Impacts of biogeographic history and marginal population genetics on species range limits: a case study of Liriodendron chinense

Species ranges are influenced by past climate oscillations, geographical constraints, and adaptive potential to colonize novel habitats at range limits. This study used Liriodendron chinense, an important temperate Asian tree species, as a model system to evaluate the roles of biogeographic history and marginal population genetics in determining range limits. We examined the demographic history and genetic diversity of 29 L. chinense populations using both chloroplast and nuclear microsatellite loci. Significant phylogeographic structure was recovered with haplotype clusters coinciding with major mountain regions. Long-term demographical stability was suggested by mismatch distribution analyses, neutrality tests, and ecological niche models (ENM) and suggested the existence of LGM refuges within mountain regions. Differences in genetic diversity between central and marginal populations were not significant for either genomic region. However, asymmetrical gene flow was inferred from central populations to marginal populations, which could potentially limit range adaptation and expansion of L. chinense.