Vicariance versus dispersal across Beringian land bridges to explain circumpolar distribution: A case study in plants with high dispersal potential

Abstract

This article aims to disentangle the importance of the Beringian land bridges during the Pliocene and Quaternary periods in order to explain the current distribution of circumpolar plants with potential for long-distance dispersal. We sampled all extant species in Carex section Glareosae (26 species and 2 subspecies) and analysed 14 DNA regions, including the nrDNA regions ETS and ITS, three nuclear single-copy genes (CATP, G3PDH and GZF), and nine cpDNA regions: 50trnK intron, atpIH, matK, ndhJ-trnF, psbA-trnH, rpl32-trnL, rps16, trnC-ycf6 and ycf6-psbM. After testing for outlier proportions, we used Bayesian inference, maximum likelihood and a species-tree approach to infer phylogenetic relationships between species; divergence times were estimated using BEAST2. We then performed biogeographical analyses using “BioGeoBEARS” to estimate ancestral areas by means of reticulate models. Finally, lineage through time (LTT) and diversification pattern analyses were performed using BAMM. Our results show that Carex section Glareosae is a monophyletic group that diverged c. 6.56 Ma (4.54–8.51 Ma at 95% highest posterior density interval). We show that within-area cladogenetic speciation events and anagenetic dispersal (including some vicariance events) play an important role in shaping distribution in species with potential for long-distance dispersal. Diversification patterns show constant diversification rates over time. The Bering Strait may have played an important role in shaping the current distribution of the species in the section, facilitating dispersal between Asia and North America during glacial periods when the Beringian land bridges were open. Nevertheless, we cannot discount long-distance dispersal as an alternative major force shaping the species distribution in the section.