of cuddly, I think.

Speaker 1: I know people probably can, you know, I think carpenter bees, they're thinking like Zylocopa, they're thinking, but this is a totally different genus.

Speaker 2: Yes, yes. They're also, I mean, they're called the carpenter bees because they'll use their mandibles to dig into the pith, but unlike the large carpenter bees, they can't get into the hardwoods, so they will only make nests in the pith of the trees.

Speaker 1: Okay, tell us a little bit of the life cycle. So it's like a lot of solitary bees, they come out of their little twig in the spring, and what happens then?

Speaker 2: Exactly, so they mate at the beginning of the spring, they mate once, and then the female will find her own nest.

Speaker 1: Oh, they don't mate the year before, like a lot of other bees.

Speaker 2: No, normally they mate in the spring. Wow. And each female will find her own nest individually with the seating in the US. That's a little bit different from the seratina in Asia and Australia where they can have multiple foundrises. Okay. And she'll make her own nest, she digs out her own nest and hollows it out, and then what I think is really cute is she'll go and forge her pollen and make a little pollen ball and lay it and put one individual egg on each pollen ball, and then she builds a little wall.

Okay. She does it in a serial manner, so if you open a nest, you can see all of her little babies in a line, each with their own little separate room.

Speaker 1: What do they make the walls out of?

Speaker 2: They reuse the pit, so they'll just kind of stack it in there and pack it together. And then at night before she goes to bed, the mother will usually knock down the wall and make sure that her babies are doing okay, remove any parasites, and bacteria, and make sure everything's clean.

Speaker 1: Wow. Yep. And then they can guard at the end of the nest. So sometimes if you look really carefully at the end, you can see her with her little stinger sticking out, and that's her babies. So some really great moms. Great moms.

That's awesome. Well, okay, well tell us a little bit. Your research interest is in seratina with respect to the evolution of social bees. And people think I think a lot of people think about social behavior. They think about honey bees. They think of these massive colonies, this really rigid division of labor. Maybe to set things up, can you paint us a picture of the diversity of social behavior that people see with the bees? What's the variation? It's not all honey bees or nothing. Yeah.

Speaker 2: So sociality, I kind of like to think of it as a spectrum with solitary bees being on one end. Those are most of the sweat bees, and a lot of the mining bees. Most of the native bees in the U.S. are considered solitary.

Okay. And then on the other end of the spectrum, you have the highly social bees, and we use a term called U.Social to describe them. And these are things like the honey bees. Most people consider the bumble bees basically U.Social. There's some debate about that, but that means that they have one reproductive and only one bee in the colony can reproduce, and then everybody else has a different task.

Speaker 1: Oh, like workers in Queens. That would be U.Social. Okay. Gotcha.

Speaker 2: So in between the solitary and the U.Social and one end, there's a whole range of other terms and different lifestyle choices that bees have adapted to. And the bees in general have, they feel almost every niche in there.

So they're particularly interesting. So the bees, the seratinas that we study are considered sub-social, and that's because they have this elongated maternal care where the mother will actually stay with the offspring. And like I just mentioned, she checks on them every night and will actually stay from the laying on the egg all the way till they're an adult and move on to their next nest. Okay.

Speaker 1: Before we get into seratina specifically and their sociality, why do people think sociality has evolved among bees in all these kinds of weird and strange ways? You know, I guess, as a being a human in a society, I think, oh, society is an awesome thing. But why do bees evolve sociality and what's driving it? Why do certain bees have a social life and others don't?

Speaker 2: One of the big drivers that most scientists agree on is the role of kin selection in hymenopterum. So just very briefly in the way that bees determine their sex, it makes it so that sisters are more related to one another than they are to their parents.

Okay. It's very different sex determination in the way humans do it. But because of that, that means that you're very related to your sisters and so you want to protect them and you kind of have this drive, this relationship to help the other one out. So that's the hypothesis of why it evolved multiple times in Hymenoptera and why you see it so commonly in that group.

Speaker 1: And Hymenoptera is ants, wasps and bees. Okay. Gotcha.

Speaker 2: Yeah, so ants are considered highly social and almost all of the species are social and the ants probably evolved just one time there. Unlike the bees where it's been gained and lost multiple times. So it makes it a little more study.

