Date of Award

2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Many animals have color signals used during aggression. While most often males are colorful and aggressive while females are cryptically-colored and less aggressive, in some species both males and females are colorful and aggressive. However, such species have received relatively less study. In the mountain spiny lizard, Sceloporus jarrovii, both males and females have bright blue abdominal patches displayed during aggressive interactions. In this exploratory study, I used this species to examine possible signaling functions of adult female color and its relationship to aggression in agonistic encounters. Chapter 1 presents a study that aimed to identify phenotypic correlates of the color signal. I quantified color attributes of natural coloration and examined associations with phenotypic measures of body size (body length, body mass), bite force, health status including white blood cell (WBC) measures, Plasmodium parasite loads, mite loads, and plasma corticosterone level. Not surprisingly, patch size was positively associated with body size. The only variable significantly correlated with blue coloration was WBC counts (negative correlation). Furthermore, WBC counts were significantly positively correlated with corticosterone level. Hence coloration may signal health. Chapter 2 presents an experimental study examining abdominal coloration and female-female interactions. I manipulated coloration by painting abdominal patches either off-white or blue, then conducted staged trials in which I presented a paint-manipulated stimulus” female to a free-ranging focal” female, and then measured responses of the free-ranging focal” female (rates of behaviors, latency to respond). I did not detect an effect of paint treatment on focal female behavior, , although I could not experimentally control size differences of females in trial pairs due to limited sample sizes. Using a Akaike Information Criterion approach, the best predictors of focal aggression were body size, bite force, and corticosterone levels, suggesting that female aggression in my data set was most influenced by body size, strength, and glucocorticoids. Future work should examine whether ultraviolet properties of the abdominal patches function in signaling and conduct a paint manipulation study in which size differences are experimentally controlled.

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