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

Abstract

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.

Small Blubber Samples (50 mg) Sufficient for Analyses of 10 Stress and Reproductive Steroid Hormones in Gray and Fin Whales via Liquid Chromatography Mass Spectrometry

“…Testosterone (3 ng/g) was detected only in one unsexed calf, ER-18-31, at a similar concentration reported for a juvenile gray whale male using LC/MS methodology (Hayden et al, 2017) but greater than mean concentrations observed at any life stage in gray whale males using immunoassays (Melica et al, 2021). No adult males were analyzed at the 50 mg ww mass, and our sample set did not include any breeding adult males, known in gray whales and other species for expressing higher concentrations (Boggs et al, 2019;Galligan et al, 2019;Melica et al, 2021).…”

“…Additionally, 17α-hydroxyprogesterone (13.8-39.8 ng/g, mean 26.76 ng/g) was detected in higher concentrations in both an adult female, ER-18-34 (13.8 ng/g) and an unsexed calf, ER-18-33 (39.8 ng/g) than in free ranging, live-captured, or stranded bottlenose dolphins (< 0.1-3.16 ng/g, Boggs et al, 2017;0-4.64 ng/g, Galligan et al, 2019;1.6-13.7 ng/g, Galligan et al, 2020) and humpback whales (< 0.5-1.87 ng/g, Dalle Luche et al, 2019). Testosterone (3 ng/g) was detected only in one unsexed calf, ER-18-31, at a similar concentration reported for a juvenile gray whale male using LC/MS methodology (Hayden et al, 2017) but greater than mean concentrations observed at any life stage in gray whale males using immunoassays (Melica et al, 2021). No adult males were analyzed at the 50 mg ww mass, and our sample set did not include any breeding adult males, known in gray whales and other species for expressing higher concentrations (Boggs et al, 2019;Galligan et al, 2019;Melica et al, 2021).…”

“…More research is warranted in the gray whale. A valuable probability model for gray whale pregnancy was recently developed using blubber progesterone concentrations detected by immunoassays (Melica et al, 2021). Melica's model exhibits a strong fit for known pregnant and non-pregnant whales and higher uncertainties for whales with intermediate progesterone concentrations.…”

“…Hormone analyses can provide fundamental information on wildlife health and fitness at both individual and population levels (Keay et al, 2006;Kershaw and Hall, 2016;Mello and Oliveira, 2016;McCormick and Romero, 2017). In cetaceans, steroid hormones have been analyzed in wild and captive animals to assess pregnancy, reproductive status, stress, and fitness in a variety of matrices, including baleen, blow, ear plug, feces, follicular fluid, milk, muscle, ocular secretions, plasma, saliva, serum, skin including blubber, and urine (Walker et al, 1988;Yoshioka et al, 1994;Iga et al, 1996;Atkinson et al, 1999;West et al, 2000;Kellar et al, 2006Kellar et al, , 2009Fair et al, 2014;Hunt et al, 2014;Thompson et al, 2014;Champagne et al, 2017;Trumble et al, 2018;Boggs et al, 2019;Carone et al, 2019;Bechshoft et al, 2020;Cates et al, 2020;Galligan et al, 2020;Lemos et al, 2020b;Graham et al, 2021;Melica et al, 2021).…”

Characterization of Circulating Androgens, Cortisol and Estrogens During Normal, Abnormal and False Pregnancy in Bottlenose Dolphins (Tursiops truncatus) Under Managed Care

“…For bottlenose dolphins, Boggs et al (2019) and Galligan et al (2020) have both reported elevated androgen concentrations in blubber from pregnant animals. Elevated concentrations of androgens and/or androgen metabolites during pregnancy have been reported in North Atlantic right whales (Eubaleana glacialis, Hunt et al, 2006;Corkeron et al, 2017), beluga (Richard et al, 2017), Yangtze finless porpoise (Neophocaena asiaeorientalis, Hao et al, 2006), blue whales (Balaenoptera musculus, Melica et al, 2021b) and humpback whales (Hunt et al, 2019) but were not observed in gray whale (Eschrichtius robustus) blubber (Melica et al, 2021a). Dalle Luche et al (2020) suggest that, during late term humpback whale pregnancy, A4 and T measurements may be more effective pregnancy biomarkers than P4.…”