From: andrick@rhrk.uni-kl.de (Ulf Andrick [Biologie])
Subject: Re: sexual selection
Summary: ESS explanation
Organization: University of Kaiserslautern, Germany
Date: Mon, 7 Sep 1992 18:53:52 GMT

szabo@techbook.com writes:
`In article <28AUG199212530422@utkvx4.utk.edu> ljones@utkvx4.utk.edu (Jones, Leslie Lamont) writes:
`
`>     I think the advantage of sexually-selected characters are better 
`>described by the "sexy son" theory. In this model, females are attracted
`>to certain males because they are hardwired to find the males attractive.
`>Instances of hardwiring have been discovered, as in the case of sword-
`>tailed fish which S.J. Gould discussed in his column a few years ago.
`>     The advantage for the female is that she will bear some sons 
`>who will be sexy, reproduce, and spread her genes, including those genes which
`>find those particular male characters sexy. It then becomes a case of runaway
`>selection, with females producing sexy sons and daughters who find the sons
`>sexy (thought there is no implied incest; the lines can propogate separately 
`>with distant cousins mating.)
`
`Both this and the kerosene-drinker explanation seem incomplete.  Where did 
`these two adaptations originate, and how could they spread?
`How did the female get "hardwired" in the first place?  Why would her
`sons prosper, if the only plumage lovers are mother and daughters, and
`there is no incest?  How is it that both plumage-loving and plumage, two
`completely different kinds of structures, arise at the same time?  What
`is the probability that they would ever be genetically linked?
`
`Let's see what happens using J. Maynard Smith's evolutionary stable 
`strategy theory.  Let's postulate gene M for growing plumage, gene m 
`for being plain, gene F for preferring plumage, and gene f for prefering 
`plain Waynes.  Assume some males fertilize multiple females, some males 

It seems that, below, it is not taken into account that females
carrying f might PREFER males expressing m.

`none, all females are fertilized by one male, and choice is entirely the 
`female's; ie polygyny.
`
`Let's introduce F into a population with all (m,f).  Neutral: she's
`going to breed with a male even if not her favorite, and she doesn't
`lose by doing so. Let's introduce M into a population of (m, f). 
`Neutral, assuming M has no cost, because f will as readily choose M as m.

Thus, f does not mean a PREFERENCE for m.

Nick Szabo shows that female selection controls the frequency
of male traits. A trait which is preferred by the females wins
against one which is not specifically preferred, though the latter
might be more useful in respect to survival.  But what if there 
is some mutation of f (or F) which makes the female carrying it 
really PREFER m in a degree comparable to the preference of
the F females for M? Here, we are at the beginning of the whole 
discussion again.

This is an occasion to summarise the reasons why such a
mutation might not spread, as discussed so far in this thread:

1. Conspicuous signals are advantageous in sexual
   communication, as they are more easily recognisable.

2. A mutation providing for the recognition of a more
   inconspicuous trait is not available to the particular
   species or has too serious side effects.

3. The preference for the conspicuous trait is there from the
   beginning and sets a boundary condition to the subsequent
   evolution. Females with a different taste choosing a
   partner that is less attractive for the majority of females 
   will produce male offspring with less chance to mate.

4. The conspicuous trait is linked (genetically or
   physiologically) to another trait of significant adaptive
   value.

5. The male displays positive qualities by surviving with the
   handicap and imparts them to the females. (The fitness of the
   males themselves is not increased, of course.)

1 and 2 seem to be most straightforward if you consider the
female recognition apparatus. 3 may at least provide for an
attenuation of the selective pressure on it. 4 seems not so
necessary to me; it cannot serve as standalone explanation for the
existence of a conspicuous trait, as the recognition of the
trait must be possible anyway. This is also true for 5, and
thus it is questionable, whether this passepartout argument makes
much sense, as it has to base on explanations, which
might be sufficient by themselves.



Ulf R. Andrick                                andrick@rhrk.uni-kl.de
Tierphysiologie
FB Biologie
Universitaet
D-W 6750 Kaiserslautern

-- 


Ulf R. Andrick                                  andrick@rhrk.uni-kl.de
Tierphysiologie
Newsgroups: sci.bio