Phylogeography and ecological differentiation of strictly Mediterranean taxa: the case of the Iberian endemic Odontites recordonii

Premise: Ecological drivers for genetic differentiation in Mediterranean climates are still underexplored. We have used the strictly Mediterranean endemic Odontites recordonii as a model species to address this question. This species is one of the three Iberian representatives of the O. vernus group, which are morphologically similar. Thus, it was additionally necessary to clarify their phylogenetic relationships.

Methods: We used amplified fragment length polymorphisms to reveal phylogenetic relationships within O. vernus group, and to reconstruct the phylogeographic patterns within O. recordonii. Additionally, ecological niche models were generated to detect refugia along the Quaternary climatic oscillations. And finally, alleles under natural selection were identified, and correlations between allele presences and environmental variables were calculated in order to shed light on the ecological drivers promoting differentiation.

Results: The three species from the O. vernus group were recovered as distinct species. Three genetic groups were found within O. recordonii and a putative refugium was detected for each one. Eighty-one alleles could be under diversifying selection, and 58 alleles showed significant correlations with environmental variables, especially with temperature and precipitation seasonality and summer drought.

Conclusions: The three Iberian species of the O. vernus group are reciprocal monophyletic taxa. The three genetic groups of O. recordonii could have been restricted to narrow refugia during the Quaternary and displayed present distributions in accordance with bioclimatic conditions. Temperature and precipitation seasonality and the intensity of summer drought are definitory climatic parameters of Mediterranean-type climates, and they could have acted as drivers of genetic differentiation on O. recordonii.