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12min chapter
When Vaginas Attack!
Science Vs
Evolutionary Dynamics of Mating Strategies
This chapter explores the intricate evolutionary battle between male and female mating strategies in the animal kingdom, highlighting unique reproductive anatomies and tactics. Examples include the control females have in water striders and the complex mating systems of rattlesnakes, emphasizing the role of female anatomy in reproductive success. The discussion humorously contrasts the diverse approaches of different species, shedding light on the broader implications for understanding both animal behavior and human sexuality.
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Episode notes
Speaker 2
Today on the show, Dr. Tiana Pirtle is walking us through vaginas of the animal kingdom. It's really an evolutionary battle between both vaginas and penises, which when you think about evolution, that is how obviously it worked, right? It doesn't really make sense that only one would be evolving.
Speaker 1
Yeah. And also it makes sense that they wouldn't necessarily be evolving in the same direction together always. Obviously both males and females want to reproduce, but females have to invest a bit more resources, time and energy into reproduction relative to males. And that's where you get the sexual conflict, where the males and the females' interests don't always align. So that's why you get some of these wild tactics and different physiology, morphology, and behaviors. So tell me how the water strider yeah so the water strider is um a great story of kind of sexual conflict evolutionary arms race in inaction um so water striders are bugs that that sit on top of the ponds and water the females have these genital shields so and i do have a model of this but unfortunately didn't make it on the on the you can't fly with that sort of weaponry but it she's got her overpositor that sits inside of her abdomen and then the overpositor where the eggs go And if she wants to mate, she will push it out and it kind of opens and the male can deliver the sperm. But if it's in this position, there's no chance the male gets to mate with her. If it's closed up, it's closed. So the female has evolved this morphology that gives her full control over who's mating with her. She has full say over who's going to father her offspring. But the males have evolved this counter strategy. And historically, it would have been described the other way around. Oh,
Speaker 2
of course, right.
Speaker 1
Generally. But the, so the male can't mate with FEMA unless she is fully on board. Open for business. So the male's response strategy is he will, to use those terms that we said are often describing males. Yeah. He will threaten her by, he sits on top of her and taps the water. And that will alert all the predators in the water. Right. And the predators will come up, and because the female's on the bottom, she has a higher chance of being eaten. So he'll just sit there. She can't fly away because he's sitting on her. And he'll just tap, do this little threatening tap dance until she either opens her ovipositor, gets eaten, or they both leave. Wow. What a strategy. The insect world is really fascinating when it comes to genitals and insects where the females have the penis. Well, we would call it a gynosome, but it would be what we think of as penis. And the male has the receiving organ. Okay.
Speaker 2
Yes, there's many ways to be a male and a female. So there's a couple more animals I want to go through. So far we've just been talking about generally one vagina,
Speaker 1
but there are animals with two. Yes. In fact, there are many animals with two. So this is the rattlesnake. So you can see there's two of them, two vaginas, two uterine. And each one can be fertilized?
Speaker 2
The
Speaker 1
males have two-pronged penis, the hemipenes. So they use them both at the same time. The hemipenes. And either one can shoot out sperm. And then they have the two vaginas, two uterus.
Speaker 2
Two clitoris?
Speaker 1
Yes. Hemiclitoris is what it's called in snakes. Does it give pleasure? A hemipene. So there's been remarkably little research about clitorises, which is remarkable because all mammals definitely have one. And I'm pretty sure pretty much all vertebrates have one as well. And we don't really know what they do for these animals, but presumably they play an important role in reproduction. Because otherwise that's a big lot
Speaker 2
of wasted energy for evolution. So tell me the evolutionary arms race going on with these snakes.
