Meeting Abstract
Mysticete whales are generally assumed to have seasonal reproductive cycles, inferred from seasonal timing of births. However, due to difficulties in obtaining endocrine samples from large whales, there is little direct evidence for potential annual cycles in the reproductive hormones. We have recently demonstrated that steroid hormones accumulate in whale baleen as it grows, such that a single piece of baleen contains a multi-year timeline of hormones along the length of the baleen plate. In females, reproductive events such as pregnancy can be accurately reconstructed from hormone profiles in baleen, but males have not yet been investigated. We present here the first testosterone data from baleen of a male whale, using a baleen plate of a single adult male bowhead (Balaena mysticetus) as an initial test case. Baleen was sampled every 2 cm along the 204 cm plate. Steroid hormones were extracted with a methanol vortex method, and testosterone was assayed with an EIA previously validated for bowhead baleen. Testosterone was detectable in all samples and showed prominent repeating cycles, with thirteen peaks evenly spaced every 16-17 cm along the full length of the baleen plate, corresponding well to estimated annual baleen growth rate for male bowheads of this size class. Though data are as yet limited to a single case study, the regularly spaced peaks match predictions for annual testosterone cycles, and suggest that whale baleen may prove a fruitful resource for investigation of reproductive cycles in the mysticete whales.
