Hormone changes indicate that winter is a critical period for food shortages in Steller sea lions

Glucocorticoid and triiodothyronine concentrations do not correlate with behavior in vicuñas (Vicugna vicugna)

State-dependent foraging theory posits that animals should make foraging decisions based on energetic condition, where animals with fewer energetic reserves prioritize foraging over other behaviors, including antipredator behaviors. However, few studies have investigated these trade-offs at an individual level in wild, free-ranging animals. We investigated the relationships between internal condition and behavior in a wild mammal, the vicuña (Vicugna vicugna), which makes state-dependent decisions about the use of two habitats with different characteristics that contribute to their internal condition. Using non-invasively collected fecal samples, we measured glucocorticoid metabolites (GCMs) and thyroid hormones (THs) as indicators of combined stress (predation and nutritional), and just nutritional stress, respectively. We video recorded 20-minute behavioral observations and focused on behaviors which often demand a trade-off between energy acquisition and antipredator behaviors-vigilance and foraging. We found differences in expression of these behaviors between the two sites but found no relationships between physiological parameters (GCMs and THs) and behavior (vigilance and foraging) at either site. We suggest that state-dependent foraging may be difficult to observe in large mammals under baseline conditions and that GCMs and THs may be insensitive to small changes in stress stimuli at this scale, and where these wild animals have the entire suite of behavioral responses available to them.

Hematologic and biochemical differences between two free ranging Yangtze finless porpoise populations: The implications of habitat

The goals of this study were to compare the serum chemistry and hematology values of wild and semi-natural free-ranging Yangtze Finless Porpoises (Neophocaena asiaeorientalis ssp. asiaeorientalis) populations and to ascertain how these values change with the different environmental condition. For this study, samples were collected from 81 YFPs, 35 living in the wild and 46 living in a semi-natural reserve. Each population was divided into 8 life history categories; Male Calf, Female Calf, Juvenile Male, Juvenile Female, Adult Male, Pregnant, Lactating and Pregnant plus Lactating. Statistically significant differences in the various parameters were observed in the same life history categories for both populations. Generally, Lipid Profile, Hepatic Enzymes, Creatine Kinase, Red Blood Cells, Hemoglobin, Hematocrit and Neutrophils were significantly higher in the Tian-E-Zhou Oxbow population while, Creatinine, Phosphate, Lactate Dehydrogenase, Bilirubin and Lymphocytes were significantly higher in the Poyang Lake YFPs. Across the groups in the Tian-E-Zhou Oxbow population, a significant decrease in serum Albumin, Alkaline Phosphatase and Calcium, while a significant increase in the Neutrophils and Platelets was observed. Similarly, in the Poyang Lake, Alkaline Phosphatase levels in the Female Calves group, High Density Lipoprotein Cholesterol in Lactating group, basophil counts in Pregnant plus Lactating group, lymphocytes counts in Juvenile Females group and Globulin and Total Protein levels in Pregnant group were significantly higher. This study in health assessments can help us to understand the effect of sex, age, reproductive status and environmental conditions on the well-being of Yangtze Finless Porpoises.

Resting metabolic rate and activity: key components of seasonal variation in daily energy expenditure for the northern fur seal (Callorhinus ursinus)

Seasonal changes in daily energy expenditure (DEE) and its key underlying components (costs of resting metabolic rate (RMR), thermoregulation, activity, and growth) were measured to determine seasonal energy requirements, bioenergetic priorities, and potential times of year when unpredicted episodes of nutritional stress would have their greatest effect on female northern fur seals (Callorhinus ursinus (L., 1758)). The mean (±SD) DEE of six captive juvenile female fur seals was 527.8 ± 65.7 kJ·kg−1·d−1 and fluctuated seasonally (lower during summer and winter, and up to 20% greater in spring and fall). RMR also changed significantly with season and was higher in the fall (potentially due to moulting or anticipated migratory activity). However, changes in RMR did not follow the same seasonal trend as those of DEE. The largest component of DEE was RMR (∼80%, on average), followed by the cost of activity (which may have driven some of the seasonal variations in DEE). In contrast, the energetic costs associated with growth and thermoregulation appeared negligible within the scope of overall energy expenditures. Elevated innate costs of RMR and higher growth rates in the fall and summer, respectively, suggest that inadequate nutrition could comparatively have greater negative effects on female fur seals during these seasons.

