Context in courtship: how do singing mice decide when to sing?
August 17, 2018 10:59 AM   Subscribe

Context in courtship: how do singing mice decide when to sing?
I promised a singing mouse poster, and I've delivered. Here's what I've been doing lately, designed to be presented at Evolution 2018 this week. Do mice with better body condition sing more because they physically can or because they want to? What's leptin, and how does it play a role in body condition scoring? And honestly, why does it matter when singing mice choose to sing and why?

Of course, I can't answer all of these questions with my work, but I definitely have some thoughts and ideas. For those of you who aren't familiar with academic poster presentations, which is what this is, the idea is that they're not really supposed to be stand-alone things. The idea is that the poster presenter stands next to the poster and walks through it, so the context and background here is quite a bit more limited than I would ordinarily explain it.

But hey, this is me! And folks consistently want to hear more about the singing mice, and I think this poster is clean enough that I can walk through it with you here, on the Internet. So I'm going to put on what I'm thinking of as an online presentation: I'll walk through my spiel and what I think is really going on here, and I'll respond and chat back and forth if folks have questions or comments or think things are interesting. (I'm going in a little more depth than I would in person, obviously, and I don't have a bottle of wine to entice any of you closer to listen to me!)

So. Let me start out by saying: I work with singing mice! They're little brown mice--that's actually their other common name, which drives me nuts. They sing, why the hell would you call them brown mice, plenty of mice are brown! They live in cloud forests in Central America, mostly--they range as far north as southern Mexico and as far south as Colombia. Male singing mice sing both in response to other males . You can hear them in these videos from my colleague Bret Pasch, although you may want to be warned: they're audible to the human ear but high-pitched enough that folks with high-frequency hearing loss might or might not be able to pick them up. If that's you, here's a close-up version with the song slowed down, which most everyone who isn't hard of hearing can hear. If you watch this one, you can see how hard the mouse is breathing in and out as it sings--each note is an exhalation of force punctuated by quick little shallow inhales.

Just for contexts, males sing apparently to attract female mice and tell other males that they can beat them up, judging from the responses you get if you play recorded songs in places where wild singing mice live. It's pretty similar to bird songs in that respect. Male singing mice aren't actually the only ones who sing--there's a minority of females who also sing (maybe 5-15 percent of females?) and about all we know about it is that their likelihood of singing doesn't seem to vary at all throughout the course of their estrous cycle. Singing females sing all the time; non-singing females never sing.

My work is more than my study system, though. When I think about my research, I always come back to the question of context: how does the context of our circumstances and our current selves shape our behaviors and our expectations? I'm broadly interested in sexuality and sexual decisions, including animal decisions, and six years ago I got interested in a bunch of theoretical arguments about why we have sexually selected traits: that is, traits that evolve specifically because they help individuals get reproductions, not because they help carriers survive.

Sometimes they're pretty counterintuitive to survival, in fact. These signals and dances and exaggerated features sometimes make males more vulnerable to predators, and of course you can't spend energy you put into a song on foraging later on instead. Resources are finite. So why do these traits evolve? There are a variety of answers, but the most popular one is that these traits say something about the survival value of a particular individual showing them off: perhaps those individuals are better at foraging, or they are good at resisting parasites, or they are just the most perfectly adapted to their environment. That individual is therefore indicating how good his or her genetic potential really is, which lets potential mates (usually females, in this context, although that's not universal) evaluate them (usually males) and select the best genetic material available to fertilize her offspring.

These traits are often what's called condition-dependent: males who are in better body condition--have more fat, or are physically denser, or who don't have diseases--have "better" traits, for values of "better" that are measured through female choice tests. (We need to do more of these in singing mouse songs--we have good evidence that female mice prefer songs that have notes closer together with shorter pauses between them, but that is all.) And these sexual advertisement traits are often actually more sensitive to changes in body condition than other traits, which is really interesting.

So me, I have some questions about whether the observation that the idea that condition dependence is common in sexually selected traits supports indicator trait theory as a reason for evolving these cool, complicated traits. For one thing, it seems like it's a little too tenuous a set of connections for indicator trait theory to explain why condition dependence is so common. The idea tends to be centered on finding out why females retain a preference over time, and so you wind up with this justification that you get condition dependence so that the trait is an honest signal of quality and it's preventing males from cheating and making a shitty trait and keeping females able to evaluate males properly.

It struck me during a talk at the first Evolution meeting I was at, way back in 2012, that it would be much simpler to assume something slightly different: what if males evolve condition dependence of these traits for their own purposes? What if it's not about the reasoning for the preference at all?

What if males are just evolving condition dependence--sensitivity to body condition--of these signaling traits because you get more benefits from investing energy into them when you have a lot to spare, but if you put energy into them

Anyway, that was my question. The compound I'm working with is called leptin, and it was originally isolated in the context of obesity research: mice who are missing the ability to make this peptide are congenitally obese, but if you restore the signal with injections they immediately slim down. (The gene is named obese after this mutant phenotype: mutant animals are called ob/ob mice. Incidentally, congentially obese mice are fuckin' adorable, like hacky sacks with feet.) Leptin is secreted by adipose tissue, so assuming everything is working like it "should," the more body fat you have available, the more leptin you should produce.

If anyone is interested in more, I'll tell more of the leptin side of the story tomorrow--it's getting late, and I'll be getting on a plane to Montpellier in the morning. But the gist of it is that it turns out leptin has its fingers in a whole lot more pies than people traditionally think of: it shapes responses to immune challenges, informs motivation to reproduce as well as motivation to engage in reproductive behavior. It's even showing some promise as a mild antidepressant.

It's pretty cool. And what I'm doing involves administering extra synthetic leptin into the singing mice to see what effect that has on their behavior in response to a social environment. More on that in the poster itself.
Role: This is my thesis work, and this poster is all my design.
posted by sciatrix (6 comments total) 14 users marked this as a favorite
This project was posted to MetaFilter by sardonyx on August 26, 2018: Context in courtship: how do singing mice decide when to sing?

posted by ellieBOA at 11:30 PM on August 17, 2018

I am so interested in more!
posted by congen at 8:37 PM on August 24, 2018

Today I learned that I have high frquency hearing loss. But I also got to hear a singing mouse, so especially thanks for the slowed-down video!

What a fascinating (and adorable!) project!
posted by Nancy_LockIsLit_Palmer at 3:31 AM on August 26, 2018

Thank you, sciatrix! Would love to hear more at your convenience. Hope you have a great conference.
posted by Bella Donna at 4:08 AM on August 26, 2018

That's a nice piece of work, sciatrix!

Although now I'm imagining a metal band comprised of singing mice doped up on leptin... you'd want them loud for a mousey metal band.
posted by Making You Bored For Science at 1:40 PM on August 26, 2018 [1 favorite]

Today I learned that singing mice videos are a great way to attract my younger cat.
posted by GenjiandProust at 3:52 PM on August 26, 2018 [1 favorite]

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