KUCHTA, S R: Color pattern evolution in a ring species: Does Ensatina eschscholtzii xanthoptica mimic newts (genus Taricha)?

The salamander Ensatina eschscholtzii in California consists of seven subspecies distributed in a ring around the Central Valley. Transitions among adjacent subspecies are generally gradual, with the exception of two sympatric, reproductively isolated subspecies in southern California. Ensatina is thus a “ring species.” Subspecies of Ensatina are distinguishable by color pattern, and color patterns are considered adaptive, yet the adaptive reasons for color pattern evolution remain speculative. I experimentally tested the hypothesis that E. e. xanthoptica is mimetic of the extraordinarily toxic newts in the genus Taricha. Sympatric E. e. xanthoptica and Taricha share a brown dorsum, yellow iris patch, and orange ventral surface; the orange ventral coloration in Taricha is aposomatic. For the experiment, 450 plasticine (soft modeling compound) models were made from a mold of an Ensatina. Half the models were painted like “xanthoptica“, and half lacked all orange and yellow (“brown”). The models were placed in random order along nine transects through closed canopy oak/bay woodland. All models were placed on a white piece of paper, so differences in predation rate could not be attributed to crypsis. The models were collected after 24-25 days and scored for attacks (plasticine models “record” attacks via imprints in the model). The “xanthoptica” models were attacked significantly less often than the “brown” models (G-test, p<0.5), and attacks were disproportionately located on the head (G-test, p<0.5). This suggests that the orange/yellow coloration deters predation, and supports the hypothesis that E.e. xanthoptica mimics newts.