Data and code from: Contrasting drivers of genetic diversity in plants across previously glaciated Northern hemisphere landscapes

Understanding how global biogeographical and evolutionary processes have
shaped continental-scale patterns of plant genetic diversity is
increasingly tractable given the proliferation of population genetic data.
Predominant theories include the geographical central–marginal hypothesis
(CMH), ecological CMH, and historical CMH, which predict decreasing
genetic diversity from range centres to margins, from suitable to marginal
environments, and from refugia to newly colonised areas, respectively. In
addition, the latitudinal (LG) and longitudinal (LoG) gradient hypotheses
predict a decrease in within-population genetic diversity along dispersal
routes across species ranges. Here, these hypotheses were tested across
North America, Europe, and East Asia, regions that experienced contrasting
patterns of post-glacial landscape fragmentation from the last glacial
maximum to the present. Data were collated from 8,333 populations
representing 435 plant species, and distances from populations to range
margins, climatic niche margins, and refugia, as well as latitude and
longitude, were calculated. Bayesian phylogenetic mixed-effects models
were applied to assess relationships between these variables and genetic
diversity, with all possible combinations of the five variables evaluated
(31 candidate models) and the best-supported model identified through
model comparison. Results indicate that geographical CMH, ecological CMH,
historical CMH, LG, and LoG have all shaped patterns of genetic diversity
across the Northern Hemisphere, although their effects varied
substantially by region and between woody and herbaceous species. The
geographical CMH primarily influenced herbaceous species in Europe and
East Asia, whereas the ecological CMH mainly affected woody species in
North America, and the historical CMH had limited effects in East Asia.
Overall, the findings support the view that patterns of genetic diversity
are shaped by interacting geographical, ecological, and historical
factors, with contrasting continental drivers reflecting differences in
glaciation history as well as life history traits. These results
underscore the value of geographical, historical, and ecological variables
as proxies for within-population genetic diversity and their utility in
identifying populations for conservation prioritisation in previously
glaciated regions of the Northern Hemisphere.