Morphological Divergence among Populations ofXantusia riversiana,a Night Lizard Endemic to the Channel Islands of California

Abstract

Morphological variation between closely related island endemics offers a unique system to study ecological and evolutionary processes. The Island Night Lizard, Xantusia riversiana (Cope, 1883), is endemic to three of the Southern Channel Islands off the coast of Southern California: Santa Barbara, San Clemente, and San Nicolas. Some authors treat the species as polytypic with the night lizards on San Nicolas (X. r. riversiana) distinct from those on Santa Barbara and San Clemente (X. r. reticulata). Previous studies failed to find strong morphological divergence, but it remains uncertain if those studies were hampered by a combination of small sample size, small number of characters, and/or the lack of modern morphometric techniques. Here we examined 172 Island Night Lizards from the three islands for nine morphometric and five meristic characters, increasing the number and types of morphological characters examined over previous studies and applying modern morphometric techniques to test for divergence a...