Stress-related and reproductive hormones in hair from three north Pacific otariid species: Steller sea lions, California sea lions and northern fur seals

SEASONAL VARIATION OF BLOOD ANALYTES ASSOCIATED WITH SKIN HEALTH IN ALASKAN ICE SEALS

Recent unusual mortality events involving skin pathology in bearded (Erignathus barbatus), ringed (Pusa hispida), and spotted seals (Phoca largha) in Alaska highlight the potential sensitivity of ice-associated species to the complex effects of climate change. The regulation of thyroid hormones, cortisol, and vitamin A have been shown to play essential roles in skin health and seasonal molt in some pinnipeds. Unfortunately, the lack of available reference data for healthy Alaskan ice seals has prevented the adequate evaluation of these factors in cases associated with mortality events. To improve understanding of blood analytes that may serve as useful markers of skin health, we compiled diagnostic information for individuals in long-term managed care following short-term rehabilitation. Thyroid hormones (TT4, TT3, and FT4d), cortisol, and vitamin A levels are reported for four ringed seals, four spotted seals, and three bearded seals at the Alaska SeaLife Center in Seward, Alaska, with serial samples obtained when possible and referenced to time of year. For ringed and spotted seals, the thyroid hormones and vitamin A showed a strong seasonal pattern with peak values obtained during the annual molt in spring, whereas cortisol values did not vary predictably between molting and non-molting periods. Trends were similar for individuals across both sex and species. Bearded seals had fewer available data for younger individuals only, but observed analyte values are provided for this understudied species. Collectively, these measurements can be used to support veterinary management of ice seals under human care and to provide initial baselines for skin health monitoring in wild populations and in stranded individuals with known skin lesions or pathology.

Evaluating suitability of saliva to measure steroid concentrations in grey seal pups

Measurement of steroids in wild pinnipeds can facilitate assessment of breeding, nutritional and stress status, and is useful in understanding behavioral responses. Even in young animals, sex steroids may be important in behavioral interactions and immune modulation. Use of saliva can avoid the large fluctuations seen in some steroids in plasma, and can negate the need for venipuncture, making it a potentially useful matrix in the wildlife. However, its utility in estimating steroid levels in wild young pinnipeds has not been evaluated. Here, we investigated the suitability of saliva for steroid hormone analysis in wild grey seal pups during their suckling and post-weaning fast periods. We collected saliva (n = 38) and plasma (n = 71) samples during the breeding season on the Isle of May, Scotland, 2012. We investigated success of sample collection, ease of preparation, accuracy and precision of analysis, and, where possible, comparability of measurements (n = 27) from saliva and plasma. Plasma sampling was rapid, whereas sampling saliva took up to five times longer. Analytical performance criteria (parallelism, accuracy, and precision (intra and inter assay co-efficient of variation (% CV)) of commercial ELISA kits to measure estradiol, testosterone and cortisol in both matrices were assessed. Estradiol and cortisol assays performed well and can be used in plasma and saliva. However, we could not confidently validate testosterone for either matrix. Saliva estradiol correlated with levels in plasma. Saliva sample preparation was faster and simpler than plasma preparation because it did not require extraction. However, given the additional time taken to obtain saliva in the wild, the possibility of blood contamination from oral damage and the lower success rate in obtaining sufficient sample for analysis, we recommend that this matrix only be used as an alternative to plasma sampling measurement in pinnipeds when animals are anaesthetized, tolerate mouth swabbing, or have been trained to accept saliva sampling in captivity.

