East‒West genetic differentiation across the Indo-Burma hotspot: evidence from two closely related dioecious figs

Understanding biodiversity patterns and their underlying mechanisms is of interest to ecologists, biogeographers and conservationists and is critically important for conservation efforts. The Indo-Burma hotspot features high species diversity and endemism, yet it also faces significant threats and biodiversity losses; however, few studies have explored the genetic structure and underlying mechanisms of Indo-Burmese species. Here, we conducted a comparative phylogeographic analysis of two closely related dioecious Ficus species, F. hispida and F. heterostyla, based on wide and intensive population sampling across Indo-Burma ranges, using chloroplast (psbA-trnH, trnS-trnG) and nuclear microsatellite (nSSR) markers, as well as ecological niche modeling.

The results indicated large numbers of population-specific cpDNA haplotypes and nSSR alleles in the two species. F. hispida showed slightly higher chloroplast diversity but lower nuclear diversity than F. heterostyla. Low-altitude mountainous areas of northern Indo-Burma were revealed to have high genetic diversity and high habitat suitability, suggesting potential climate refugia and conservation priority areas. Strong phylogeographic structure and a marked east‒west differentiation pattern were observed in both species, due to the interactions between biotic and abiotic factors. Interspecific dissimilarities at fine-scale genetic structure and asynchronized historical dynamics of east‒west differentiation between species were also detected, which were attributed to different species-specific traits.

We confirm hypothesized predictions that interactions between biotic and abiotic factors largely determine the patterns of genetic diversity and phylogeographic structure of Indo-Burmese plants. The east‒west genetic differentiation pattern observed in two targeted figs can be generalized to some other Indo-Burmese plants. The results and findings of this work will contribute to the conservation of Indo-Burmese biodiversity and facilitate targeted conservation efforts for different species.