Skull Foramina Asymmetry in East Greenland and Svalbard Polar Bears (Ursus maritimus) in Relation to Stressful Environments

Evaluation of physiological stress in free-ranging bears: current knowledge and future directions

Stress responses, which are mediated by the neurogenic system (NS) and hypothalamic-pituitary-adrenal (HPA) axis help vertebrates maintain physiological homeostasis. Fight-or-flight responses are activated by the NS, which releases norepinephrine/noradrenaline and epinephrine/adrenaline in response to immediate stressors, whilst the HPA axis releases glucocorticoid hormones (e.g. cortisol and corticosterone) to help mitigate allostatic load. There have been many studies on stress responses of captive animals, but they are not truly reflective of typical ranges or the types of stressors encountered by free-ranging wildlife, such as responses and adaptation to environmental change, which are particularly important from a conservation perspective. As stress can influence the composition of age and sex classes of free-ranging populations both directly and indirectly, ecological research must be prioritised towards more vulnerable taxa. Generally, large predators tend to be particularly at risk of anthropogenically driven population declines because they exhibit reduced behavioural plasticity required to adapt to changing landscapes and exist in reduced geographic ranges, have small population sizes, low fecundity rates, large spatial requirements and occupy high trophic positions. As a keystone species with a long history of coexistence with humans in highly anthropogenic landscapes, there has been growing concern about how humans influence bear behaviour and physiology, via numerous short- and long-term stressors. In this review, we synthesise research on the stress response in free-ranging bear populations and evaluate the effectiveness and limitations of current methodology in measuring stress in bears to identify the most effective metrics for future research. Particularly, we integrate research that utilised haematological variables, cardiac monitors and Global Positioning System (GPS) collars, serum/plasma and faecal glucocorticoid concentrations, hair cortisol levels, and morphological metrics (primarily skulls) to investigate the stress response in ursids in both short- and long-term contexts. We found that in free-ranging bears, food availability and consumption have the greatest influence on individual stress, with mixed responses to anthropogenic influences. Effects of sex and age on stress are also mixed, likely attributable to inconsistent methods. We recommend that methodology across all stress indicators used in free-ranging bears should be standardised to improve interpretation of results and that a wider range of species should be incorporated in future studies.

State of knowledge on current exposure, fate and potential health effects of contaminants in polar bears from the circumpolar Arctic

The polar bear (Ursus maritimus) is among the Arctic species exposed to the highest concentrations of long-range transported bioaccumulative contaminants, such as halogenated organic compounds and mercury. Contaminant exposure is considered to be one of the largest threats to polar bears after the loss of their Arctic sea ice habitat due to climate change. The aim of this review is to provide a comprehensive summary of current exposure, fate, and potential health effects of contaminants in polar bears from the circumpolar Arctic required by the Circumpolar Action Plan for polar bear conservation. Overall results suggest that legacy persistent organic pollutants (POPs) including polychlorinated biphenyls, chlordanes and perfluorooctane sulfonic acid (PFOS), followed by other perfluoroalkyl compounds (e.g. carboxylic acids, PFCAs) and brominated flame retardants, are still the main compounds in polar bears. Concentrations of several legacy POPs that have been banned for decades in most parts of the world have generally declined in polar bears. Current spatial trends of contaminants vary widely between compounds and recent studies suggest increased concentrations of both POPs and PFCAs in certain subpopulations. Correlative field studies, supported by in vitro studies, suggest that contaminant exposure disrupts circulating levels of thyroid hormones and lipid metabolism, and alters neurochemistry in polar bears. Additionally, field and in vitro studies and risk assessments indicate the potential for adverse impacts to polar bear immune functions from exposure to certain contaminants.

Screening of organic pollutants in pet hair samples and the significance of environmental factors

Organic pollutants (OPs) represent a wide range of chemicals that are potentially harmful for human and wildlife health. Many of these pollutants have been identified as endocrine disruptors that can alter hormonal balance producing adverse biological effects such as neurotoxicity, reproductive disorders, carcinogenicity and hepatotoxicity. For years, hair has been selected as a non-invasive source to assess levels of animal contamination. In the present study, a multiclass screening method for determining about 60 organic pollutants in pet hair was designed and validated for qualitative and quantitative purposes. Concentrations from different classes of organochlorine, and organophosphate pesticides (OCPs, and OPPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (NDL-PCBs and DL-PCBs), polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs) were identified in the selected pet hair samples from Ourense (NW, Spain). We detected most of these pollutants in the selected hair pets. The mean concentrations found ranged from 89 to 6556ng/g for OPEs, from 8.6 to 1031ng/g for PAHs, from 8.6 to 256ng/g for PBDEs, from 29 to 184ng/g for OPPs, from 0.29 to 139 for OCPs, from 0.30 to 59ng/g for NDL-PCBs and from 1.2 to 14ng/g for DL-PCBs. To our knowledge, this is the first study to document the presence of OPs in pets from North-West Spain and it could provide baseline information for future monitoring of OPs in the area.