Relationships between age, diet, and stress-related hormones and reproduction in American marten (Martes americana)

American marten (Martes americana) in Interior Alaska are at the northwestern limit of their North American range. To investigate factors that may be associated with reproduction we determined the cementum age and the presence or absence of blastocysts in 118 female martens for 3 years (2012, 2014, and 2016) in two regions. For each marten we collected fur samples and measured steroid hormone concentrations (cortisol, testosterone, and progesterone) and stable isotopes (δ15N and δ13C values, a proxy for diet). These parameters reflect the diet and endocrine activity between June and October when fur is grown. We also collected two claws from a subset of 39 female marten from one region in 2012 and 2014. Progesterone concentrations were measured in one whole claw and from a second claw divided into proximal (recent growth) and distal sections. Differences in the probability of blastocysts being present were associated with geographic region and sample year suggesting that reproduction in female marten varies on a fine scale. We found the that presence of blastocysts was positively associated with marten age and δ15N values in fur but negatively associated with fur cortisol concentrations. These findings suggest that the likelihood a female marten will reproduce in a given year is influenced, in part, by the proportion of protein in their diet and stressors encountered during late summer and fall, months before active gestation begins.

Testosterone levels in hair of free-ranging male northern fur seals (Callorhinus ursinus) in relation to sampling month, age class and spermatogenesis

Information about the reproductive status of free-ranging pinnipeds provides useful insight into their population dynamics, which is essential to their management and conservation. To determine the reproductive status of individual animals, blood sampling is often required despite being impractical to collect in open water. Hair as an endocrine marker has been used to less invasively assess the reproductive status of terrestrial animals. However, it is unknown whether pinniped reproductive status can be assessed from hair samples. Here, we examine testosterone levels in hair obtained from 57 male northern fur seals and used it to compare their age class and spermatogenesis during the non-breeding season off Hokkaido. We isolated testosterone from the samples using gas chromatography and measured testosterone levels using time-resolved fluoroimmunoassay. Testosterone levels in hair increased towards the breeding season. In May, testosterone levels were the highest in seals aged between 4 and 7 years, followed by those over the age of 8 years and under the age of 4 years. Spermatids, the final phase of spermatogenesis, were present in the seals sampled between April and June, even though testosterone levels were low in April. The seals with spermatids in May showed the highest testosterone levels. Our results demonstrate that seals with higher testosterone levels in May are likely to be mature males (≥4 years). Since hair can be collected using biopsy darts in the field, it will be possible to less invasively determine testosterone levels of male seals in the future.

Whiskers as a novel tissue for tracking reproductive and stress-related hormones in North Pacific otariid pinnipeds

Keratinized tissues, including whiskers, are ideal for acquiring a record of physiological parameters. Most tissues provide a snapshot of physiological status; however, whiskers may support longitudinal sampling for reproductive and stress-related hormones, if hormones are incorporated as whiskers grow and concentrations change with physiological state. Whiskers from female Steller sea lions (Eumetopias jubatus) and northern fur seals (Callorhinus ursinus) were serially sectioned and pulverized and steroid hormones were extracted. Standard methods were used to validate enzyme immunoassay kits for cortisol, progesterone, 17β-estradiol and testosterone. All hormones were measurable in whisker segments from both species with progesterone concentrations showing cyclical patterns, which appear to signify previous pregnancies or luteal phases. Yearly progesterone concentrations were greater in years a pup was produced compared with years when no pup was observed. Free-ranging female Steller sea lions had reproductive rates between 0 and 1.0 (0.53 ± 0.33, n = 12) using a yearly progesterone concentration of 30 pg/mg or greater to classify a reproductive year as producing a pup and below 30 pg/mg as non-reproductive. Cortisol concentrations were greater near the root and rapidly declined, lacking any obvious patterns, throughout the rest of the whisker. Progesterone and testosterone concentrations were able to help determine sex of unknown individuals. Immunohistochemistry revealed that steroid hormones most likely do not leach out of whiskers based on the deposition patterns of progesterone and cortisol being present throughout the whisker length. Overall, measuring steroid hormones in whiskers can reveal individual reproductive histories over multiple years in sea lions and fur seals. Cyclical patterns of δ15N were useful for identifying periods of up to ~10 years of growth within whiskers, and measuring both stable isotopes and hormones may be useful for differentiating periods of active gestation from diapause and potentially track multi-year reproductive histories of female otariids.