Stress Induced Color Change in Southern Pacific Rattlesnakes (Crotalus helleri)

Claunch, Natalie M.

Frazier, Julius A.

Department of Biological Sciences

California Polytechnic State University

San Luis Obispo, CA 93407, USA

Moore, Ignacio T.

Department of Biological Sciences

Virginia Polytechnic Institute and State University

Blacksburg, VA 24061, USA

Metachrosis, or color change, in reptiles has been of interest to herpetologists for a long time. Some species use it for thermoregulation or crypsis, but in many species the function and physiological mechanisms of metachrosis remain unknown. Anecdotes from herpetologists claim that some species, including rattlesnakes, undergo metachrosis when captured and placed in bags or buckets. A possible explanation for this color change is the release of their primary stress hormone, corticosterone. In this study, we implanted twenty-six wild Southern Pacific rattlesnakes (Crotalus helleri) intra-coelomically with either corticosterone or sham silastic implants. At 0 weeks (pre-implant), 2 weeks, and 4 weeks post-implant, the snakes were recaptured, bled, and photographed under standardized lighting in a curtained box. We used Adobe Photoshop to quantify light value of the dark and light bands of the snakes’ tails and examined the relationship of these variables to baseline corticosterone levels. In addition, at 4 weeks post-implant, we assessed color change resulting from elevation of corticosterone from baseline levels after one hour of acute confinement stress. We found that baseline and acutely elevated corticosterone, regardless of implant treatment, were positively correlated with the lightness value of the light bands, but had no relationship with that of the dark bands. This ultimately led to increased contrast between the light and dark bands in snakes with higher corticosterone. This study is the first to quantify the relationship between corticosterone and color change in snakes, suggesting that hormones might mediate color change in response to stressors.