Abstract
Knowledge of interspecific divergence and population expansions/contractions of dominant forest trees in response to geological events and climatic oscillations is of major importance to understand their evolution and demography. However, the interspecific patterns of genetic differentiation and spatiotemporal population dynamics of three deciduous Cerris oak species (Q. acutissima, Q. variabilis and Q. chenii) that are widely distributed in China remain poorly understood. In this study, we genotyped 16 nuclear loci in 759 individuals sampled from 44 natural populations of these three sibling species to evaluate the plausible demographical scenarios of the closely related species. We also tested the hypothesis that macro- and microevolutionary processes of the three species had been triggered and molded by Miocene–Pliocene geological events and Quaternary climatic change. The Bayesian cluster analysis showed that Q. acutissima and Q. chenii were clustered in the same group, whereas Q. variabilis formed a different genetic cluster. An approximate Bayesian computation (ABC) analyses suggested that Q. variabilis and Q. acutissima diverged from their most common ancestor around 19.84 Ma, and subsequently Q. chenii diverged from Q. acutissima at about 9.6 Ma, which was significantly associated with the episodes of the Qinghai–Tibetan Plateau (QTP). In addition, ecological niche modeling and population history analysis showed that these three Cerris oak species repeatedly underwent considerable ‘expansion–contraction’ during the interglacial and glacial periods of the Pleistocene, although they have varying degrees of tolerance for the climatic change. Overall, these findings indicated geological and climatic changes during the Miocene–Pliocene and Pleistocene as causes of species divergence and range shifts of dominant tree species in the subtropical and warm temperature areas in China.
Highlights
Historical and ecological factors such as geological and/or climatic processes have a profound impact on biodiversity and sustainability at every level of the biota, from genes to spatial distribution [1,2,3,4]
Leaf materials were collected from 44 wild populations (N = 759) of the three Cerris oaks, which distributed in subtropical China, including populations (N = 336) of Q. variabilis, populations (N = 338) of Q. acutissima, and 5 populations (N = 85) of Q. chenii (Table S1, Figure 1)
The values of Ho were much lower than HE (Table S1), and these three oak species have different degrees of deviation from Hardy–Weinberg equilibrium (HWE) in most populations (Table S8), which were associated with excess of homozygous caused by inbreeding or mating among relatives (Table S1)
Summary
Historical and ecological factors such as geological and/or climatic processes have a profound impact on biodiversity and sustainability at every level of the biota, from genes to spatial distribution [1,2,3,4]. The interactions among these processes would create multiple ecological niches, favoring high rates of intra- and interspecific diversification [5,6]. The subgenus Cerris, namely the Old World oaks, includes Cerris, Ilex and Cyclobalanopsis sections. Limited information was obtained to resolve interspecific divergence and demographic history of the three closely related Cerris oak species (Q. acutissima, Q. chenii and Q. variabilis) that widely distributed in China
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