Phylogeography of Quercus aquifolioides provides novel insights into the Neogene history of a major global hotspot of plant diversity in south-west China
Résumé
Aim Hotspots of biodiversity are often associated with areas that have undergone orogenic activity during recent geological history. Mountain uplifts are known to catalyse species radiation but their impact on evolutionarily stable taxa such as many trees remains little understood. The oak Quercus aquifolioides is endemic to yet widely distributed across the Hengduanshan Biodiversity Hotspot in the Eastern Himalayas. Here, we investigate how the region's Neogene and Quaternary history has driven the species' past population dynamics and the resulting extant patterns of intraspecific diversity.
Location Hengduanshan Biodiversity Hotspot in SW China.
Methods We sampled 58 populations throughout the species range and genotyped a total of 959 individuals at four chloroplast DNA fragments and 11 nuclear microsatellite loci. Phylogenetic reconstructions, molecular dating techniques and ancestral area reconstructions were used in combination with population genetic statistics to infer the biogeographical history of Q. aquifolioides. The phylogeographical study was complemented by a survey of fossil records and a niche modelling exercise.
Results Combined molecular and fossil evidence indicates that Q. aquifolioides descended during the late Miocene from the central Qinghai-Tibet Plateau into Tibet and the western Sichuan Plateau, and from there, into the area of highest endemism in the Hengduan Mountains sensu lato. Great apparent population stability and a haplotype ‘radiation’ in this area contrasted with marked extinction–recolonization dynamics and reduced population diversity in Tibet. We found evidence for extremely limited seed gene flow but extensive pollen gene flow (global FST: cpDNA = 0.98, nSSR = 0.07) with signals of asymmetric pollen dispersal from the Hengduan Mountains into Tibet.
Main conclusion Our results provide insights of unprecedented detail into the ancient biogeographical history of the Hengduanshan Biodiversity Hotspot, suggesting that past environmental changes in the region may have catalysed radiative diversifications within species much in the same way as among species.