Brook trout personality, genetics could help populations adapt to habitat change

UNIVERSITY PARK, Pa. — As humans, we celebrate the personal characteristics, family traits and habits that make each of us unique. We recognize that individuals can come together in a team or community to provide diverse perspectives and collectively address challenges by contributing different strengths.

When we look at a wildlife species like brook trout, we might not immediately recognize whether a diversity of personalities and characteristics also exist in their populations. It's a question that fisheries researcher Shannon White, a doctoral degree student in Penn State's ecology program, is examining to identify whether certain traits and behaviors may help brook trout populations adapt to habitat pressures including warming climate conditions.

"If we get a better understanding of brook trout ecology, we might get better answers for management," said White, who is studying the behavioral traits, movement habits, heat tolerance and genetics of wild brook trout, as a member of the Pennsylvania Cooperative Fish and Wildlife Research Unit in the College of Agricultural Sciences.

"Brook trout conservation is a priority because they're a valued fish species and the only native trout in the eastern United States," said White. "They net billions of dollars in recreational fishing and tourism revenue and have an essential ecological role, both as a consumer of specific stream invertebrates and as a food source for birds and other predators."

researcher at left

Researcher Shannon White (left) with assistants implants a transmitter into a wild brook trout, which will allow her to track the fish's movement and monitor its behavior.

Image: Courtesy Shannon White

Survival pressures

The brook trout, Salvelinus fontinalis, is declining across its eastern United States range due to the loss of quality stream habitat. In Pennsylvania watersheds, more than a third of the species' populations no longer exist, and another 39 percent of local watersheds host brook trout populations now less than half their original size.

Eastern brook trout require clean, cold waterways or lakes to thrive, and optimal habitats have become scarce with the loss of cool, forest-shaded stream corridors. Brook trout also compete with non-native brown trout, which are stocked for angling and have a higher thermal tolerance. With temperatures varying in river systems, brook trout must seek out the coldest locations. While White sees potential for both sport fish to be managed, she explained brown trout competition often pushes brook trout higher into small headwater tributaries, restricting them to limited areas and resources. Expectations for warming stream temperatures suggest a future of growing pressures for remaining brook trout populations in Pennsylvania and the eastern U.S.

"The question is, how are brook trout going to survive these compounding threats? With climate change, many terrestrial species like birds can relocate — with fish, and especially with brook trout, they often get trapped," said White. "We need to consider if there are specific genes or behaviors that create adaptable and moving fish — we'll want to conserve that genetic content to maintain robust populations that can survive climate change a bit better."

brook trout research

Shannon White leads an electro-fishing crew in her research on a brook trout stream in Pennsylvania's Northern Tier. Some of her assistants are students from Susquehanna University.

Image: Courtesy Shannon White

Personality and adaptation

To investigate how personality affects brook trout responses to habitat changes, White has employed several laboratory experiments in constructed aquatic environments. In one, brook trout were introduced to a maze environment with a food source situated near visual cues such as a plant or rock — once they acclimated, the maze was rearranged to see if fish could relocate their food near the same environmental cues. The personalities of the fish were also recorded before they were introduced to the maze. Fish can generally be categorized as either "bold" or "shy," and readily demonstrate their personality when placed in a small personal tank — shy fish remain still or cower in a corner, while bold fish actively seek an escape by swimming in circles or jumping.

The study results, which White and her colleagues have submitted for upcoming publication in the journal Behavioural Processes, showed significantly different responses. Shy fish learned to relocate their food source based on the position of environmental cues, while bold fish traveled the maze without locating food.

"Bold fish aren't as good at forming small spatial maps — so they go looking for new locations when their habitat changes, while shy fish stay and try to solve the problems they encounter," explained White. "It's good to have a mix of these behaviors. Bold fish can colonize new areas if a population is wiped out by a natural event like a flood; shy fish will stay put and maintain a trout presence in their original habitat. If you wipe out either, you have problems."

brook trout tissue sample

Researchers extract a gill filament from an adult wild brook trout. Taking tissue samples like these allow analysis of gene expression to determine traits that best allow fish to survive.

