Synergistic effects of sea ice-free periods and contaminant exposure on energy metabolism in polar bears

The polar bear is among the most vulnerable species to climate change because it depends on sea ice when it hunts for ringed seals. Longer ice-free summer seasons and greater seasonal variation in sea ice extent are particularly demanding for pregnant or lactating females and may ultimately affect reproductive success and population growth. Polar bears are also exposed to high levels of contaminants. The combination of the effects of pollutants and climate change has been hypothesized to be a worst-case scenario for Arctic wildlife. The use of energy reserves during sea-ice free periods may lead to increased tissue concentrations of pollutants. In addition, recent knowledge suggests that exposure to pollutants may have a detrimental effect on several physiological processes that are essential in helping polar bears adapt to rising temperatures and shrinking sea ice habitat. Therefore, we hypothesize that exposure to contaminants may lead to suboptimal energy metabolism in polar bears during ice-free periods. In order to explore our hypothesis, we compared aspects related to condition, health, energy metabolism and contaminant status in female polar bears sampled in Svalbard in spring and autumn. We collected a large sampling material that was analyzed for the planned parameters. We collected 112 samples from female polar bears during April and September in 2012 and 2013 at different locations of Svalbard, with contrasted sea ice conditions. We analyzed the samples for contaminant levels, stable isotope ratios, fatty acid composition, thyroid hormones, mRNA expression of genes involved in fat metabolism, blood clinical-chemical parameters and oxidative stress status. As new initiatives related to the project, we have studied metabolism at detail level using metabolomics. In addition, we analyzed DNA damage and mRNA expression of genes related metabolic processes and oxidative stress. Further, we have developed a method and studied effects of pollutants on polar bear fat cells in vitro. We have also new collaboration to measure telomere length, which protects DNA from damage. Two postdocs and 5 MSc students have been involved in the project. The main result is that sea ice conditions are related to polar bear diet, body fatness and concentrations of contaminants. Polar bears feed more on seabirds in areas with less sea ice whereas polar bears inhabiting areas with more stable sea ice conditions are more selective towards seals. Waterfowls and reindeer also make a part of autumn diet in areas where the sea ice retreats. Furthermore, solitary females were more selective, and feed on higher trophic level species compared to females with cubs. A larger proportion of polar bears fast in autumn compared to spring. When there is little sea ice, polar bear are at their thinnest and lipid-soluble contaminants become more concentrated in their body compared to when there is more sea ice. On the other hand, concentrations of contaminants that bind to proteins (PFAS) are higher in polar bear females that eat high at the food web and in those who are fasting. Levels of thyroid hormones, that regulate metabolism, were generally higher in spring compared to autumn although this seasonal effect was mainly observed in solitary females. Some of the hormones were negatively related to contaminant concentrations, particularly in spring. Relationships between transcript levels of genes related fat metabolism, blood biochemical parameters, metabolomics and contaminant levels suggest that fat metabolism is affected by contaminant exposure in polar bears. In vitro studies on polar bear cells indicate that contaminants may affect fat accumulation in polar bears.

The combination of the effects of pollutants and climate change has been hypothesized to be a worst-case scenario for arctic wildlife. The Barents Sea subpopulation of polar bears (Ursus maritimus) is subject to pronounced loss of sea ice habitat due to c hanging climate. In addition, this subpopulation is defined as a "hotspot" population in terms of contaminant exposure in Arctic wildlife. Prolongation of sea ice-free summer seasons is expected to challenge polar bears energetically. Since recent knowled ge suggests that contaminants may interfere with energy metabolism, we hypothesize that exposure to contaminants may lead to suboptimal energy metabolism during sea ice-free periods in polar bears. In order to explore the hypothesis, we will compare aspec ts related to fasting and health status, energy metabolism and contaminant exposure in 60 female polar bear sampled from Svalbard first in spring (April) and re-sampled the following autumn (September). First, we will investigate the influence of local se a ice cover on fasting and health status of polar bears measured as body condition, serum biochemistry and oxidative stress status. Second, we will investigate fasting processes at the physiological, molecular and biochemical level. Third, we will look at effect of fasting on toxicokinetics and biotransformation of a wide range contaminants including legacy and emerging organochlorinated, -brominated and -fluorinated compounds. Finally, we will combine the information of fasting status and processes, heal th parameters and contaminants to investigate whether energy metabolism differs between individuals that at exposed to different levels of contaminants. The proposed study will bring new information about both the effects of climate change and contaminant exposure in an apex arctic predator. This information is highly relevant both for scientific community and management agencies.