Intraspecific variation in reproductive characters is associated with the strength of sexual selection in the hermaphroditic land snail Cornu aspersum

Abstract

Intraspecific variation in sexual traits may arise from a variety of processes such as genetic drift, sexual selection, or spatial heterogeneity of environmental conditions. Recent empirical studies suggest that sexual selection may vary with environmental conditions accelerating differentiation of sexual traits among populations. Land snails are simultaneously hermaphroditic animals characterized by low mobility and limited dispersal, so that life cycle characteristics of their populations are strongly influenced by local environmental conditions. In this study, we report results on intraspecific variation in sexual selection intensity as well as in behavioral and anatomical reproductive traits in the land snail Cornu aspersum. We performed a common garden experiment of adult snails originating from four populations from either of two regions in Greece differing in habitat temperature and predictability of rainfall during their reproductive season. Our results indicate substantial intraspecific variation in the opportunity for sexual selection, which was associated with differences in both behavioral and anatomical reproductive characters. Snails from populations that experienced unpredictable habitat conditions expanded their reproductive activity period, exhibited higher mating frequency, and showed longer copulation duration, relative to snails living in more predictable habitats. Additionally, snails originating from populations with unpredictable habitat conditions showed a distinct reproductive morphology with a shorter bursa tract length, which we interpret as indicative of an enhanced ability to hydrolyze the received spermatophores. We conclude that local environmental conditions experienced by the different populations could have triggered differences in the opportunity for sexual selection, which may ultimately lead to allopatric speciation through sexual selection. Environment-dependent sexual selection is considered to promote allopatric speciation of distant populations. However, empirical studies testing for geographic differences in the strength of sexual selection and associated reproductive characters are scarce. In C. aspersum, variation in both behavioral and anatomical reproductive traits among populations is well-documented, but the extent to which this is driven by diverse pressures of sexual selection under heterogeneous environmental conditions among populations remains unexplored. We demonstrate that snails from two geographically distant regions of Greece, with contrasting natural habitats, differ mainly in their behavioral traits and in several morphological traits, which are associated with differences in the opportunity for pre- and post-copulatory sexual selection.