Jeroen Speybroeck wrote:Thomas, these authors may be cautious in their conclusions, but any other explanation really seems unlikely to me.
Karim, the genetic data of meridionalis is unlike that of current knowledge on any of the other species you mention. These are not just inferences but based on genetic data providing insight in unnaturally low levels of genetic variability and estimations of an origin after the era of intercontinental land bridges. Your type of reasoning, otherwise, leads to rejection of any ancient introduction, or what else?
For Hyla meridionalis, yes the published data point toward two separate ancient introductions: from north Morocco to southern France and from south Morocco to southern Spain. What makes it different from most other species that I mentioned is, assuming a sufficient haplotype sampling, the distance between the introduced populations and their places of origin.
However I do not see why you consider the situation to be different for D. pictus which is clearly introduced from Algeria to SW France and from Tunisia to Sicily with no differentiated lineage and no land bridges ever existing.
European populations of Macroprotodon brevis, Malpolon monspessulanus and Hemorrhois hippocrepis also present very low levels of genetic variability and the same haplotypes occurring on both sides of the strait of Gibraltar. Which only point toward a recent origin (introduction or colonization as snakes are more efficient in colonizing islands).
For M. lebetina the same haplotypes as been reported both in Milos and in eastern Anatolia which can only indicate an introduction.