Hello students.  This is Plants and Animals in Southern California and today I thought we would talk about sexual selection.  So, remember from before we were talking about natural selection and we might have some squirrels and among the population of squirrels, so from one individual to the next the squirrels might vary in how fluffy their tails are.  And some squirrels might have greater survival or greater reproductive success, because of the fluffiness of their tail.  And let's say fluffy tails really make for great squirrels that are able to survive well and be stress free and make lots of baby squirrels.  And so what would happen is that over many generations you would have a change in allele frequency at any given genetic locus that increased the fluffiness of tails.  You'd get a genetic locus one.  It would go to almost 100 percent of the allele that makes for the fluffiest tail.  And then at genetic locus two it would go to 100 percent of what makes for the fluffy tail and so on, so that you might think of as survival selection.  Now, survival selection that's kind of good for the species.  It's not because it's good for the species that it spreads, but it nevertheless makes for squirrels that are really able in that environment where there's lots of trees.  Sexual selection on the other hand makes for animals that have kind of bizarre features.  So, let's start with something like deer where they have antlers.  And if the-- if one stag is able to dominate over the other stags and rise up high in the hierarchy then that stag gets to be the father of the future Bambies.  And what that means is that those future Bambies are also carrying the genes that they got from their father including the genes for making big antlers, big top antlers.  So, that means that you can have a process that's making stags have bigger tougher antlers even though it's kind of bad.  You know like these stags have to put a lot of energy into making the big antlers and then maybe they get tangled up in the shrubbery sometimes.  So, it's sort of a pain in the butt having antlers all the time.  And you know it's a big investment on the part of the stag.  So, it's kind of like a process, which yes it is adapting the organism, but it's adapting the organism just for being a dominate male that gets to be the father of lots of offspring.  It's not really making it better in terms of its ability to live in the community.  In fact, you might know the giant Irish elk.  It's extinct now, but it had great big antlers, huge antlers.  And at least one line of thinking is that what happened is sexual selection made these antlers so great, but then their climate changed and the species was no longer a big healthy species, say the difference between a healthy animal and a healthy species.  And because it had the antlers you know maybe that made it even worse whereas other species of deer that didn't have such big antlers didn't go extinct.  So, this process of sexual selection is variance among individuals in how many matings they get dependent on their characters.  And those characters could be characters whereby males fight with other males or females fight with other females.  It could also be characters that are ones of decoration so animals that are more brightly colored might be more attractive to the opposite sex.  And that's part of the explanation for all of these extravagant beautiful colors and ornaments that exist in all sorts of animals.  And actually you could even maybe extend it to plants.  So, it's possible that the showiness of petals and the sweetness of nectar is really something like sexual selection, due to something like sexual selection.  Okay, so the-- let's back up a little bit.  You can have this sexual selection process and it could affect the characteristics of the males.  There's also the potential for sexual selection to affect the characteristics of the females.  Sometimes that's called reverse sexual selection.  So for instance, there's this bird called Wilson's Phalarope and in Wilson's Phalarope the males take care of the young after they're hatched.  And it's the females, the brightly colored sex not the males.  The males are cryptically colored, which is more common of females in other species.  And you can have sexual selection that happens through direct interference between members of one sex so I might call that you know like male, male interference or female, female interference.  And then you can also have sexual selection and it's not mutually exclusive that's due to choice by the other sex.  So, you could have sexual selection on male characters that's due to female choice or sexual selection on female characters that's due to male choice or both, although usually they would be different characters.  The--I mean if we're pointing it out it's usually because there's different--it's different characters that are involved.  And there's all sorts of cool mechanisms whereby this can occur.  Sometimes it might be that the evolution of the choice is happening because there's selection on let's say the females to choose fathers that will have genes that are good and make for healthy offspring.  So, that would be called the good genes hypothesis.  Another possibility is that there's selection among the females to be choosy, call that selection among different female individuals to be choosy of their mates and the benefit for the females is that they're son would also be sexy.  See if they choose a sexy father then their sons will be sexy and so their sons will get more matings than their share.  And so the females then would have more grandchildren that if they mate with some dweeb and then produce sons you know that nobody wants to mate with.  It's called the sexy son hypothesis.  And so the good genes hypothesis, the sexy son hypothesis they can all sort of work together to make for this thing.  Now, actually once economy starts entering into it, it becomes more complicated.  So, what I've been talking about is a situation where one sex does all the work, usually females and the other sex does nothing.  And that might be true for these deer and it's probably true of a fair number of insects you know, but there's other animals.  For instance, katydids where the male produces this great spermatophore thing that the female then eats and it's you know a lot of energy to produce that spermatophore.  And then you would start having both sexes having some kind of sexual selection on them in a complicated way.  So, if we consider songbirds, songbirds are often sexual dimorphic.  The males tend to be showier and they definitely tend to sing more and the females are, you know they're quiet.  And if they migrate they come up into the cold places a little bit later.  So, the males come up first and then they duke it out with other males and form territories.  And then the females come up and check out the territories and chose birds based maybe on their singing, but also on the quality of their territory, which is also based on the quality of their singing, because the territories are carved by males coming up against other males.  Maybe not exactly fighting, but coming up against other males.  And then one other interesting thing about this whole fighting thing is a lot of its bluff.  A lot of it's kind of ritualized like they fight, but then as soon as it's clear who's going to win then the one who is going to be a loser you know shows that they're submissive and doesn't actually get hurt.  And the one that wins doesn't actually risk getting hurt either.  You know all they've done is just show that they're stronger.  The task for you is to try to understand this in a non-anthropomorphic way.  To try to understand it in terms of how selection is acting among individuals that have genes for these behaviors without imagining that the animals understand any of it.  The females who are attracted to males that are showy they end up passing their own genes onto granddaughters and those genes are genes that make them choosy.  Okay, well that's all I have to say about that.