Speaker 1: In the evolution of bees, there have been bees that have been social, and then over time they've gone back to solitary.

Speaker 2: Exactly. Yeah, and it's happened multiple times in different lineages across all of the bee groups. Fascinating. Okay. It gives us a few more comparisons to work with.

Speaker 1: Okay, so there's this genetic precondition that makes it more favorable to develop sociality, but why does it sometimes appear and sometimes not?

Speaker 2: I think ecological pressures play a big role in it. So there are some conditions that need to be met in order for social behavior to evolve. So you need this opportunity for maternal care. So the mom has to stay with the offspring to kind of form that group. So you see that evolved in multiple lineages. Also the risk of predation. So if you're in a group, it's easier to protect yourself when predators or parasites come.

Okay. And then you also see that division of labor to protect yourself from ecological conditions. And then I guess the final big piece of that is nest limitations. So if there aren't enough nests, sometimes it's easier to just stay at home and help raise your brothers and sisters than it is to go off and start a nest on yourself and risk not being able to find one.

Speaker 1: As many of us in a tough job market can attest to.

Speaker 2: And it's a little too close down.

Speaker 1: Well, let's take a break. I want to round this out. This curious little bee and the evolution of sociality. Let's take a break and you can break that down for us. Okay.

Well, we're back. Now, small, these small carpenter bees seem like such a strange candidate for asking questions about sociality. They're, you know, when I see them, I think, oh, they're like a solitary stem nesting bee. So what made you choose to study the social behavior of these bees? What is their social behavior?

Speaker 2: Well, I chose these bees in particular because we like to think of them as a bee on the brink of sociality. And my interest has always been in the evolution of social behavior. So I think to better study that, you kind of need to start with bees that haven't fully evolved and aren't at this one end of the spectrum but are really at the beginning stages of that. So we would like to take a look back at history. Maybe this bee is how your social behavior started or one of the ways it started.

Speaker 1: Because like with honeybees are probably like a million steps that took place that are all invisible to us. And you can't really understand it well. Okay, gotcha.

Speaker 2: All right. Some social bees are kind of in step one through ten out of a million steps.

Speaker 1: Okay, that makes a lot of sense. Okay, so tell us a little bit about what what what makes them social.

Speaker 2: So Sarah, kind of is particularly interesting. The mom is a really fit mother, what she can do is in her very first baby that she lays, she'll make it a female. And this female daughter is much smaller than any of the rest of her daughters. And because she was laid first, she also becomes an adult first, and then we'll actually serve as the worker for the nest when she becomes an adult.

So the mother is able to coerce her to do all the cleaning. Sometimes she'll forage, sometimes she'll guard. So we kind of think of her as like the Cinderella daughter for the nest. And she has to do all these extra foraging trips and protection. This is a really high cost of her fitness. And so usually she won't survive the winter. Butch, because she doesn't survive the winter, she's helping her brothers and sisters survive.

Speaker 1: Okay, let me get this straight. So we got this stem that we're talking about this like rose stem. Or when the female goes, she hollows it out and then she makes her first baby kind of runty. Exactly. And then this runty baby, somehow, okay, this is something I don't get. So when I think of like a mason bee, I think, oh, the mason bee goes in and she lays all these, you know, makes all these cells as you described with the seratina, but they all stay there till next year and then come out. So how does that female, tell it, yeah, and how does she get past all the rest of those? I'm confused. Give me the lowdown. How does this work? How does she help?

Speaker 2: That is actually, it's a great question. Because their nests are so small and sometimes I don't know how they can get past each other, but they seem to make the nests wide enough so two bees can pass, not that easily, but relatively easily. So when the door falls this daughter, the Cinderella daughter is born, she'll climb over, she'll break down all of those walls that the mom built and climb over her, still developing brothers and sisters, and gets to the end of the nest and then meets her mom.

And in my mind, I imagine they have this very serious conversation and there's actually some hiding and wrestling involved. Then the mom will be like, you know, you got to go help your brothers and sisters. So get out there and get them some food. So they can build up fast stores and they can survive the winter. Because where I live up in New Hampshire, it is really cold in the winter and those little bees need a lot of survival.

