Date of Award


Document Type

Campus Access Thesis


Biological Sciences

First Advisor

Blaine D Griffen


Recent evidence suggests that physiological characteristics may be the proximate cause of some animal behaviors. To investigate this claim we conducted two studies examining the relationship between physiology, via internal energy stores, and behavior in the sand fiddler crab,Uca pugilator. Energy stores were quantified through determination of the condition of the hepatopancreas, an internal organ in crustaceans that houses nutrients used in growth and reproduction.

In the first study, energy stores and their relationship with personality in females was examined. Personality is defined as stable expression of a behavioral trait and naturally occurs in one of two ways: context-specifically or context-generally. The former is characterized by consistent responses in only one ecological scenario, whereas the latter is characterized by consistency that spans scenarios. We collected measurements of two behaviors per individual within the contexts of predator avoidance and exploration of a novel environment. Correlations within and between these measurements were examined, as well as their relationship with the mass and lipid content of the hepatopancreas. Results suggest the majority of crabs were bold in the context of hiding time yet shy in the exploration context. This context-specific behavior was not explained by physiology. Our results suggest that flexible expression of personality traits may occur in the absence of an underlying physiological driver.

In the second study, differences in the energy stores of courting and foraging male fiddler crabs were examined. There is abundant evidence that male sexual signaling in this genus is condition-dependent and that current energy reserves may limit courtship behaviors. Therefore, males engaged in each activity were sampled every two weeks for the duration of a mating season and the mass of their hepatopancreases were compared. Sediment organic content was also measured at each sampling event to track food availability throughout the study. We found that hepatopancreas mass was only weakly related to activity (waving or foraging). Additionally, this physiological variable was not significantly affected by variation in sediment organic content within the habitat. Our results suggest that natural fluctuations in food availability and energetic state are not the primary drivers of male fiddler crab behavioral decisions.