Naturally stressed? Glucocorticoid profiles in blubber of blue and gray whales in response to life history parameters.

The goal of the present study was to carry out a thorough methodological validation and describe baseline profiles for glucocorticoid hormones (cortisol and corticosterone) in blubber from blue (n = 77) and gray (n = 103) whales from the eastern North Pacific Ocean. For each species, we modelled cortisol and corticosterone concentrations in response to life history parameters (age, sex, reproductive status) and season or geographic location. In blue whales, cortisol concentrations did not vary significantly by age class, sex, or reproductive status, whereas corticosterone was significantly lower in immature than in adult females (p < .001). In gray whales, cortisol concentrations were significantly higher in lactating whales (p < .05), while corticosterone was significantly different between females and males (p = .001) and elevated in calves (p = .003). In gray whales, corticosterone concentrations were significantly lower in males sampled later in the year (August to November) compared to both sexes sampled between March and August (p = .05), but no seasonal trend occurred in blue whales. Our results indicate that glucocorticoid actions vary between species and sex in large whales. Analysis of multiple hormones improves our understanding of the physiology of maintaining metabolic homeostasis or coping with chronic stressors.

Blubber endocrine profiles provide insights into reproductive biology in blue whales from the eastern North Pacific Ocean.

The goal of the present study was to complement existing data of testosterone and progesterone in blue whale (Balaenoptera musculus) blubber from the eastern North Pacific Ocean to evaluate effects of seasonality and location on these hormones and to better assess reproductive status of individuals. Physiological parameters regarding reproduction are fundamental for describing population dynamics, and hormones can be a valid tool to estimate those for wildlife populations. In this study, blubber tissue was validated for testosterone and progesterone assays. Hormone concentrations were measured in 69 (35 males and 34 females) blubber samples from live (n = 66) and stranded (n = 3) animals collected between 2002 and 2016 from a known winter reproductive ground in the Gulf of California (GoC) and summer feeding areas along the United States West Coast (USWC), specifically off the states of California and Oregon. Results were combined with sighting histories as a tool to determine reproductive status of individual whales. Testosterone concentrations in adult male blue whales were significantly higher (p < 0.05) in blubber biopsies sampled off the USWC between the months of June and November compared to those sampled in the GoC between February and April. Elevated testosterone concentrations likely indicate physiological preparation for reproductive activity while the animals were present off the USWC. Progesterone concentrations were significantly elevated in pregnant females, confirming progesterone as an indicator of pregnancy in blue whales. Probabilities of being pregnant were estimated for adult females with unknown sighting histories based on progesterone concentrations. Testosterone in females was detected and measured only in pregnant whales suggesting its biosynthesis or metabolism is altered during gestation. These results provide updated and new information on the reproductive cycle of blue whales in the eastern North Pacific, posing new milestones to better estimate the timing of the mating season for this endangered population.

Application of endocrine biomarkers to update information on reproductive physiology in gray whale (Eschrichtius robustus).

Most of our knowledge on reproductive biology of gray whales dates back to scientific research conducted during commercial whaling in the late 1950s and 1960s. The goal of the present study was to provide updated insights on reproductive physiology of gray whales, using progesterone and testosterone as biomarkers. We measured hormone concentrations using enzyme immunoassay (EIA) techniques in blubber biopsies collected from 106 individual whales from March to November over a span of 12 years (2004-2016) between California and Alaska. We found testosterone concentrations in males to increase significantly with age (P = 0.03). Adult males showed significantly elevated testosterone concentrations when sampled in the fall compared to the summer (P = 0.01), likely indicating physiological preparation for mating. We measured testosterone concentrations in females of different age classes, but no statistical differences were found. We found significantly higher progesterone concentrations in pregnant females compared to non-pregnant females and adult males (P< 0.001), indicating progesterone is a valid biomarker for pregnancy in gray whales. Both female and male calves had elevated progesterone concentrations, suggesting maternal transfer via lactation. We fit a mixture of two normal distributions to progesterone data from all non-calf females to identify clusters of high and low progesterone and estimated the probability of being pregnant for whales of unknown reproductive status. With this approach we identified likely pregnant and non-pregnant animals. This study represents an important milestone on reproductive profiles in this population, that can be used to estimate more accurate and precise reproductive parameters to be used for better understanding population dynamics of gray whales.