Male Drosophila fruit flies perform an elaborate ritual when they court a female. The male first turns towards the female, follows her, taps her, vibrates his wings to produce a species-specific song, licks her genitalia, curves his abdomen toward her and, if all goes well, the pair finally copulate. These complex routines may help flies test whether a potential mate is the correct species and sex, and may allow females to gauge the genetic desirability of a courting male.
Unlike the courtship behaviors of most animals, the genetic basis for these fly rituals is well characterized, making them an excellent model for understanding how sexual selection can shape behavior. In the April issue of G3, Gaertner and Ruedi et al. assessed genetic variation in the progression between phases of the courtship sequence. Such variation serves as the raw material for selection, and ultimately, evolution.
Using the Drosophila Genetic Reference Panel—a large, genetically diverse panel of inbred lines—the authors found evidence for heritable variation in the classical courtship sequence, particularly in the tendency to start courting and in the speed of progression. They also identified two candidate genes affecting this variation.
In this guest post, co-authors Bryn Gaertner, Associate Medical Writer at Prescott Medical Communications Group, and Beth Ruedi, the GSA’s Director of Education and Professional Development, interviewed each other about how they became interested in fly sex, the vital place of model organisms in behavioral research, and life after the lab.
Who are you?
Bryn Gaertner: I’m Bryn Gaertner! I majored in psychology in undergrad and have always been fascinated with differences in behavior. Specifically, what are the natural genetic variations that cause individuals to have different behaviors and responses to the environment. So, I went to graduate school to pursue that.
Beth Ruedi: That’s almost exactly how I would describe my interests! I find it fascinating that there’s any sort of genetic component that influences the behavioral response to a stimulus, but I also particularly like that it’s never that cut-and-dried.
BG: Exactly. It’s comforting knowing it’s never going to be solely determined by one thing or the other.
BR: Did you ever get asked the “nature vs. nurture” question?
BG: ALL. THE. TIME. My brother and I are both statisticians at heart. He does this great work looking at how the environment a child has grown up in will influence how well he or she will do in school and what interventions might need to be made. So I went the hardcore genetics route, and he went the hardcore environmental component route…we have some really interesting conversations.
BR: I’ll bet! And actually, you’ll never be able to parse out why you are both statisticians—was it nature or nurture?? Because you and your brother shared both!
BG: Well, in this case I would say it was more nature; my parents both have statistician-like minds, but it’s not like they grilled us about ANOVAs.
BR: Right, like “Hey kids! Breakfast time! And also, let’s talk about bell curves!”
BG: Did you get asked about nature vs. nurture?
BR: Goodness yes, nearly any time I told anyone what I studied. I’m also adopted, so people used to ask me that starting from a very early age, before I was a trained biologist. I always delight in answering “Both!”
Going back to what drew me to behavioral research, I most especially loved sexual behavior. When I was a kid, I asked incredibly inappropriate questions — guess I still do. I think it’s fascinating how people will choose a mate. Or, I suppose, choose to “mate the one they’re with.” I was also the weird kid who would stand behind a tree for two hours watching deer in the woods. Behavior, I love it. How else would it explain watching flies have sex for a decade?
How did this project get started?
BR: I am so happy to have worked on this paper with you! I had gathered all of the behavioral data before I finished my postdoc, but then left academia.
BG: The whole thing was pretty serendipitous. When I started my postdoc, I knew I was interested in social behavior; my grad work was in nematode worms (C. elegans), and worms don’t really do social behavior. But flies do! [Senior author] Trudy [Mackay] suggested that I start working on fruit fly aggression. I was thinking about whether some “stereotyped” behaviors—behaviors that supposedly always happen in a particular fixed pattern—are truly stereotyped. That’s the idea of fixed-action patterns. Where do they come from? Are they variable? How do they evolve if they’re fixed in the population? Then I hear about your data and I think, “Oh! Well, we could analyze data that’s already there!”
It was great because I was coming in as an impartial observer. I was analyzing the data, and I didn’t have the benefit of looking at all the videos of the flies mating—or the pleasure of observing hundreds of thousands of flies mating like you did. The first thing that I did just for funsies was color code a spreadsheet of all of the behaviors in the observation period, in all of the fly lines, from red to green in terms of escalating sexual activity.
