A Macrogenetic Analysis of Isolation Mechanisms Reveals Habitat
Fragmentation as the Primary Driver of Genetic Divergence in Mammals.
Abstract
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Understanding the processes that drive spatial genetic differentiation
is essential for understanding how populations adapt to environmental
change. By evaluating the relative influence of these drivers, we can
gain insights into evolutionary dynamics and the potential for species
to respond to shifting landscapes. Three well-accepted drivers of
spatial patterns in genetic variation are isolation-by-distance (IBD),
where individuals are more genetically similar the closer they are
geographically; isolation-by-environment (IBE), where gene flow is
reduced due to selection against migrants in unsuitable ecological
conditions; and isolation-by-resistance (IBR), where landscape features
limit dispersal. We employed a macrogenetic approach, conducting a
multi-species, multi-driver, meta-analysis of published genomic SNP data
to identify general patterns driving spatial genetic differentiation of
mammals globally. Three species distribution models were built per
species to test different aspects of IBR, using combinations of
landscape and bioclimatic variables. Using two model selection
techniques, we find that landscape resistance models better explain
genetic differentiation than bioclimatic resistance models. Among the
three drivers, IBR was most frequently selected as the best model of
genetic differentiation in mammals across both model selection tests,
with IBD a close second and IBE the worst performing model. However, the
importance of IBE increased with increasing spatial scale, with
populations spread over larger distances more likely to be diverging due
to IBE than IBR or IBD. Our findings suggest that anthropogenic habitat
fragmentation significantly shapes genetic variation in mammals
worldwide, underscoring the importance of mitigating the impacts of
habitat fragmentation to prevent isolation and extinction of mammalian
species.