Snail sex and the city: Divergence in genital anatomy in an urban land snail

Urbanization causes changes in the function and structure of ecosystems. This leads to adaptive and non-adaptive evolution of organisms living in cities. Habitat fragmentation can play an important role, especially for less mobile species like land snails. One evolutionary impact of urban fragmentation that has been understudied is changes in morphological traits related to sexual selection. The present study aims to investigate the effect of increased urbanization on co-evolution of the male and female reproductive organs in the grove snail (Cepaea nemoralis), a simultaneous hermaphrodite. Grove snails were collected in three different cities in the Netherlands along urban-rural transects. Male (sperm donor) and female (sperm recipient) reproductive traits were measured for 271 individuals. The expectation was that, due to a decrease in population density in urban areas, both the male and female reproductive organs would show changes that can be explained as resulting from reduced mating competition. Our results confirmed that there is an effect on the male spermatophore-producing parts and the female spermatophore-receiving parts. In addition, there was a positive correlation between the size of the male spermatophore-producing and female spermatophore-receiving organs. These findings invite for further research into the biotic and abiotic factors that influence sexually-selected morphological traits in urbanized areas.

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