Quaternary radiation of bifid toadflaxes (Linaria sect. Versicolores) in the Iberian Peninsula: low taxonomic signal but high geographic structure of plastid DNA lineages

Abstract

Phylogeographic analysis provides insights into the micro-evolutionary mechanisms driving recent radiations. Here we conducted a phylogeographic analysis of the Iberian clade of Linaria subsect. Versicolores. This lineage includes eight species and subspecies endemic or subendemic to the Iberian Peninsula that diversified in the Quaternary. We obtained 159 sequences of three plastid DNA regions from 53 individuals of the study group representing all recognized taxa. Phylogenetic, haplotype network, dating and population genetic analyses were conducted. In addition, the radiation hypothesis (common ancestry and rapid speciation) was tested. The results revealed two major clades that diverged in the Pleistocene. Low taxonomic signal of plastid DNA sequences was found as a result of rapid diversification. Indeed, the study group is herein described as an evolutionary radiation because of its common ancestry and diversification rates in line with those of other recent plant radiations. Interestingly, a high geographic structure of plastid DNA lineages was revealed, with a major genetic discontinuity separating south-eastern populations from those of the rest of Iberia. Based on dating results, we rule out a marine barrier as the cause behind this discontinuity, and hypothesize a role of edaphic specialization in differentiation of the two major clades. These results provide relevant information on the evolutionary dynamics of recent plant radiations in the western Mediterranean hotspot.