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

Abstract

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 0.8-38years. 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 8-12years. 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 (≥13years), those classified as aged (≥31years) 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.