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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

  • itself.

  • You can think of the alternatives as being parasites

  • on the prior condition.

  • Now, there is probably no group of organisms in which the

  • diversity of mating tactics and parental styles has been more

  • broadly and diversely developed than in fish.

  • If you're interested in this stuff, the fish hold more

  • material for investigation than practically any other group.

  • A survey of alternate male mating tactics in fish came up

  • with these kinds of definitions, and I want to run through them

  • for a moment, just so you have those words

  • clear in your head.

  • So there are three different kinds of parasitic male

  • reproductive behaviors.

  • So the sneakers are using speed or stealth to get access to a

  • spawning.

  • So they don't necessarily look like a female.

  • They just kind of hang back, let the spawning start,

  • and then they whip in.

  • The female mimics actually deceive the territorial or

  • guarding males into thinking that they are something to mate

  • with, and then a female comes in and

  • when she spawns the female mimics then reveal their true

  • colors and release sperm, rather than eggs;

  • surprise, surprise.

  • And the pirate males are males that steal fertilization by

  • being big bullies.

  • So they let some other guy do all the work of cleaning a

  • territory and setting up a nest and going through all of the

  • trouble of displaying and attracting a female,

  • and then just as she arrives they whip in,

  • and because they're bigger and tougher they push him out.

  • So that's a pirate.

  • Okay?

  • Now there are also cooperative male reproductive behaviors.

  • Satellite males can display and can contribute to territorial

  • defense and parental care.

  • And so we don't have to view this as strictly a short-term,

  • selfish kind of exploitation.

  • There can be cooperative mating going on,

  • and it will stabilize if it's really win-win,

  • so that everybody in it is winning something from the

  • interaction.

  • So if you just look at these morphologies,

  • the satellites, the sneakers and the mimics are

  • usually lacking sexually selected ornaments,

  • and the guards and the pirates usually have such ornaments.

  • Okay?

  • So the pirates kind of look like the guards.

  • They're not so much morphologically differentiated

  • as they are behaviorally differentiated.

  • This is a phylogenetic distribution of these

  • alternative reproductive tactics.

  • And the white is group spawning; the grey is mate

  • monopolization, with no alternatives reported;

  • the stripes are an equivocal, unresolved ancestral state;

  • and the black ones are the alternative male reproductive

  • tactics.

  • Now you can see that there have been quite a few.

  • I can read off--you can't probably see all of this,

  • but those are cyprinids there; some of those have alternative

  • tactics.

  • Some gobies have alternative tactics.

  • The wrasses here are in the Labridae.

  • But there are some alternative reproductive tactics in the

  • cichlids and so forth.

  • You can see--the interesting thing,

  • and the take-home point from that picture is hey,

  • fish do a lot of different things, and they have

  • independently converged on alternative male reproductive

  • tactics multiple times; which you can see from the fact

  • that the black is spottily distributed across the

  • phylogenetic tree.

  • Now if you go through that tree and you analyze it--we assume

  • that we're usually starting from mate monopolization;

  • so a guarding male and one female.

  • And then you ask yourself, well what happens from that?

  • And it looks like out of that ancestral state there has been

  • some evolution of group spawning,

  • and there's been some transition from that back

  • through mate monopolization.

  • There seems to have been some move from group spawning

  • directly over to alternative reproductive tactics.

  • And if we take a closer look at where you go into alternative

  • reproductive tactics, it looks like the most frequent

  • one is that sneakers pop up.

  • That seems to be the easiest, at least the most frequent

  • evolutionary transition.

  • And from sneakers, or from mate monopolization,

  • you can get female mimics; you can get satellite males.

  • So this is the cooperative one.

  • And then the pirates are not so common.

  • So I'm going to step through a case which is pretty well

  • analyzed.

  • It's in one way more complicated than the simple

  • situation, and in another way, in terms of the kinds of things

  • you can measure, rather simple.

