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 i n lizards have revealed patterns of geographic variation that reflect both population vicariance and in situ selection-mediated responses to the ecolo gical heterogeneity of the islands. This study tested different models of d ifferentiation in a continental species, the agamid Agama impalearis, in wh ich spatial separation is much greater than that in island species. Pattern s of among-site differentiation in morphology were described and a characte r-resampling technique used to investigate their robustness. Putative cause s were evaluated by testing multivariate patterns of differentiation agains t models based on historical and present-day effects using matrix associati on randomization tests. This strongly suggested the action of both vicarian ce/secondary contact and current climatic conditions in shaping the pattern s of morphological variation. The former appears to be the result of range contraction into refugia separated by the Atlas mountain range during glaci al conditions, with subsequent secondary contact during warmer interglacial periods. Scalation showed a very clear association with geographic differe nce in thermal regime, even after the vicariance/gene-flow induced non-inde pendence had been taken into account. This latter finding indicates that pa tterns observed in other lizards are quite general.