Genetic similarity influences mating behavior and fitness in a simultaneous hermaphrodite snail, Physa gyrina

Behavioral tendencies during mating interactions, and their fitness consequences, have important effects on mating patterns. Mating preferences should reflect fitness patterns, and genetic similarity of mates influences fitness via inbreeding or outbreeding effects. If both inbreeding and outbreeding reduce fitness, then mates of intermediate relatedness should be preferred. I tested whether the relatedness of mates affected behavior and fitness with a hermaphrodite snail, Physa gyrina. I also tested whether body size(s) and the context in which mating interactions occurred influenced the behavioral dynamics between potential mates. I tested for treatment effects from factors such as familiarity between individuals, perceived risk of predation and sexual motivation.;I found that genetic similarity of mates affected fitness. Both highly inbred and outbred pairs suffered reduced fitness compared to pairs of intermediate relatedness, indicating a pattern of optimal outbreeding. Behavioral strategies varied with gender-roles. 'Females' resisted as 'males' escalated interactions in the reduced fitness treatments. In contrast, 'male' behaviors generally did not differ among treatments. Thus, the genetic similarity of mates affected fitness, and gender-specific behavioral mating strategies of simultaneously hermaphroditic individuals adaptively reflected those fitness patterns.;The behavioral dynamics of mating interactions were influenced by the context in which the interactions occurred and the body sizes of the potential mates. Familiarity between snails affected behavioral dynamics: unfamiliar pairs escalated interactions further with fewer resistance behaviors than familiar pairs. An individual's previous experiences also influenced mating interactions. Snails previously exposed to chemical cues from unfamiliar individuals were more likely to occupy the male role, and had lower copulation rates, than those exposed to cues from familiar individuals. Predation risk increased antipredator responses and reduced the mating frequency. Altering the sexual motivation levels (by isolating individuals) also significantly affected behavioral dynamics. Isolation resulted in decreased avoidance responses, with concomitant increases in transition rates and numbers of copulations. Matings occurred sooner after longer isolation periods, but also experienced higher error rates, e.g. misalignment during copulation attempts. Body size affected gender roles, behavioral escalation and fitness.