JAHAYES@MIAMIU.BITNET (10/02/90)
I sent this note to one of the contributors and then later decided it was of sufficiently general relevence to post it. ----------- Date: Mon, 01 Oct 90 14:08:59 EST From: JAHAYES@MIAMIU Subject: Re: FISH: sex ratio of 1 male : 100 females, why? To: frazier@oahu.cs.ucla.edu ======================================================================== True, but you're invoking group selection. If the fitness of that school is represented by W, then the females (say, 100 of them) contribute 1/2 of that fitness (since they contribute half the DNA in the following generation), so the average female fitness is 1/2 * 1/100 * W, but the male gets his entire half to himself for a resulting fitness of 1/2 * W. Sure it's advantageous to be a male, but it sucks to be a female (there's a lesson in that for us all :-). Clearly, evolution would favor females who become males despite the presence of other male(s), until the average return is equal for either sex, i.e. a ratio of 1:1 (see R.A. Fisher's brilliant 1930 text The Genetics of Natural Selection for a fuller explanation of this). While there are several different mechanisms that can produce a biased sex ratio and still be evolutionarily stable, I believe the evidence in virtually all protogynous fish is that the school is highly inbred. As a consequence, there is no within-school competition for mates; if you, or your sibling, produces the offspring makes little difference (well, if you're full sibs you share 50% of genes on average, so if your sib produces 10 offspring or you can produce one, your fitness is higher if you help your sib and have NO offspring yourself. This explains the single-queen nature of social hymenopterans, too...). Since the male is just a cheap bag of sperm, and sperm are cheap to produce, eggs are the limiting factor for that group's fitness. It makes sense to have as many females as possible, thus, one male. Josh Hayes, Zoology Department, Miami University, Oxford OH 45056 voice: 513-529-1679 fax: 513-529-6900 jahayes@miamiu.bitnet, or jahayes@miamiu.acs.muohio.edu Now look inside; what do you see? That's easy: that's a pickle.