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From: JAHAYES@MIAMIU.BITNET
Newsgroups: sci.bio
Subject: followup to fish sex ratio thread
Message-ID: <90274.141808JAHAYES@MIAMIU.BITNET>
Date: 1 Oct 90 19:18:08 GMT
Organization: Miami University - Academic Computer Service
Lines: 40

I sent this note to one of the contributors and then later
decided it was of sufficiently general relevence to post it.
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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.