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Texas State biologists land grant to study Amazon mollies

Chronicle of Higher Education (05/26/2004)

SAN MARCOS – A unique species of fish comprised only of females has earned researchers at Texas State University-San Marcos a three-year, $300,000 grant from the National Science Foundation.

Caitlin Gabor, Ph.D., and Andrea Aspbury, Ph.D., won the grant to study Amazon mollies, a species native to the brackish waters along the coast of South Texas and Northeastern Mexico. What makes the Amazon molly so intriguing is that they are a unisexual, clonal species in which all members are genetically-identical females. Amazon mollies possess eggs complete with a complete set of chromosomes inherited from the mother. Reproduction is triggered by mating with male sailfin mollies, an act which stimulates the egg to develop, even though the male sailfin molly contributes no genetic material to the offspring.

“A male that mates with an Amazon molly gets no genetic representation in the offspring, because the offspring are simply clones of their female parent. Therefore, we expect that these males would not choose to mate with the Amazon mollies,” Gabor said. “However, Amazon mollies have persisted in the wild for more than 100,000 years, implying that throughout their evolutionary history male sailfin mollies make mating mistakes at a frequency high enough to maintain the populations of Amazon mollies. The males are essentially sexually parasitized by Amazon mollies.”

The grant will support Gabor and Aspbury’s research into this “sexual parasitism,” focusing on a range of mating preferences of male sailfin mollies in regards to Amazon and sailfin molly females.

“Our work will specifically address differences in female morphology as well as how males may avoid costs of mating with Amazons by conserving sperm production,” Gabor said. “Our results will hopefully shed light on the mechanisms by which species such as Amazon mollies can persist as sexual parasites as well as how males may minimize the costs associated with such parasitism.”