Gone with the plate: the opening of the Western Mediterranean basin drove the diversification of ground-dweller spiders

We analyse 49 specimens representing populations of most Parachtes species and close relatives. Our results reveal that both the sequence of species formation in Parachtes and the estimated divergence times match the geochronological sequence of separation of the main islands, suggesting that the diversification of the group was driven by Tertiary plate tectonics. In addition, the confirmation that Parachtes diversification matches well-dated geological events provides a model framework to infer substitution rates of molecular markers. Divergence rates estimates ranged from 3.5% My-1 (nad1) to 0.12% My-1 (28S), and the average divergence rate for the mitochondrial genes was 2.25% My-1, very close to the "standard" arthropod mitochondrial rate (2.3% My-1).Our study provides the first unequivocal evidence of terrestrial endemic fauna of the major western Mediterranean islands, whose origin can be traced back to the Oligocene separation of these islands from the continent. Moreover, our study provides useful information on the divergence rate estimates of the most commonly used genes for phylogenetic inference in non-model arthropods.The estimation of the timing of evolutionary events from DNA sequence information has become a major research topic in evolutionary biology. Although the use of molecular data to estimate divergence times goes back to the mid 60's of the past century [1], the number of studies that include time estimation has increased rapidly over the last decade due to the ever increasing amount of DNA sequence data and the development of new algorithms that relax the limiting assumptions of the molecular clock (see reviews of [2-4]). Information on timescales has shed light not only on the origin of taxonomic groups but has also allowed for the testing of biogeographic and climatic hypotheses, the estimation of rates of species diversification, and the investigation of rates of molecular evolution, among other topics [5].Genetic distances are transforme