Global patterns of population genetic differentiation in seed plants

Evaluating the factors that drive patterns of population differentiation
in plants is critical for understanding several biological processes such
as local adaptation and incipient speciation. Previous studies have given
conflicting results regarding the significance of pollination mode, seed
dispersal mode, mating system, growth form, and latitudinal region in
shaping patterns of genetic structure, as estimated by FST values, and no
study to date has tested their relative importance together across a broad
scale. Here we assembled a 337-species dataset for seed plants from
publications with data on FST from nuclear markers and species traits,
including variables pertaining to the sampling scheme of each study. We
used species traits, while accounting for sampling variables, to perform
phylogenetic multiple regressions. Results demonstrated that FST values
were higher for tropical, mixed-mating, non-woody species pollinated by
small insects, indicating greater population differentiation, and lower
for temperate, outcrossing trees pollinated by wind. Among the factors we
tested, latitudinal region explained the largest portion of variance,
followed by pollination mode, mating system and growth form, while seed
dispersal mode did not significantly relate to FST. Our analyses provide
the most robust and comprehensive evaluation to date of the main
ecological factors predicted to drive population differentiation in seed
plants, with important implications for understanding the basis of their
genetic divergence. Our study supports previous findings showing greater
population differentiation in tropical regions and is the first that we
are aware of to robustly demonstrate greater population differentiation in
species pollinated by small insects.