  • So this is a wrasse that lives in the Mediterranean,

  • and Suzanne Alonzo, in this department,

  • studied it for her Ph.D.

  • thesis and her post-doc.

  • And Suzanne gave me these slides.

  • It is a case in which the nesting males are providing

  • parental care; so the guarding males,

  • if you like.

  • They are the ones that build the nest.

  • There are smaller non-nesting males that come in and sneak

  • spawns.

  • A nest takes about ten days.

  • So you can go out and get a pretty good sample.

  • You can fly over to Corsica, put on your wetsuit,

  • get in the water, stay there for three months,

  • you're going to go through a whole bunch of nesting cycles.

  • About one-third of all nests are deserted,

  • and they can be deserted either because there's an

  • intra-specific or an inter-specific interaction.

  • And it is the females that choose spawning situations.

  • Okay?

  • They're not really choosing males or territories;

  • they're choosing to go into a situation in which they see one

  • male, many males, a certain kind of general

  • topography, that kind of thing.

  • So this is Suzanne.

  • This is a male on his nest, and he is nesting in algae.

  • Okay?

  • So this is a big mat of algae, and he has cleared out a hole

  • in it.

  • This is a female, and the nest is below her.

  • By the way, these guys are about that big.

  • And here's a bunch of female mimics.

  • And often if you go to a nesting site you will see oh

  • anywhere from two to ten of these, hanging around.

  • So one of the questions you can ask yourself--and this is where

  • Suzanne used evolutionary game theory in kind of a simple way;

  • it's pretty much a cost-benefit analysis--should you guard or

  • should you sneak?

  • In other words, should you invest your energy

  • in guarding your nest and in guarding your female,

  • or should you try to increase your sperm production?

  • Okay?

  • So that's the basic assumption.

  • Either it's guarding or it's sperm production.

  • If you guard, one assumes that's decreasing

  • the risk of sperm competition.

  • If you do get into the sperm production racket,

  • then it's thought to be a fair lottery,

  • which means that the probability of a fertilization

  • is just directly proportional to what frequency your sperm are in

  • the pool of sperm that's being produced.

  • And these fish have external fertilization,

  • so you can pretty much estimate that by analyzing a sample of a

  • cloud of sperm produced at a spawning.

  • The guarding males don't know if they're in sperm competition,

  • because the female mimics look like females.

  • Okay?

  • So the male is guarding and he thinks he may have a number of

  • females around him, and it's hard for him to know

  • whether they're females or not.

  • That's not true of the female mimics;

  • they know that they're going to be in sperm competition.

  • So this just gives you an example of how a behavioral

  • ecologist would think about that problem.

  • Okay?

  • You do a Cartesian reduction, you break it down into its

  • elements, and you write down what would

  • be your reproductive success if you were guarding mates.

  • Well there would be some risk of sperm competition.

  • There would be the amount of sperm that you as the guarder

  • produced per mating.

  • There would be the sperm from other males.

  • Just this is the assumption of equal frequency.

  • Okay?

  • So this is the proportion of eggs you'll get if you do that,

  • and this is the probability of no sperm competition over here.

  • So that's your reproductive success.

  • If there's no sperm competition, you'll get them

  • all.

  • If there is sperm competition, you'll get this proportion.

  • And if you look at it--if you're allocating the sperm

  • production, which is what you might be

  • concentrating on if you were a sneaker,

  • well this would be your risk; proportion fertilized,

  • probability of no sperm competition and so forth.

  • Okay?

  • So basically if you're a guarder, and you're considering

  • the allocation within your own body to these two possibilities,

  • you just ask, "When am I going to get

  • more out of guarding than I am going to get out of sperm

  • production?"

  • And that simplifies to this; which is that the relative cost

  • of mate guarding has got to be smaller than the relative cost

  • of sperm production.

  • So that's the--I just--this is presented actually not to have

  • you try to write down equations, or replicate them,

  • or think that they're going to be on the test.

