A MOLECULAR PHYLOGENY OF TRUE SALAMANDERS (FAMILY SALAMANDRIDAE) AND THE EVOLUTION OF TERRESTRIALITY OF REPRODUCTIVE MODES

Key innovations enable species to conquer new habitats. Within the fam ily Salamandridae, particular adaptations to terrestrial life, such as the anatomy and physiology of the feeding apparatus, courtship behavi our and in some cases viviparity, allowed the 'true' salamanders (gene ra Chioglossa, Mertensiella, Salamandra) to shift from a semi-aquatic to a more terrestrial life cycle. We sequenced 423 base pairs of the 1 6S RNA gene of the mitochondrial DNA. for all species of the 'true' sa lamanders. Based on the resulting phylogeny we discuss the evolution o f terrestrial reproductive modes within this species group. We especia lly tested two hypotheses of monophyletic origin of specific adaptatio ns to terrestriality within the 'true' salamanders: Mertensiella cauca sica/Mertensiella luschani, whose congeneric relationship has already been questioned on the basis of morphological, behavioural and molecul ar data, and Salamandra atra/Salamandra lanzai, the two species of Alp ine salamanders, which are characterized by melanism and matrotrophic viviparity. We tested alternative tree topologies and included additio nal published and unpublished data on morphology, allozyme polymorphis ms, and further mtDNA sequences. Maximum parsimony and maximum likelih ood analyses always rejected the hypothesis of monophyly of the two Me rtensiella species. Although data on courtship behaviour of 'true' sal amanders indicate the loss of a symplesiomorphic tail projection in Sa lamandra and Chioglossa, the most parsimonious explanation may at pres ent be a convergent evolution of the projection as indicated by recent histological studies. Although our DNA sequence and additional allozy me data suggest that S. atra and S. lanzai do not form a monophyletic group despite their geographic proximity and shared traits, we cannot reject their monophyly. Using the flooding of the Strait of Gibraltar five million years ago for the separation of African and European spec ies, a molecular 16S RNA clock was calibrated with 0.7% total sequence divergence per million years. Estimated times of divergence for furth er evolutionary splits within 'true' salamanders coincide with paleoge ographical data.