Year of Award

2010

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

Vanessa Ezenwa

Commitee Members

Creagh Breuner, Jon Graham, Scott Creel

Keywords

aggression, behavioral ecology, glucocorticoids

Abstract

Testosterone plays an important role in male competitive ability, and it may play a similar function in females. Female-female competition for resources is often associated with high testosterone, both within females and in comparison to males. Positive associations between testosterone and competition are most likely to be seen in systems with high female-female competition. Resource defense polygyny may be one such system since females congregate on high-quality nutrient sources, leading to substantial opportunities for interference competition. I studied female Grant’s gazelle (Nanger granti), a classic resource defense polygynous species, to investigate female competition and its relationship to testosterone. I found substantial evidence for competition between females. Females frequently engaged in agonistic behavior, on average initiating over two agonistic bouts per hour, and higher-ranking females initiated more agonism than lower-ranking females. Testosterone appeared to play an important role in competitive ability. Immunoreactive fecal testosterone metabolites (fT) were strongly positively correlated to both dominance rank and number of agonistic bouts initiated per hour, but only agonism was associated with fT when dominance and agonism were accounted for simultaneously. Females had similar fT concentrations as males. fT was positively associated with immunoreactive fecal glucocorticoid metabolites (fGCM), and this relationship was not due to associations between dominance and fGCM. Month also influenced testosterone physiology. Females had lower fT during a drought than after rains had begun. In addition, fT increased more from August to November in high-ranking females than in low-ranking females. My results suggest that female-female competition may be substantial in resource defense polygynous systems. Testosterone might play an important role in mediating competitive ability in females, but it was also associated with higher glucocorticoid secretion. Future studies on females would be well served to investigate the consequences of testosterone secretion and how they relate to female competition.

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© Copyright 2010 Lars Stefan Ekernas