  • It is presented to show you that when you approach a new

  • problem you use very simple logic,

  • and you try to keep it as simple as you can,

  • and you just try to see if there might be any surprises

  • that arise from using very simple logic.

  • And I hope that that is a motivating comment,

  • because you can actually get quite far in these circumstances

  • just by using very simple logic.

  • You don't have to think that scientific research is based on

  • things that are so technically obtuse that you won't be able to

  • see through them.

  • So to get back to our fish, back from the algebra to the

  • fish, the nesting males don't know if they'll be in sperm

  • competition.

  • The female mimics know they're always going to be in sperm

  • competition.

  • And the fertilization rates are about 100%.

  • So the nesting males are able to reduce their risk of sperm

  • competition through mate guarding.

  • And there really is evidence.

  • This is the proportion of spawns that are snuck;

  • this is the number of mimicking males at the nest.

  • And the number of--if you just go out there,

  • you know, with your mask and snorkel,

  • and you're writing down how many males are at the nest,

  • what this kind of work does is it tells you that the number of

  • males that you see at the nest actually is a rough predictor of

  • the amount of sperm competition, which is going on.

  • And the proportion of spawns which are actually successfully

  • snuck does increase with the number of mimicking males at the

  • nest.

  • Okay, so what's going on with sperm competition?

  • Well this is sperm per spawn, times a million.

  • And if there's just--and you--by the way,

  • the way that you do this is you watch the spawn,

  • and you go down there with a sampling device,

  • which is a plastic tube, that will take in a liter or so

  • of water, and you put the mouth into the

  • middle of the spawn, and you suck in a sample,

  • and then you take it back, spin it down and analyze it.

  • So that's how you get the data.

  • If a pair is spawning, the male has produced

  • relatively little sperm, and if there are sneakers that

  • are going in-- so this is a pair plus one

  • sneaker-- this is the additional amount

  • of sperm that he is putting into the spawning.

  • So he has obviously taken advantage of the fact that he

  • doesn't have to put energy into guarding, and he has allocated

  • that into spawning.

  • However, because of the behavior and the dominance of

  • the guarding male, who is larger,

  • he is usually able to get closer to the female,

  • and in fact he is actually getting more offspring out of

  • his 1.5 million sperm than the sneaker is out of his

  • approximately 5 million sperm.

  • So these males are actually getting well paid by investing

  • in guarding, rather than allocating the sperm.

  • And the model is predicting that mate guarding should lead

  • to higher success; that's by an analysis that

  • actually includes more data than I have put up here.

  • So the sneakers are essentially males that are making the best

  • of a bad job, and they suffer from high

  • variance in mating success.

  • So they try, and they go from one male to

  • another, and they try repeatedly over the course of the season.

  • And the percentage of eggs they're able to fertilize is

  • going up and down a lot with each spawning;

  • whereas the guarding males are getting less variance and a

  • better geometric mean of total eggs fertilized throughout the

  • spawning season.

  • Now that's an interesting view of the world,

  • and I think that it's the basic view of the world that comes out

  • of almost every analysis of frequency dependence using game

  • theory.

  • It is a world in which there isn't an optimal solution.

  • It's a world in which there are losers.

  • It's a world in which there is conflict.

  • And certainly this is a mating system in which long-term

  • conflict is always going to be there,

  • and it's basically because the more guarders there are,

  • the more opportunities there are for sneakers;

  • and the more sneakers there are, the lower the mating

  • success of sneakers is going to be.

  • So they will always be maintained at intermediate

  • frequency and they'll never go away.

  • It's a nice habitat.

  • The water is pretty clear.

  • It's fairly chilly.

  • It's about 18 to 20 degrees Centigrade.

  • So it's not the warmest place in the world to work,

  • but it's good clear water for observation.

