Using a new RAD-sequencing approach to study the evolution of Micromeria in the Canary islands

As found in other oceanic islands, the Canary Islands include a large number of single island endemic species, some of which form clades that are broadly distributed within the archipelago. The genus Micromeria (Lamiaceae), for instance, includes groups of morphologically similar but ecologically diverse species on each island, representing a great model to investigate niche shifts and adaptation within the Canary Archipelago. Previous attempts to reconstruct phylogenetic relationships within the genus did not lead to robust phylogenies, presumably due to introgression and/or incomplete lineage sorting. In this study, we use a newly developed RAD-sequencing method to improve phylogenetic resolution and to better understand relationships among the Canary Island endemic Micromeria. Overall, we obtained 3571 loci that were genotyped for a total of 46 individuals of Micromeria. Our data reconstructed a highly resolved phylogeny, and corroborated the latest species reclassification of the M. varia s.l. species complex, the taxonomically most complicated group within the genus. Furthermore, taxa occupying similar ecological conditions in different islands, were shown to be closely related. This is the case of taxa from the laurel forest from La Gomera and Gran Canaria, suggesting that the laurel forest likely worked as a filter, only allowing the establishment of colonizers already pre-adapted to these conditions. We also found introgression between these species so it is also possible that the genes that facilitated the adaptation to laurel forest were swapped between Gran Canaria and La Gomera. The observations obtained in this study also allowed us to explain the role of introgression in the origin of M. varia s.l. species complex.