Molecular biogeography: using the Corsica‐Sardinia microplate disjunction to calibrate mitochondrial rDNA evolutionary rates in mountain newts (Euproctus)

Abstract

AbstractMitochondrial DNA (mtDNA) sequence variation was examined in the three species belonging to the newt genus Euproctus: E. asper, E. montanus, and E. platycephalus, and in three other species belonging to the same family: Triturus carnifex, T. vulgaris and Pleurodeles waltl. The Euproctus species inhabit mountain streams in the Pyrenean region, Corsica, and Sardinia, respectively. This vicariant distribution is believed to be a result of the disjunction and rotation of the Sardinia‐Corsica microplate from the Pyrenean region and suggested dates for each cladogenetic event are available. A total of 915 bp from 12S and 16S ribosomal rRNA genes were compared for each taxon. These are the first mt‐rDNA sequence data for salamanders. Sequences were used to reconstruct phylogenetic trees, investigate evolutionary rates for these genes, calibrate them with absolute time since divergence, and compare rates with published ones.Using P. waltl as the outgroup, all phylogenetic methods used (parsimony, maximum likelihood, and Neighbor Joining) produced trees with identical topologies and similar bootstrap values associated with each node. These sequence data cannot unambiguously resolve the splitting events leading to the main radiation of the genus Triturus and the origin of the genus Euproctus. These events may well have occurred very close in time, consistent with other sorts of data. Although it is unlikely strict linearity holds for all kinds of substitutions, relative rate tests of the molecular clock hypothesis could not reject clock‐like behavior of sequence changes along Euproctus lineages. Estimates of absolute rates of base changes are 0.35% per Myr since divergence for all substitutions and 0.14% per Myr for transversions; these estimates are similar to other vertebrate estimates. A comparison with distance measures from allozyme studies agrees quite well with regard to relative divergences of the three Euproctus species.