Divergence in the Island Night Lizard Xantusia riversiana (Sauria: Xantusiidae)

The island night lizard, Xantusia riversiana Cope (Fig. 1), is found only on Santa Barbara, San Clemente, and San Nicolas Islands off southern California (Fig. 2). The species is sufficiently divergent in morphology from its mainland relatives, X. vigilis Baird and X. henshawi Stejneger (Fig. 1), that it has been placed in the monotypic genus Klauberina by Savage (1957, 1963). Regardless of whether it is accorded generic (Savage 1957) or subgeneric (Bezy 1972) rank, X. riversiana is clearly more divergent than the other living vertebrates of the California Channel Islands, suggesting that it may have been present longer than other species on one or more of the islands. Moreover, casual observations indicate that there may be greater morphological differences between the island populations of X. riversiana than were documented by earlier work (Savage 1951, Smith 1946). In an effort to further clarify the evolutionary history of the species, we have compared electrophoretically determined genetic-distances and divergence time estimates between the island populations with those between the species of Xantusia, and have reappraised inter-island differences in karyotypes, scalation, coloration, body size, clutch size, and variability.