Swordtails, small poeciliid fishes endemic to the Atlantic drainages of
Mesoamerica, get both their common and generic name from the conspicuous,
sword-like ornament in males of many species. Work in the lab focuses on
the northern swordtails, a monophyletic group found in the Río Panuco basin,
in the foothills of Mexico's Sierra Madre Oriental. Most of our research
involves a remarkable
hybrid zone between
the divergent
X. malinche and
X. birchmanni. We use a variety
of techniques ranging from molecular genetics of swordtail populations,
to observations of mating behavior in the field, to playback of
synthetic animations in the laboratory.
Female swordtails have an ancestral mating preference for swords that appears
to reflect a general
bias for large apparent size.
Despite this permissive, ancestral preference, swords have been secondarily
lost at least three times in the evolution of the northern swordtails
(see phylogeny above). Mexican tetras, a major predator,
also have an ancestral preference for large, ornamented males. Female
preference for swords, meanwhile, has been
secondarily lost
in species subject to high predation risk. Male swordtails, in turn, have
evolved ultraviolet color patches that signal to females in a
private channel invisible to predators. Females in one species also attend
to a
Y-linked color polymorphism:
blue males are more attractive to females, while gold males employ aggressive
strategies with females and other males.
Ongoing research with postdoc
Bob Wong and Ph.D. student
Heidi Fisher
focuses on the role of mating behavior in the evolution of hybrid zones
between
X. birchmanni and
X. malinche. Males exhibit recombinant
display traits outside the range of variation of either parental species.
We are using both natural and synthetic recombinants to characterize male and
female mating preferences. In collaboration with
Paul Barber and
Francisco García
de León, we are using an array of molecular markers to address directionality
of hybridization and spatial and temporal variation in allele frequencies.
With graduate student
Jessica Buckingham
and Wong, we are also investigating the mechanisms of shoaling in
Xiphophorus.
Swordtails shoal assortatively with respect to body size, and also exhibit
a directional preference for larger shoals. When swordtails are forced to
decide between a larger shoal of dissimilar-sized individuals, and a smaller
one of similar-sized individuals, they shoal at random (Wong and Rosenthal,
Ethology, in press). Buckingham's work focuses on how swordtails
make numerical comparisons.
The
Xiphophorus home page is a
wonderful resource on the genus.
en Español
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