Data from: Pleistocene speciation in the genus Populus (Salicaceae)

The macro-evolutionary consequences of recent climate change remain
controversial and there is little paleobotanical or morphological evidence
that Pleistocene (1.8-0.12 Ma) glacial cycles acted as drivers of
speciation, especially among lineages with long generation times, such as
trees. We combined genetic and ecogeographic data from two closely related
North American tree species, Populus balsamifera and P. trichocarpa
(Salicacaeae) to determine if their divergence coincided with and was
possibly caused by Pleistocene climatic events. We analyzed 32 nuclear
loci from individuals of P. balsamifera and P. trichocarpa to produce
coalescent-based estimates of the divergence time between the two species.
We coupled the coalescent analyses with paleodistribution models to assess
the influence of climate change on species’ range. Further, measures of
niche overlap were used to investigate patterns of ecological
differentiation between species. We estimated the divergence date of P.
balsamifera and P. trichocarpa at approximately 75 Ka, during the middle
of the Wisconsin glaciation (115–12 Ka). Significance tests of niche
overlap, in conjunction with genetic estimates of migration, suggested
that speciation occurred in allopatry, possibly resulting from the
environmental effects of Pleistocene glacial cycles. Our results indicate
the divergence of keystone tree species, that have shaped community
diversity in northern North American ecosystems, was recent and may have
been a consequence of Pleistocene-era glaciation and climate change.