CHARACTER DISPLACEMENT IN SOME CNEMIDOPHORUS LIZARDS REVISITED - A PHYLOGENETIC ANALYSIS

Ecological studies have demonstrated the role of competition in struct uring communities; however, the importance of competition as a vehicle for evolution by natural selection and speciation remains unresolved, Study systems of insular faunas have provided several well known case s where ecological character displacement, coevolution of competitors leading to increased morphological separation, is thought to have occu rred (e.g., anoline lizards and geospizine finches), Whiptail lizards (genus Cnemidophorus) from the islands of the Sea of Cortez and the su rrounding mainland demonstrate a biogeographic pattern of morphologica l variation suggestive of character displacement, Two species of Cnemi dophorus occur on the Baja peninsula, one relatively large (Cnemidopho rus tigris) and one smaller (Cnemidophorus hyperythrus). Oceanic islan ds in the Sea of Cortez contain only single species, five of six havin g sizes intermediate to both species found on the Baja peninsula, On m ainland Mexico C. hyperythrus is absent, whereas C. tigris is the smal ler species in whiptail guilds, Here we construct a phylogeny using nu cleotide sequences of the cytochrome b gene to infer the evolutionary history of body size change and historical patterns of colonization in the Cnemidophorus system, The phylogenetic analysis indicates that (i ) oceanic islands have been founded at least five times from mainland sources by relatives of either C, tigris or C. hyperythrus, (ii) there have been two separate instances of character relaxation on oceanic i slands for C. tigris, and (iii) there has been colonization of the oce anic island Cerralvo with retention of ancestral size for Cnemidophoru s ceralbensis, a relative of C, hyperythrus. Finally, the phylogenetic analysis reveals potential cryptic species within mainland population s of C, tigris.