Multiple scale patterns of shell and anatomy variability in land snails: The case of the Sicilian Marmorana (Gastropoda: Pulmonata, Helicidae)

Abstract

Certain major aspects of phenotypic diversity are still largely unexplained. When phenotypic patterns do not relate to habitat variables, fine analysis of morphological patterns and their distribution sheds light on the origin of diversity. Among invertebrates, snails are an ideal model for studying the roles of the neutral processes and selection involved in creating diversity. To understand patterns and processes of variability on different scales (regional: areas; local: sites), morphological variability of two sets of characters (shell and genitalia) was quantified in a group of rock-dwelling land snails of the genus Marmorana (Pulmonata, Helicidae). To analyse shell variability, partitioning of the overall variation into size and shape components was analysed by a principal component-based approach. Shell shape and size variability is not significantly influenced by any environmental pressure. Variability at site scale is mainly attributed to shell size, which is a trait demonstrated to have a high degree of phenotypic plasticity. No sharp changes were observed for genitalia. Moreover, allometries between shell size and genitalia measurements involve a few populations. The observed multiple scale patterns are in line with the hypothesis that genital variance may be selectively controlled to maintain function. © 2008 The Linnean Society of London.