Stress physiology in marine mammals: how well do they fit the terrestrial model?

Stressors are commonly accepted as the causal factors, either internal or external, that evoke physiological responses to mediate the impact of the stressor. The majority of research on the physiological stress response, and costs incurred to an animal, has focused on terrestrial species. This review presents current knowledge on the physiology of the stress response in a lesser studied group of mammals, the marine mammals. Marine mammals are an artificial or pseudo grouping from a taxonomical perspective, as this group represents several distinct and diverse orders of mammals. However, they all are fully or semi-aquatic animals and have experienced selective pressures that have shaped their physiology in a manner that differs from terrestrial relatives. What these differences are and how they relate to the stress response is an efflorescent topic of study. The identification of the many facets of the stress response is critical to marine mammal management and conservation efforts. Anthropogenic stressors in marine ecosystems, including ocean noise, pollution, and fisheries interactions, are increasing and the dramatic responses of some marine mammals to these stressors have elevated concerns over the impact of human-related activities on a diverse group of animals that are difficult to monitor. This review covers the physiology of the stress response in marine mammals and places it in context of what is known from research on terrestrial mammals, particularly with respect to mediator activity that diverges from generalized terrestrial models. Challenges in conducting research on stress physiology in marine mammals are discussed and ways to overcome these challenges in the future are suggested.

Validation and application of noninvasive glucocorticoid and thyroid hormone measures in free-ranging Hawaiian monk seals

We validate fecal glucocorticoid (GC) and thyroid (T3) hormone metabolite measures in the Critically Endangered Hawaiian monk seal for the first time, and examine variation in the concentrations of these hormones in individuals across the species' range. We test hypotheses that monk seals from declining subpopulations have relatively high GCs and low T3 on average suggesting impacts of food limitation, and that this hormone pattern is more apparent in immature animals compared to adults, as food limitation is specifically indicated as a principal cause of poor body condition and survival of juvenile monk seals. We opportunistically sampled scat from 84 individually identifiable monk seals during the 2010 breeding season from two geographic regions, the main Hawaiian Islands (MHI) and the Northwestern Hawaiian Islands (NWHI). The MHI subpopulation of monk seals is growing, whereas subpopulations at many sites in the NWHI are in decline. Best fit general linear models predicting variation in GCs and T3 (examined separately) were similar (after accounting for significantly elevated hormone concentrations associated with molt and possibly lactation); both included sample date, region, and monk seal age as predictors. GC concentrations were significantly lower in MHI versus NWHI monk seals and decreased as the breeding season progressed. T3 concentrations were significantly lower in immature monk seals compared to adults. GC and T3 concentrations were positively correlated at 4 NWHI sites; prey may be adequate for physiological growth or maintenance at these sites but relatively stressful to acquire. GCs were highest at French Frigate Shoals, (a NWHI site) while T3 was relatively low here, indicating a possible signal of food limitation. GCs were lowest in the MHI. Disturbance associated with living near a high human population in the MHI appears to impact monk seal physiology less than other stressors encountered in the remote and highly protected NWHI where human presence is extremely low.

Body condition and endocrine profiles of Steller sea lion (Eumetopias jubatus) pups during the early postnatal period

Body condition indices have been useful in assessing the health of domestic and free ranging populations of terrestrial mammals. Given the high energy demand and rapid growth during the postnatal period of Steller sea lion (Eumetopias jubatus) (SSL) pups, body condition was expected to be related to concentrations of a suite of hormones (cortisol, aldosterone, thyroxine, triiodothyronine, leptin) previously associated with changes in body mass and composition in developing pinnipeds. Blood samples were collected from free ranging SSL pups of known ages and sex. A body condition index (BCI) previously developed for SSL pups based on a mass and length relationship was applied to 61 SSL pups ranging in age from 5 to 38days old. BCI was not related to pup age. Overall, male pups were larger than females and older pups were larger than younger pups. Aldosterone was negatively correlated with BCI only in female pups, whereas no relationship was observed between aldosterone and BCI in males. Further, male pups had higher aldosterone concentrations than females. Concentrations of cortisol, total and free thyroxine (T4), and total triiodothyronine (T3) decreased when regressed against the elapsed time between researchers' arrival on the rookery and removal of pup from the holding corral for blood collection. While the overall variation attributed to the rookery disturbance was low (r(2)<0.293), it may be of significance for future studies on free ranging pinnipeds. This study adds to the current knowledge of the postnatal changes in free ranging SSL pups by providing ranges of the BCI and several hormone concentrations from an apparently stable population.

