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Open Access Highly Accessed Research article

Why do snails have hairs? A Bayesian inference of character evolution

Markus Pfenninger1*, Magda Hrabáková2, Dirk Steinke3 and Aline Dèpraz4

Author affiliations

1 Abteilung Ökologie & Evolution, J.W. Goethe-Universität, BioCampus Siesmayerstraße, 60054 Frankfurt/Main, Germany

2 Deparment of Zoology, Charles University, Viniènà 7, 128 44 Praha 2, Czech Republic

3 Department of Biology, University of Konstanz, Postbox 5560 M618, 78457 Konstanz, Germany

4 Département d'Ecologie et Evolution, Université de Lausanne, Bâtiment de Biologie, Dorigny, 1015 Lausanne, Switzerland

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Citation and License

BMC Evolutionary Biology 2005, 5:59  doi:10.1186/1471-2148-5-59

Published: 4 November 2005

Abstract

Background

Costly structures need to represent an adaptive advantage in order to be maintained over evolutionary times. Contrary to many other conspicuous shell ornamentations of gastropods, the haired shells of several Stylommatophoran land snails still lack a convincing adaptive explanation. In the present study, we analysed the correlation between the presence/absence of hairs and habitat conditions in the genus Trochulus in a Bayesian framework of character evolution.

Results

Haired shells appeared to be the ancestral character state, a feature most probably lost three times independently. These losses were correlated with a shift from humid to dry habitats, indicating an adaptive function of hairs in moist environments. It had been previously hypothesised that these costly protein structures of the outer shell layer facilitate the locomotion in moist habitats. Our experiments, on the contrary, showed an increased adherence of haired shells to wet surfaces.

Conclusion

We propose the hypothesis that the possession of hairs facilitates the adherence of the snails to their herbaceous food plants during foraging when humidity levels are high. The absence of hairs in some Trochulus species could thus be explained as a loss of the potential adaptive function linked to habitat shifts.