MOLECULAR BIOGEOGRAPHY - USING THE CORSICA-SARDINIA MICROPLATE DISJUNCTION TO CALIBRATE MITOCHONDRIAL RDNA EVOLUTIONARY RATES IN MOUNTAIN NEWTS (EUPROCTUS)

Mitochondrial 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 sam e family: Triturus carnifex, T. vulgaris and Pleurodeles waltl. The Eu proctus species inhabit mountain streams in the Pyrenean region, Corsi ca, and Sardinia, respectively. This vicariant distribution is believe d to be a result of the disjunction and rotation of the Sardinia-Corsi ca microplate from the Pyrenean region and suggested dates for each cl adogenetic event are available. A total of 915 bp from 12S and 16S rib osomal rRNA genes were compared for each taxon. These are the first mt -rDNA sequence data for salamanders. Sequences were used to reconstruc t 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) pro duced trees with identical topologies and similar bootstrap values ass ociated with each node. These sequence data cannot unambiguously resol ve the splitting events leading to the main radiation of the genus Tri turus and the origin of the genus Euproctus. These events may well hav e occurred very close in time, consistent with other sorts of data. Al though it is unlikely strict linearity holds for all kinds of substitu tions, relative rate tests of the molecular clock hypothesis could not reject clock-like behavior of sequence changes along Euproctus lineag es. Estimates of absolute rates of base changes are 0.35% per Myr sinc e divergence for all substitutions and 0.14% per Myr for transversions ; these estimates are similar to other vertebrate estimates. A compari son with distance measures from allozyme studies agrees quite well wit h regard to relative divergences of the three Euproctus species.