Influence of Pliocene and Pleistocene climates on hybridization patterns between two closely related oak species in China

Background and Aims Contemporary patterns of genetic admixture reflect imprints of both ancient and recent gene flow, which can provide us with valuable information on hybridization history in response to palaeoclimate change. Here, we examine the relationships between present admixture patterns and past climatic niche suitability of two East Asian Cerris oaks (Quercus acutissima and Q. chenii) to test the hypothesis that the mid-Pliocene warm climate promoted while the Pleistocene cool climate limited hybridization among local closely related taxa. Methods We analyse genetic variation at seven nuclear microsatellites (1111 individuals) and three chloroplast intergenic spacers (576 individuals) to determine the present admixture pattern and ancient hybridization history. We apply an information-theoretic model selection approach to explore the associations of genetic admixture degree with past climatic niche suitability at multiple spatial scales. Key Results More than 70 % of the hybrids determined by Bayesian clustering analysis and more than 90 % of the individuals with locally shared chloroplast haplotypes are concentrated within a mid-Pliocene contact zone between similar to 30 degrees N and 35 degrees N. Climatic niche suitabilities for Q. chenii during the mid-Pliocene Warm Period [mPWP, similar to 3.264-3.025 million years ago (mya)] and during the Last Glacial Maximum (LGM, similar to 0.022 mya) best explain the admixture patterns across all Q. acutissima populations and across those within the ancient contact zone, respectively. Conclusions Our results highlight that palaeoclimate change shapes present admixture patterns by influencing the extent of historical range overlap. Specifically, the mid-Pliocene warm climate promoted ancient contact, allowing widespread hybridization throughout central China. In contrast, the Pleistocene cool climate caused the local extinction of Q. chenii, reducing the probability of interspecific gene flow in most areas except those sites having a high level of ecological stability.

Automated summary

This study examines the relationship between present admixture patterns of two East Asian Cerris oaks and past climatic niche suitability, finding that paleoclimate change shapes present admixture patterns by influencing historical range overlap. Specifically, the mid-Pliocene warm climate promoted ancient contact and widespread hybridization, while the Pleistocene cool climate limited interspecific gene flow except in areas with high ecological stability.