Polymorphic Protection Hypothesis Not Supported in the Bunchgrass Lizard, Sceloporus slevini

Undergraduate #14
Discipline: Biological Sciences
Subcategory: Ecology

Dallas Davidson - Virginia State University

Pattern polymorphism, the presence of two or more patterns (morphs) within a species, serves as a model system for testing hypotheses in evolution and ecology. Research on polymorphism is important in its broad scope and the implications for species survival. For example, the “polymorphic protection hypothesis” proposes that pattern polymorphism decreases predation by visual predators on the more cryptic pattern. However, despite the potential advantage of pattern polymorphism to a species, of the 97 species of ectothermic spiny lizards (Sceloporus spp.), only Slevin’s Bunchgrass lizard, Sceloporus slevini, exhibits pattern polymorphism. We tested the polymorphic protection hypothesis, positing that the unicolor pattern (lacks dorsal pattern of spotting) provides a greater degree of cryptic coloration and is thus less vulnerable to predation than the regular pattern. To test this hypothesis we examined individuals from three populations of S. slevini in southeastern Arizona. Data recorded for each individual were: GPS location, sex, snout-vent length to nearest 0.01 mm, pattern (regular or unicolor) and tail autonomy (breakage). Tail autonomy is one indicator of predation pressure in lizards. We used paired T-tests to examine if significant differences existed between body sizes of the morphs. Chi-square tests were used to test intra-population comparisons of size and tail autonomy. Data were collected from 349 lizards. Regular patterned individuals made up 80% of the captures, while unicolor individuals represented 20%. There was no significant size differences between morphs. The percentage of tail autonomy between morphs and sexes showed no significant difference. In conclusion, we found no support for the polymorphic protection hypothesis. Future research will focus on the role of female mate choice between morphs, determining the genetic basis for pattern polymorphism and exploring the role of pattern polymorphism in species survival under increasing environmental temperatures.

References: Anderson, J.D. 1972. Pattern polymorphism in the Bunch-grass lizards, Sceloporus scalaris slevini. Journal of Herpetology 6:80.
Forsman, A., J. Ahnesjo, S. Caesar and M. Karlsson. 2008. A model of ecological and evolutionary consequences of color polymorphism. Ecology 89:34-40.
Karpestam, E., S. Merilaita and A. Forsman. 2014. Natural levels of colour polymorphism reduce performance of visual predators searching for camouflaged prey. Biological Journal of the Linnean Society 112:546-555.

Funder Acknowledgement(s): We thank D. Hardy, A. Harris, and A. White for help in the field. L. Kennedy at the Audubon Appleton-Whittell Research Ranch and the Southwestern research Station of the New York Museum of Natural History provided logistic support. This study was supported in part by a grant from the National Science Foundation HBCU-UP to Dr. Christian d'Orgeix, Department of Biology, Virginia State University, Petersburg, VA 23806.

Faculty Advisor: Christian d'Orgeix,