One plus one makes seven: Intricate phylogeographic patterns in Odontites vernus (Orobanchaceae: Rhinantheae) in the Iberian Peninsula

Abstract

The Odontites vernus group is the most widespread of the genus Odontites, occupying the temperate regions of Eurasia and northern Morocco. The group contains three species, all inhabiting the Iberian Peninsula, where O. vernus s.l. (sensu lato) exhibits remarkable morphological variability and includes diploid and tetraploid individuals corresponding to the two subspecies that occur there. We collected 301 individuals from 100 sampling sites covering the entire distribution of O. vernus in the Iberian Peninsula and genotyped them using 12 simple sequence repeat (SSR) markers. Their ploidy level was estimated by flow cytometry, and two cpDNA regions (rps16 intron and trnK-rps16) were sequenced. We found 129 diploids and 172 tetraploids distributed following a mosaic parapatry model, while only two mixed-ploidy populations were discovered. The 20 haplotypes found fit two well-defined haplogroups, to some extent correlated with estimated ploidy levels. The frequencies of the SSR alleles shared by both cytotypes, as well as those of the private alleles corresponding to the tetraploid cytotype, indicate that tetraploids likely originated at least twice through autopolyploidy. Additionally, the results from SSR markers were structured in a higher number of groups than did the cpDNA sequences. Thus, the genetic distance analysis detected four groups, but the Bayesian analysis of population structure identified seven, with only low levels of gene flow detected among groups. The distributions of the seven genetic groups coincide with well-known refugium areas within the Iberian Peninsula during the climatic oscillations of the Quaternary. Thus, the results give additional support to the “refugia within refugia” hypothesis.