Liquid chromatography tandem mass spectrometry for the quantification of steroid hormone profiles in blubber from stranded humpback whales (Megaptera novaeangliae)

Reproductive Steroid Hormone Patterns in Baleen of Two Pregnant Humpback Whales (Megaptera Novaeangliae)

Understanding reproductive physiology in mysticetes has been slowed by the lack of repeated samples from individuals. Analysis of humpback whale baleen enables retrospective hormone analysis within individuals dating back three to five years before death. Using this method, we investigated differences in four steroid hormones involved in reproduction and mating during confirmed pregnant and non-pregnant periods in two female humpback whales (Megaptera novaeangliae) with known reproductive histories based on sightings and necropsy data. Cortisol, corticosterone, testosterone and estradiol concentrations were determined via enzyme immunoassay using subsamples of each baleen plate at 2 cm intervals. There were no significant differences in cortisol or corticosterone during pregnancy when compared to non-pregnancy (inter-calving interval), but there were significant differences between the two whales in average glucocorticoid concentrations, with the younger whale showing higher values overall. For testosterone, levels for the younger female peaked at parturition in one pregnancy, but also had spikes during nonpregnancy. The older female had three large spikes in testosterone, one of which was associated with parturition. Estradiol had large fluctuations in both whales but had generally lower concentrations during non-pregnancy than during pregnancy. There were peaks in estradiol before each pregnancy, possibly coinciding with ovulation, and peaks coinciding with the month of parturition. Both estradiol and testosterone could be useful for determining ovulation or impending birth. Using baleen to investigate retrospective steroid hormone profiles can be used for elucidating long-term patterns of physiological change during gestation.

Rapidity and Precision of Steroid Hormone Measurement

Steroids are present in all animals and plants, from mammals to prokaryotes. In the medical field, steroids are commonly classified as glucocorticoids, mineralocorticoids, and gonadal steroid hormones. Monitoring of hormones is useful in clinical and research fields for the assessment of physiological changes associated with aging, disease risk, and the diagnostic and therapeutic effects of various diseases. Since the discovery and isolation of steroid hormones, measurement methods for steroid hormones in biological samples have advanced substantially. Although immunoassays (IAs) are widely used in daily practice, mass spectrometry (MS)-based methods have been reported to be more specific. Steroid hormone measurement based on MS is desirable in clinical practice; however, there are several drawbacks, including the purchase and maintenance costs of the MS instrument and the need for specialized training of technicians. In this review, we discuss IA- and MS-based methods currently in use and briefly present the history of steroid hormone measurement. In addition, we describe recent advances in IA- and MS-based methods and future applications and considerations.

Blubber Cortisol-Based Approach to Explore the Endocrine Responses of Indo-Pacific Humpback Dolphins (Sousa chinensis) to Diet Shifts and Contaminant Exposure

The detrimental effects of contaminant exposure and changes in the availability of food resources are still of concern for Indo-Pacific humpback dolphins (Sousa chinensis) of the Pearl River Estuary (PRE). Here, we validated and applied a blubber cortisol biomarker approach to assess the physiological responses of PRE dolphins to various pollutants and diet changes during 2008-2018 (n = 70). For calves, generalized additive models (GAMs) revealed that cortisol levels varied significantly by month and were positively correlated with the body length, owing to significant maternal transfer of hormones. The significantly positive correlation between length-adjusted cortisol levels in calf and the annual calf mortality ratios suggested that during years of high calf mortality, these animals were highly stressed before they die. For noncalves, blubber cortisol levels in diseased animals were significantly higher than those in "healthy" ones. Chromium (Cr) and dichlorodiphenyltrichloroethanes displayed a significant and positive relationship with blubber cortisol levels, suggesting that contaminant-mediated endocrine disruption effects may have occurred in noncalves. The GAMs indicated a decreasing trend of noncalf's blubber cortisol levels over an 11-year span, which can be explained by their declining contaminant accumulation levels due to a significant dietary shift from eating highly contaminated fishes to less polluted ones.

