Abstract

Recent captive white whale (also called beluga whale) (Delphinapterus leucas) breeding successes have led to an increased effort to manage white whale reproduction among several zoos and aquariums in North America. Knowledge of cetacean reproductive physiology is necessary for optimal captive management and propagation. Most studies have concentrated on bottlenose dolphins (Tursiops truncatus) or killer whales (Orcinus orca), and the basic parameters of their reproductive cycles have been determined, but little research has been devoted to white whales. The bottlenose dolphin and killer whale are polyestrous year round, while the white whale has a strictly seasonal reproductive pattern. The endocrine knowledge of these other species, therefore, is not directly applicable to the white whale. In addition, the reproductive physiologic research that has been conducted on the white whale has focused on the female reproductive cycle. The present study investigated the seasonal pattern of testosterone secretion in male white whales.

A double-antibody [¹²⁵I] testosterone radioimmunoassay (ICN, Costa Mesa, CA) was validated for unextracted male white whale serum or heparinized plasma. The antiserum cross-reacts 100% with testosterone, 3.4% with 5 alpha-dihydrotestosterone, 2.2% with 5 alpha-androstane-3B-17B-diol, 2.0% with 11-oxotestosterone, and < 1% with all other steroids tested. Parallel displacement curves were obtained by comparing serial dilutions of pooled white whale serum with testosterone standards. Inter-assay coefficients of variation for the two separate internal controls were 16.8% and 8.5%. Intra-assay coefficients of variation were < 10% and assay sensitivity was 0.05 ng/ml. Recovery of known amounts of unlabeled testosterone added to a pool of diluted white whale serum was 123.4% ± 11.9% (y = 0.06 + 1.05x, r² = 0.99). RIA of eluates after HPLC¹ revealed all immunoreactivity to be associated with a single peak that co-eluted with testosterone.

Six (The New York Aquarium, SeaWorld San Antonio, Mystic Aquarium, U.S. Navy Marine Mammal Program, John G. Shedd Aquarium, and Vancouver Aquarium Marine Science Centre) North American institutions that maintain male white whales participated in this study. Serum or heparinized plasma samples (304 samples; 2-60 samples/animal) were received from 11 males (ranging in age from 3-21 yr at the time of sampling) obtained over a 15-yr interval (1983 to 1998). The lowest mean levels of circulating testosterone occurred in September (0.9 ng/ml) and the highest mean levels occurred 6 mo later in March (4.95 ng/ml). Mean testosterone levels gradually rose throughout the fall and were elevated (> 3.5 ng/ml) from January through April. Testosterone then declined to the nadir in September (Table 1). Due to the small number of samples across ages the data were not divided into age groups. Inclusion of samples from sexually immature whales probably lowered mean testosterone values.This collaborative endocrinology study resulted in the successful development of a validated assay for circulating white whale testosterone. In addition it described a pattern of cyclic seasonal testosterone variation in the male white whale consistent with the seasonal reproductive pattern of the species. These results augment and complement ongoing reproductive physiology studies of the female white whale that we are conducting. Together, the data generated will contribute to our knowledge of comparative reproductive physiology. In addition, it will provide valuable information that can be used by animal managers and veterinarians to better manage white whale reproduction or assess causes of reproductive failure.

Table 1. Mean circulating testosterone levels of male white whales (Delphinapterus leucas).

Acknowledgments

The authors acknowledge and thank the keepers, trainers, and veterinary technicians at all the institutions whose assistance made this project possible. We also thank Charles Potter, Smithsonian Institution and Kendall Mashburn, Smithsonian Institution Conservation and Research Center for technical assistance and Dr. Brian Joseph, The Point Defiance Zoo and Aquarium, for support of the collaborative whale management program. This project was funded by a grant from the Wildlife Conservation Society's Species Survival Fund.

References

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