Genetic and environmental determinants in the evolution of alternative mating strategies in the sailfin molly, Poecilia latipinna (Poeciliidae: Poecilia: Mollienesia)

Understanding the genetic and environmental factors responsible for differences in size, morphology and behavior can aid in determining how alternative male mating strategies evolve in natural populations. One important environmental factor is nutrition, as it underlies growth of both body size and morphological traits that are linked to alternative mating strategies in many animals. In sailfin mollies, Poecilia latipinna, male size is fixed at maturity, highly variable within populations and correlated with dorsal fin morphology and expression of alternative male mating behaviors. Large males with exaggerated dorsal fins use courtship behavior while small males with reduced dorsal fins use sneaking behaviors. Intermediate males are more flexible, switching from courting to sneaking depending on social situation. In my thesis research I used a breeding design to determine (1) the genetic (G), environmental (E) and GxE effects on the development of life history traits including body size, (2) if differences due to diet (low protein versus high protein) can shift the allometric relationship between morphological trait and body size and (3) the G, E and GxE determinants in the expression of alternative mating strategy. In males, genetic effects influenced the expression of courtship display rate while diet during ontogeny affected mass growth rate as well as several morphological traits including the shape of the dorsal fin. As predicted, the slope of the relationship between dorsal fin area and standard length shifted more than the relationship between non-ornamental traits (e.g., gonopodium length) and body size with male offspring reared on the control diet exhibiting steeper slopes than those who received the experimental diet during ontogeny. Females also showed differences in mass growth rate due to diet, but morphological trait allometry was not shifted for most characters. Overall, environment played a larger role than expected for male traits that were thought to be genetically controlled, providing an exciting avenue for future research.