Fay, Michelle (1998)
The Effects of Trapping and Handling Stress on Measured Hormone Levels in Free-Living Rodents.
Bachelor of Science, Harvey Mudd College, Biology.
Advisor: Gene Fowler.
One focus of biological study in recent years has been the correlation of circulating levels of hormones with reproductive behavior, particularly mating systems. In order to study hormone of animals living in the wild, the animals must be captured before a blood sample can be collected. In the case of nocturnal rodents, capturing animals may consist of setting out baited live-traps at dusk, and collecting the traps at dawn. However, this method may yield unrepresentative hormone measurements; if being trapped causes stress, stress hormones may change the levels of reproductive hormones contained in blood samples. Stress is known to inhibit secretion of reproductive hormones so that an organism can conserve energy for the more immediate need of reacting to the stressor. The current study examines the question of whether trapping stress substantially affects measured reproductive hormone levels in wild rodents, as a precursor to a comparative study of annual reproductive hormone profiles in three species (Peromyscus californicus, Peromyscus maniculatus, and Neotoma fuscipes) with distinct mating systems. This question was approached by comparing hormone levels in rodents whose blood was sampled immediately upon collection of the trap in the morning with hormone levels in rodents subjected to additional stress before blood was sampled. Additional stress was found to increase levels of corticosterone, a major stress hormone, implying that rodents are not maximally stressed in the morning after a night in the trap.