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Keywords:

  • Amphibians;
  • Atylodes;
  • Bering Land Bridge;
  • Hydromantes;
  • Mediterranean Basin;
  • Messinian Salinity Crisis;
  • mitochondrial DNA;
  • phylogeography;
  • Pleistocene glaciations;
  • Speleomantes

Abstract

Aim  To infer the phylogenetic relationships and biogeography of Hydromantes, with special emphasis on the European taxa. In particular, we aimed to test: (1) the monophyly of the European species and current views on their interrelationships; and (2) previously proposed timings of the separation of European and American Hydromantes, and of biogeographically important events within Europe.

Location  California and the Western Mediterranean Basin, specifically south-east France, Italy, and the island of Sardinia.

Methods  Partial sequences of mitochondrial genes (cytochrome b and 12S rRNA) were obtained from 45 specimens of Hydromantes, including all European extant species and subspecies, and two species from California. In addition, a fragment of the mitochondrial 16S rRNA gene was amplified for 16 specimens. Data sets were aligned using ClustalX, and well-supported phylogenetic trees were produced using maximum-likelihood, Bayesian and maximum-parsimony methods. Estimates of divergence times were obtained with the program r8s, the molecular clock being calibrated using the opening of the Strait of Gibraltar, the final event in the Messinian Salinity Crisis of 5.3 Ma.

Results  Separation between the American and European clades occurred approximately 13.5 Ma, most probably before or after westward dispersal across the Bering Land Bridge. In Europe, divergence started in the late Miocene, when Hydromantes (A.) genei separated from other members of the genus 9 Ma and colonized south-west Sardinia. Movement between the European mainland and Sardinia, by a member of the subgenus Speleomantes, occurred in the Messinian Salinity Crisis, after the Mediterranean Basin desiccated almost completely 5.96 Ma. Subsequent widespread aridification fragmented the geographical ranges of Hydromantes, which live in cool and humid conditions, resulting in the origin of the six species in the subgenus Speleomantes. In contrast, a second period of diversification, in continental Europe 2–1.3 Ma, was probably caused by very cold interludes during the climatic oscillations that characterized the Pleistocene.

Main conclusions  The molecular clock used here indicates that the separation of Californian and European Hydromantes occurred more recently than previously believed, and the same is true of some subsequent phylogenetic divergences within Europe. Estimated dates for these divergence events are consistent with known geophysical and climatic events that could have caused or facilitated them.