Moving from field studies to ex vivo models for understanding and predicting toxicological responses to multiple stressors in marine mammals

Human activities are increasingly threatening biodiversity and ecosystems. One of the largest threats is chemical pollution. As marine predators, marine mammals can accumulate high levels of pollutants in their fat stores. In addition, they are also potentially affected by a range of other stressors, including shipping traffic, climate change, resource limitations and overall degradation of their habitats. Exposure to these stressors have the potential to create stress yielding to elevated levels of stress hormones. These combined chronic stressors are likely to affect marine mammals' health and survival. Killer whales and polar bears are among the most polluted animals on Earth. Killer whales are also in the spotlight of an intense whale tourism, while polar bears are at the forefront of climate change up in the Arctic. Alterations caused by pollutants, and stress related to climate change and whale tourism may thus interact, with possible combined effects associated with serious health consequences. Yet, our understanding in pollutants response in marine mammals remain poorly understood, and there is a lack of knowledge on the consequences when animals must cope with several stressors at the same time. These stressors can potentially have impacts on blubber composition and function. Blubber is a multi-functional endocrine and complex organ involved in a multitude of physiological processes playing key roles in health and diseases. To date, most of our toxicological knowledge relies on traditional approaches, which consist in examining the associations between the concentration of pollutants and specific health metrics. Although valuable, this approach suffers from important limitations to establish a mechanistic understanding and a causal link between pollutant exposure and health issues. In SLICE, we propose to complement this approach with the development of an alternative methodology through an ex vivo model. Practically, we plan to expose small blubber slices (<1mm thick) from different marine mammal species to cocktail of pollutants and/or stress hormones (to mimic other stressors like climate change or whale tourism), and assess how the tissues react. We will specifically investigate modifications in gene expressions and spill-over consequences on energy storage. We also plan to run correlative studies to compare outputs from both approaches. So far, we have collected biopsy samples from killer whales and polar bears and the research questions addressed by SLICE have been enlarged to additional whale's species including sperm whales, long-finned pilot whales and humpback whales. Fresh biopsies have been processed in the lab during the sampling events and we have been able to set up the method to keep the tissue slices alive and functional. Frozen biopsies have also been processed in the lab for pollutants and lipids analyses and we have stated to analyse the data. The project objectives as well as the first results have been communicated to the scientific community, stakeholders and larger audience through scientific publications, scientific conferences, popular science articles, and seminars.

Marine mammals are relevant sentinels of oceans and human health. Arctic top predators, such as killer whales and polar bears, are among the most polluted species on Earth. They are also exposed to additional anthropogenic stressors such as climate change, resource limitations, habitat loss, and human coastal activities. However, cause-effect and mechanistic understanding in pollutants response in marine mammals remain poorly understood, and there is a lack of knowledge on the combined effects of multiple stressors. There is a need to develop alternative solutions and move from a reductionist perspective to a holistic and integrative strategy to understand the complex patterns of responses. In SLICE, we will combine experimental and field-based studies, together with the application of toxicogenomic approaches to advance the knowledge on toxicological responses to multiple stressors in killer whales and polar bears. We will develop an alternative methodology through an ex vivo adipose tissue slices model for both species and use it to characterize genome-wide transcriptional and lipidomics responses to pollutants and stress. This novel cost-effective ethically sustainable tool enables to test responses to pollutants and stress separately or simultaneously, which is an important step forward to deepen our understanding of toxicological responses to multiple stressors in marine mammals. In parallel, we will conduct correlative field studies to assess potential combined effects with pollutants and stress related to climate change for polar bears and whale tourism for killer whales. As charismatic megafauna, polar bears and whales have a strong potential to raise environmental awareness. Scientific knowledge generated by the project (and beyond) on threats of anthropogenic stressors will be communicated to the the scientific community, the public (focusing on young) and relevant stakeholders.