Environmental Stressors and Wildlife Health

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Environmental stressors such as contaminants and disease can cause physiological imbalance in all types of wildlife. WERC’s Drs. Lizabeth Bowen and A. Keith Miles develop gene transcription profiles to detect organisms’ physiological responses to environmental stressors and provide resource managers with early warnings for potential effects on wildlife and ecosystem health.

From the southwestern deserts of the U.S. to the Arctic ice, WERC’s Drs. Lizabeth Bowen and Keith Miles partner with Federal, state, and local groups to study the effects of environmental stressors on wildlife. By studying affected organisms’ gene transcription patterns, they can detect wildlife responses to threats in the environment on the most basic biological level and provide resource managers with early warnings for potential declines in wildlife health.

Effects of Changes in the Environment on Alaska’s Nearshore Ecosystem

Together with the USGS Alaska Science Center, Drs. Bowen and Miles develop gene transcription profiles that can help resource managers detect physiological changes in wildlife in response to environmental stressors. In particular, the scientists are studying four species found on the coasts of Alaska: sea otters, brown bears, razor clams, and mussels. Their projects provide insight into the potential effects of dietary clams and mussels on brown bear physiology, and assess mussels’ response to alternative states of the environment (e.g. brackish water vs. seawater, acidic versus neutral pH). Study results will also aid in the development of a monitoring tool that links changing ocean conditions to nearshore food web dynamics.

Image: Sea Otter in Monterey Bay, California

A sea otter swims in Monterey Bay, California. (Credit: Tania Larson, U.S. Geological Survey. Public domain.)

Sea otters

Fluctuating sea otter (Enhydra lutris) numbers in the eastern Pacific have raised questions for resource agencies that manage this species. To this end, Drs. Bowen and Miles obtained samples from more than 400 sea otters from Southern California to the Aleutian Islands, Alaska, to identify factors that may contribute to sea otter population growth or decline. The researchers identified specific genetic markers that otters produce in response to stressors such as nutrient deficiency or exposure to contaminants. The genes targeted in this study are linked to physiological systems that regulate immune system function, inflammation, cell protection, tumor suppression, cellular stress-response, and production of enzymes that neutralize contaminants in the body. These genes can be influenced by biological, physical, or anthropogenic impacts and therefore provide insight into types of stressors present in the environment.

Drs. Bowen and Miles demonstrated the effectiveness of using gene transcription to determine environmental quality in a study of sea otters nearly two decades after the 1989 ‘Exxon Valdez’ oil spill. Sea otters sampled from oiled areas within Prince William Sound in 2008 had higher transcription of genes associated with tumor formation, cell death, heat shock, and inflammation than those from areas less impacted by the spill. Subsequent sampling in 2012 showed a notable decline in transcription of these genes, indicating a likely improvement in the quality of the environment. Sea otters in central California exposed to runoff from a major coastal forest fire in 2008 showed a similar gene transcription pattern as the Prince William Sound population, with declines in transcription of these genes one year after the fire.


Photo of a brown bear eating an intertidal invertebrate

An Alaskan brown bear spotted eating an intertidal invertebrate in nearshore waters. (Credit: Jim Pfeiffenberger, National Park Service. Public domain.)

Nearshore marine ecosystems are unique. Located within the interface between land and sea, these environments are shaped by biological influences from both the coast and offshore currents, and by changes in the physical environment, e.g., ocean warming, acidification, and sea level rise. The nearshore habitats of National Parks in southwest Alaska are also facing management concerns that include increasing coastal visitation and expanded commercial and industrial development. All of these issues have the potential to significantly degrade resources in coastal ecosystems.

Understanding these systems is critical to the National Park Service’s mission to conserve ecosystems for future generations. Understanding the relationships between coastal and terrestrial ecosystems, and between wildlife and park visitors, will help the USGS provide the NPS with the information it needs.