  • Now one of the interesting parts of behavioral ecology that

  • has received a lot of emphasis in the last- increasingly in the

  • last twenty years is the behavioral ecology of gametes.

  • So what's actually going on when we consider the alternative

  • tactics of sperm, or the alternative tactics of

  • eggs, and can we actually see

  • alternative tactics reflected at the level of the sperm,

  • as well as the level of the adult?

  • And this is a case in which we can.

  • So the sperm that are produced by males that are adopting

  • different tactics actually have different swimming speeds.

  • So the open circles are pirates; the boxes are territorial males;

  • the sneakers are these filled dots;

  • and the triangles are satellite males.

  • And this is a cichlid fish from Lake Tanganyika that broods in

  • shells, and has this range of alternative male behaviors.

  • And if you look at how fast the sperm can swim,

  • they have, in the first minute, they all have better swimming

  • speeds than after about a minute or so.

  • So what happens is they go through their energy stores

  • really quickly-- it's like that first minute is

  • really important, so they all sprint for a

  • minute--but then the sneakers manage to hang on better over

  • the next five or six minutes.

  • So this is an interesting case where the whole organism,

  • alternative morphology and behavior,

  • is associated with a syndrome at the gamete level of changes

  • in swimming speed.

  • This hasn't been much investigated,

  • and my guess is that there's a lot more stuff like this going

  • on than we already know about.

  • Well how about other fish?

  • Well a lot of the things that you're probably familiar with

  • happen to be species in which alternative male reproductive

  • tactics are well described.

  • One of the classic ones is the bluegill sunfish,

  • and another are the West Coast salmon.

  • So this is male bluegill, and this is a male Coho.

  • And these numbers here are actually years.

  • Okay?

  • So the bluegill is a fairly long-lived sunfish,

  • and the female is born and matures at- grows up and matures

  • at about four years, and then has probably about

  • another three to four years of reproductive life.

  • The male makes a decision after say late in its first year.

  • So if it's born say in June, then a year later,

  • in August or September, the male is making a decision

  • either to become a sneaker and a female mimic,

  • or to commit to growing for another five years before it

  • will mature into the dominant guarding male form.

  • Now these are pictures of what's going on.

  • The bluegills like, by the way, most centrarchids,

  • dig a nest and deposit- and the male is going to be guarding

  • eggs that are deposited there.

  • And the sneaker will come in and basically come into a

  • breeding assemblage, and actually get in between the

  • male and the female, while the eggs and sperms are

  • being released.

  • He actually pushes in between them, he's sandwiched in between

  • them when he releases his own sperm.

  • In West Coast salmon, which are genus

  • Oncorhynchus, Pacific salmon,

  • the difference in size is even more dramatic,

  • and the difference in life history is huge.

  • So again in the summer of, you know,

  • following say the first birthday, the male is making a

  • decision either to stay at home in the stream,

  • or go to sea.

  • And let me remind you that salmon are anadromous they run

  • up streams to spawn.

  • They lay their eggs into well aerated gravel reds in the

  • spring, in the stream.

  • When they hatch out, depending on the species,

  • they either spend a little time or a lot of time in fresh water.

  • Many of them go to sea.

  • And what they get by going to sea--which by the way is a very

  • risky thing to do; it's dangerous;

  • you run a gauntlet of predators going downstream;

  • you get out into the North Pacific and you have to deal

  • with seals and killer whales and all kinds of things that want to

  • eat you while you're growing up; and you may very well swim 3000

  • miles out of a river anywhere from California to Alaska,

  • out into the Gulf of Alaska.

  • What you get for that is rapid growth.

  • You can eat all kinds of stuff in the ocean that's not

  • available in fresh water.

  • So you take a huge mortality risk to get the benefit of

  • growing large.

  • Then when you come back, the female will basically make

  • a nest in the stream.

  • They have fantastic homing ability.

