Phylogenetic and biogeographic insights into long-lived Mediterranean Cupressus taxa with a schizo-endemic distribution and Tertiary origin

Mediterranean Cupressus taxa (C. atlantica, C. dupreziana and C. sempervirens) exemplify a schizo-endemic distribution resulting from vicariant speciation related to climate-induced contraction and fragmentation of their ancestral geographical range. Here, we investigate the evolutionary history of Mediterranean Cupressus taxa and the phylogeographic structure of C. atlantica and C. sempervirens to resolve systematic uncertainty and evaluate patterns of genetic diversity, using Bayesian inference based on plastid DNA and nuclear microsatellite markers. Based on our data, the eastern Mediterranean and African Cupressus lineages were clearly delineated. African C. atlantica and C. dupreziana showed species-specific haplotypes and were well separated from eastern Mediterranean C. sempervirens. The diversification of Mediterranean Cupressus was estimated to encompass the period between the early Miocene and the late Pleistocene, coinciding with the aridification events that occurred in the Mediterranean. The disjunct distribution of Mediterranean Cupressus taxa is reflected in their interspecific genetic divergence, providing support for their separation at the species rank. Genetic diversity of C. atlantica and C. sempervirens was high, but the level of differentiation in C. sempervirens was higher than that in the endemic C. atlantica. A minor geographically dependent distribution of diversity was detected for C. atlantica relative to that identified for C. sempervirens, which probably reflects relatively recent range fragmentation and a decline in population size. In C. sempervirens, a clear pattern of differentiation corresponding to the geographical regions of the range of the taxon was inferred, confirming the prominent role of geological and palaeoclimatic factors in the evolution of Mediterranean species and supporting the pattern of differentiation reported for other tree species in the eastern Mediterranean.