Variation of bowhead whale progesterone concentrations across demographic groups and sample matrices

Abstract

Bowhead whale Balaena mysticetus progesterone concentrations were measured in different sample matrices (serum, blubber, and urine) to investigate (1) concordance among sample type and (2) variation among life-history class. Samples were collected from subsistence-hunted whales (n = 86) taken from 1999 to 2009. In general, irrespective of sample matrix, pregnant females had the highest concentrations by orders of magnitude, followed by mature animals of both sexes, and subadults had the lowest concentrations. Subadult males and females had similar progesterone concentrations in all sample matrices measured. When pregnant animals were included in our analyses, permuted regression models indicated a strong positive relationship between serum and blubber progesterone levels (r2 = 0.894, p = 0.0002). When pregnant animals were not included, we found no significant relationship between serum and blubber levels (r2 = 0.025, p = 0.224). These results suggest that progesterone concentrations are mirrored in these sample types over longer periods (i.e. on the order of weeks to months, time frame of reproductive changes) but not shorter periods (i.e. on the order of hours to days, time frame of daily fluctuations). This conclusion is consistent even for progesterone concentrations measured in females that had recently changed pregnancy states (either new mothers or newly pregnant animals), for which blubber progesterone levels seem to lag those in the serum. Finally, urine progesterone had statistically significant positive relationships with serum (r2 = 0.136, p = 0.0460) and blubber progesterone (r2 = 0.150, p = 0.0421). Our results suggest that progesterone concentrations first peak in the serum, then in the urine, and finally in the blubber.