The Amazon molly Poecilia formosa, the first all-female fish species known to science.
The Hubbses were also experimenting
at this time with crossing Poecilia formosa
with other species. And it is here that the
next amazing revelation about the Amazon
molly occurred. When they crossed Poecilia
formosa with other species of mollies, or
even unrelated poeciliids like Gambusia
affinis, the progeny that emerged were
indistinguishable from their mother.
Poecilia formosa cloned itself! The sperm
from these males simply activated the
process. The Hubbses described Poecilia
formosa as reproducing “gynogenetically,”
wherein “development is initiated by sperm
which for some reason is prevented from
taking part in heredity.”
One must remember that this was
before Watson and Crick and the
discovery of chromosomes. Advanced
organisms (this includes us) have two sets
of chromosomes. One set is contributed
by the female via a haploid cell known
as an ovum (commonly referred to as
an “egg”), and the other transported
by the male via a haploid sperm cell.
Fertilization creates a single diploid cell
known as a zygote.
In Poecilia formosa, the diploid zygote
cell already exists, with two sets of
chromosomes exactly like its mother.
Sperm from donor males just activates cell
reproduction…or does it?
Not So Fast…
In the 1960s, Klaus Kallman, the famed
geneticist with the New York Aquarium,
began experimenting with P. formosa by
crossing the Amazon molly with pet-shop
black mollies. The results were startling.
About one percent of the progeny had traits
from both parents, such as black blotches
over their body. If the Amazon molly clones
itself, how could this be?
DNA analyses revealed that these
pigmented Amazon mollies had 69
chromosomes, compared to the 46 in
natural Poecilia formosa specimens. They
were triploid fish! The complete set of
Poecilia formosa ( 46) in the female’s zygote
was combined with the haploid sperm cell
( 39) of the male black molly.
Later, in the 1970s, triploid specimens
were discovered in populations of diploid
Poecilia formosa in the wild, and are now
considered to be a significant proportion
of the populations. These triploids are
not Poecilia formosa per se, but a hybrid
of P. formosa and another molly. Since the
mollies in this range are not blackened,
ALA CONVENTION TO BE
BEST, BIGGEST YET!
May 1–4, San Antonio, Texas
At the time of this writing, the
consortium of hobbyists led by Charles
Clappsaddle of Goliad Fish Farms and
The Houston Livebearers Association
(HLA) are planning an amazing four-day 2008 Convention of the American
Livebearer Association. Our longest
convention ever, it will feature multiple
collecting trips, speakers, a fish show,
tours of the Xiphophorus Genetic Stock
Center, and much more! Log on to
the Houston Livebearers Association
website for updates and registration: