Character displacement in some Cnemidophorus lizards revisited: A phylogenetic analysis

Ecological studies have demonstrated the role of competition in structuring 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 cases where ecological character displacement, coevolution of competitors leading to increased morphological separation, is thought to have occurred (e.g., anoline lizards and geospizine finches). Whiptail lizards (genusCnemidophorus ) from the islands of the Sea of Cortez and the surrounding mainland demonstrate a biogeographic pattern of morphological variation suggestive of character displacement. Two species ofCnemidophorus occur on the Baja peninsula, one relatively large (Cnemidophorus tigris ) and one smaller (Cnemidophorus hyperythrus ). Oceanic islands in the Sea of Cortez contain only single species, five of six having sizes intermediate to both species found on the Baja peninsula. On mainland MexicoC. hyperythrus is absent, whereasC. tigris is the smaller species in whiptail guilds. Here we construct a phylogeny using nucleotide sequences of the cytochromeb gene to infer the evolutionary history of body size change and historical patterns of colonization in theCnemidophorus system. The phylogenetic analysis indicates that (i ) oceanic islands have been founded at least five times from mainland sources by relatives of eitherC. tigris orC. hyperythrus , (ii ) there have been two separate instances of character relaxation on oceanic islands forC. tigris , and (iii ) there has been colonization of the oceanic island Cerralvo with retention of ancestral size forCnemidophorus ceralbensis , a relative ofC. hyperythrus . Finally, the phylogenetic analysis reveals potential cryptic species within mainland populations ofC. tigris .