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From: chiaraviglio@husc2.UUCP (lucius)
Newsgroups: sci.bio
Subject: Re: An All Female Species of Fish!
Message-ID: <1258@husc2.UUCP>
Date: Mon, 20-Apr-87 01:41:37 EST
Article-I.D.: husc2.1258
Posted: Mon Apr 20 01:41:37 1987
Date-Received: Mon, 20-Apr-87 02:45:54 EST
References: <1055@thebes.UUCP> <2837@mit-hermes.AI.MIT.EDU>
Organization: Harvard Univ. Science Ctr., Cambridge, MA
Lines: 40
Keywords: you probably saw it here first
Summary: This stuff is true, but. . .

In article <2837@mit-hermes.AI.MIT.EDU>, jpexg@mit-hermes.AI.MIT.EDU (John
Purbrick) writes:
> In article <1055@thebes.UUCP>, greenber@swatsun (Peter Greenberg) writes:
> > There is a species of fish, known as the Amazon molly, inhabiting the
> > sluggish waters of northeastern Mexico, which perpetuates itself without
> > benefit of males.....
> 
> If this is the species' method of reproduction (essentially, cloning of
> female individuals) how does the species retain its identity? I would have
> expected that each individual would pass on mutations to its descendants,
> and since each fish has only one chain of ancestors (its mother, grandmother,
> etc) the species would inevitably break up into many diverging strains. 

	This is true, but as long as only one ecological niche exists to which
these fish have access (that is, ecological niches that are so radically
different that the fish cannot compete at all with organisms holding those
niches do not count), selective pressure will tend to keep the species
phenotypically fairly uniform.  Traits which are selectively neutral would
accumulate, thus forming several strains, but again selection would prevent
much change that would otherwise cause divergence.  Multiple species
eventually could be isolated from such a population if chromosomal
rearrangements caused restrictions on hybridization if true sexual reproduction
did become available again.

> When I was a kid my brother had a collection of stick insects, which seemed
> able to reproduce optionally without male input (ie, a lone insect seemed
> able to lay fertile eggs). Is this likely?

	A certain stick insect does reproduce mostly parthogenically.  On the
order of 1 in every 1000 or so individuals is male.  Thus, recombination still
has a chance to distribute alleles between lineages of these insects, although
much more slowly than in species which only reproduce sexually.

-- 
	-- Lucius Chiaraviglio
	   lucius@tardis.harvard.edu
	   seismo!tardis.harvard.edu!lucius

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