Speaker 1
Okay. Well, so snakes, these rattlesnakes, they reproduce quite slowly. They're long-lived, slow-growing animals. So I believe they don't become sexually mature until they're about 13. And they also don't produce very many clutches. So what these snakes do, and a lot of other species in the animal queendom do, is they'll store sperm. So these guys have like a special organ that will store the sperm. Okay. Over winter for years even. Oh, wow. I believe there's a tortoise or a turtle that stored sperm for four years. And then produced a clutch from
Speaker 2
it. Wow. They've got like a little IVF
Speaker 1
fringe in there. These snakes will go around and mate with the males they come across. They can be quite indiscriminate because they can keep all the sperm they find and deal with it later. That is
Speaker 2
amazing. They could
Speaker 1
store it for that long. Yes, and then there's some evidence to suggest that snakes, alligators, sharks, all these species that are storing sperm can then select which sperm to use for which clutch. And we don't exactly know how they're doing this, but there's quite a complex dialogue happening between the sperm the vagina environment. So the female will mate
Speaker 2
with a bunch of different males, store the sperm, and then we think when she releases an egg, she'll somehow, using the word choose generously, but she'll somehow be like, all right, well, for this egg, what we really need is this sperm. We want this sperm. Well, in the ejaculate, you have quite
Speaker 1
a diverse range of sperms. This sperm has crappy genetics. We're not going to choose that one. Oh, this one has got great receptors on the outside. We're going to help this one go forward. Interesting. And you'll be the one to fertilize my eggs and that'll increase
Speaker 2
my baby's chance of survival. Amazing. So clearly
Speaker 1
some animals
Speaker 2
have evolved these bells and whistles, these sperm storage facilities. Corkscrews. Corkscrews. Badger folds. Yes. Genital shields. No shade to my vagina or anyone else listening, but it's pretty cut and dry as far as I'm concerned. And the alpaca, not throwing it
Speaker 1
under the bridge, but like also just kind of looks like a tube. Yeah. Why is it that- Which, you know, I do still love it though. It's one of my favorites. It's very regal looking, isn't it? It is very regal. It's just like a very long tube. Coincides with a very long, thin penis. I could only imagine. Well, this vagina does many amazing things still. Tell me about the alpaca. What's happening here? So this vagina is punctured by a very long penis that has a little hook on the end of it.
Speaker 2
Wait, wait, wait, wait, wait, wait, wait.
Speaker 1
What does the alpaca penis look like? Terrifying. It's long and thin and it has a collagenous hook on the bottom. Alpacas are quite unusual in the mammal world in that the, so most penises stay in the vagina, deposit the sperm within the vaginal canal. Yes. The cervix will often kind of function as a bit of a quality control checkpoint, and the sperm have to make it through the cervix. The trapdoor. Yeah. Of the cervix, yes. Whereas for these guys, the penis punctures through, the little hook pokes through the cervix and deposits the the sperm straight into the uterus oh okay
Speaker 2
um does feel efficient which is does yeah if i'm if i'm gunning for the male alpaca yes good strategy i would say good work evolution
Speaker 1
and you know this is potentially because uh male alpaca, what we call dribble ejaculators. Hello now. Dribble ejaculators. So the ejaculate dribbles out very slowly. So mating can take up to an hour in alpacas. It's like anywhere from 20 to 60 minutes. And it happens in a very reclined repose. The female alpaca will sit on the ground the male will get on top of her and sometimes she'll lay down on her side have a nap wait for him to finish his job and so um other species the ejaculate comes out with force get familiar with those yeah yeah yeah so you know needs a little bit of force to get through the cervix. Whereas I guess, you know, if you're dribbling, you might as well put it where it needs to go. Of course, that makes sense. I guess this nondescript normal vagina can look the way it does because the female has a high degree of control behaviorally. So if she's not intimating, she'll just stand up and walk away. Or if she doesn't want it in the first place, she just won't lay down. So she hasn't necessarily needed to evolve all these fancy bells and whistles to stop sperm from getting to where she doesn't want it to go.
Speaker 2
Because she can just get up and leave. Oh, that's so interesting. So we find that in the animals, like to go back to the dark, where it is more forcible and the males are really coercing that sexual behaviour, then you have to evolve a vagina that can handle that, that can sneakily... Well, that will give you the final say. Right, but with some animals like alpacas, the sort of evolutionary arms race actually comes from the behaviour. Presumably, yeah. That you can just walk away, I'm done with this dribble. So it is interesting. We do often see, as you've talked about at the beginning of the show, we often see sex as this battle where the slutty male is fighting to impregnate.
Speaker 1
But it's never described as slutty for the male. Like promiscuous is used for females that mate multiple times, but the male is just multiple matings. Oh,
Speaker 2
right. The male is just being a male. We've
Speaker 1
had this since Darwin, this very narrow view of what a female should and shouldn't be. You know, monogamous was the word that Darwin used to describe females. Coy, passive, chaste, loyal, dutiful mothers. But that's not what we see in the animal kingdom. Also, you know, we haven't even touched on this, you know, homosexuality and homosexual behaviors in animals. Very common. And there's many different ways to reproduce and be a male and a female in the world. And I think appreciating that diversity in the animal world will hopefully help us appreciate that diversity in the human world. That's right, where there's
Speaker 2
so much diversity within species, let alone amongst species. Yeah,
Speaker 1
yeah. And yeah, the patriarchy has had scientific credence for too long from this very narrow view of males and females and reproductions.
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