Dissertation Research: Maintenance of a Color-pattern Polymorphism in Green Swordtails, Xiphophorus helleri: Natural and Sexual Selection

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Animal and plant species are remarkably variable in many characters, e.g., body coloration in snow geese and petal color in morning glories. A fundamental question in biology is how genetic variation is maintained in wild populations. Many species in the fish genus Xiphophorus show uniformly gray forms as well as forms with different black pigment patterns; this variation has a simple genetic basis. In this study Dr. Rosemary Grant and Christiane Meyer investigate the maintenance of spotted and gray forms in X. helleri with field surveys of natural populations as well as laboratory experiments testing hypotheses on the interplay of mate choice, predation, and season-dependent visibility. X. helleri is a suitable model system because these fish are easily bred in the laboratory and can also be studied in the clear, shallow waters of their natural habitat.The color pattern in Xiphophorus provides a tangible link between the external characteristics of an organism and their underlying genetic mechanisms, and furnishes a tractable system with which to explore fundamental biological phenomena. This project will educate laypersons, grade schoolers and college students in theoretical and practical aspects of the research and train research assistants, both in Belize and New Jersey.