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From: greenber@swatsun (Peter Greenberg)
Newsgroups: sci.bio
Subject: An All Female Species of Fish!
Message-ID: <1055@thebes.UUCP>
Date: Tue, 14-Apr-87 19:34:18 EST
Article-I.D.: thebes.1055
Posted: Tue Apr 14 19:34:18 1987
Date-Received: Sun, 19-Apr-87 12:57:13 EST
Organization: Swarthmore College, Swarthmore PA
Lines: 36
Keywords: you probably saw it here first

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. The species, which probably resulted from a cross between
closely related molly species which live in the area, is all female. The
Amazons, which like other fish of the family Poecilidae (the guppy is another
member) give birth to live young and bestow no parental care on their young
(they are cannibals, in fact), require impregnation by males of one of the
other closely related species. Amazon molly eggs are diploid, unlike most
other gametes. The male sperm provides the necessary stimultion to develop.
However, the genetic material contributed by the male is almost always dis-
carded after fertilization. The diploid zygote is thus a clone of its mother,
and has none of its "father's" genes at all. In rare cases, the paternal genome
persists, and triploid individuals are formed. There are local triploid pop-
ulations, I think, which are similarly all-female and need other species'
sperm to initiate development. I do not remember the ploidy of the offspring.

Genetics types should get a kick out of this, as well as evolutionists who
like to talk about the cost of sex. Here is a vertebrate that circumvents the
much-celebrated 50% cost of sex. I should also point out that the Amazon, like
other Poecilidae, shows lots of geographical diversity in morphology.

My notes on this subject are archived in my closet. If anyone shows interest
I'll drag 'em out and inflict the net with them. I love biology gee-whiz
stories! I inflicted a biology seminar I took last semester with them, but
I want to expand my audience. 

Oh, by the way, this phenomenon, called gynogeny, I think, is not wholly 
comfined to the Amazon molly. It is also found in some species of lizards in
the desert southwest. I have its name in my aforementioned notes.  


-- 
Peter Greenberg, Swarthmore College, Swarthmore, PA 19081 
AT&T:(215) 328-8384 or 8610
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