title: Divergence maintained by climatic selection despite recurrent gene flow: a case study of Castanopsis carlesii (Fagaceae).
abstract: Local adaptation to different environments has the potential to maintain divergence between populations despite recurrent gene flow and is an important driver for generating biological diversity. In this study, we investigate the role of adaptation in the maintenance of two parapatric varieties of a forest tree. We used sequence variation of chloroplastic DNA and restriction site-associated DNA to investigate the genetic structure of two varieties of Castanopsis carlesii in subtropical China and relate it to climatic variation. We used niche reconstruction methods to investigate niche differentiation between the two varieties and to estimate the past distribution of this species. A deep divergence was observed between the two varieties, but evidence of introgression and genetic admixture was detected in two phenotypically and geographically intermediate populations. Niche reconstruction suggests that the distribution of the two varieties was disjunct during periods of global cooling and that the two varieties occupy significantly different niches. The genetic structure was mainly driven by environmental factors, and 13 outlier loci under divergent selection were correlated with climatic variation. These results suggest that the two varieties evolved in allopatry and came back into secondary contact after the last glacial maximum and that they are an evolutionary example of divergence maintained by climatic selection despite recurrent gene flow.
authors.affiliation: Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, 510642, China. sun-ye@scau.edu.cn, sun-ye@scbg.ac.cn.|Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China. sun-ye@scau.edu.cn, sun-ye@scbg.ac.cn.
authors.forename: Ye
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Institut des Sciences de la Forêt Tempérée, Université du Québec en Outaouais, 58 rue Principale, Ripon, Quebec, J0V 1V0, Canada.|Quebec Centre for Biodiversity Science, McGill University, 1205 Dr. Penfield Avenue, Montreal, Quebec, H3A 1B1, Canada.
authors.forename: Yann
authors.initials: Y
authors.lastname: Surget-Groba
authors.affiliation: Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Shaoxiong
authors.initials: S
authors.lastname: Gao
mesh_terms: D002681:China; D002980:Climate; D018742:DNA, Chloroplast / Q000235:genetics; D029962:Fagaceae / Q000235:genetics*; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population
chemical_list: D018742:DNA, Chloroplast
keywords: Castanopsis carlesii; divergence; gene flow; niche reconstruction; restriction site-associated DNA; secondary contact