Geographic variation in Agama impalearis from Morocco:: evidence for historical population vicariance and current climatic effects

Morphological and molecular surveys of within-island geographic variation in lizards have revealed patterns of geographic variation that reflect both population vicariance and in situ selection-mediated responses to the ecological heterogeneity of the islands. This study tested different models of differentiation in a continental species, the agamid Agama impalearis, in which spatial separation is much greater than that in island species. Patterns of among-site differentiation in morphology were described and a character-resampling technique used to investigate their robustness. Putative causes were evaluated by testing multivariate patterns of differentiation against models based on historical and present-day effects using matrix association randomization tests. This strongly suggested the action of both vicariance/secondary contact and current climatic conditions in shaping the patterns of morphological variation. The former appears to be the result of range contraction into refugia separated by the Atlas mountain range during glacial conditions, with subsequent secondary contact during warmer interglacial periods. Scalation showed a very clear association with geographic difference in thermal regime, even after the vicariance/gene-flow induced non-independence had been taken into account. This latter finding indicates that patterns observed in other lizards are quite general.