Postglacial recolonization at a snail's pace (Trochulus villosus): confronting competing refugia hypotheses using...

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Accurate localization of Last Glacial Maximum (LGM) refugia is vital for understanding species' evolutionary history and predicting responses to climate change.
• Previous phylogeographical studies often lack the intensive sampling needed to precisely pinpoint LGM refugia.
• The hairy land snail (Trochulus villosus), with its restricted range in Switzerland, presents an ideal model for intensive phylogeographical investigation.

Purpose of the Study:

• To precisely localize the LGM refugia of the hairy land snail (Trochulus villosus) using a fine-scale sampling design.
• To investigate the phylogeographical structure and demographic history of T. villosus populations.
• To identify potential glacial refugia and assess recolonization scenarios.

Main Methods:

• Collected samples from 52 populations of T. villosus (455 individuals) across its range.
• Analyzed mitochondrial DNA sequences (COI and 16S) to identify genetic lineages.
• Employed Bayesian skyline plots for demographic inference, ancestral character reconstruction for refugium identification, and microsatellite analysis for further validation.
• Modeled the LGM niche and compared recolonization scenarios using Akaike information criterion.

Main Results:

• Identified two divergent mitochondrial DNA lineages with distinct geographical distributions.
• Ancestral character reconstruction identified candidate refugia in the French Jura and Central Switzerland, both ice-free during the LGM.
• Microsatellite data suggested the possibility of additional refugia.
• Niche modeling indicated suitable LGM conditions in inferred refugia and potentially alpine nunataks.
• A 'two refugia' recolonization scenario best explained the observed genetic diversity patterns.

Conclusions:

• The study successfully refined the understanding of T. villosus's LGM refugia, identifying two primary locations.
• Combining fine-scale sampling with diverse analytical approaches is effective for pinpointing glacial refugia and understanding species' responses to environmental change.
• The findings provide crucial insights for conservation strategies and predicting the impact of future climate change on this species.