Data from: Small-scale patterns in snowmelt timing affect gene flow and the distribution of genetic diversity in the alpine dwarf shrub Salix herbacea

Current threats to biodiversity, such as climate change, are thought to
alter the within-species genetic diversity among microhabitats in highly
heterogeneous alpine environments. Assessing the spatial organization and
dynamics of genetic diversity within species can help to predict the
responses of organisms to environmental change. In this study, we
evaluated whether small-scale heterogeneity in snowmelt timing restricts
gene flow between microhabitats in the common long-lived dwarf shrub Salix
herbacea L. We surveyed 273 genets across 12 early- and late-snowmelt
sites (that is, ridges and snowbeds) in the Swiss Alps for phenological
variation over 2 years and for genetic variation using seven SSR markers.
Phenological differentiation triggered by differences in snowmelt timing
did not correlate with genetic differentiation between microhabitats. On
the contrary, extensive gene flow appeared to occur between microhabitats
and slightly less extensively among adjacent mountains. However, ridges
exhibited significantly lower levels of genetic diversity than snowbeds,
and patterns of effective population size (Ne) and migration (Nem) between
microhabitats were strongly asymmetric, with ridges acting as sources and
snowbeds as sinks. As no recent genetic bottlenecks were detected in the
studied sites, this asymmetry is likely to reflect current meta-population
dynamics of the species dominated by gene flow via seeds rather than
ancient re-colonization after the last glacial period. Overall, our
results suggest that seed dispersal prevents snowmelt-driven genetic
isolation, and snowbeds act as sinks of genetic diversity. We discuss the
consequences of such small-scale variation in gene flow and diversity
levels for population responses to climate change.