And it was just this beautiful picture of different lines having essentially different “greening” trends as they got closer to sexy time. You could see some lines were always green all the time, meaning that almost all the males started mating right away, advancing through all the courtship behaviors in less than 30 seconds. Then you had other lines where males always stayed in the yellows, so they spent a lot of time doing behaviors that were mid-range in intensity. It made it pretty obvious that there was a lot of variation in the pattern of behavior, and that it seemed to have at least some genetic basis.
BR: Yes, and the human brain can pick out patterns better than almost anything, they say.
BG: Yes, exactly. And then the question is, “ok, we see these patterns. How do we then quantify them in a way that’s testable and falsifiable?” In other words, how do we turn the patterns we observe into science? That’s kind of our job, or what we’re in training to do, as grad students and postdocs.
Why study fly (and worm) behavior?
BR: Let’s go back to worms. You used C. elegans, a well-studied model organism, doing your graduate work. Why worms, Bryn?
BG: Well, you and I are both interested in the genetics of behavior, but also the environmental component of behavior. To be rigorous about either one, you need to tease them apart.
BG: One reason this type of question is beneficial is that human behavior is important to understand, both for things like mental disorders, and for social dynamics that can shape policy and organizational behavior and many other things. But that’s really hard. What we want to be able to do is at least try to grasp the fundamentals, so we use organisms with less slightly complex brains than humans.
Nematode worms have 302 neurons (compared to our 100 billion), and they have a very short life cycle, and they have—as far as we know—nothing that translates to pain.
BR: Oh, that’s nice!
BG: Yeah, that’s reassuring when you are using them in a lab. And they’re only a millimeter long, they breed very quickly, and have a short life cycle. But, they’re not particularly interesting when it comes to social behaviors.
Model organisms allow you to pull apart the behavior you’re looking at, because you can do better controlled experiments more ethically, and in a more high-throughput way. But foundational research is also science for the sake of understanding the world. The justification isn’t as easy to convey, but at the same time, that’s where the major scientific discoveries have come from.
BR: And you can’t translate anything to human health or well-being unless you understand the basic building blocks of the underlying biological process itself. My grandfather used to ask me that question all the time. We’d have all these conversations about behavior and my graduate work, and he’d ask, “Beth, why are you wasting your time looking at fruit flies?” And I completely understand where that question was coming from. My answer would always be two-fold: one, anything we learn in fruit flies can inform what we know about humans; and two, I believe in knowledge for knowledge’s sake. I think it’s important to understand how a genetic variant leads to a particular behavioral phenotype and what kind of environmental influences have happened along the way. It’s very difficult to get behavioral analyses of humans that are purely quantitative and objective like you can for model organisms because you usually need to rely on people to self-report. And people are not always reliable!
BG: To recap what we’ve said, basic science not only helps us understand humans better, but it also helps us understand the world around us.
What are you doing now?
BG: There are so many wonderful careers out there that aren’t being a PI in a research university! One dubious upside to not having the funding to stay in science is that you’re forced to think long and hard about what you like to do. And you can figure out what your calling is, or your second calling if your first one was a scientist but that didn’t pan out. And for me it’s science communication. I love talking to people about science.
And so I work for a medical communications group and we translate clinical data into communicative data—
BR: Something understandable for the rest of the world.
BG: Now what about you? What do you get to do?
BR: I’m very fortunate in that I have a job that I really love. I was excited about graduate school and passionate about my project, but I was never planning on being a researcher.
BG: So, why did you go to grad school?
BR: I wanted to teach people about why biology is awe-inspiring and also teach them how to do their own research. I was planning on emulating my undergrad advisor. I wanted to teach at a small liberal arts school. And then this job at a professional society came up and was a good fit. Now I get to do things on a much wider scale than I if I were a professor at a small school. I work with great people who are professors at small schools as well as people at the larger research universities. It’s so incredibly fun.
BG: This has actually been quite an enjoyable interview and fun time.
BR: Yes, thank you for taking the time to sit down and talk with me about fly sex and worms and behavior and the state of the field, and make this the best blog post ever in the whole world.
BG: This will be the best blog post ever in the history of all things.
BR: Can we say this is the official end of the interview?
BG: OK, this is the official end of the interview.
Gaertner, B. E., Ruedi, E. A., McCoy, L. J., Moore, J. M., Wolfner, M. F., & Mackay, T. F. (2015). Heritable Variation in Courtship Patterns in Drosophila melanogaster. G3: Genes| Genomes| Genetics, 5(4), 531-539. doi:10.1534/g3.114.014811 http://www.g3journal.org/content/5/4/531.full