Evaluation of adrenocortical function in Florida manatees (Trichechus manatus latirostris)

VALIDATION OF ENZYME-LINKED IMMUNOSORBENT ASSAY TECHNIQUES TO MEASURE SERUM DEHYDROEPIANDROSTERONE (DHEA) AND DHEA-S IN NARWHALS (MONODON MONOCEROS)

Narwhals (Monodon monoceros) are increasingly exposed to anthropogenic disturbances that may increase their stress levels with unknown consequences for the overall population dynamics. The validation and measurement of chronic stress biomarkers could contribute toward improved understanding and conservation efforts for this species. Dehydroepiandrosterone (DHEA) and its sulfated metabolite DHEA-S are collectively referred to as DHEA(S). Serum DHEA(S) concentrations combined in ratios with cortisol [cortisol/DHEA(S)] have been shown to be promising indicators of chronic stress in humans, domestic animals, and wildlife. During field tagging in 2017 and 2018 in Baffin Bay, Nunavut, Canada, 14 wild narwhals were sampled at the beginning and end of the capture-tagging procedures. Serum DHEA(S) were measured with commercially available competitive enzyme-linked immunosorbent assays (ELISA) developed for humans. A partial validation of the ELISA assays was performed by the determination of the intra-assay coefficient of variation, confirmation of the DHEA(S) dilutional linearity, and the calculation of the percentage of recovery. Mean values (nanograms per milliliter ± standard error of the mean) of narwhal serum cortisol, DHEA(S), and cortisol/DHEA(S) ratios, at the beginning and at the end of handling, respectively, are reported (cortisol = 30.74 ± 4.87 and 41.83 ± 4.83; DHEA = 1.01 ± 0.52 and 0.99 ± 0.50; DHEA-S = 8.72 ± 1.68 and 7.70 ± 1.02; cortisol/DHEA = 75.43 ± 24.35 and 84.41 ± 11.76, and cortisol/DHEA-S = 4.16 ± 1.07 and 6.14 ± 1.00). Serum cortisol and cortisol/DHEA-S were statistically higher at the end of the capture (P= 0.024 and P= 0.035, respectively). Moreover, serum cortisol at the end of handling was positively correlated to total body length (P = 0.042) and tended to be higher in males (P = 0.086). These assays proved easy to perform, rapid, and suitable for measuring serum DHEA(S) of narwhals and that calculated cortisol/DHEA(S) are potential biomarkers for chronic stress in narwhals and possibly other cetaceans.

Untapped potential of physiology, behaviour and immune markers to predict range dynamics and marginality

Linking environmental conditions to the modulators of individual fitness is necessary to predict long-term population dynamics, viability, and resilience. Functional physiological, behavioral, and reproductive markers can provide this mechanistic insight into how individuals perceive physiological, psychological, chemical, and physical environmental challenges through physiological and behavioral responses that are fitness proxies. We propose a Functional Marginality framework where relative changes in allostatic load, reproductive health, and behavior can be scaled up to evidence and establish causation of macroecological processes such as local extirpation, colonization, population dynamics, and range dynamics. To fully exploit functional traits, we need to move beyond single biomarker studies to develop an integrative approach that models the interactions between extrinsic challenges, physiological, and behavioral pathways and their modulators. In addition to providing mechanistic markers of range dynamics, this approach can also serve as a valuable conservation tool for evaluating individual- and population-level health, predicting responses to future environmental change and measuring the impact of interventions. We highlight specific studies that have used complementary biomarkers to link extrinsic challenges to population performance. These frameworks of integrated biomarkers have untapped potential to identify causes of decline, predict future changes, and mitigate against future biodiversity loss.

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.