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  • Prof: Okay, let's get going.

  • This first slide really is just an update on the content of my

  • lecture last time, and it actually has two

  • messages; there's the direct message and

  • then there's the meta-message.

  • Andrea interpreted my lecture last time as me making the claim

  • that parents usually don't intervene in fights between

  • their offspring.

  • And so she had this nice paper that she'd read on hyenas that

  • showed that actually mother hyenas do intervene in the

  • squabbles between the baby hyenas,

  • and that they do so probably because in some seasons they're

  • actually able to get enough food--

  • if there are twins born, say that are sisters,

  • that are fighting with each other in the first week of

  • life-- to actually rear both of them.

  • And that's an important qualification.

  • So I want you all to know about it.

  • But the meta-message is this.

  • I really appreciate being informed about things like this.

  • I have to cover an incredibly broad range of biology in this

  • course, and I can't read all of the latest literature in all of

  • it.

  • And so if any of you feel moved, by the work that you have

  • done on your papers, to increase my knowledge by

  • sending in a little qualifier on one of my lectures,

  • I would be delighted to receive it;

  • then my lectures next time around will be a little bit more

  • current.

  • So.

  • Student: Can you check your microphone?

  • Is it on or off?

  • Prof: Open to all kinds of criticism.

  • >

  • Okay, today we're going to talk about alternative breeding

  • strategies.

  • And I asked Alex actually to come up with one of his

  • incredibly neat videos today, and he had trouble on YouTube,

  • and other places, finding a really neat video of

  • alternative breeding strategies, in males.

  • You'll see some slides.

  • They are dramatic, and they really are all focused

  • around one basic idea, and I just want to show-

  • indicate that at the beginning.

  • And it's actually in the simplest example,

  • in the bullfrog example.

  • Okay?

  • And the whole issue of having an alternative breeding strategy

  • revolves around frequency dependence.

  • So the usual scenario is that at some point in the

  • evolutionary past a male has achieved a dominant mating

  • status, and that sexual selection has

  • then driven the evolution of his behavior and his morphology--

  • the mating system, polygeny, polyandry,

  • whatever; in which case it would be a

  • female who would achieve the dominant mating status--

  • so that there was a focal pair, and that that biology got

  • pushed to a certain degree.

  • But once it evolved, it created the opportunity for

  • alternatives.

  • And so that's the theme of the whole lecture;

  • okay, it's alternative ways of getting a mating.

  • And as you'll see there are quite a few issues that are

  • interesting, and it covers a pretty broad range of different

  • kinds of organisms.

  • So this is the paradigmatic example.

  • And this often happens in various kinds of frogs,

  • not just bullfrogs, that the male calls,

  • the female hears the male calling, moves toward the pond,

  • and the male will then grasp the female with incredibly

  • strong forearms.

  • And if any of you are interested in frogs,

  • or had one in your pocket, you may have noticed that males

  • have different forearms than females.

  • They really have Popeye the Sailorman, bulked up,

  • steroid forearms, and once they get onto a female

  • it's actually extremely hard to pry them off.

  • You might be two hundred times their weight,

  • but boy they are hard to get off, and that's because that's

  • where all of their reproductive success is.

  • If they can stay locked onto her when she releases her eggs,

  • they will get the babies.

  • Of course what then happens is that a small male will jump on,

  • on top of the large male.

  • If a small male gets onto the female first,

  • the large male will grab both of them and practically squeeze

  • the small male to death.

  • Now the point of this is that the behavior of the dominant

  • male, and the female who's attracted

  • to him, created the opportunity for the

  • alternative behavior of the small male.

  • If that hadn't already been there, the alterative wouldn't

  • exist.

  • In the spring in the meadow that was behind our house in

  • Switzerland, when the male frogs started

  • calling in the pond in our neighbor's garden,

  • and the females started coming down through the meadow,

  • the male frogs that were waiting for the females to move

  • by would jump onto them, and then the females would have

  • to carry those guys on their backs,

  • around 100 meters, to get to the pond;

  • during which time, you know, other frogs would be

  • trying to jump on.

  • So it's a very--part of the intensity of this is driven by

  • the ephemerality of the pond.

  • If it weren't the case that the pond was only going to be there

  • for a little while, and only really suitable for

  • raising baby frogs for a little while,

  • it wouldn't be so intense.

  • But that's the case, and it is incredibly intense.

  • It all happens in a period of about twenty-four to forty-eight

  • hours.

  • Now a similar kind of alternative--well similar in the

  • abstract sense; a similar alternative mating

  • strategy has evolved in figs and fig wasps.

  • And figs and fig wasps are one of the wonders of ecology and

  • evolution.

  • There are--I don't want to be precise because in fact I don't

  • think we really know.

  • But let's say there are more than 500 species of figs in the

  • world--many of them in tropical rainforests;

  • many of them critical ecological resources providing

  • food throughout seasons when other trees are not providing

  • food-- and each one of these species

  • of figs, in general, has its own fig

  • wasp, and if it didn't have that fig wasp,

  • it couldn't get pollinated.

  • So what's going on here is that the figs are sacrificing some of

  • their own seeds to raise the wasps that pollinate them.

