A test of the centre–periphery hypothesis using population genetics in an East Asian Tertiary relict tree

Abstract

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.

Genomic insights into genetic diversity and local adaptation of a dominant desert steppe feather grass, Stipa breviflora Griseb.

“…In addition, our results demonstrated a spatial configuration of decreasing genetic diversity from the center to the peripheral populations, as indicated by the trend of Ho, He, and p (Table 1). This center-toedge pattern of genetic diversity has also been observed in many other species, such as Emmenopterys henryi (Xu et al, 2021), Euptelea pleiosperma (Wei et al, 2016), and Taxus wallichiana var. mairei (Liu et al, 2019).…”

Ecological marginality and recruitment loss in the globally endangered freshwater pearl mussel

“…Concave hull is a simple yet accepted and standard method for estimating range edge from a set of occurrences (Burgman & Fox, 2003). For a second and a density‐dependent way to measure centrality, a kernel density layer was constructed (Xu et al, 2021) using the mussel data points; where populations are densely distributed, they get a high value, and vice versa where populations are scarcely distributed. This measurement is based on the assumption that population density is correlated with habitat quality.…”

Assessing Niche Dynamics and Population Connectivity in an Endangered Tree Species, Emmenopterys henryi: Implications for Conservation and Management

“…This stately canopy tree stands as the sole survivor of a once extensive and species-rich genus that flourished in the boreotropical floras of North America and Eurasia [36]. Empirical studies of E. henryi have predominantly focused on various aspects, including community structure [37], population dynamics [38], genetic differentiation [39], demographic history [40], and reproductive capacity [38]. However, the current distribution of E. henryi in China is becoming increasingly fragmented and diminished, primarily due to anthropogenic factors such as overlogging, tourism, and habitat loss [37].…”