Within the marine nearshore zone of the Gulf of Alaska, intertidal invertebrates are an important food source for many predators that include brown bears and sea otters. Gulf of Alaska intertidal communities are vulnerable to catastrophes such as earthquakes and hydrocarbon contamination from the Exxon Valdez oil spill, and recent stressors such as ocean acidification and warming, increased vessel traffic, and oil exploration in Cook Inlet. Using molecular tools, Drs. Bowen and Miles seek to quantify the links between nearshore ecosystem function and terrestrial ecosystem function from a top-down, bottom-up food web approach, with coastal brown bears as the apex predator and intertidal bivalves as the primary consumer. Do brown bears and their prey have transcription profiles that indicate strong terrestrial influence, or are intertidal invertebrates influenced more by oceanic processes? Could potential detrimental effects of, e.g., acidification, subsequently affect brown bear populations? Ultimately, this study will assess how changes to the nearshore marine system might affect the shoreline ecosystem and subsequent visitor opportunities in the Gulf’s National Parks.


The brown bear (Ursus arctos) is an apex predator, and thus an ideal sentinel species for detecting potential threats to the food web and ecosystem. Using molecular-based gene transcription, Drs. Bowen and Miles analyzed blood from 130 brown bears sampled at three National Parks and Preserves in Alaska. Although the subject populations appear stable and exist within protected environments, the scientists noted differences in transcript profiles. The most prevalent differences were among locations. The transcript patterns among groups reflect the influence of environmental factors, such as nutritional status, disease, and exposure to foreign substances from oil spills or pollution. These transcription profiles also represent baselines for each unique environment by which future measures can be made to identify early indication of population-level changes due to, for example, increasing Arctic temperatures. Some of those environmental changes may benefit brown bears, but other effects such as the manifestation of disease or indirect effects of oceanic acidification may have negative impacts.


Desert Bighorn Sheep Disease Dynamics

From the 1970s through 2014, more than 14,000 adult desert bighorn sheep died of pneumonia within the western U.S. Today, this disease remains the biggest obstacle to sustaining bighorn sheep populations. Drs. Bowen and Miles are monitoring the gene transcription patterns of desert bighorn sheep to assess populations for subtle yet significant changes in their physiology. The study results can provide insight into the reasons why the pathogen can have little to no impact on health and recruitment in herds of bighorn sheep, or cause pneumonia die-offs across all ages, followed by years of pneumonia deaths in lambs. Determining which factors contribute to this difference in herd response to respiratory disease, and how management actions can improve post-disease herd performance, is a key question for sheep managers across North America. Visit the full project page to learn more.


Heat Stress in Migrating Yukon River Chinook Salmon

Chinook salmon (Oncorhynchus tshawytscha) in the Arctic-Yukon-Kuskokwim region are experiencing widespread declines that could be related to rising water temperatures. Within the Yukon watershed, higher water temperatures could increase energy demands on salmon migrating upstream and make it impossible for them to reach freshwater spawning areas alive. Chinook salmon populations support a thriving fishery, and their collapse could affect local economies.

Drs. Bowen and Miles are testing Chinook salmon for evidence of heat stress by examining the response of heat shock proteins and gene transcription from salmon captured during spawning migration in reaches throughout the Yukon River watershed, including areas known to have high temperatures. Visit the full webpage on this project to learn more details.


Polar Bears Health and Disease Dynamics

A polar bear walks across rubble ice in the Alaska portion of the southern Beaufort Sea

A polar bear walks across rubble ice in the Alaska portion of the southern Beaufort Sea, April 8, 2011. (Credit: Mike Lockhart, USGS. Public domain.)

In 2012, 28% of polar bears sampled in a study in the southern Beaufort Sea region of Alaska had varying degrees of alopecia, or hair loss, and reduced body condition. Concurrently, scientists found elevated numbers of sick or dead ringed seals in the southern Beaufort, Chukchi, and Bering seas, resulting in the declaration of an unusual mortality event by the National Oceanic and Atmospheric Administration. The causes of these events are unknown, and researchers have been unable to detect related physiological changes within individual animals using classical diagnostic methods.

Drs. Bowen and Miles used gene based technology to investigate the circumstances responsible for the susceptibility of certain polar bears to hair loss and reduced health. Using transcriptomic analysis, Drs. Bowen and Miles identified enhanced immune response, viral defense, and response to stress in polar bears with alopecia. The results provide an example of an alternative technique for searching for and identifying the factors driving disease that would be less costly, more focused, and more efficient than classical methods. This technology will help resource managers design systems of surveillance and investigation that provide early warning of health concerns in wildlife species important to humans. Visit the separate project page.