Marine wildlife researchers prefer minimally invasive methods when collecting samples for endocrine studies. Samples like respiratory vapor (‘blow’) and blubber are commonly used but have yet to be validated for these purposes for many cetacean species. A recent study reported by Mingramm and Keeley in General and Comparative Endocrinology examined the performance of blow and blubber hormone monitoring for evaluating the reproductive and adrenal condition of captive bottlenose dolphins. Part of the study’s goal was to validate sample collection techniques when assessing female dolphin reproductive status and male dolphin reproductive and maturity status.
Along with standard sampling techniques for serum and blubber, blow samples were collected with inverted 250 mL plastic containers containing nylon mesh secured with parafilm. Concentrations of progesterone, testosterone, estradiol, and cortisol in blow samples were measured using assays and reagents previously validated for serum from Coralie Munro and Arbor Assays. Variability caused by seawater contamination, nylon sampling materials and variable sample volumes was addressed by normalizing blow hormone concentrations relative to urea nitrogen levels (UN, a potential endogenous standard), using the Urea Nitrogen (BUN) Detection kit (K024-H1/H5) from Arbor Assays. Normalized blow hormone levels were expressed as a nanogram of hormone per milligram of UN in the sample and compared to hormone levels in serum and blubber samples.
Patterns in hormone levels were similar for serum and blubber. For example, progesterone levels were significantly higher in pregnant than non-pregnant females. This pattern was not detected in blow samples because hormone measurements were strongly influenced by a range of sampling-related factors, such as seawater contamination and variable sample volumes. The normalization correction measures had little influence on blow hormone results, and further refinement of blow hormone monitoring methods is required before blow samples can be used for reproductive or adrenal assessments of bottlenose dolphins. In contrast, blubber should be suitable for detecting pregnancy and possibly male sexual maturity. Further sampling of adult male dolphins is warranted to confirm whether blubber testosterone levels vary seasonally and determine if it is suitable for detecting certain temporally restricted endocrine events such as acute stress. This work helps to clarify the potential applications and limitations of using blow and blubber hormone measurements as indicators of cetacean physiological condition.