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Brook trout are revealing intriguing genetic capabilities that enable them to cope with rising temperatures, potentially safeguarding their survival amid increasingly frequent heatwaves. Historically regarded as a coldwater species inhabiting the streams and lakes of the eastern United States and Canada, brook trout are facing significant threats from climate change, with over half of their habitat classified as highly sensitive to warming. A recent study from researchers at Penn State uncovers that these fish possess a genetic mechanism for adapting to thermal stress, suggesting that these adaptations can be transmitted across generations.
“We observed significant adaptability in brook trout in response to heat stress, reflecting their ability to acclimate and enhance their tolerance to elevated temperatures,” explained Jason Keagy, the study’s lead researcher and assistant research professor in wildlife behavioral ecology. “Our assessment spanned two heatwaves, with a notable increase in expression changes during the second wave, possibly indicating that the initial heatwave prepared the fish for the subsequent stress.”
Published in the *Science of the Total Environment*, the study details how gene expressions related to immune responses were heightened, while those linked to oxygen transport diminished under elevated temperatures during two successive heatwaves in July and August of 2022 in four smaller streams in central Pennsylvania.
“By analyzing these gene-expression signatures, we can effectively gauge the physiological stress levels within brook trout,” Keagy noted.
Throughout the heatwaves, the research team tracked temperature variables and performed RNA analyses on 116 brook trout across various timeframes in the four streams. They extracted RNA from the fish’s gills without harm and sequenced it, allowing them to quantify the expression levels of 32,670 distinct genetic transcripts crucial for various cellular functions. It was found that the gene-expression responses to temperature fluctuations were relatively consistent among fish from all four streams.
The team identified 43 genes displaying varying expression levels over time, with 42 directly associated with changes in water temperature. Some of these genes, including those responsible for heat-shock and cold-stress proteins, corroborate findings from previous studies on temperature adaptation.
Keagy emphasized that brook trout begin to face growth rate declines when water temperatures exceed 61 degrees Fahrenheit, with acute thermal stress occurring above 68 degrees Fahrenheit. The critical thermal maximum for these fish approaches 84 degrees Fahrenheit. Furthermore, he highlighted concerns that the increasing frequency and severity of extreme weather events are likely to diminish suitable habitats for brook trout. This is exacerbated by factors like deforestation and the introduction of competing species, such as brown trout.
“The impact of extreme weather may be more consequential for species loss than changes in average yearly temperatures, posing significant risks to cold-blooded species that are heavily influenced by their surroundings,” Keagy explained.
Conducting this research under natural conditions posed significant challenges. “This was a substantial undertaking,” Keagy stated. “We monitored local weather forecasts to identify heatwaves, capturing fish before, during, and after each event. The challenge lay in the unpredictable nature of stream water temperatures. Thanks to our dedicated graduate student Sarah Batchelor and the innovative data analysis from postdoctoral scholar Justin Waraniak, we navigated these complexities effectively.”
This research marks a pioneering exploration in landscape transcriptomics—a novel field recently proposed by an interdisciplinary group at Penn State. The hypothesis suggested that genetic signatures could signal specific environmental stressors affecting wildlife, making this study one of the first to implement these methods. Another recent publication from the same college also explored stress responses in bumblebees.
“This study highlights the importance of landscape transcriptomics for understanding how wild organisms respond to short-term environmental stressors,” Keagy remarked. “The implications of this research could inform future investigations aimed at uncovering the genetic diversity that enables resilience to heatwaves, ultimately improving our predictions for brook trout populations facing climate change challenges.”
This study received funding from the Penn State College of Agricultural Sciences Strategic Networks and Initiatives Program and the U.S. Department of Agriculture’s National Institute of Food and Agriculture.
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