The Role of Social Environment and Genomic Plasticity in the Maintenance of Alternative Mating Strategies in Sailfin Mollies

Sailfin molly fish, Poecilia latipinna, members of the family Poeciliidae, show extensive polymorphism in male body size, degree of ornamentation and mating behavior repertoires. They are a striking example of a species with alternative male mating strategies that result from an association between life history trait variation and developmental plasticity of mating behaviors. Sailfin molly male body size correlates to their lifelong mating strategy and male size at maturity is fixed and shows a continuous range of male sizes in natural populations. In this species, some phenotypes have ‘fixed’ mating strategies (either sneaking copulations by small males or courting females by large males) while intermediate-sized males respond plastically to their social environment and switch their mating strategy from either courting or sneaking behavior depending on the social context of male competitors in their environment. Using RNAseq, we profiled differential gene expression between the brains of males with the fixed mating strategies (small versus large males), and among social rearing conditions (presence of females or males of small or large size) in males with the more plastic mating strategy (intermediate males). Larger genomic responses were discovered between males with the alternative fixed mating strategies than among males with the plastic strategy. We found that genes relevant in memory and associated processes were significantly small male-biased more often than by chance, while genes involved in protein synthesis and immunity were up-regulated in large males significantly more often. We also found that social condition during ontogeny does not appear to strongly influence differential gene expression between small and large size classes of males with fixed mating strategies, but social rearing environment does influence gene expression patterns to some degree in intermediate males, particularly in response to juvenile development with a social environment containing small males. Our results revealed that fixed mating strategies by large and small male sailfin mollies have broad neurogenomic responses due to alternative mating strategy use, while more plastic mating strategies of intermediate males are more influenced by the social conditions these males experience during ontogeny