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.

Ontogeny and morphological variability of shell in populations of Leptinaria unilamellata (d’Orbigny, 1835) (Mollusca, Pulmonata, Subulinidae)

“…The small shell aperture area has been interpreted as an adaptation to reduce water loss during aestivation (Santos and Monteirom 2001; Fiorentino et al 2008). Concerning spire index, Okajima and Chiba (2009) observed that shells with low-spired are better balanced and more adapted to locomotion on horizontal surfaces.…”

“…The majority of the land snail species have been described simply on the basis of shell characteristics. During the XVIII century, naturalists had already observed variations in shell morphological patterns (Fiorentino et al 2008). However, it was only from observation that shell shape presents a bimodal distribution that functional aspects of shell morphology began to be investigated (Fiorentino et al 2008).…”

“…During the XVIII century, naturalists had already observed variations in shell morphological patterns (Fiorentino et al 2008). However, it was only from observation that shell shape presents a bimodal distribution that functional aspects of shell morphology began to be investigated (Fiorentino et al 2008). These functional aspects are related to biotic and abiotic aspects like predation and desiccation risks and shell balance (Dewitt et al 1999; Chiba and Davison 2007; Okajima and Chiba 2009; Wada and Chiba 2013).…”

“…Recent studies concerning some species of land snails have revealed that the shell morphometrics can provide evidence of differentiation among populations (Conde- Padín et al 2009; Fiorentino et al 2008). In many cases, morphologic analysis combined with molecular and/or anatomical data, can support changes in taxonomy of the studied groups (Raahauge and Kristensen 2000; Choh et al 2006), for example, descriptions of new species from the detection of species complexes, or in other hand, the reduction of recognized species number by synonymy, based on the finding that the variation observed corresponds to a polymorphism (Paraense 1976; Carvajal-Rodriguez et al 2005; Velasquez 2006; Carstensen et al 2009).…”

Historical biogeography of Tyrrhenian land snails: The Marmorana–Tyrrheniberus radiation (Pulmonata, Helicidae)

“…Land snails are good organisms for studying phylogeography because they tend to preserve phylogeographical patterns (Pfenninger et al, 2007), due to their limited dispersal capacity and particular habitat requirements. Specifically, congeneric rock-dwelling species are seldom sympatric, more often they occupy small allopatric or parapatric ranges (Schilthuizen and Gittenberger, 1996;Welter-Schultes, 1998;Schilthuizen et al, 2004;Fiorentino et al, 2008a) with extremely limited gene flow between demes on a scale of only a few tens of metres (Schilthuizen and Lombaerts, 1994).…”