Genetic structure in Orkney island mice: isolation promotes morphological diversification

Area of Science:

• Evolutionary Biology
• Island Biogeography
• Population Genetics
• Morphometrics

Background:

• House mice (Mus musculus domesticus) have colonized islands globally after human expansion.
• Island colonization involves founder events and bottlenecks, complicating the assessment of adaptive versus stochastic evolutionary processes.
• Understanding evolutionary drivers in isolated populations is crucial for evolutionary biology.

Purpose of the Study:

• To investigate the relative importance of adaptive and stochastic processes in the insular evolution of house mice.
• To analyze genetic and morphometric variation in Orkney house mouse populations.
• To assess the congruence between genetic structure, morphological differentiation, and human population structure.

Main Methods:

• Mitochondrial DNA and microsatellite analyses were used to assess genetic variation and population structure.
• Morphometric analysis quantified the shape variation of the first upper molar.
• Brownian motion model was employed to test evolutionary hypotheses.

Main Results:

• Significant genetic structure was found within the Orkney archipelago, indicating isolated and stable insular populations.
• Morphological analyses revealed differentiation from Western European populations and geographic structure within Orkney, congruent with genetic divergence.
• Morphological diversification followed a Brownian motion model, supporting a dominant role of random genetic drift.

Conclusions:

• Random genetic drift, rather than local adaptation, appears to be the primary driver of morphological evolution in Orkney house mice.
• The genetic and morphological structuring of house mice mirrors recent findings on human population structuring in Orkney.
• House mice can serve as a valuable bioproxy for understanding historical human settlement patterns and social structures at a local scale.