Speaker 1: Okay. So as you described in The Bees, this happens frequently because this runty daughter, this Cinderella daughter is really related pretty highly to her sisters. So she has a lot invested in their success. Yeah.

Speaker 2: So if she doesn't survive, that her sisters and brothers survive and do well, then her genes are also passed in the next generation. So it's still a benefit for her as well.

Speaker 1: So how does she help? What does she do? What are her kind of jobs? Does she do all the stuff that the mom does, except laying eggs?

Speaker 2: She does a lot of foraging. So unlike some other bee species, seratina will eat while they're adults too and they eat a lot before they overwinter to prepare their lipid stores. And a big aspect is defense. So there's really high parasitism rate anywhere between 30 and 50% depending on the area. Oh. So one of them stays guard while the other one goes to forage. So we see much more success in nests that have a door full of this daughter because someone can stay to defend the nest while the other one is out foraging.

Speaker 1: So she may not forage very much. She may just spend the bulk of her tasks just closing the hole again.

Speaker 2: Yes, exactly. And finding it often dangerous. No, it's an important job.

Speaker 1: Okay. All right. So this is really, so is there usually just one daughter or Cinderella daughter or can there be multiple ones or what's the range that we see?

Speaker 2: Usually just one. And what we're finding now is that the Cinderella daughter is very common across multiple species of seratina. And it's been in all the ones we've looked in. But what we're also seeing now is that in some other seratina species, especially in Asia and Australia, we actually have two mothers of two sisters bounding nests together. Instead of having this door full of the start of the worker and a reproductive that are actually sisters. And so, they are starting to see this range of sociality just within the Seratina genus. And that's where you can start to do some comparisons between these species.

Speaker 1: Just, can I, one natural history kind of tangent. So, you know, I'm thinking about mason bees, you know, they're going to, those adults never come out till the next year. But in seratina, all the adults will emerge in the year that they're laid and then they'll winter as adults.

Speaker 2: They do overwinter as adults. Some will overwinter in their maternal nest and some will go and find an old nest. Usually the boys, a lot of times the mom will kick the boys out of the nest and let the girls stay overwinter. But it's very dependent on the female. Okay.

Speaker 1: And so they're going to forge in the same year that they were laid. They'll go out and so you may see a very, they don't forage for themselves.

Speaker 2: The mom or the door felt his daughter was forged for them as an adult. So they won't start their foraging until the next spring. Like they're active foraging.

Speaker 1: The last, the one thing I've always noticed with seratina and I don't know the species that in the Pacific Northwest, as they seem to have a very long, they're around for a long time. You see them first thing in the spring, you see them right in the fall. Is that because of this, they're kind of, am I seeing the same, is it possible I'm seeing the same nest active all year round?

Speaker 2: Yeah. So there's a big peak right in the spring while the mother is provisioning for the nests. And then there's another one near the end of the fall when all the adults have been born and the mother goes out to forge for them. Fantastic.

For adult adults as well. Yeah. So in the middle of the season, they kind of are on the, once she has all of her baby's legs, she'll nest to protect them. She won't do as much foraging for herself. Okay.

Speaker 1: Back to sociality. So do all the species have this, what was the name of the daughter? You didn't say Cinderella, you said something else.

Speaker 2: We also call her the dwarf eldest daughter.

Speaker 1: Dwarf eldest. Okay. Gotcha. Okay. The dwarf does all of the species... The second basic rule of the daughter is catchier.

Speaker 2: Do all of the species have this behavior?

Speaker 2: So far, all the ones we've studied do have this. I mean, we have 26 species in the US and only about three of them are well studied and we know very much about their natural history. So there's still a really large gap of knowledge there. Okay. Okay.

Speaker 1: So tell us a little bit about the kind of research questions that you asked and to get at these questions of the broader, why does the sociality evolve?

Speaker 2: So I kind of started by looking at how the dwarf eldest daughter evolved and what the mother is doing to produce this dwarf eldest daughter. I was really interested in her, what we call phenotype. So what she looks like her characteristics.

The first thing we looked at was what she was eating to see if it was different, and what the composition was. Serotonin is really interesting because it makes a pollen ball and the pollen ball is everything that the bee will need to grow from an egg to an adult bee. So all the nutrition that they need is packed into this one ball. So all that information is there for us to get.