Image: Penn State

Personality and movement in wild populations

The field portion of White's study is taking place in three stream tributaries that run into Loyalsock Creek, located in northern Pennsylvania's Lycoming and Sullivan Counties. Using electrofishing to catch and release fish, White has assessed the personality of 300 wild brook trout individuals. She has also collected blood and tissue samples and implanted radio telemetry trackers in 150 trout to follow their movements. A few trends are appearing in her initial results.

"So far, personality in this natural population has really varied," said White. "Some localized populations show boldness in 80 to 90 percent of individuals; others have only 10 percent. Our working theory is that personality is variable, and there's not a standard proportion of bold or shy fish in all populations. Personality expression also has genetic and environmental drivers. For example, in areas where brown trout limit brook trout from exploring habitats, it could be driving shy behavior. Brown trout also grow faster and could be eating bold young brook trout that are actively moving and easier to predate, which means fewer bold brook trout will survive and reproduce."

White is looking forward to analyzing trends in the movement behaviors recorded for the tagged fish.

"Movement is one of the most critical survival behaviors because the species needs individual fish that can find specific habitats," said White. "And we need to try to conserve genetic groups that know how to move to the right temperature habitats like cold groundwater upwellings in streams, or areas where they can avoid brown trout competition. When we look through the data, I think we'll see these fish are behaving in ways we haven't thought about before, such as moving between stream tributaries to find optimal habitat."

Genetic factors

Through genetic analysis of the tissue and blood samples she has collected, White also hopes to learn about the role genetics may play in brook trout adaptation. Pairing genetics and field observations may uncover individuals who joined a population from other locations, and contributed outside genes that are expressed in personality, movement behaviors and tolerance to changes like warming conditions.

One of the key brook trout questions centers around which genes generate the heat-shock proteins that help fish preserve healthy cells during warmer conditions — and what environmental influencers prompt the trout to turn those genes on or off. So far, research has suggested brook trout express the genes under not only thermal increases, but other environmental stressors such as low water levels; the genes are also being expressed at an early age, and when fish are still occupying temperatures several degrees below the upper-end of their thermal tolerance.

"It could mean they could adapt to warming water temperatures better than expected," said White. "If they are producing the proteins readily, they may develop some resistance and survive longer, at least if temperatures are warming at a slow pace."

Double Run with brook trout inset

 In Pennsylvania watersheds, more than a third of wild brook trout populations no longer exist, and another 39 percent of local watersheds host brook trout populations now less than half their original size. 

Image: By Shanon White

Management implications

Now at the mid-point of her research, White is beginning to see potential for her studies to add tools to brook trout conservation plans.

"In a lot of management strategies, we might think in terms of conserving brook trout as a species, or Pennsylvania's brook trout or a watershed's brook trout," said White. "The idea of conserving specific behaviors isn't always something we consider. But it's something we might insert into a management plan if we know the important factors for individuals. It's a management tool on a different scale."

White hopes her findings on behavior, movement and thermal tolerance may help conservationists focus their efforts. When local managers plan conservation practices for the high-quality streams in their areas, adding smaller-scale data may help them focus efforts first on stream reaches that also contain trout populations with essential genetics or behaviors. And new information on trout heat tolerance and movement behavior could identify moderate-quality habitats that could be remediated by replanting streams edges or removing waterway barriers in areas with actively-moving brook trout.

"One of the goals of this research is to show the importance of considering behavior and genes in wildlife conservation. My specific goal for brook trout is to demonstrate the value of looking at different habitat units, and thinking about scales of management, so we begin to consider behavior, genetics, individuals, populations, everything — and create a more holistic strategy."

White also promotes local participation in brook trout conservation, and is pleased that the species generates a lot of public interest, especially with organizations like Trout Unlimited and regional watershed groups. She regularly conducts community outreach presentations, and speaks with students and volunteers who would like to learn more about fisheries science or contribute to local conservation projects. She shares online updates on her brook trout research at www.TheTroutlook.com

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Last Updated January 16, 2017