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From: michaelm@bcsaic.UUCP (Michael Maxwell)
Newsgroups: sci.bio
Subject: Re: The Red Queen (really: Eyeless fishes)
Message-ID: <149@bcsaic.UUCP>
Date: Fri, 9-Jan-87 12:06:04 EST
Article-I.D.: bcsaic.149
Posted: Fri Jan  9 12:06:04 1987
Date-Received: Thu, 15-Jan-87 21:47:37 EST
References: <741@aecom.UUCP> <927@husc6.UUCP> <124@bcsaic.UUCP> <2103@jade.BERKELEY.EDU>
Reply-To: michaelm@bcsaic.UUCP (Michael Maxwell)
Distribution: na
Organization: Boeing Computer Services AI Center, Seattle
Lines: 41

In article <2103@jade.BERKELEY.EDU> dean@violet.berkeley.edu (Dean Pentcheff) writes:
>In article <124@bcsaic.UUCP> michaelm@bcsaic.UUCP (Michael Maxwell) writes:
>>I suggested this [genetic drift] in answer to an exam question once, as 
>>the origin of blind
>>(eyeless) cave fish.  (The incidence of eyeless fish is quite high, but for
>>obvious reasons the eyeless ones seldom make it very far in life up here.)
>>The professor didn't like my answer...his point was that there had to be a
>>selective advantage to blindness in cave life.  I didn't believe so at the
>>time, and I'm still skeptical.  Anyone care to comment?
>
>I'm not sure, but I suspect that eyelessness in cave fish arose
>independently from several groups of (eye-bearing) fish.  If this is
>the case, it seems unlikely that cave fish stemming from different
>ancestral groups would share the _same_ trait due to drift, given that
>there are only a few characters that tend to be different in cave fish
>(lack of eyes, lack of pigment).  If, on the other hand, the trait
>conferred a selective advantage, then its appearance in several groups
>is reasonable.  The advantage (presumably) has something to do with
>energy savings for the eyeless fish (though this is a rampantly
>"selectionist" argument).
>
>-Dean	(dean@violet.berkeley.edu)

This is what the prof said--there had to be a selective advantage.  My feeling
is that there simply couldn't be any selective DISadvantage--as there is in
fact no disadvantage to blindness or lack of pigment in caves.  There
WOULD be a disadvantage to almost any other simple change, hence the "only"
changes that show up in the distinct groups of cave fish are these two.
(Improved tactile perception would be an ADvantage--but probably much more
unlikely to arise in a short time frame than lack of eyes or pigment.)  Oh, one
other difference that has appeared in at least some groups of cave fish (I
doubt whether it has been extensively tested, it may appear in others) is
lack of circadian rhythms.  Again, it seems that if this were lost from a
couple individuals in a very small population, it might be perpetuated simply
by chance (i.e. due to chance fluctuations in the population which might kill
off all but their offspring).
-- 
Mike Maxwell
Boeing Advanced Technology Center
	arpa: michaelm@boeing.com
	uucp: uw-beaver!uw-june!bcsaic!michaelm