Serum cortisol in California sea lion pups (Zalophus californianus californianus)

Marine ecosystems are exposed to a wide variety of factors that may produce disturbances in their structure and functioning. The Gulf of California supports fisheries, tourism, intensive agriculture, mining, and more recently, shrimp aquaculture. Under such conditions, animals are forced to cope with several changes in their environment that can contribute to animal welfare problems. Serum cortisol level analysis may be a particularly useful means of assessing the physiological status of mammals potentially affected by increasing human activity in the Gulf of California, such as the California sea lion (Zalophus californianus californianus). In this study, we report for the first time the serum cortisol concentration of free-living, wild California sea lion pups. The analysis was performed in eleven rookeries along the Gulf of California. Two consecutive blood samples (S1 and S2) were obtained from 56 sea lion pups following a capture, handling and anaesthesia regime, and cortisol was measured by radioimmunoassay. Female pups showed higher serum cortisol than males in the first sample. In males, the second sample was significantly higher than the first. Cortisol levels in the two samples of both sexes combined differed between the Southern and Midriff-region rookeries. This information could be useful to assess welfare in wild populations of sea lions and to determine anthropogenic factors in the Gulf of California that may contribute to stress and reduced welfare.

Seasonal influence on the response of the somatotropic axis to nutrient restriction and re-alimentation in captive Steller sea lions (Eumetopias jubatus)

Fluctuations in availability of prey resources can impede acquisition of sufficient energy for maintenance and growth. By investigating the hormonal mechanisms of the somatotropic axis that link nutrition, fat metabolism, and lean tissue accretion, we can assess the physiological impact of decreased nutrient intake on growth. Further, species that undergo seasonal periods of reduced intake as a part of their normal life history may have a differential seasonal response to nutrient restriction. This experiment evaluated the influence of season and age on the response of the somatotropic axis, including growth hormone (GH), insulin-like growth factor (IGF)-I, and IGF-binding proteins (BP), to reduced nutrient intake and re-alimentation in Steller sea lions. Eight captive females (five juveniles, three sub-adults) were subject to 28-day periods of food restriction, controlled re-feeding, and ad libitum recovery in summer (long-day photoperiod) and winter (short-day photoperiod). Hormone concentrations were insensitive to type of fish fed (low fat pollock vs. high fat herring), but sensitive to energy intake. Body mass, fat, and IGF-I declined, whereas GH and IGFBP-2 increased during feed restriction. Reduced IGF-I and IGFBP with increased GH during controlled re-feeding suggest that animals did not reach positive energy balance until fed ad libitum. Increased IGF-I, IGFBP-2, IGFBP-3, and reduced GH observed in summer reflected seasonal differences in energy partitioning. There was a strong season and age effect in the response to restriction and re-alimentation, indicating that older, larger animals are better able to cope with stress associated with energy deficit, regardless of season.

Fecal triiodothyronine and thyroxine concentrations change in response to thyroid stimulation in Steller sea lions (Eumetopias jubatus)

Variation in concentrations of thyroid hormones shed in feces may help to identify physiological states of animals, but the efficacy of the technique needs to be validated for each species. We determined whether a known physiological alteration to thyroid hormone production was reflected in hormone concentrations in the feces of Steller sea lions (Eumetopias jubatus). We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in feces following two intramuscular injections of thyrotropin (thyroid-stimulating hormone, TSH) at 24h intervals in four captive female sea lions. We found fecal T3 concentrations increased 18-57% over concentrations measured in the baseline sample collected closest to the time of the first TSH injection (p=0.03) and 1-75% over the mean baseline concentration (p=0.12) for each animal of all samples collected prior to injections. Peak T3 concentrations were greater than the upper bound of the baseline 95% confidence interval for three animals. The peak T3 response occurred 48h post-injection in three animals and 71h in the fourth. Post-injection T4 concentrations did not differ between the baseline sample collected closest to the time of the first TSH injection (p=0.29) or the mean baseline concentration (p=0.23) for each animal. These results indicate that induced physiological alterations to circulating thyroid hormone concentrations can be adequately detected through analyses of fecal T3 concentrations and that the technique may provide a means of non-invasively detecting metabolic changes in Steller sea lions.