A MOLECULAR PHYLOGENY FOR MARINE TURTLES - TRAIT MAPPING, RATE ASSESSMENT, AND CONSERVATION RELEVANCE

Nucleotide sequences from the cytochrome b gene of mitochondrial DNA w ere employed to resolve phylogenetic controversies and to assess molec ular evolutionary rates in marine turtles (Chelonioidea). Findings of special relevance to conservation biology include discovery of a dista nt relationship between Natator and other cheloniid species, the parap hyly of Chelonia mydas with respect to Chelonia agassizi, and genetic distinctiveness of Lepidochelys kempi from Lepidochelys olivacea. A lo ngstanding debate in evolutionary ecology was resolved by phylogenetic mapping of dietary habits, which indicates that the spongivore Eretmo chelys imbricata evolved from a carnivorous rather than a herbivorous ancestor. Sequence divergences at intergeneric and interfamilial level s, when assessed against fossil-based separation times, support previo us suggestions (from microevolutionary comparisons) that mitochondrial DNA in marine turtles evolves much more slowly than under the ''conve ntional'' vertebrate clock. This slow pace of nucleotide replacement i s consistent with recent hypotheses linking substitution rate to gener ation length and metabolic pace.