Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ucla-cs!sdcrdcf!burdvax!bpa!cbmvax!vu-vlsi!hvrunix!swatsun!greenber From: greenber@swatsun (Peter Greenberg) Newsgroups: sci.bio Subject: Re: An All Female Species of Fish! Message-ID: <1081@carthage.UUCP> Date: Mon, 20-Apr-87 21:08:05 EST Article-I.D.: carthage.1081 Posted: Mon Apr 20 21:08:05 1987 Date-Received: Fri, 24-Apr-87 01:06:18 EST References: <1055@thebes.UUCP> <2837@mit-hermes.AI.MIT.EDU> Organization: Swarthmore College, Swarthmore PA Lines: 88 Keywords: you probably saw it here first Summary: some details on the Amazon Molly, gynogenetic fish. I promised to post details on this fish if interest warrants, and interest does warrant, so here goes. I begin by quoting an oldish book on livebearing aquarium fish, appropriately titled "Livebearing Aquarium Fishes" by Kurt Jacobs (1971, Macmillan, Lib. Cong. Cat. Card Number 73-91384, translated from the German work of 1969). ----------------------------------------------------------------------------- Poecilia formosa (Girard 1859) Amazon Molly Family: Poeciliidae Subfamily: Poeciliinae Tribe: Poeciliini ... Synonyms: Limia formosa (Girard 1859) Mollienisia formosa ... Distribution: Central America, Atlantic regions of Mexico to Panama; 15-30 degrees N. Habitat: Tributaries and small streams. Size: this is probably a natural hybrid of which only females occur; these are about 80mm long Genetic peculiarities: in their paper entitled 'Apparent parthenogenesis in nature, in a form of fish of hybrid origin' (Science 76 (1933) 628-630), the American ichthyologists C.L. and Laura C. Hubbs wrote that the hybrid formosa only occurs in nature as females, and in company with Poecilia shenops or P. latipinna. But because the males of Poecilia shenops and P. latitpinna are morpholgically very different, these authors explained this dicovery as a case of gynogenesis, that is , of parthenogenetic development initiated by sperm which for some reason is prevented from taking part in heredity. If this is true, this would would be the first, but not the only case of gynogenesis in vertebrates. Under similar environmental conditions Lacerta saxicola armeniaca and L. s. rostembekowski also have populations consisting only of females. [????] ... Experiments involving the back-crossing of female P. formosa with males of P. shenops, P. latipinna and other closely related species of Poecilia have always yielded offspring only. Even when 20 or more such back-cross generations have been bred, the fish did not differ from their female ancestor. ... Breeding: when mated with P. shenops or P. latipinna, the females produce 20-100 or more young every 4-6 weeks. The young, which are about 10mm long, always develop into females. ... Food: omniviorous. ... ----------------------------------------------------------------------------- Well, I have forgotten where my notes on this subject really are.... but I seem to remember that some very recent research by a bunch of workers from Texas (I think) who specialize in this fish supports the above assertion. More importantly, it was determined that P. formosa was probably formed by a hybridization between shenops and latipinna in the small area where these two species overlap. As for the question about how the species maintains its identity, as each line of females is independent and should therefore diverge, the answers are several. First of all, since all the fish are living in similar environements, you would not expect them to deviate in substantive ways, assuming that they are already well adapted. Secondly, there are several geographic races, as is the case with other poecilidiae. Finally, it is generally *sexual* reproduction that encourages variability. Anyway, there are plently of asexual species of organisms, and while most enjoy some form of genetic exchange, if only by something like viral transduction or conjugation, many probably do not. Also, P. formosa is of recent origin, I seem to remember, and seems to be doing well, but Poecilia is a volatile genus, so maybe formosa is not long for the world. But it was certainly fun while it lasted ;-) . Sorry for the lack of hard references, but times are tough. TRUST ME, I AM ALMOST A COLLEGE GRADUATE! Anyone else have any facts or insight. -- Peter Greenberg, Swarthmore College, Swarthmore, PA 19081 AT&T:(215) 328-8384 or 8610 UUCP: ...{{seismo | inhp4}!bpa | {sun | rutgers}!liberty}!swatsun!greenber ARPA: swatsun!greenber@bpa.BELL-ATL.COM