Expansion after expansion: dissecting the phylogeography of the widely distributed spur-thighed tortoise, Testudo graeca (Testudines:Testudinidae)

Studying phylogeographic histories in wide-ranging species provides key insights into those processes shaping current species’ distributions and genetic structuring. In this work, we extend previous sampling and analyse data from three mitochondrial genes to explore in-depth the phylogeography of the spur-thighed tortoise (Testudo graeca), the most widely distributed of Western Palearctic tortoise species. The combination of loci with different evolutionary rates and new fossil data in molecular clock analyses allow us to infer a dual diversification burst of the species, which took place since the Mio-Pliocene for the eastern subspecies and during the Pleistocene for the subspecies distributed in North Africa. The latter seems to correspond to a more or less contemporary diversification burst, which resulted in the current west–east allopatric/parapatric distribution of the North African lineages. In addition to the previously known genetic lineages, a new one was discovered in Libya. Within a more recent framework, we use estimates of genetic diversity and demographic inferences from molecular data to address the origin of three extant Western European populations. The comparison of their current genetic signatures supports the recent introduction of T. graeca into Majorca and Sardinia and an ancient origin of the populations in south-eastern Spain. The fossil history of T. graeca supports our findings from the most comprehensive and unifying phylogeographic study conducted to date for T. graeca. Our work highlights T. graeca as a paradigmatic system for studying phylogeographic processes that act in very different temporal and geographical contexts.