  • And this clearly has evolved from an ancestral situation in

  • which the wasps were actually parasitizing the figs,

  • and ripping them off, but now has evolved into a

  • mutualistic and very complicated mutualistic relationship.

  • The strategies of both the figs and the wasps vary.

  • You'll see in a minute that sometimes the figs are

  • monoecious, sometimes they're diecious;

  • in other words, sometimes they are producing

  • fruits that only have male flowers or only have female

  • flowers, and sometimes they're producing

  • fruits that have both kinds of flowers in the same fruit.

  • And the wasps have really highly differentiated strategies

  • that depend on whether they're copulating inside the fig,

  • outside the fig, and so forth,

  • and sometimes you get both kinds of strategies in the same

  • species of wasp.

  • So here's a fig, and here are some of the wasps

  • that would be living on it.

  • And this is about how big they are.

  • Okay?

  • So they're pretty small.

  • And in fact if you've gone to a nice organic store,

  • and you have eaten figs from a nice organic store,

  • there is a certain probability that you've increased your

  • protein intake, and you probably haven't even

  • noticed.

  • Now, the figs can make either long or short styled flowers.

  • And what that means is that they are making flowers which

  • are going to be targeted by fig wasps, or not targeted by fig

  • wasps, for their babies.

  • And if we--if you work through this diagram,

  • you'll see that the figs that have long styled flowers are

  • going to be getting pollinated, and there aren't going to be

  • any larvae developing on them.

  • These are the ones that are going to make new figs.

  • Okay?

  • And the figs that make short styled flowers are going to be

  • chosen--in this species of fig; this isn't for all,

  • but this is for one of the 600 species of figs--

  • they will be chosen by the wasp that will oviposit in them,

  • and the wasps will eclose.

  • They will mate; in many cases they will mate

  • inside the fig, and then when the females leave

  • the fig, the timing of the fig's flower

  • maturation is such that as the females force their way out of a

  • narrow aperture, there are flowers bearing

  • pollen right next to that aperture on the inside,

  • and the female takes them out, and then she flies off to

  • oviposit in another fig, which is how the pollination is

  • achieved.

  • So they had to set up two separate ways of making seeds;

  • the ones that the wasps would use and the ones that would make

  • future figs.

  • Other fig species have partitioned this in other ways.

  • Okay?

  • So there's an interesting complexity of evolution that's

  • gone on in this relationship.

  • Now the alternative mating strategies are that there will

  • be fighting males or dispersing males.

  • You don't need to pay too much attention to this;

  • this just shows that the more winged males there are,

  • the more females get mated by a winged male, that's all.

  • But there is a frequency dependent thing going on inside

  • one of those figs, as the males are hatching out.

  • If they fight with each other and kill each other,

  • then the survivor will be the only male who is in that fig,

  • or one of the few males in that fig,

  • who can mate with the females that are coming out.

  • So there is--you know, if you commit to that strategy,

  • you are committing to an extremely aggressive,

  • live by the sword die by the sword,

  • kind of existence, and it all gets carried out in

  • a dark little fig, and you're just waiting for the

  • first female to hatch out so that you can mate with her,

  • and you get as many as you can, and then you never fly,

  • because you don't have any wings.

  • You die in the fig.

  • So that's your protein intake; it's dead males.

  • On the other hand a certain number of the females are going

  • to manage to get out of the fig without being mated inside,

  • and if you can go out and find them,

  • outside, then you don't have to commit to fighting.

  • However, there are very strong morphological tradeoffs between

  • the two kinds of things.

  • You can't do both well; so you're committing to doing

  • one or the other well.

  • And how much each pays depends on the local biology.

  • How likely is it that the female will be able to get out

  • of a seed, an eclose, and get her wings

  • ready to go, and get out of there before one

  • of these fighting males comes over and gets her?

  • So that's what creates the frequency dependence.

  • And you can see these things are radically morphologically

  • different from one another.

  • This is a case in which the alternative reproductive tactics

  • are really resulting in changes that you could just pick up by

  • looking at the things.

  • You might need a hand glass to see it very clearly,

  • because these guys are down about one millimeter long.

  • But it has resulted in major morphological change.

  • And, by the way, these, from an evo-devo

  • perspective, this is neat because all of these forms are

  • elicited essentially from the same genotype.

  • These guys are haploid; these are the males.

  • This is the female; she's diploid.

  • Otherwise they have the same genotype,

  • and these alternatives here are probably being determined just

  • by one autosomal locus with two alleles,

  • that are determining whether or not you are a type that flies

  • out of the nest or stays in the nest and fights.

  • And you can see that the female is equipped with really a

  • beautiful, exquisitely long ovipositor to get her egg into

  • the fig seed.

  • Okay.

  • So we've seen that bullfrogs and fig wasps--the bullfrog

  • biology is relatively straightforward;

  • the fig wasp biology is almost arbitrarily complex.

  • But they both create situations in which alternative male mating

  • tactics are possible.

  • And the thing that drives that is that there is a very well

  • developed, evolved, prior biology,

  • that means an alternative has an opportunity to insinuate