Speaker 1: Oh, so it's like a little cliff bar or something. Exactly. Exactly.

Speaker 2: So we were able to look at some of the plant species that they were using and found that for the dwarf eldest daughter, the mom usually forages from a variety of plant species all in the area. A lot of sumac, clover species, and some roses. And then while the season progresses and she lays her later bee, she starts to forge closer to home.

So a lot of the ones in England make nests in sumac and it seems like that's where they're foraging. So it's like she gets lazier as the season goes along. But this also correlates to different macronutrients that we're seeing. So the dwarf eldest daughter actually receives less protein than the other brothers and sisters. And we think that that probably impacts her growth and development and why you see this significantly smaller daughter.

Speaker 1: This is something that seems to be a more general characteristic with the evolution of sociality that these subordinate bees that in multiple taxa are kind of not fed well. That's like a mechanism in general. Is that right? Exactly.

Speaker 2: Yeah, we're seeing that trend in all sorts of bees. In the honey bees to produce a queen, it needs a royal jelly. Oh, right. And that's a nutrient-rich packet that allows the development to be turned into a queen. You see some of that stuff in bumblebee species as well to make the queens instead of the workers. In the seratina, you don't have such a difference in development between the reproductives and the workers. So in Seratina, the workers are capable of having babies. They have ovaries and they can develop unlike the honey bees they are born sterile, and the workers are. So seratina are called facultatively sterile, which means that they choose to not lay eggs or a forced not to lay eggs by their nest. Whereas the honey bees can't lay eggs because they don't have ovaries.

Speaker 1: Gotcha. Okay. So how did you figure this out? Like how do you figure out the nutritional value of a little pollen ball hidden away in the twig? Sounds like a lot. Hard to kind of get at those questions in the first place.

Speaker 2: Yeah. I mean, the seating is much easier to work with than some of the sweat bees, which nest underground. So they're in the stick. They're really easy to collect out in the field. I highly recommend people go out and look for them. They're really easy to find.

They're super common and it's easy to just get a little knife and slice through. You can open it up and look at the nest. And then you can collect the pollen ball pretty easily. We used some pinpricks to kind of knock out the different pollen types. And then we stained them and we were able to identify the plants based on the pollen types. And then to look at like the proteins and the sugars, you can just use GC mass back to look at most of those. So it's mostly just grinding things up and then running them through a machine.

Speaker 1: So you would look at the nutrition over time in the nest. When you take that pollen ball out, it seems it's destructive. You couldn't, you'd have to sort of, how did you get around that problem? How do you kind of compare something?

Speaker 2: I mean, you can take part of the pollen ball. We found that the amount of food they have is directly correlated to the body size of the bee. So if you took away a third of the pollen ball, the bee can still develop fine, but it's just going to be a little bit smaller than it would have been if it had all of that food.

Speaker 1: But you can, you can open the nest and then put it back together again in there. They're cool. Yeah.

Speaker 2: And you can raise them in the nest community. We are in the lab. We just use little tiny tubes with caps and we poke a hole in them and put them in the incubator. And they'll develop fine, in the humidifier.

Speaker 1: That's amazing. That's really cool. I find this whole thing really fascinating. It's a species that I thought was solitary and it's sort of like now learning that it isn't, it has this fascinating behavior and it is based on the kind of nutritional choices that the foundress is making to get this, get this whole process going. Yeah.

Speaker 2: That's what I love about the native bees. I feel like the more we learn about each species, the more secret world it has. They all seem to do something interesting. We just need to spend a little time learning more about their natural history.

Speaker 1: Well, I know you and I first met at a planning meeting for a native bee workshop in the native bee survey. And you know, I often think about this as there's a lot of value in just, you know, characterizing the bees. But there's this other thing of just learning something about their natural history. It's just so you know that this is the name and it's different from this one. Its behavior could be completely different.

Speaker 2: Absolutely. I mean, most of the native bees, we don't even know where they live, if they're solitary or social, what their feeding preferences are. Like there's a lot of work to be done and a lot of interesting things. I think we can still learn about bees around us.

