Stage- and weather-dependent dispersal in the brown garden snail Cornu aspersum

Dispersal decisions are often condition-dependent, influenced by the interaction of individual phenotype and environmental conditions. Terrestrial Gastropods are simultaneous hermaphrodites, a reproductive system rarely studied in the context of dispersal. Moreover, the energetic cost of their movement is one of the highest among animals. Despite these features, which make them valuable models to understand the trade-offs between dispersal and other life-history traits, their dispersal strategies have been barely explored. We studied the movements of subadults and adults of the brown garden snail Cornu aspersum in a semi-natural 4-patch network, for 2 months in 2011 (a dry year) and 1 month in 2012 (a wet year). We assessed the effects of life-history stage (subadult/adult) and weather conditions on dispersal propensity and dispersal speed. Snails were more mobile under humid and warm weather, but nearly all individuals left patches when the relative humidity was close to 100 % in 2012. Because such humidity levels are potentially lethal to C. aspersum, we argue these extreme emigration rates might be an emergency escape response to harmful conditions. Despite a theoretically higher cost of movement, we found that subadults emigrated more, and dispersed faster and further, than adults. Thus, and contrary to what was expected, direct costs of movement do not play the main role in shaping dispersal in C. aspersum. Observed differences between subadults and adults in dispersal behaviour are discussed in the context of intraspecific competition, inbreeding avoidance and relative costs of male and female reproduction.