Steroid hormone profiles and body conditions of migrating male humpback whales (Megaptera novaeangliae)

Simultaneous analysis of multiple steroid hormones from remotely obtained blubber biopsies has the potential to concurrently provide information regarding stress and reproductive status from free-swimming cetaceans, while also investigating correlations between hormone concentrations and other health biomarkers. In this study we measured blubber concentration profiles of eight reproductive and adrenal steroid hormones (17α-hydroxy-progesterone, testosterone, androstenedione, progesterone, cortisol, 11-deoxy-corticosterone, oestrone, and oestradiol) together with body condition, as determined by the inverse Adipocyte Index, of 101 male humpback whales. Whales were sampled randomly at two time points, while migrating to and from their northeast Australian breeding grounds, allowing for intra- and inter-seasonal profile analysis. Testosterone, progesterone and cortisol together with androstenedione 17α-hydroxyprogesterone, and oestrone concentrations (the latter quantified for the first time in live biopsied male humpback whales) decreased between the northward and southward migrations. Decreasing testosterone levels during the height of humpback whale conceptions suggests asynchronicity between blubber testosterone levels and the expected peak of male fertility. Statistically significant relationships between levels of certain steroid analytes were observed and appeared to change between the early and late breeding seasons. During the northward migration, testosterone, progesterone, androstenedione, oestrone and 17α-hydroxyprogesterone levels were positively correlated. Cortisol concentrations correlated positively with those of testosterone during the northward migration, but negatively during the southward migration. Androstenedione and testosterone were positively correlated with adiposity during the late breeding season. These hormone-hormone and hormone-adiposity correlations may be reflective of the activation of certain steroid hormone synthesis pathways, or alternatively, of concomitant physiological stimuli. As steroid hormones work in concert, information on multiple steroid hormones is needed to interpret endocrinological status and understand the relationships between these compounds and ancillary health markers. This study provides steroid hormone profiles of wild male humpback whales, as well as the first insight into seasonal male endocrinology as a function of adiposity.

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.

Stress and reproductive events detected in North Atlantic right whale blubber using a simplified hormone extraction protocol

As studies quantifying steroid hormones in marine mammal blubber progress, methodological refinements may improve the utility and consistency of blubber hormone measurements. This study advances blubber extraction methodologies by testing a simplified extraction protocol that reduces time and complexity compared to a protocol widely used in cetacean blubber studies. Using blubber samples archived from remote biopsy (n = 21 live whales) and necropsy collection (n = 7 dead whales) of North Atlantic right whales (NARW; Eubalaena glacialis) of known life history states, we performed analytical and biological validations to assess the feasibility of measuring reproductive (testosterone, progesterone) and glucocorticoid (cortisol) hormones in blubber via enzyme immunoassay following the simplified extraction. Analytical validations (parallelism, accuracy, extraction efficiency, repeatability) showed the simplified extraction produced similar results to the extended protocol, offering a more efficient and consistent technique. In live, apparently healthy whales, blubber testosterone concentrations (mean ± SE) were significantly higher in males (2.02 ± 0.36 ng/g) compared to females (0.81 ± 0.15 ng/g). Blubber progesterone was highest in a confirmed pregnant female (60.3 ng/g), which was 12-fold greater than the mean concentration of non-pregnant females (4.56 ± 0.88 ng/g). Blubber cortisol concentrations in whales that died from anthropogenic causes averaged 5.31 ± 2.28 ng/g, whereas most live, healthy whales had cortisol values below 1 ng/g. Among living whales, a whale actively entangled in fishing gear had the highest blubber cortisol measurement (3.51 ng/g), exhibiting levels similar to whales that died from acute entanglement (2.88 ± 0.42 ng/g). Overall, the highest blubber cortisol concentration (18.0 ng/g) was measured in a dead whale with a severe chronic entanglement, approximately 30-fold greater than mean blubber cortisol of apparently healthy whales (0.58 ± 0.11 ng/g). The methodological approach presented here provides a reference for researchers interested in an alternative, streamlined technique for hormone extraction of cetacean blubber and contributes to the diverse tool set for stress and reproductive assessments of endangered NARWs.

