greenber@swatsun (Peter Greenberg) (04/15/87)
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
UUCP: ...{{seismo | inhp4}!bpa | {sun | rutgers}!liberty}!swatsun!greenber
ARPA: swatsun!greenber@bpa.BELL-ATL.COM jpexg@mit-hermes.AI.MIT.EDU (John Purbrick) (04/19/87)
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. 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?
chiaraviglio@husc2.UUCP (lucius) (04/20/87)
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 Please do not mail replies to me on husc2 (disk quota problems, and mail out of this system is unreliable). Please send only to the address given above.
greenber@swatsun (Peter Greenberg) (04/21/87)
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 evs@duke.UUCP (04/30/87)
In article <1055@thebes.UUCP> greenber@swatsun (Peter Greenberg) writes: >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. The geometrid moth, Alsophila pometaria (fall cankerworm), also exhibits gynogeny (also called pseudogamy = mating is required for viable eggs but the sperm is discarded). The majority of the Long Island, NY population consists of parthenogenetically reproducing females which must mate to produce viable eggs. Electrophoresis shows that there is usually no paternal contribution to the genome of the offspring. See: Mitter, C., and D. J. Futuyma. 1977. Parthenogenesis in the fall cankerworm, Alsophila pometaria (Lepidoptera: Geometridae). Ent. Exp. Appl. 21: 192-198. The problem of how separate parthenogenetic lines can maintain species indentity is long standing. In fact, according to the biological species concept separate parthenogenetic lines consitute separate species, if the lines are completely reproductively isolated. This is not the case for the fall cankerworm since a paternal contribution is sometimes found in the offspring genome. For a discussion of how to categorize parthenogenetic lines see: Mayr, E. 1963. Animal species and evolution. Harvard. Univ. Press, Cambridge, Mass. 797pp. -- UUCP: {decvax, seismo}!mcnc!duke!evs ARPA: evs@cs.duke.edu CSNET: evs@duke Ed Simpson, P.O.Box 3140, Duke Univ. Medical Center, Durham, NC, USA 27710
dant@tekla.tek.com.tek.com (Dan Tilque;1893;92-789;LP=A;60/C) (05/04/87)
Ed Simpson writes: > >The problem of how separate parthenogenetic lines can maintain species >indentity is long standing. In fact, according to the biological species >concept separate parthenogenetic lines consitute separate species, if the >lines are completely reproductively isolated. > One aspect of parthenogenic reproduction which seems to be common in all of the species mentioned so far, is that the parthenogenisis seems to be stimulated by mating behavior or sperm from the males of a related species. This implies that the parthenogenic females have to remain recognizable as females by those which engage in mating behavior with them. They also would have to continue to share at least part of the same habitat as those males. (Lucius C. made a reference to this in an earlier posting.) I would think that these two restrictions would help maintain the identity of the species. --- Dan Tilque dant@tekla.tek.com
gagen@bgsuvax.UUCP (kathleen gagen) (05/04/87)
In article <9576@duke.cs.duke.edu>, evs@duke.cs.duke.edu (Ed Simpson) writes: > In article <1055@thebes.UUCP> greenber@swatsun (Peter Greenberg) writes: > >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. > There are a variety of organisms that reproduce parthenogenically. The round worm C. elegans, use frequently in the study of developmental genetics, is one example. Each C. elegans individual is a self-fertilizing hermaphrodite. Occasionally, a male is produced. Another example is the laboratory-produced "lazy girl" stock of Drosophila (the common fruit fly). The "lazy girls" are parthenogenic females that have been derived from normally reproducing stocks. They differ from their "parent" strain in both morphology and behavior. For these reasons, and the criterion or reproductive isolation, this strain can be thought of as a separate species. ____________ Kathi Gagen gagen@bgsuvax.uucp Dept. of Biological Sciences ....bgsuvax!gagen Bowling Green State University Bowling Green, Ohio
evs@duke.cs.duke.edu (Ed Simpson) (05/04/87)
In article <1640@zeus.TEK.COM> dant@tekla.tek.com (Dan Tilque) writes: >One aspect of parthenogenic reproduction which seems to be common in all >of the species mentioned so far, is that the parthenogenisis seems to >be stimulated by mating behavior or sperm from the males of a related >species. This implies that the parthenogenic females have to remain >recognizable as females by those which engage in mating behavior with them. > >They also would have to continue to share at least part of the same >habitat as those males. (Lucius C. made a reference to this in an earlier >posting.) > >I would think that these two restrictions would help maintain the >identity of the species. In the case of the fall cankerworm mentioned earlier, egg maturation in the parthenogenetic female is stimulated by mating with a male (of the same species) from the sexually reproducing segment of the local population. On occasion, the male sperm is successful in fertilizing the egg. This would provide a small degree of gene flow between parthenogenetic lines. Even very low gene flow rates could prevent significant genetic divergence between lines, thus, maintaining the species identity. The same thing could be happening with the mollies. For a discussion of the effects of gene flow on genetic divergence between populations see J. Antonovics, The Nature of Limits to Natural Selection, Ann. Missouri. Bot. Garden 63:224-247, 1976. -- UUCP: {decvax, seismo}!mcnc!duke!evs ARPA: evs@cs.duke.edu CSNET: evs@duke Ed Simpson, P.O.Box 3140, Duke Univ. Medical Center, Durham, NC, USA 27710
gagen@bgsuvax.UUCP (05/05/87)
In article <1640@zeus.TEK.COM>, dant@tekla.tek.com.tek.com (Dan Tilque;1893;92-789;LP=A;60/C) writes: > > One aspect of parthenogenic reproduction which seems to be common in all > of the species mentioned so far, is that the parthenogenisis seems to > be stimulated by mating behavior or sperm from the males of a related > species. This implies that the parthenogenic females have to remain > recognizable as females by those which engage in mating behavior with them. I can think of at least two exceptions to this statment: (1) In Cenorhabditis elegans (I hope that I spelled that right), parthenogenic females do not require the presence of male stimulation to produce offspring. (C. elegans is a self-fertilizing roundworm.) (2) The behavior of the artificially produced Drosophila strain "lazy girl" is altered in that the "lazy girls" repell male advances. > _____________ Kathi Gagen gagen@bgsuvax