Chloroplast population genetics reveals low levels of genetic variation and conformation to the central–marginal hypothesis in Taxus wallichiana var. mairei, an endangered conifer endemic to China

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.

The History and Diversity of Rice Domestication as Resolved From 1464 Complete Plastid Genomes

“…While nucleotide diversity was low in the domesticated groups compared to the wild groups, haplotype diversity was higher ( Hd : Or-wj-I = 0.744, Or-wj-II = 0.887, Or-wj-III = 0.801; Supplementary Table 8 ). However, the high haplotype diversity in cultivated groups is mainly the result of many single step changes from one or two highly abundant haplotypes possibly reflecting the relaxation of natural selection and correlated increase in effective population sizes among domesticated lineages ( Petit and Barbadilla, 2009 ; Liu et al, 2019 ). This contrasts with the wild genetic clusters wherein many multiple step branching events typify the diversity of haplotypes ( Figure 4 and Supplementary Figure 10 ).…”

A noteworthy case of rewilding Chinese yew from a garden population in eastern China

“…1). However, Chinese yew has low seed yield, low seed germination rate and survival rate of seedlings, relatively slow growth, and low genetic diversity, so it is difficult to form a large range of natural communities (Ru et al, 2006;Liu et al, 2019). The yews can be associated tree species in the deciduous forests, evergreen forests, broad-leaved forests, or even bamboo forests.…”

Elevational differences of the two closely related Taxus species in sympatric, evidence from species distribution modeling

“…While for T. mairei , bio11 was the most contribution factors, but bio18 was the most important factors. and Liu et al (2019) supported precipitation was the most important climatic factor that restricted the habitat distribution of the T. mairei. Poudel et al (2012) also held that low winter and very high summer rainfall made T. mairei only distributed in the East of the Himalayas in Nepal.…”