  • It has been calculated that a salmon say swimming up the

  • Fraser River, or the Columbia,

  • and it's smelling the different tributaries that are coming into

  • the river, it can detect a difference of

  • one molecule concentration between its left and its right

  • nostril.

  • So it will tack the right way, going up stream,

  • to get into the particular ground where it's going to make

  • this nest.

  • And when it makes the nest, you have a fish which is

  • probably about this big, which is tossing boulders,

  • which are about this big, out of the way,

  • to dig out its nest and excavate a place where it can

  • lay its eggs.

  • And in comes a male, who has gone out to sea and

  • weathered all of those tribulations and whatnot,

  • and he is coming home to spawn.

  • And lurking there on the sidelines are these guys that

  • never went to the ocean.

  • They're tiny, weenie little guys.

  • They never took the risk, but they run in and sneak a

  • spawning.

  • Okay?

  • This is the size difference, on the spawning ground.

  • And the eggs are released and they fall down into the gravel,

  • and actually the insemination is going to go on down in the

  • gravel.

  • So it's not as though this is something that's easy to

  • control.

  • Doubtless, if you are an adult ocean going male,

  • you are a bit irritated to have these little whippersnappers

  • there stealing your matings from you.

  • But they're so small that they can actually go down and hide in

  • the gravel.

  • So, in fact, it's a stable polymorphism.

  • Both--the female would never actually release her eggs if

  • there weren't a big guarding male there.

  • These little guys just don't elicit that kind of reaction

  • from her.

  • So his presence is creating this opportunity for them.

  • Okay?

  • Now it turns out that there are sneakers and guarders also in

  • dung beetles; you know, just go across the

  • entire Tree of Life and you will find almost every chink in a

  • mating system being exploited.

  • So if you look across sixteen different species of dung

  • beetles, that have sneakers,

  • you can document that the sneakers have larger testes,

  • and that sneaker frequency actually influenced male

  • expenditure on ejaculate.

  • So this is a case in which the guarding males can see that

  • there's a sneaker there, and if there is a sneaker

  • there, they up the amount that they put into the ejaculate.

  • So there is a flexible local response that's triggered by

  • this.

  • This is one such species.

  • Now why is it that I've been talking about males?

  • Why haven't I been talking about females?

  • Student: Is it because the males are usually the ones

  • that left. Prof: Usually they are.

  • And so in what kind of a mating system do you think you might

  • have the potential for the evolution of an alternative

  • female reproductive strategy?

  • Student: Well poly-- Prof: Yes, polyandry.

  • Something like this.

  • This is a pair; this is a male and a female

  • jacana.

  • They are in the Amazon.

  • My wife took the picture, from the front of a Zodiac.

  • And she's got about four or five of these guys,

  • that she's guarding.

  • So she has a territory that's about an acre,

  • on which four or five males are sitting on eggs,

  • and she is defending all of them.

  • And you can see that her fighting spurs here on her wings

  • are a bit larger than the male's, and she takes the lead

  • in defense.

  • So she actually charged the Zodiac and tried to drive off a

  • boat that was 1000 times her weight.

  • In this kind of a situation you might think that an alternative

  • female reproductive tactic could evolve.

  • In fact, polyandry is so rare in the animal world that there's

  • very little evidence for it.

  • But certainly abstractly that's the sort of situation in which

  • it could occur.

  • The other naturally is more cultural.

  • That would be in the harems of the great dynasties;

  • lots of alternative female reproductive tactics there.

  • So the main issues that we see in alternative breeding

  • strategies are first this idea of frequency dependence.

  • And if there's anything you remember, you know,

  • from this lecture, when you're fifty-years-old,

  • this is it.

  • Okay?

  • It's that once you get a guarding male and a female well

  • evolved, they then form a focus for

  • further evolution that creates the opportunity for a frequency

  • dependent minority behavior, like sneaking or pirates or

  • female mimics.

  • The condition dependence of this is well established;

  • and let me talk about that for a minute.

