Microsatellite data of 21 EST-SSR loci from all 503 Emmenopterys henryi samples

Aim: Several hypotheses are available to predict change in genetic
diversity at expanding peripheral ranges. However, empirical evidence to
test predictions of the centre-periphery hypothesis (CPH) at contracting
range limits is scarce. To address this issue, we assessed spatial
patterns of genetic variation, effective population size, and contemporary
and historical gene flow in a widespread, Tertiary relict tree species
from subtropical China. Location: Warm-temperate deciduous forests of
subtropical China. Taxon：Emmenopterys henryi (Rubiaceae) Methods: We
applied kernel density estimation to determine the centre of the species’
geographical range. Using microsatellite markers, we assessed genetic
structure and diversity in 36 populations (503 individuals) sampled in the
centre and periphery across the species’ range. We further examined both
historical and contemporary gene flow. Finally, we applied coalescent
methods to simulate population demography. Results: In support of CPH
predictions, the highest density of E. henryi coincided with the
geographical centre of the species’ distribution range, and genetic
diversity significantly declined with distance from this range centre.
Historical migration from the core to the edge was significantly higher
than in the opposite direction, whereas contemporary migration followed an
opposite pattern. Central and peripheral populations had similar levels of
genetic differentiation. Main conclusions: Core-to-edge patterns of
genetic diversity, but not genetic differentiation, were consistent with
the CPH in E. henryi. Also in line with the CPH, historical (but not
contemporary) migration from the core to the edge was significantly higher
than in the opposite direction. Results suggest that the complex
topography in subtropical China and population demographic processes may
strongly influence whether CPH predictions are met in different population
genetic parameters.