Jonathan Richmond

The Western Skink

Jonathan Richmond San Diego State University San Diego, CA

The Western Skink ( Eumeces skiltonianus ) is a small and secretive lizard that is seldom seen by humans. Its wary nature and extreme agility makes it very difficult to catch for both predators and the researchers attempting to study them. With a maximum snout-vent length of 75.0mm, these lizards are typically found under natural debris (i.e. leaf litter, rocks, fallen branches, etc.) in relatively moist conditions. Rocky habitats near streams with abundant plant cover are usually good areas to look for skinks, but they are also known to occur on dry hillsides away from water. They frequent broken chaparral, grassland, pinion juniper, open pine-oak and pine forests. It is the only scincine lizard (i.e. belonging to the family Scincidae) that occurs on Santa Catalina Island, and is most active during the early part of spring when rainfall is most prevalent

Western skinks have vivid color patterns that enable them to readily escape predators. Juveniles and adults have prominent white stripes that extend along the sides of the body and on the back. When disturbed, these lizards propel themselves with a rapid snake-like motion. This side-to-side movement, combined with the bright striping on their back, makes it difficult for predators to pinpoint an exact spot to grasp the animal. Juveniles of predator is quick enough to touch any part of the tail. More often than not, a small portion of the writhing tail is all that is left behind as the lucky lizard escapes into nearby leaflitter.

It is unclear as to how Western skinks arrived on Santa Catalina Island. A general consensus exists that these lizards may have rafted out to the island sometime in the distant past using natural debris as floatation devices. This same mode of dispersal has been used to explain the occurrence of numerous other reptile and amphibian species on the Channel Islands, and has recently been observed in Green Iguanas in the Caribbean within the past year. This species is also found on mainland western North America, Southwestern Canada, and northern Baja California. Three geographic forms (or subspecies) of the Western Skink have been described throughout its geographic range, and it is currently unclear as to which form the Western Skinks on Santa Catalina Island are most closely related. Western skink ( Eumeces skiltonianus ) My research at San Diego State University focuses on the © 1999 Jonathan Richmond mechanisms and processes underlying speciation events. In other words, what are the causal factors contributing to speciation within given groups of organisms. To study this question, I have been using DNA sequences from the Western Skink and its close ev olutionary relatives to infer the phylogeny, or evolutionary history of a species complex. The Western Skink belongs to a species complex commonly referred to as the skiltonianus group. Within this group, four closely related species are currently recognized: the Western Skink ( E. skiltonianus ), the Gilbert's Skink (E. gilberti ), the San Lucan Skink ( E. lagunensis ), and the four-lined Asiatic Skink ( E. quadrilineatus ). The results of the DNA data indicate that there may actually be a number of different species within the currently recognized single species, particularly in the Western Skink and the Gilbert's Skink. In cases such as this, DNA data has helped to elucidate "cryptic species" by detecting independent evolutionary trajectories within a group of closely related organisms. Speciation of the skiltonianus group appears to have been driven by a number of factors, namely fragmentation of once continuous populations into smaller isolated populations. These isolated populations subsequently evolved unique attributes as a result of genetic drift and natural selection. Although these differences are detectable at the genetic level, the external appearance of these lizards is so remarkably similar that researches have previously classified different populations as single species. As more DNA results are interpreted, taxonomic revisions will undoubtedly take place. I hope to soon learn where the Western Skinks from Santa Catalina Island fit into the evolutionary history of the skiltonianus group, which will require a return trip this spring when the lizards become more active. My research is currently Jonathan Richmond in the ongoing at San Diego State University and I welcome any field questions that people may have regarding skinks, myself, © 1999 Jonathan Richmond or of biology in general (or of anything for that matter!).

Jonathan Q. Richmond 5500 Campanile Drive Department of Biology San Diego State University San Diego, CA. 92182-4614 Phone: 619-550-9976 e-mail: [email protected]