Available at: https://digitalcommons.calpoly.edu/theses/1504
Date of Award
MS in Biological Sciences
Emily Taylor, PhD
Hydration is a critical element for many physiological processes in vertebrates, such as protein production, innate immunity, and behavioral processes such as daily activity and thermoregulation. Few studies have directly assessed the effect of hydration on these animals in nature. While it seems intuitive that drought is stressful to animals, studies examining drought are typically observational and fail to assess how the hydration state of these animals influences their physiology and behavior. We tested for an effect of hydration on several physiological and behavioral parameters in Northern Pacific rattlesnakes (Crotalus oreganus oreganus) by experimentally manipulating hydration levels in the field. Two treatment groups were created: one of these received supplemental hydration twice a month from May to September (hydrated) while the other did not (control). Pregnant females were brought to the lab before parturition to collect data on litter characteristics. We radio-tracked snakes to examine any effects on movement, measured SVL and mass of each snake throughout the study for assessment of body condition, and collected blood samples for stress hormone physiology. Finally, we used intra-coelomic temperature data loggers to track body temperature data for each individual snake every two hours.
Our results suggest that supplemental water and thus hydration has a significant effect on reproduction as all four hydrated females gave birth to a litter, while no control females gave birth. We saw no effect on movement parameters; however, males had larger home ranges and moved a larger total distance than females, regardless of hydration status. Interestingly, body condition was significantly higher in hydrated snakes, suggesting that hydrated individuals were acquiring more food than control snakes. We saw no effect on stress hormone physiology. There was no influence of hydration on any behavioral parameters such as time spent above or below ground, or time spent in a particular body position. Finally, there was a significant interaction of treatment group and sex on seasonal body temperature. Hydrated females had higher mean body temperatures than all other treatment group and sex combinations. However, all hydrated females were also pregnant, which confounds this result. Similar results were seen when body temperature was analyzed by time of day. Females overall had higher body temperature than males.
These results suggest that hydration may have a profound influence on reproduction and has the potential to affect body condition and thermoregulation. The lack of an effect on movement and stress physiology should not be overlooked, however. This study is the first to experimentally manipulate hydration in free-ranging rattlesnakes and one of the few to manipulate hydration in vertebrates. More studies are needed to support a pivotal role of hydration in physiology and behavior of reptiles and we encourage the use of experimental field manipulations to answer these questions.