Leks, Sex

Finally, a reasonable analogy for selection with replacement:

"At mating time peacocks gather in large congregations called leks at which they strut their stuff and show off their wares to peahens. Not all the peacocks get to mate and some get to mate several times."

No more distasteful mentions of certain Juarez dives! You get the feeling that would have burdened the otherwise classy LaTex presentation. Now I get repute, plus another silly citation!

Readings today mostly concerned sex. I'm thinking I might include aspects, along the lines of the clever Werner-Dyers (1991) model. Nothing spatial, of course, just the idea of females choosing from an assortment of eager males. Or not.

So here's our first question. Asexual reproduction provides for 100% gene transfer between generations, as well as a population that can breed twice as quickly. What possible benefits of a sexual arrangement could outweigh these costs?

There's been a host of ideas. Asexual reproduction is a bad idea because you also transfer a buildup of harmful mutations, which would otherwise be ironed out with time (Muller's ratchet). Darwin's tangled bank analogy tells us that, if you want part of the genetic landscape, you need to pick a niche nobody's picked yet (ie - you need to be different). Sexual reproduction also means you're more adaptive, so you can counter parasites quickly (Red Queen hypothesis). We haven't even mentioned that you get to have sex!

All these proposals have weaknesses, and though Red Queen is popular today, it's by no means fully adequate to explain the development of sex.

The second question is, dioecy. How did the male/female dichotomy begin? This has a more interesting answer: it's evolutionarily stable! It's evolved independently from many separate hermaphroditic systems. There are even two necessary mutations: male-sterility in the female population, and female-sterility in the males! (Gynodioecy and androdioecy, the mid-points between the mutations, are also stable under certain conditions.)

Dense notes here.

In such anisogamic systems, gamete size determines sex. Females have larger, fewer gametes, and so have greater investment. How does this happen? Bothersomely-worded answer:

"A system where one sex produces large sex cells and the other small has been shown to be evolutionary stable. A system where both sexes produce only small sex cells can be invaded by those individuals who produce larger sex cells. While a system where both sexes produce large sex cells can be invaded by cheats who produce small sex cells."

The motivation is all physical, which makes me think I won't bother with sex. And you know what, I don't even know if peahens can mate twice in leks. God damn.