Patterns of cortisol and corticosterone concentrations in humpback whale (Megaptera novaeangliae) baleen are associated with different causes of death

Baleen whales are subject to a myriad of natural and anthropogenic stressors, but understanding how these stressors affect physiology is difficult. Measurement of adrenal glucocorticoid (GC) hormones involved in the vertebrate stress response (cortisol and corticosterone) in baleen could help fill this data gap. Baleen analysis is a powerful tool, allowing for a retrospective re-creation of multiple years of GC hormone concentrations at approximately a monthly resolution. We hypothesized that whales that died from acute causes (e.g. ship strike) would have lower levels of baleen GCs than whales that died from extended illness or injury (e.g. long-term entanglement in fishing gear). To test this hypothesis, we extracted hormones from baleen plates of four humpback whales (Megaptera novaeangliae) with well-documented deaths including multiple and chronic entanglements (n = 1, female), ship strike (n = 2, male and female) and chronic illness with nutritional stress (n = 1, male). Over ~3 years of baleen growth and during multiple entanglements, the entangled whale had average corticosterone levels of 80-187% higher than the other three whales but cortisol levels were similar to two of the other three whales. The nutritionally stressed and chronically ill whale showed a slow increase in both cortisol and corticosterone spanning ~3 years, followed by a sharp decline in both hormones before death, possibly indicative of adrenal failure in this moribund individual. This whale's correlation between cortisol and corticosterone was significant but there were no correlations in the other three whales. Our results show that cortisol and corticosterone concentrations vary according to the type and duration of illness or injury. Single-point GC concentrations should be interpreted with caution as low values can occur in whales experiencing pronounced stress and individual baselines can be highly variable. Baleen analysis is a promising tissue type for retrospective analyses of physiological responses to various stressors affecting baleen whales.

Corticosterone in central North Pacific male humpback whales (Megaptera novaeangliae): Pairing sighting histories with endocrine markers to assess stress

Developing a better understanding of the stress response is critical to ensuring the health and sustainability of marine mammal populations. However, accurately measuring and interpreting a stress response in free-ranging, large cetaceans is a nascent field. Here, an enzyme immunoassay for corticosterone was validated for use in biopsy samples from male humpback whales (Megaptera novaeangliae). Analyses were conducted on 247 male North Pacific humpback whale blubber samples, including 238 non-calves and 9 calves that were collected on the Hawaiian breeding and Southeast Alaskan feeding grounds from 2004 to 2006. Significant relationships were found when corticosterone concentrations were examined by year, age class and distribution between locations. When examined by year, corticosterone concentrations for male humpback whales were higher in Hawaii in 2004 than in 2005 and 2006 (p < 0.05). Corticosterone concentration also varied by age class with initially high concentrations at birth which subsequently tapered off and remained relatively low until sexual maturity was reached around age 8-10 years. Corticosterone concentrations appeared to peak in male humpback whales around 15-25 years of age. Blubber biopsies from Alaska and Hawaii had similar mean corticosterone concentrations, yet the variability in these samples was much greater for whales located in Hawaii. It is clear that much work remains to be done in order to accurately define or monitor a stress response in male humpback whales and that specific attention is required when looking at age, sex, and yearly trends. Our results suggest that a stress response may be most impacted by age and yearly oceanographic conditions and needs to be initially examined at the individual level.

