EVOLUTIONARY GENETICS OF BIRDS. VI. A REEXAMINATION OF PROTEIN DIVERGENCE USING VARIED ELECTROPHORETIC CONDITIONS

The recent application of multilocus protein-electrophoretic techniques to avian taxa has led to a rather surprising generalization: genetic distances between lower taxa of birds are exceptionally small compared to those observed between many other vertebrates of equivalent levels of taxonomic distinction (Smith and Zimmerman, 1976; Barrowclough and Corbin, 1978; Avise et al., 1980a, 1980b, 1980c, 1982; Barrowclough et al., 1981; Yang and Patton, 1981; Patton and Avise, unpubl.; Avise and Aquadro, 1982). For example, species of amphibians currently placed within a given genus are, on average, 11-22 times more divergent than congeneric avian species when assayed by common gel electrophoretic conditions (for a comprehensive review of genetic distances in vertebrates, see Avise and Aquadro, 1982). Genetic distances among fish, mammal and reptile congeners typically fall intermediate to those exhibited by amphibians and birds. This "conservative" pattern of protein evolution is not restricted to passerine birds but has also been observed in anseriforms (waterfowl: Patton and Avise, unpubl.) and procellariiforms (tube-nosed birds: Barrowclough et al., 1981). Evidence also exists for a conservative level of immunological divergence in albumins and transferrins among avian orders (Prager et al., 1974; but see Wilson et al., 1977). Perhaps the most striking example of the apparent protein conservatism in birds involves