  • Several times I have mentioned with the fish that it's in the

  • late summer, right after their first

  • birthday, that they're making a decision to go one way or

  • another.

  • That decision, whether you're going to grow

  • up, develop into a guarder or into

  • a sneaker or a female mimic, is often determined by your

  • condition at that point.

  • Have you been able to grow fast or are you growing slowly?

  • And if you are at the upper end of your growth cohort,

  • if you're one of the really good growers,

  • you probably commit, if you're a salmon,

  • to going to sea; if you are a bluegill sunfish

  • to growing up, spending another five years to

  • become a guarder; and if you're at the lower end

  • of that, you will commit to becoming a female mimic or a

  • sneaker.

  • And it's important to see that that's a condition-dependent

  • strategy, and it can depend on a lot of things.

  • It doesn't necessarily depend just on the genetic quality of

  • that particular individual; it can depend on the growth

  • history, the local environment, anything that's going to lead

  • to either a rapid or a slow growth curve.

  • So condition-dependence in these situations is well

  • established.

  • Female choice is often an open issue.

  • You might think that females might want to favor one or the

  • other of two male morphs, but in fact I think if you

  • think about it for a minute, there may not be much reason

  • for female choice.

  • Can anybody tell me why there might not be?

  • There you are, you're a female.

  • You've got thousands of years of evolutionary history to

  • inform your decisions.

  • You see the guarder and the sneaker.

  • Should you prefer one?

  • Yes Blake?

  • Student: Super male is more successful and manages to

  • fertilize her eggs, since they're more fit,

  • and you want your sons to have that >.

  • Prof: That's right.

  • But what happens in the frequency dependence of the two?

  • What happens to the frequency of the two morphs,

  • the sneakers and the guarders?

  • Let's suppose they're at evolutionary equilibrium.

  • What's the relative fitness?

  • They'll be equal.

  • So if you're looking at two guys that actually because of

  • the frequency dependent process have come to an evolutionary

  • equilibrium, and you're scratching your head

  • and trying to decide, should I make a choice between

  • them?

  • The answer is evolution doesn't care.

  • Those guys are going to give you the same number of

  • grandchildren.

  • That's another factor that stabilizes this interaction.

  • It's not just the fact that males are competing with each

  • other; it's that once their

  • competition has come to an equilibrium, there isn't any

  • reason for the females to prefer one over the other.

  • They're going to get the same number of grandchildren out of

  • both.

  • Yes?

  • Student: But if the female is more prepared and

  • >

  • with really big males, and the females will only spawn

  • when they see one of those, not when they see the small

  • guys.

  • Prof: The females, remember, have an evolutionary

  • history of having started out in that situation,

  • and so the lack of female preference is probably more that

  • they're not chasing away the sneakers.

  • And they do, by the way, want to get their

  • eggs into a nest.

  • Right?

  • And only the guarder is going to do that for them.

  • So in that sense they have to prefer the guarder because he'll

  • take care of their eggs.

  • But when they're actually in the mating situation,

  • and they have the option of going five inches to the left or

  • five inches to the right, and they can see that they're

  • surrounded by a guarder and a bunch of sneakers,

  • they don't--in that situation they don't care.

  • Because their eggs are going to get into that guarder's nests,

  • whether they're fertilized by the guarder or by the sneaker.

  • But I take your point, they do have to get the eggs

  • into a guarder's nest.

  • So sperm adaptations are quite interesting, and they're

  • increasingly well understood.

  • There is a growing literature on gamete evolution,

  • and it turns out that gamete evolution can be quite

  • complicated.

  • I think some of you have run into the concept of Kamikaze

  • sperm or sperm that themselves have split up into different

  • tactics in the female reproductive tract,

  • and things like that.

  • That's an interesting thing to look into.

  • So that's it for today.

  • And next time is the last lecture, and I'm going to talk

  • about selfishness, altruism and cooperation.

Prof: Okay, let's get going.

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