Two decades of biomonitoring polar bear health in Greenland: a review

Summary

We present an overview of studies of anthropogenic pollutants in East Greenland polar bears over the period of 1999-2011. East Greenland polar bears are among the most polluted species, not just in the Arctic but globally, and represent an excellent biomonitoring species for levels and effects of global pollution in an apex predator. Therefore, an international multidisciplinary team joined to monitor and assess the patterns and concentrations of contaminants and their potential negative impact on polar bears. The review showed that East Greenland polar bears are exposed to a mix of chlorinated, brominated and fluorinated organic compounds as well as mercury which are all known to have endocrine, immune and organ-system toxic properties. For example, the concentrations of PCBs (polychlorinated biphenyls) in blubber ranged approximately 800-21,000 ng/g lw while mercury concentrations in liver and kidney ranged 0.1-50 μg/g ww. Regarding health endpoints, bone density seemed to decrease as a function of time and OHC (organohalogen compound) concentrations and further T-score for adult males indicated risk for osteoporosis. .The size of sexual organs decreased with increasing OHC concentrations. In the lower brain stem, mercury-associated decreases in NMDA-receptor levels and DNA-methylation was found The present review indicated that age was one of the major drivers for liver and renal lesions, although contaminants and infectious diseases may also play a role. Lesions in thyroid glands were most likely a result of infectious and genetic factors and probably, together with endocrine disrupting chemical (EDCs), the reason for disturbances/fluctuations in blood plasma thyroid hormone concentrations. Except for bone density reductions and neurological measures, all findings were supported by case-control studies of Greenland sledge dogs exposed long-term orally to similar combinations of contaminant concentrations. The studies of sledge dogs also indicated that the mixture of contaminants and fatty acids in the blubber of prey similar to that of polar bears induces cellular as well as humoral immune toxic changes. These controlled studies using model species for polar bears indicate that the correlative findings between health endpoint and contaminants in polar bears could be a cause-and-effect relationship. Physiologically based pharmacokinetic (PBPK) modelling showed that the risk quotients were ≥1 for ΣPCB, dieldrin and PFOS, which indicate an increased risk of prenatally reproductive pathology. In conclusion polar bears are susceptible to long-range transported chemicals that may have various adverse effects on multiple organ systems such as the reproductive and immune system.

Health effects from long-range transported contaminants in Arctic top predators: An integrated review based on studies of polar bears and relevant model species

The aim of this review is to provide a thorough overview of the health effects from the complexed biomagnified mixture of long-range transported industrial organochlorines (OCs), polybrominated diphenyl ethers (PBDEs), perfluorinated compounds (PFCs) and mercury (Hg) on polar bear (Ursus maritimus) health. Multiple scientific studies of polar bears indicate negative relationships between exposure to these contaminants and health parameters; however, these are all of a correlative nature and do not represent true cause-and-effects. Therefore, information from controlled studies of farmed Norwegian Arctic foxes (Vulpes lagopus) and housed East and West Greenland sledge dogs (Canis familiaris) were included as supportive weight of evidence in the clarification of contaminant exposure and health effects in polar bears. The review showed that hormone and vitamin concentrations, liver, kidney and thyroid gland morphology as well as reproductive and immune systems of polar bears are likely to be influenced by contaminant exposure. Furthermore, exclusively based on polar bear contaminant studies, bone density reduction and neurochemical disruption and DNA hypomethylation of the brain stem seemed to occur. The range of tissue concentration, at which these alterations were observed in polar bears, were ca. 1-70,000 ng/g lw for OCs (blood plasma concentrations of some PCB metabolites even higher), ca. 1-1000 ng/g lw for PBDEs and for PFCs and Hg 114-3052 ng/g ww and 0.1-50 microg/g ww, respectively. Similar concentrations were found in farmed foxes and housed sledge dogs while the lack of dose response designs did not allow an estimation of threshold levels for oral exposure and accumulated tissue concentrations. Nor was it possible to pinpoint a specific group of contaminants being more important than others nor analyze their interactions. For East Greenland polar bears the corresponding daily SigmaOC and SigmaPBDE oral exposure was estimated to be 35 and 0.34 microg/kg body weight, respectively. Furthermore, PFC concentrations, at which population effect levels could occur, are likely to be reached around year 2012 for the East Greenland polar bear subpopulation if current increasing temporal trends continue. Such proposed reproductive population effects were supported by physiological based pharmacokinetic (PBPK) modelling of critical body residues (CBR) with risk quotients >or=1 for SigmaPCB, dieldrin, SigmaPFC and SigmaOHC (organohalogen contaminant). The estimated daily TEQ for East Greenland polar bears and East Greenland sledge dogs were 32-281-folds above WHO SigmaTEQ guidelines for humans. Compared to human tolerable daily intake (TDI), these were exceeded for PCBs, dieldrin, chlordanes and SigmaHCH in East Greenland polar bears. Comparisons like these should be done with caution, but together with the CBR modelling and T-score estimations, these were the only available tools for polar bear risk evaluation. In conclusion, polar bears seem to be susceptible to contaminant induced stress that may have an overall sub-clinical impact on their health and population status via impacts on their immune and reproductive systems.