Justine K. O'Brien; Karen J. Steinman; Todd R. Robeck*
SeaWorld and Busch Gardens Reproductive Research Center, SeaWorld Parks and Entertainment Inc., San Diego, CA, USA
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 throughout periods ranging from 2 to 22 years in 14 male killer whales (Orcinus orca) aged 0.8–38 years, for examination of the relationships of age, sexual maturation status (STATUS), season, and environmental temperature (monthly air temperature, A-TEMP) with hormone production using a mixed model linear regression 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 months, and a positive association (p < 0.05) of testosterone with A-TEMP was noted. 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 spring and summer than the fall. Among adult males (≥ 13 years), those classified as aged (≥ 31 years) had concentrations of T 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 not affected by STATUS, season, nor 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.
The authors thank the curatorial, training, and veterinary staff at SeaWorld San Diego, San Antonio, and Orlando for blood sample collection and processing, and the SeaWorld and Busch Gardens Reproductive Research Center staffs and intern students for sample collation and hormone assays. The authors are also grateful to Mr. Brad Andrews of SeaWorld Parks and Entertainment (SEA) for continued support of this research.
* Presenting author