Abstract
The central–marginal hypothesis predicts that geographically peripheral populations should exhibit reduced genetic diversity and increased genetic differentiation than central populations due to smaller effective population size and stronger geographical isolation. We evaluated these predictions in the endangered conifer Taxus wallichiana var. mairei. Eight plastid simple sequence repeats (cpSSRs) were used to investigate plastid genetic variation in 22 populations of Taxus wallichiana var. mairei, encompassing nearly its entire distribution range. Low levels of plastid genetic variation and differentiation were detected in the populations, and the findings were attributed to low mutation rates, small population sizes, habitat fragmentation and isolation, and effective pollen or seed dispersal. Hunan and Hubei were identified as major refugia based on the number of private haplotypes and species distribution modeling. Trends in plastid genetic diversity and genetic differentiation from central to peripheral populations supported the predictions of the central–marginal hypothesis. In scenarios wherein the future climate becomes warmer, we predict that some peripheral populations will disappear and southern and southeastern regions will become significantly less habitable. Factors that include the levels of precipitation during the driest month, annual precipitation level, and annual temperature range will be decisive in shaping the future distribution of these populations. This study provides a theoretical basis for the conservation of T. wallichiana var. mairei.
Highlights
Knowledge of population genetic patterns across a species' geo‐ graphical range is of crucial importance to predict its responses to climate change (MacArthur, 1972; Trumbo et al, 2016)
T. wallichiana var. mairei had low levels of genetic variation its polymorphic bands (PPB) was slightly higher than other conifers (Table 5)
The low genetic diver‐ sity observed in T. wallichiana var. mairei may reflect a lack of ac‐ cumulated nucleotide mutations in its plastid genome over the long evolutionary timescale
Summary
Knowledge of population genetic patterns across a species' geo‐ graphical range is of crucial importance to predict its responses to climate change (MacArthur, 1972; Trumbo et al, 2016). Empirical tests of the CMH have found support in a range of plant taxa (Hampe & Petit, 2005; Myking, Vakkari, & Skrøppa, 2009), but not others (Dixon, Herlihy, & Busch, 2013; Garner, Pearman, & Angelone, 2004; Munwes et al, 2010) It is quite chal‐ lenging to disentangle the causes of a central–marginal structure of genetic diversity, because factors such as biological characters, persistent historical influences, effects of current demographic and ecological variables, population sampling strategies, and molecu‐ lar markers applied for analysis may all exert impacts (Loveless & Hamrick, 1984; Schiemann, Tyler, & Widén, 2000; Wagner, Durka, & Hensen, 2011). Our goals were (a) to reveal the level of plastid genetic diversity and genetic differentiation; (b) to test the central–marginal hypothesis by examining the plastid ge‐ netic variation between central and marginal populations; and (c) to define the ecologically suitable area for these populations and deter‐ mine the decisive climatic factors limiting their distribution
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