Genetic diversity and phylogeography of Eversmannia subspinosa (Fabaceae)

Eversmannia is a mono- or olygotypic genus, part of the Hedysareae tribe, characterized by a shrub growth habit and the presence of spines, distributed in Middle Asia. Eversmannia includes the widely distributed E. subspinosa and three taxonomically unclear local endemics restricted to type localities in the Pamir Alay mountain foothills. Here, we study the genetic diversity and phylogeography of E. subspinosa using four plastid DNA markers. The study revealed 26 E. subspinosa haplotypes mostly grouped into two distinct lineages on the basis of phylogenetic reconstructions. We also studied two of the three described local endemics that both shared the most abundant haplotype with E. subspinosa and can thus be considered conspecific. The 26 haplotypes were, however, mostly private and differed from each other by numerous nucleotide substitutions. The divergence times and geographic expansion estimates suggest Eversmannia rapidly diversified and underwent population expansion in the early Pleistocene roughly (1.76)–1.32–(0.95) Mya reaching the extent of its current range by roughly (0.55)–0.32–(0.13) Mya. Its populations were probably subject to subsequent local expansions and extinctions during Pleistocene glaciations and the Caspian transgression/regression cycles. This idea was supported by negative neutrality tests and the identification of different type mismatch distributions, indicating expansion in population size at the level of species, but also both expansion and stability across major genetic groups.