Data from: Genetic differentiation in spite of high gene flow in the dominant rainforest tree of southeastern Australia, Nothofagus cunninghamii

Nothofagus cunninghamii is a long-lived, wind-pollinated tree species that
dominates the cool temperate rainforests of southeastern Australia. The
species’ distribution is more or less continuous in western Tasmania but
is fragmented elsewhere. However, it is unknown whether this fragmentation
has affected the species’ genetic architecture. Thus, we examined N.
cunninghamii using 12 nuclear microsatellites and 633 individuals from 18
populations spanning the species’ natural range. Typical of
wind-pollinated trees, there was low range-wide genetic structure
(FST=0.04) consistent with significant gene flow across most of the
species’ range. However, gene flow was not high enough to overcome the
effects of drift across some disjunctions. Victorian populations
(separated from Tasmania by the 240 km wide Bass Strait) formed a genetic
group distinct from Tasmanian populations, had lower diversity (mean
allelic richness (Ar)=5.4 in Victoria versus 6.9 in Tasmania) and were
significantly more differentiated from one another than those in Tasmania
(FST=0.045 in Victoria versus 0.012 in Tasmania). Evidence for
bottlenecking was found in small populations that were at least 20 km from
other populations. Interestingly, we found little divergence in
microsatellite markers between the extremes of genetically based
morphological and physiological altitudinal clines suggesting adaptive
differentiation is strongly driven by selection because it is likely to be
occurring in the presence of gene flow. Even though the cool temperate
rainforests of Australia are highly relictual, the species is relatively
robust to population fragmentation due to high levels of genetic diversity
and gene flow, especially in Tasmania.