Speaker 1: Fascinating. That's really great, Sarah. Hey, I've got some questions I ask all our guests. So let's take a break and I'm going to come back and ask you them. OK, great.

OK, welcome back. So we have these three things we ask all our guests. I'm curious what your answer is going to be. First is there a book that you really want people to know about or was influential to you?

Speaker 2: My favorite insect book is called The Other Insect Societies by James Costa. And when I first started my PhD, I was studying social aphids. And they're just kind of a random social group.

Speaker 1: Social aphids?

Speaker 2: Yes, I used to study social aphids. They're social aphids. OK. They're also they're very different because the bees usually depend on reproduction and foraging is their main social task. But for things like aphids and termites, their main social task is defense. So you see a lot of adaptations towards bigger like arms to hold on to things. Venoms, some bigger mandibles to attack things. So a very different form of sociality.

Speaker 1: And what do you what do you like about the book? What's what was what's good about it?

Speaker 2: I've never heard of it. So Jim does a great job of looking across all insect tax and exploring the sociality, everything from maternal care and the web spinners all the way up to the defense soldiers and the aphids in the thrips. So each chapter is based on a different order of insects.

So you just want a little quick tidbit with some interesting facts about a different order of insects. You have that. And it's a lot of great stories with really well-developed research and all of the papers are cited in there.

So if you want to do more research about it, those are all available. And he's just a really talented writer and he shows his love of insects in general with that book.

Speaker 1: Oh, this is fantastic. I will link it on the show notes so people can find it. And I'm definitely going to find a copy for myself.

Speaker 2: I highly recommend it. It's a good read.

Speaker 1: All right. Our next question for you is there a go-to tool for doing the kind of work that you do as a tool that you find indispensable?

Speaker 2: The carpentry is like I mentioned, actually really convenient to study because you can go outside with a pair of like shears and just cut their nests. Usually, we'll put a little piece of masking tape over the end so no one escapes. But it's really very basic ecology going out there and exploring and collecting the nests. You can also catch seratina and some of them like pan traps. They're very easy to catch there. But unfortunately, you can't study their behavior if you're using pan traps. So I just recommend a pair of good shears if you want to go out and look at the nests.

Speaker 1: Let me ask you a question. How you find this little hole so you're looking around, somebody goes to a spirea hedge and finds a bunch of them and then finds the hole in there. And so what do you do? You just keep you. How far up do you clip?

Speaker 2: I would clip all the way to the bases of the stick just to make sure you don't cut the nest in half. And then if you just take a knife and put it through the hole you can just kind of peel back the nest.

I wear gloves because I've cut myself more than once, but be careful. And then if you open it, you can usually open it just perfectly in two. And then they all list all the pollen balls and just line up in there.

Speaker 1: Oh, amazing. Okay. All right. Garden shears or special seratina shears that only Sarah sells. Check out her website. And we will link. You've got a website. So we'll make sure to link that also on the show notes so people can learn more about what you're doing.

Okay. The last question I have for you is whether it's going to be so favorite pollinator species. And I imagine for you, it'll be Seratina, but maybe you have a favorite.

Speaker 2: Um, I mean, the Seratina calcarata is close to my heart because I've spent a lot of time with them and they're this just like beautiful metallic blue color. And then the girls have this yellow mask on their heads. So they're actually really beautiful. And I love what great moms they are. So I have to go with them. The agapostum. Some of those species are really beautiful too. Some of those. We don't know nearly as much about those socialities. So maybe that's the next direction to go.

Speaker 1: Do all the females have a yellow stripe or is it not? I've seen some with little yellow and I always thought, oh, maybe that's the male character, but it's not.

Speaker 2: It's the males will have sometimes the tiniest bit of yellow, but usually much less than the females by comparison. So it's usually a pretty good way to distinguish the males from the females. And it's relatively seratina-specific. Okay.

Speaker 1: So not, not just calcarata. Did I say that right? Right.

Speaker 2: Yeah. No, it's in all of the species that I've seen so far. Okay.

Speaker 1: Fantastic. Well, thank you so much. There's still a lot of summer left. So there's a great opportunity for people to go out and look for these nests.

Speaker 2: It's not too late. It's my pleasure. Thank you so much for having me.

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