Both vicariance and dispersal have shaped the genetic structure of Eastern Mediterranean Euphorbia myrsinites (Euphorbiaceae)

Abstract

The Eastern Mediterranean is considered both a reservoir for plant evolution and a cradle for lineage diversification, but most plant groups from this area remain unstudied. To explore phylogeographic patterns within Eastern Mediterranean Euphorbia myrsinites, covering the area from the Apennines to Central Anatolia, we sequenced nuclear ribosomal ITS and the plastid trnT–trnF region and generated amplified fragment length polymorphism (AFLP) fingerprints, along with relative genome size (RGS) data. Our data reveal a complex evolutionary history of E. myrsinites since its origin at the Pliocene/Pleistocene boundary, resulting in a genetic structure that was shaped by fundamentally different processes acting at different time levels. Despite their weak glaciation in the Pleistocene, the high mountain ranges of the western and southern Balkan Peninsula triggered the initial divergence within this species due to vicariance in the Adriatic-Ionian and the Aegean-Pontic Pleistocene refugia. Subsequent range expansions led to the intriguing situation that both clusters nowadays occur in close spatial proximity. In addition, stronger genetic differentiation in the Aegean-Pontic area probably reflects less severe impacts of glaciations and higher environmental stability throughout the Pleistocene in this area, as compared to the Amphi-Adriatic region. The colonization of the Apennine Peninsula from the Balkan Peninsula took place later in the species’ evolutionary history, probably over land bridges connecting both peninsulas in the Pleistocene. On the western Balkan Peninsula the main phylogeographic split is situated along the Neretva river valley. To the north of this valley we detected no population structure whereas strong genetic differentiation in the southerly adjacent areas confirms the “refugia-within-refugia” hypothesis.