THE WHOLE PREMISE OF MY ARGUMENT SEEMS WRONG: IT APPEARS THE ASEXUALS PRODUCE ASEXUAL OFFSPRING THUS CREATING WHOLE ASEXUAL POPULATIONS.
This post is about snails, but I hope won't be bored an introductory digression all about sex. After all, I've heard that lots of people are interested in it; and happily for this blog, even just the science of sex is fascinating. But for those with short attention spans: here is picture of a snail.
The science of sex is fascinating largely because we don't really know why [sexual reproduction][wsrevo] is so popular in nature. We don't lack theories; rather, we have too many. Suggested purposes include preventing mutations, increasing genetic diversity, and keeping germs on the hop. But we do not know if any of these, or all of them put together the just enormous cost.
What cost is that? It is the cost of the entire male sex. Think about it; about half the resources available to any sexual species are used up by organisms that eat, and drink and fight -- but usually don't do much towards the serious Darwinian business of getting the next generation up and running. Biologists call this the [two-fold cost of sex][wsrtwc], and there is a seeming need for huge benefits to outweigh this cost.
Now enter the New Zealand mudsnail Potamopyrgus antipodarum bearing a small piece of this puzzle. When I was in school, I learned that snails were hermaphrodites; but it seems they do things differently in New Zealand. This species has sexually reproducing males and females, but it also has asexual females who reproduce on their own.