Abstract
How the often highly endemic biodiversity of islands originated has been debated for decades and it remains a fervid research ground. Here, using mitochondrial and nuclear gene sequence analyses, we investigate the diversity, phylogenetic relationships, and evolutionary history of the mayfly Baetis gr. rhodani on the three largest north-western Mediterranean islands (Sardinia, Corsica, Elba). We identify three distinct, largely codistributed, and deeply differentiated lineages, with divergences tentatively dated back to the Eocene-Oligocene transition. Bayesian population structure analyses reveal a lack of gene exchange between them, clearly indicating that these lineages belong to three putative species. Their phylogenetic relationships with continental relatives, together with the dating estimates, support a role for three processes contributing to this diversity: (1) vicariance, primed by microplate disjunction and oceanic transgression; (2) dispersal from the continent; and (3) speciation within the island group. Thus, our results do not point toward a prevailing role for any of the previously invoked process. Rather, they point to a variety of equally contributing, and most probably still not fully appreciated processes, as the best scenario for the origin of the diverse and endemic biota of this group of islands.
Footnotes
Dipartimento di Scienze Ecologiche e Biologiche, Università della Tuscia. Viale dell’Università s.n.c., I-01100 Viterbo, Italy. phone: +39-0761-357414
Conflict of interest The authors have no conflict of interests to declare.