Date of Award

Fall 2007

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Michelle P Scott


Several environmental factors and endocrine mechanisms were examined which may affect the intensity of aggression displayed by female red-backed salamanders (Plethodon cinereus) during nest guarding. In a set of behavioral experiments, female were challenged by conspecific intruders during egg guarding and intensity of aggression was scored. Four variables were examined: (1) clutch age, (2) clutch size, (3) sex of intruder, and (4) body size of the attendant. In a second set of experiments, tissue samples were taken from challenged and unchallenged brooding females to compare testosterone (T) titers. A novel non-lethal technique was developed for extraction and assay of T using autotomized tail tissue, and a seasonal profile of T for males and females was determined.

My results suggest that: (1) there are consistent behavioral differences among individuals in females' response to an intruder, (2) females defend late-stage eggs more aggressively than early-stage eggs, (3) females aggressively defend both large and small clutches, (4) females are aggressive toward both male and female intruders and (5) aggression is not correlated with body size. T titers are highest in males in autumn when females are competing for mates, and highest in gravid females in spring when they are searching for nest sites. T is significantly higher in brooding females that are challenged by a conspecific intruder than in unchallenged females.