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

Area of Science:

• Evolutionary biology
• Gastropod biology
• Animal morphology

Background:

• Adaptive significance of costly biological structures is crucial for evolutionary maintenance.
• Haired shells in Stylommatophoran land snails lack a clear adaptive explanation, unlike other shell ornaments.
• The genus Trochulus presents an opportunity to study the evolution of shell hair in land snails.

Purpose of the Study:

• To investigate the correlation between the presence of shell hairs and habitat conditions in the genus Trochulus.
• To understand the adaptive function of shell hairs in land snails.
• To test hypotheses regarding the evolutionary maintenance of shell hair.

Main Methods:

• Bayesian framework of character evolution analysis.
• Comparative analysis of shell hair presence/absence with habitat conditions.
• Experimental investigation of shell adherence properties.

Main Results:

• Haired shells represent the ancestral state in Trochulus, with independent losses occurring three times.
• Loss of shell hairs is correlated with a transition from humid to dry habitats.
• Experiments demonstrated increased adherence of haired shells to wet surfaces, contrary to previous locomotion hypotheses.

Conclusions:

• Shell hairs likely facilitate snail adherence to herbaceous food plants in high humidity environments during foraging.
• The absence of hairs in certain Trochulus species can be explained by the loss of this adaptive function linked to habitat shifts.
• This study provides a functional explanation for the evolution and maintenance of shell hairs in land snails.