Blubber cortisol levels in humpback whales (Megaptera novaeangliae): A measure of physiological stress without effects from sampling

Baleen whales are vulnerable to environmental impacts due to low fecundity, capital breeding strategies, and their reliance on a large amount of prey resources over large spatial scales. There has been growing interest in monitoring health and physiological stress in these species but, to date, few measures have been validated. The purpose of this study was to examine whether blubber cortisol could be used as a measure of physiological stress in humpback whales. Cortisol concentrations were initially compared between live, presumably 'healthy' whales (n = 187) and deceased whales (n = 35), which had died after stranding or entanglement, or washed ashore as a carcass. Deceased whales were found to have significantly higher cortisol levels (mean ± SD; 5.47 ± 4.52 ng/g) than live whales (0.51 ± 0.14 ng/g; p < 0.001), particularly for those animals that had experienced prolonged trauma (e.g. stranding) prior to death. Blubber cortisol levels in live whales were then examined for evidence of life history-related, seasonal, or sampling-related effects. Life history group and sampling-related factors, such as encounter time and the number of biopsy sampling attempts per animal, were found to be poor predictors of blubber cortisol levels in live whales. In contrast, blubber cortisol levels varied seasonally, with whales migrating north towards the breeding grounds in winter having significantly higher levels (0.54 ± 0.21 ng/g, p = 0.016) than those migrating south towards the feeding grounds in spring (0.48 ± 1.23 ng/g). These differences could be due to additional socio-physiological stress experienced by whales during peaks in breeding activity. Overall, blubber cortisol appears to be a suitable measure of chronic physiological stress in humpback whales.

Androstenedione and testosterone but not progesterone are potential biomarkers of pregnancy in Humpback Whales (Megaptera novaeangliae) approaching parturition

The blubber steroid hormone profiles of 52 female humpback whales migrating along the east coast of Australia were investigated for seasonal endocrine changes associated with reproduction. Individuals were randomly sampled during two stages of the annual migration: before reaching the breeding grounds (northward migration; June/July), and after departing from the breeding grounds (southward migration; September/October). Assignment of reproductive status of the sampled individuals was based on season, single-hormone ranks and multi-variate analysis of the hormonal profiles. High concentrations of progesterone (>19 ng/g, wet weight), recognised as an indicator of pregnancy in this species, were only detected in one sample. However, the androgens, testosterone and androstenedione were measured in unusually high concentrations (1.6-12 and 7.8-40 ng/g wet weight, respectively) in 36% of the females approaching the breeding grounds. The absence of a strong accompanying progesterone signal in these animals raises the possibility of progesterone withdrawal prior to parturition. As seen with other cetacean species, testosterone and androstenedione could be markers of near-term pregnancy in humpback whales. Confirmation of these androgens as alternate biomarkers of near-term pregnancy would carry implications for improved monitoring of the annual fecundity of humpback whales via non-lethal and minimally invasive methods.

The influence of physiological status on the reproductive behaviour of humpback whales (Megaptera novaeangliae)

For most cetacean species, there is little known about how an individual's physiology influences its behaviour. Humpback whales (Megaptera novaeangliae) are a good candidate to examine such links as they have a well-described distribution and behaviour, can be consistently sampled using remote biopsy systems, and have been the subject of several previous endocrine studies. The objective here was to examine whether a female humpback whale's social state (i.e. escorted by a male or not) is related to her endocrine condition, and whether male dominance ranking is related to testosterone levels. Skin and blubber biopsies were collected from the east and west Australian humpback whale populations in 2010-2016 (n = 252) at multiple times throughout the winter-spring breeding season. Steroid hormones were extracted from blubber and concentrations of progesterone (a marker for pregnancy), testosterone (a marker of male testicular activity) and oestradiol (a potential marker of ovarian activity) measured using enzyme-immunoassays. Principal escorts-the dominant males in mixed sex groups-had significantly higher blubber testosterone levels (mean ± SE; 1.43 ± 0.20 ng/g wet weight) than subordinate, secondary escorts (0.69 ± 0.06 ng/g wet weight). Females that were escorted by males typically possessed elevated blubber oestradiol levels (1.96 ± 0.25 ng/g wet weight; p = 0.014); few were considered to be pregnant (p = 0.083). 'Unescorted' females displayed characteristically lower blubber oestradiol levels (0.56 ± 0.06 ng/g wet weight). Together, these results are consistent with 'challenge hypothesis' theory and suggest the existence of associated reproductive patterns in humpback whales.