This study investigates the evolutionary forces acting on a potent oncogene and putative speciation gene in the Southern Platyfish, Xiphophorus maculatus. The Xmrk gene in X. maculatus causes the formation of aggressive melanomas in hybrids between X. maculatus and a closely related species, Xiphophorus helleri. As a result, this has been a classic system for both skin cancer and speciation research. However, relatively little is known about the evolutionary genetics of Xmrk. This research will use sophisticated molecular techniques and mathematical models to estimate the strengths and types of evolutionary forces acting on Xmrk. Specifically, this research will determine whether genetic evidence exists for reproductive isolation between X. maculatus and X. helleri caused by Xmrk and the strength of selection operating on Xmrk.

This study will advance our understanding of the evolutionary forces acting on cancer genes. It will also provide much needed data on the molecular basis of reproductive isolation in natural populations. The molecular, mathematical, and computational techniques developed for this project will advance the capabilities of future research in these areas. This research is a collaborative effort between scientists at the University of Texas at Austin and at Centro de Investigaciones Biológicas del Noroeste in La Paz Mexico. International collaboration is a critical component of modern research and developing strong bonds between universities in Mexico and the United States greatly advances the science in both countries.

Project Report

Fish in the genus Xiphophorus provide a remarkable opportunity to study two key evolutionary processes. The first is the evolution of cancer. Since the 1940s, geneticists have used these fish as model organisms for the study of melanoma. The melanoma is genetically determined and is similar to skin cancer in humans. In this project, we sequenced DNA from the gene responsible for repressing the melanoma in healthy fish. We identified a region of the gene that may be important for determining whether an individual fish will develop melanoma. The results have interesting implications for human disease because a similar type of genetic variation is also thought to be important for human diseases such as asthma. Further, a related gene is an important tumor repressor in humans. A second research opportunity offered by these fish is the study of how new species form. When a species that carries the oncogene hybridizes with a species that lacks the repressor, some of their offspring develop melanoma. This results in a genetic barrier between the species and promotes the emergence of new species. Our results suggest a new paradigm for how genetic incompatibilities between species evolve that differs from the classical hypothesis that evolutionary biologists have discussed for 75 years.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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George W. Gilchrist
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University of Texas Austin
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