Meeting Abstract
Understanding the maintenance of phenotypic variation in the face of strong erosive processes (e.g., directional selection and drift) is a paradox in evolutionary biology. Variation in life histories and mating behavior persists in many species, even in the face of strong selection. This discrepancy between theory and nature might be resolved by considering social environment. In group-living species, social interactions can mediate both developmental mechanisms and fitness consequences of phenotypes, thus promoting variation. To examine how social environment might shape the development of life history and mating behavior variation, we used sailfin mollies, Poecilia latipinna, a livebearing fish that exhibits extreme variation in male life history and mating behavior. Full siblings (N=5 per treatment per family) were reared from birth in one of five social treatments (1 small male + 2 females, 1 large male + 2 females, 3 adult females, 3 unrelated juveniles, or no non-focal fish). Upon maturation, age, size and mating behavior were recorded for each male. Life history phenotype was affected by social treatment; compared to other treatments, males reared with 3 females took longer to reach maturity (F4,27=2.96, p=0.038) and tended to have larger body sizes once mature (F4,27=2.36, p=0.080). There was no effect of male social treatment on male mating behavior (gonopodial thrusts: F4,25=0.45, p=0.76; courtship displays: F4,25=0.15, p=0.96). These results demonstrate that social context shapes male life history phenotype, but not behavior at maturity, and suggest that natural seasonal variation in social environments could maintain the dramatic male life history variation in this species. Mating behavior may be affected by social environment in subsequent mating bouts, a hypothesis is currently being tested.
