Variation in adult shell morphology and life-history traits in the land snail Oreohelix cooperi in relation to biotic and abiotic factors

Abstract

In this study, we explore factors influencing variation in adult shell morphology and life-history characteristics (offspring size and number) in the ovoviviparous land snail, Oreohelix cooperi, from the Black Hills, South Dakota and Wyoming, USA. To date, no study of shell morphology and life-history characteristics in ovoviviparous land snails has included a combination of datasets including genetic data, life-history traits, shell morphology and multiple environmental factors. We report that differences in shell size among populations are strongly related to mean annual temperature (and the highly correlated variable elevation) and population density (measured as shell density). In addition, shell size varies among populations, despite an apparent lack of population genetic differentiation. Common factors thought to influence adult shell size, like precipitation and calcium levels, do not have a significant effect in this study. Adult size strongly influences per-clutch reproductive output, with larger snails having larger and more offspring. As mean annual temperature and shell density affect adult shell size, they also indirectly affect per-clutch output. The results suggest that a large portion of the life-history variation in O. cooperi is environmentally induced, as has been found in oviparous land snails and brooding freshwater bivalves. © The Author 2007. Published by Oxford University Press on behalf of The Malacological Society of London, all rights reserved.