Hank: Hello! Welcome to SciShow talk show, that day on SciShow where we talk to interesting people about interesting things. Today, we have joining us Douglas Emlen, also known as Doug, author of "Animal Weapons", a book about the various arm races that have gone on between all sorts of animals including, turns out, us. Doug, hi!
Doug: Hello. Thanks for having me here.
Hank: How's it going? Yeah, absolutely.
Doug: It's going great.
Hank: So, I love science books and I was excited to find out that there was someone right here in my very small town of Missoula, Montana who had written one. Uh, tell us a little bit first about your research. Who do you research?
Doug: I work on beetles is what it comes down to. And I want to qualify that the book is on animal weapons and I work on animal weapons, but I work on a special subset of weapons which are the really, really big weapons and I just have to confess at the outset, I have been crazy about animals that are so bizarre looking and extreme that when you look at them, they look like they shouldn't be possible.
These are animals that look like they should tip over [Hank laughs] or they should trip or they should get tangled in the trees or the branches when they move, because the things sticking off of their bodies are that extreme and so, in the case of the beetles, there are thousands of species that have horns sticking off the front of their bodies. It can be coming off the thorax or the shoulder blades or coming off the heads. There are species with one horn, two horns, five horns, all sorts of weapons coming off these things and most of my research concerns--
Hank: [takes beetle, mumbles] I want one, so he doesn't have things to grab on to.
Doug: --sort of the genetics and the development and the evolution of these weapons.
Hank: So like why it happens, how it happens?
Doug: You got it, all of it. I started out years ago looking at beetles that were even smaller than these guys, little tiny dung beetles that had crazy horns coming off their bodies and we really didn't know much about what they did so a lot of the research was watching them in the wild and figuring out how they used the horns and they're basically analogous to what you'd see as antlers in elk or deer. The males have the weapons. Females don't. And they use them in these battles over access to females and these things are extreme.
Th-they're expensive to produce, they're awkward and expensive for these guys to carry, they make it more difficult for them to maneuver, to do basically anything. I mean, imagine having an extra leg on your head for everything that you do. It would get in the way all the time, but the ultimate currency that matters in life is reproduction. And they help a lot when it comes to getting access to reproduction. These things tend to crop up in species where there's intense competition among males over access to a limited number of reproductively available females and in those battles, that is literally do or die. If you fail to breed, you're done. I mean, that's it. That's the end of the game in the evolutionary sense. So, so these guys, these weapons matter a lot in competition for reproduction.
Hank: So, this is a big set of, is a big weapon, but it doesn't feel huge to me. I was wondering if you could show me an actual, like, like-
Doug: Put it into context for you?
Hank: Put into context.
Doug: I can do that. Can I get up and go get it?
Hank: Yeah, go get it.
[SciShow Transition]
Doug: We are back on, alright. So, to scale that up to a more appropriate size for us to appreciate, I happen to have a pair of elk antlers. And again, the key point is these antlers, relative to the size of that bull elk, are actually smaller than some of the horns that these beetles produce and carry around on their bodies. And I can promise, and I can give it to you if you want, these things are heavy. I mean, it's - it's incredible to imagine a bull carrying this around, you know, on top of their heads for everything they did!
Hank: That's - that's like as big as they get, right?
Doug: This is a pretty decent sized male. They get a little bit bigger.
Hank: Yeah, because I see - I see elk but I don't see them this far away and so I have a hard time imagining that they really are that big.
Doug: And, they're that expensive. When these weapons get big, they get expensive. They get very, very expensive for these animals to produce and the antlers are a really good example to illustrate that point.
Hank: Well, they do all that work to produce them and they're so energetically expensive to even have, to carry--
Doug: I promise you can just sit here and do your exercises with these things, they weigh a ton.
Hank: I want to. Let me see.
Doug: But, um, not only is it expensive for these animals
Hank: Can I even? Oh my god.
Doug: To carry that everywhere they go
Hank: Hello, buddy.
Doug: but producing
Hank: Uuuoohh... I'm not a strong man.
Doug: I'll let him hold it.
[laughing]
Doug: It costs a lot for the animals to produce it. There's been some really neat studies looking at how much it costs the males to actually produce that and the most recent estimates suggest it costs a bull elk as much to produce a rack of antlers as much as it costs a cow to raise two calves all the way to weaning. That's a huge investment.
Hank: Oh yeah. You could be
Doug: And one of the ways to appreciate that
Hank: making so many more babies. If you were, if you were sharing that wealth.
Doug: Exactly. Well, no that's the point. They wouldn't be making any babies if they didn't allocate the wealth. And that's a really good place to point out the cost. They're building bone. And they need phosphorus and calcium in order to make the bone and they can't get enough of that from the, the forest they feed on. So some of these studies suggest that these guys--
Hank: Cannibalize from their own bones?
Doug: They do. They shunt it. They leach these things out of the rest of their skeleton to pour it into these weapons. And then they throw their weapons away at the end of the season. So these males actually go through a brittle bone osteoporosis period exactly during the rut, when they need these things and they're smashing into rival males in these knockdown, drag out, do-or-die battles.
And again, elk are sort of an example that we can see and relate to, and because they're heavy it's easy to appreciate how expensive they are, but it's, it's important to recognize that there are all kind of animals that do that, right? So there's rhinoceros beetles, there's dung beetles, there's flies, there's crabs, there's shrimp with huge claws. There're thousands of species out there where the males are doing exactly the same thing. They're shunting huge amounts of resources into these weapons for one purpose. Just to duke it out, fight over access to females.
Hank: But there are, there are other reasons to have weapons. Cause traditionally, we think weapons are for... killing. Uh, and these don't do that much killing, I imagine.
Doug: Nope. Well... no.
Hank: Occasionally.
Doug: Occasionally. No, that's actually one of the fun twists that came out of reading about these arms races, is one of the things that happens in this kind of a weapon. You've got the very small number of males with the huge weapons, you have lots of the population somewhere in between with sort of intermediate weapons, and you've got the smallest males with the fewest resources and the tiny tiny little weapons. The weapons end up becoming hugely disparate in size from animal to animal within a species within a population. And it makes them a good signal.
Hank: Mhmm
Doug: It's not an accident that the really big, best-conditioned male has the huge weapons. It's because he is in the best condition and the healthiest and the most resistant to parasites and had access to the best food and that's why that male had the really big weapons. That's the male that's gonna win the fight. So if you're a male and you're going up to another male and you gotta decide do I wanna launch into this thing, it makes really good sense to look at the weapons first. But what it means is these males don't actually fight as often as you'd think they would.
Hank: Right. They're just signalling.
Doug: They can fight.
Hank: Right, of course.
Doug: And they will fight.
Hank: I can definitely see...
Doug: But what happens is most of the encounters end up getting resolved without a fight.
Hank: So we have weapons used as a deterrent, as a signal, but then there are also weapons that are developed that are actually used for death and killing.
Doug: There are.
Hank: And you know, you look at, you look at lions, they got big teeth,
Doug: Yeah.
Hank: But it's not like this, you know, they don't have like teeth sticking out of their face. And they're just not like hitting- cause they gotta be sleek, they gotta be fast...
Doug: Right.
Hank: But there are some animals that have crazy, crazy teeth. And that...
Doug: And I got one of those too.
Hank: Okay, sh- let's talk about that.