The Maintenance of Unisexuality: Behavior, Hormones, and Genetic Diversity in a Unisexual-Bisexual Mating Complex

Texas State University - San Marcos, San Marcos TX

Investigators

Abstract

Unisexual species consist of only females (there are no males), and their persistence is an evolutionary paradox because they do not benefit from the increase in genetic variation that results from sexual reproduction. Gynogenesis is a type of unisexual reproduction that occurs when an all-female species must mate with males of closely related species (hosts) to stimulate the development of their eggs, but a male's sperm does not fertilize the eggs. Gynogenetic species face two major challenges. Because they produce only female offspring, they reproduce at a higher rate than sexual species, which can cause extinction of the sexual host via competitive exclusion (followed afterward by extinction of the gynogens). Furthermore, males of the host species should evolve to avoid mating with unisexuals because they do not pass on their genes when mating with gynogens. Solving this paradox can shed light on costs and benefits of sexual and unisexual reproduction. This research addresses hypotheses about maintenance of unisexuals in a mating system consisting of the gynogenetic fish, the Amazon molly, and its hosts, the sailfin molly and the Atlantic molly. This project investigates how hormone levels of the male hosts and the relative abundance of Amazon mollies affect the propensity of males to mis-mate with Amazon mollies, and will determine whether extinction and colonization of inter-connected populations can explain the maintenance of Amazons mollies, even though they should outcompete their host in a local population. The project will provide information about how complex interactions between species influence the evolution of reproductive strategies. The interesting nature of this system makes it appealing for K-12 and college students. This work will include participation by students and the investigators will give talks and conduct outreach activities related to these studies. Finally, this project will involve underrepresented groups in biology.