How the Xiphophorus Problem Arrived in San
Marcos, Texas
Klaus D. Kallman
Department of Ichthyology, Division of Vertebrate Zoology, American Museum of Natural History, Central Park West at 79th
Street, New York, NY 10024, U.S.A.
The Genetic Stock Center can trace its origin to Myron
Gordon’s doctoral research at Cornell University. He began
his scientific work in 1924 while still an undergraduate stu-
dent with 6 platyfish of a domesticated stock, and the fol-
lowing year he added some swordtails. Platyfish and sword-
tails were not new to him because already as a teenager he
had kept many tropical fish. But a great enthusiasm for
genetics was aroused by Professor A.C. Fraser in the De-
partment of Plant Breeding. Other professors at Cornell
who took a great interest in his work were H.D. Reed (Zo-
ology), who was his official sponsor, and G.C. Embody
(Limnology) and R.A. Emerson (Plant Breeding). Dr. Gor-
don concentrated first on platyfish, working out the genet-
ics of various pigment patterns, and then on swordtails. He
coined the terms micromelanophore and macromelano-
phore (Gordon, 1926).
It is an incredible coincidence that at the same time,
Dr. Curt Kosswig in Germany also started research on
swordtails. Neither Gordon nor Kosswig knew of the other’s
existence. But their initial contributions to the Xiphophorus
melanoma problem were not the same (Atz, 1941). Kosswig
(1928) pointed out that the melanoma was hereditary and
in some way associated with melanophore patterns from the
platyfish, while Gordon (1931) clearly identified the
macromelanophore gene of X. maculatus as being respon-
sible for the tumor.
The complementary relationship between laboratory
and field research that has made the study of Xiphophorus so
exciting and successful was initiated early in Gordon’s ca-
reer, and one hopes it will be continued in the future.
Whereas the development of melanoma in certain platyfish-
swordtail hybrids was predictable, the sporadic appearance
of such growths in some platyfish presented a problem.
While working on his thesis at Cornell, Gordon reasoned
that platyfish were known only from the hobby and had
been bred for many years under domestication and hybrid-
ized with swordtails. He could not determine whether platy-
fish of natural populations also developed pigment cell ab-
normalities or whether the occurrence of melanoma in the
domesticated platyfish was due to the introgression of hel-
leri genes. The sample of 83 platyfish from Mexico in mu-
seum collections was too small to provide the answer. He
also thought it possible that platyfish and swordtails might
hybridize in nature, because Meek (1904) had found them
together in one location. He must go to Mexico himself!
None of the modern collecting paraphernalia were
available to Gordon. There were no maps or rental cars, and
only a few paved roads. He went in a model T Ford, loaded
with camping equipment, shotguns, letters of introduction
to every conceivable agency, and with milk and oil cans for
shipping fish back to the United States.
In 1930 only 6 of the 22 presently described species of
Xiphophorus were known, and virtually nothing was known
about their habitat and distribution. Platyfish were assigned
to Platypoecilus and swordtails were known as Xiphophorus.
Gordon knew that 3 scientific collections of platyfish had
been made. The first consisted of 2 fish collected by La Salle
prior to 1866 in “Central America,” a locality description
utterly useless if you are trying to find the fish (Gordon,
Received January 31, 2001; accepted March 30, 2001.
E-mail Xiphkallman@aol.com
Mar. Biotechnol. 3, S6–S16, 2001
DOI: 10.1007/s10126-001-0022-5
© 2001 Springer-Verlag New York Inc.
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