Genetic variation in Goniolimon speciosum (Plumbaginaceae) reveals a complex history of steppe vegetation

Abstract

We hypothesized that the spatial pattern of genetic variation in different ecological groups of steppe plant species is not similar. To test this hypothesis, we studied genetic variation of the typical steppe plant Goniolimon speciosum (Plumbaginaceae), which is spread across the whole of the Asian steppe, and compared it with the published data on genetic variation of several mountain-steppe species. To elucidate the phylogenetic position of and genetic structure in G. speciosum, we sequenced the nuclear ribosomal internal transcribed spacer (ITS) and plastid trnH-psbA and trnQ-rps16 regions. Goniolimon speciosum was shown to have originated in Central Asia in the Pliocene. We revealed two genetic groups in G. speciosum: a south-eastern (Dahuria, north-eastern Mongolia, southern shore of the lake Baikal and eastern Tyva) group and a broadly distributed western group. This split of evolutionary lineages is estimated to have occurred in the mid-Pliocene. Some samples from the central part of the species area (riverheads of Yenisei and Ob) formed an intermediate genetic group, where most plants had western ITS ribotypes and southeastern plastid haplotypes. This polyphyletic group could have originated due to multiple secondary contacts and subsequent hybridization events. The geographically structured genetic subdivision of the western lineage, based on the ITS data, indicates multiple northward colonizations of G. speciosum from Central Asia that occurred, according to our estimates, in the early Pleistocene. Thus, the history of steppe vegetation is more complicated than has been previously suggested, basing upon limited taxonomic sampling of steppe plants. Species with different ecological preferences have a different history.