Effects of body size on courtship role, mating frequency and sperm transfer in the land snail Succinea putris

Sex role preferences in simultaneous hermaphrodites may vary with individual condition and partner quality across consecutive matings. Theoretical and empirical studies have highlighted an individualʹs body size and its relation with the partnerʹs body size as potential factors that influence the preferred sex role. We studied effects of body size of focal individuals and partners on (1) mating frequency and mating interval, (2) courtship role and (3) number of sperm donated in successive copulations in the land snail Succinea putris where ‘active’ individuals mount the shell of their ‘passive’ partner before penises are intromitted reciprocally. We found body size-dependent differences in mating behaviour between small and large individuals: (1) smaller individuals of mating pairs were more likely to adopt the active role, (2) small individuals seemed to prefer inseminating larger partners, (3) a positive relation between body size and sperm number donated was found, (4) large individuals adjusted sperm number to their partnerʹs body size, and (5) the smallest number of sperm was donated by large focal individuals to small partners. In addition, the number of sperm donated (1) increased with longer mating intervals and (2) decreased in later copulations indicating that the number of previous matings may affect male resource allocation. Our results support the view of models of sex role preferences, gender conflicts and solutions to gender conflicts that predict that the preferred sex role is variable within a species (e.g. size-dependent sex allocation models and the gender ratio hypothesis).