Meeting Abstract
Northern (Glaucomys sabrinus) and southern (G. volans) flying squirrels have glucocorticoid (GC) levels that are considerably higher than those in the majority of vertebrates, but oddly, this is coupled with virtually no binding capacity for their GCs via the protective carrier protein, corticosteroid-binding globulin. These GC values however, come from blood samples taken after squirrels had been in live-traps for 2-3 hours. Obtaining baseline values for endocrinological and haematological variables is valuable for assessing the response of vertebrates to events in their environment, and thus in the current study, we compared baseline plasma total cortisol levels (collected within 3 minutes of capture) to acute stress-induced levels in the same individuals (collected after 30 minutes of trap-restraint stress) to evaluate stress axis-function in two species with unique physiology. We also measured five other indices of stress responsiveness (androgens, free fatty acids, glucose, hematocrit and neutrophil:lymphocyte ratio) and compared these with values reported for other vertebrates. In both species, baseline cortisol levels were among the highest reported for any vertebrate, exceeding stress-induced levels in most other species. Although, as predicted, cortisol and free fatty acids increased with acute stress, the remaining variables displayed patterns that differed from most other species. The selective factors driving the stress response in New World flying squirrels remain elusive, but this lineage may provide an interesting new model for the study of stress axis function and its evolution among wild, domestic and laboratory vertebrates.
