STRUCTURAL AND MOLECULAR APPROACHES TO THE PHYLOGENY OF AMPHIBIA

The structuralistic and molecular approaches to the phylogeny of livin g amphibians are briefly reviewed with emphasis on recent paleontologi cal findings supporting their possible origin from Paleozoic branchios aurids; however the scarcity of early Mesozoic fossils improves the we ight of neontological research on the problem of interorder relationsh ips of lissamphibians. Ontogenetic studies have provided many new fact s of phyletic interest, even if the larvae of urodeles on the one hand , and of anurans on the other, seem to assume extremely different biol ogical roles, and are then scarcely comparable with each other. Change s in temporal programming of moprphogenetic processes severely modify adult morphophysiology at a probably low genetic cost; neoteny and ped omorphosis have effectively characterized the natural history both of extinct and living amphibians, and seem to constitute powerful preadap tive mechanisms opening new econiches and paralleling the radiation of speciose genera or tribes of lissamphibians. Heterochronic processes find a counterpart at karyological level because both genome size and karyotype morphology are modified with the ontogenetic repatterning ch aracterizing these taxa. The importance (if any) of repetitive DNA fra ctions (especially satellite sequences) in the production of microevol utionary changes is currently under examination, and in the future wil l probably modify the perhaps too mechanicistic vision linking protein changes to specific evolutionary trends, giving more weight to the ro le played by non-transcriptive genomic components in the control of mo rphogenetic processes, and thus in producing adaptation and evolution.