Androgen and glucocorticoid production in the male killer whale (Orcinus orca): influence of age, maturity, and environmental factors.

Circulating concentrations of testosterone and its precursor androstenedione, as well as dehydroepiandrosterone (DHEA) and the adrenal hormones cortisol and corticosterone were measured at monthly intervals in 14 male killer whales (Orcinus orca) aged 0.8-38 years. Analyses were performed for examination of the relationships of age, sexual maturation status (STATUS), season, and environmental temperature (monthly air ambient temperature, A-TEMP) with hormone production using a mixed effects linear regression model with animal ID as the random variable. Hormone profiles, derived from enzyme immunoassay procedures validated herein, established that simultaneous up-regulation of androstenedione and testosterone production occurs at puberty, when males are aged 8-12 years. Androgen (testosterone and androstenedione) production in pubertal and adult males was influenced by season, with highest (p < 0.01) concentrations observed in spring and summer months. A significant effect of STATUS and season on DHEA production was also documented, with higher (p < 0.05) concentrations in pubertal and adult males compared to juvenile males, and higher (p < 0.05) concentrations in the months of summer than the fall. Among adult males (≥13 years), those classified as aged (≥31 years) had concentrations of testosterone and both glucocorticoids that were lower (p < 0.05), and those of androstenedione that were higher (p < 0.05) than their younger counterparts. The cortisol:corticosterone ratio for adult males was 7 : 1, and both glucocorticoids were affected by STATUS (p < 0.05), but not season or A-TEMP. Results of this research enhance our understanding of reproductive and adrenocortical function in healthy male killer whales and provide baseline profiles of hormone production for use in the species' health assessment and conservation.

Glucocorticoids of bison bulls in relation to social status.

A primary response to stress is an increase in circulating adrenal glucocorticoids (GC) such as cortisol. Two hypotheses propose differential stress responses to agonistic and aggressive interactions in social groups. If subordinate animals are subjected to social and psychological stressors leading to chronic GC elevation, the 'stress of subordination' hypothesis predicts that GCs will be higher in subordinates than dominants. Alternatively, if dominant animals are subject to physiological stressors (e.g., fight at higher rates than subordinates) or hierarchies are unstable, the 'stress of domination' hypothesis predicts higher GCs in dominant individuals. Both models predict that GC levels will peak during the breeding season. We tested these predictions in bison bulls (Bison bison) using fecal steroid analysis to characterize GC concentration and behavioral observations to determine dominance rank, copulatory success, and tending status of bulls. Fecal samples were collected during 2003 from adult bison bulls during pre-rut (June), rut (July-August), and post-rut (September). Matched sample data indicated that mean GC levels (ng/g feces) of bulls strongly peaked during the 4-week rut, doubling from pre-rut to rut and then declining again during post-rut. High ranked dominant bulls maintained higher GC levels than lower ranked subordinate bulls. Dominance rank was positively correlated with copulatory success and age, and dominant bulls were more likely to tend (guard) cows as they approached estrus. There was a positive correlation between GC level and copulatory success, with prime-aged bulls (> or =7 years) obtaining the most copulations. GC levels were positively correlated with bull androgen levels determined in a previous study. These results support the 'stress of domination' hypothesis, indicating that dominant bison bulls pay a significant physiological price for high social status and the opportunity to mate.