Geographical pattern of isolation and diversification in karst habitat islands: a case study in the Primulina eburnea complex

AIM: This study aimed to clarify species boundaries as well as phylogenetic relationships among species of the Primulina eburnea complex, a rapidly diversifying group of edaphic specialists confined to karst habitat islands in southern China. We investigated patterns of genetic isolation and diversification in this complex. LOCATION: Limestone karsts in southern China. METHODS: We analysed data from three chloroplast DNA (cpDNA) regions and eight nuclear microsatellite loci, representing five closely related species in the P. eburnea complex sampled from 62 populations across its entire distributional range. We conducted a Bayesian phylogenetic analysis, constructed maximum parsimony haplotype networks and assessed population genetic diversity, population differentiation and geographical structure within and between species. RESULTS: Of the 60 identified haplotypes, eight were shared between populations and only one was shared between species. Both cpDNA and the nuclear markers revealed a high level of population genetic differentiation and a strong phylogeographical structure. Four main genetic clusters were identified according to their geographical proximity, although geographical structuring differed slightly between the cpDNA and the nuclear loci. The pattern of genetic structure of both the cpDNA and microsatellite genomes can be explained by patterns of isolation by distance (IBD), across both the distribution of the complex and the populations of individual species. MAIN CONCLUSIONS: This is the first study to investigate geographical isolation and speciation in a clade associated with karst habitat islands in southern China. Geographically structured population differentiation of the P. eburnea complex suggests that divergence is mainly driven by genetic drift, with little evidence of gene flow. Allopatric speciation is the main mode of diversification in the group. These results highlight the importance of geographical isolation in promoting population differentiation in karst habitat islands.