Meeting Abstract
Whale baleen accumulates steroid hormones as it grows, such that a single baleen plate can be used to reconstruct an individual’s endocrine history over the timespan of baleen growth, 1-2 decades in bowhead whales (Balaena mysticetus). We analyzed testosterone (T) and corticosterone (B) in baleen of nine adult males from eastern Canada and Greenland to infer breeding season and frequency, and associated adrenal activity. Baleen plates of 184-314 cm length were drilled at 2 cm intervals (each interval representing ~1-2 mo), followed by assay of immunoreactive T and B. T concentrations cycled along baleen of all nine males. Average T periods ranged from 21 cm in the smallest whales to 14 cm in the largest whales, consistent with annual bowhead baleen growth rates and differential growth rate associated with age (slower in older individuals). Change in T peak amplitude over time was significantly related to whale body length (a proxy of age), suggesting influences of sexual immaturity, reproductive competition, and possible reproductive senescence. Annual T peaks were strongly correlated with stable nitrogen isotope (δ15N) peaks in summer but with an offset of several months, indicating elevated T concentrations during spring, the purported breeding season. B concentrations cycled synchronously with T in some males, while variation was irregular in others, consistent with known bowhead whale breeding behavior (i.e. likely differences in reproductive competitiveness). We conclude that male bowheads experience annual testosterone cycles, and that baleen hormone analysis enables investigation of reproductive seasonality in whales.
