Many European organisms have very localised populations, related but distinct species separated by relatively short geographical distances. This has long been assumed to be a result of species being driven into refugia during the Pleistocene glaciation, where they became reproductively isolated due to genetic drift. However recent studies have lent to a better understanding of the genetic structures of such populations, and the likelihood of them becoming reproductively divided during glaciation events, and has led many scientists to conclude that many of these speciation events actually occurred during the Messinian Salinity Crisis, between 5.9 and 5.3 million years ago, when the Mediterranean almost completely dried up and many adjacent areas became uninhabitable due to aridity, forcing species unable to cope with these conditions into refugia further to the north.
In a paper published in the journal BMC Evolutionary Biology on 4 September 2012, Mafalda Barata of the Centro de Investigação em Biodiversidade e Recursos Genéticos at Campus Agrário de Vairão, the Departamento de Biologia at the Faculdade de Ciências da Universidade do Porto and the Institute of Evolutionary Biology in Barcelona, Salvador Carranza also of the Institute of Evolutionary Biology in Barcelona, and David Harris, also of the Centro de Investigação em Biodiversidade e Recursos Genéticos at Campus Agrário de Vairão, the Departamento de Biologia at the Faculdade de Ciências da Universidade do Porto, publish the results of a study into the population structure of Atlas Dwarf Lizards, Atlantolacerta andreanskyi, sugesting that these show a similar pattern of genetic endemism.
The Atlas Dwarf Lizard, Atlantolacerta andreanskyi. Reptarium.
Barata et al.tested both mitochondrial and nuclear DNA from Lizards from eight seperate populations in the High Atlas Mountains of Morocco, each apparently isolated from the others, since the Lizards are restricted to alitudes above 2400 m. Since these Lizards are (unusually for a reptile) restricted to the cooler environments of the mountain tops, they would, in theory, have been able to move downwards during cooler parts of the Pleistocene, allowing interbreeding of the populations if there were not genetically isolated by this time.
The study found that the Lizards were divided intp six genetically distinct lineages, which appeared to have diverged between 7.6 and 2.4 million years ago. Barata et al. did not go as far as to name these lineages as separate species, but did note that Atlantolacerta andreanskyi could better be regarded as a complex of cryptic species.
Map showing the distributions of populations of the Atlas Dwarf Lizard, Atlantolacerta andreanskyi. The color dots represent the localities of the populations sampled; Jebel Awlime (yellow), Jebel Sirwa (pink), Oukaimeden (red), Toubkal (orange), Tizin Tichka (dark blue), Jebel Azourki (light blue) ,Outabati (light green), and Jebel Ayache (dark green). The white dots are from an earlier population study of the Lizards, which considered only their distribution. Barata et al. (2012).
See also A giant Monitor Lizard from the Miocene of Samos, Greece, Velvet Geckos and Broad-headed Snakes; understanding the population structure of a favored prey item in order to help protect an endangered predator, News species of Girdled Lizard from the Democratic Republic of Congo, A new species of Semiaquatic Spectacled Lizard from southern Peru and Reptiles on Sciency Thoughts YouTube.
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