title: Why do snails have hairs? A Bayesian inference of character evolution.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Abteilung Okologie & Evolution, J.W. Goethe-Universität, BioCampus Siesmayerstrasse, 60054 Frankfurt/Main, Germany. Pfenninger@zoology.uni-frankfurt.de
authors.forename: Markus
authors.initials: M
authors.lastname: Pfenninger
authors.forename: Magda
authors.initials: M
authors.lastname: Hrabáková
authors.forename: Dirk
authors.initials: D
authors.lastname: Steinke
authors.forename: Aline
authors.initials: A
authors.lastname: Dèpraz
mesh_terms: D000220:Adaptation, Biological; D000825:Animal Structures; D000818:Animals; D001499:Bayes Theorem; D005075:Biological Evolution; D017931:DNA Primers / Q000737:chemistry; D003627:Data Interpretation, Statistical; D017753:Ecosystem; D004777:Environment; D006197:Hair; D006813:Humidity; D008386:Marine Biology; D008390:Markov Chains; D009068:Movement; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D012908:Snails / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology*; D013045:Species Specificity
chemical_list: D017931:DNA Primers