Organismal effects of heat in a fixed ecological niche: Implications on the role of behavioral buffering in our changing world

• Published in: The Science of the total environment Vol. 893; p. 164809
• Main Authors: Woodruff, Mary J., Sermersheim, Layne O., Wolf, Sarah E., Rosvall, Kimberly A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-10-2023
• Subjects: Acclimation; Acclimatization; Animals; Animals, Wild; Avian; Behavior; Brain; Climate change; Corticosterone; Ecosystem; Heat tolerance; Juvenile; Resilience; Stress; Temperature; Thermal adaptation; Juvenile; Climate change; Brain; Thermal adaptation; Heat tolerance; Avian; Behavior; Stress; Resilience; Acclimation
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.164809

Increasingly frequent and intense heatwaves generate new challenges for many organisms. Our understanding of the ecological predictors of thermal vulnerability is improving, yet, at least in endotherms, we are still only beginning to understand one critical component of predicting resilience: exactly how do wild animals cope with sub-lethal heat? In wild endotherms, most prior work focuses on one or a few traits, leaving uncertainty about organismal consequences of heatwaves. Here, we experimentally generated a 2.8°C heatwave for free-living nestling tree swallows (Tachycineta bicolor). Over a week-long period coinciding with the peak of post-natal growth, we quantified a suite of traits to test the hypotheses that (a) behavioral or (b) physiological responses may be sufficient for coping with inescapable heat. Heat-exposed nestlings increased panting and decreased huddling, but treatment effects on panting dissipated over time, even though heat-induced temperatures remained elevated. Physiologically, we found no effects of heat on: gene expression of three heat shock proteins in blood, muscle, and three brain regions; secretion of circulating corticosterone at baseline or in response to handling; and telomere length. Moreover, heat had a positive effect on growth and a marginal, but not significant, positive effect on subsequent recruitment. These results suggest that nestlings were generally buffered from deleterious effects of heat, with one exception: heat-exposed nestlings exhibited lower gene expression for superoxide dismutase, a key antioxidant defense. Despite this one apparent cost, our thorough organismal investigation indicates general resilience to a heatwave that may, in part, stem from behavioral buffering and acclimation. Our approach provides a mechanistic framework that we hope will improve understanding of species persistence in the face of climate change.
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•Intensifying heatwaves highlight the need to understand how heat affects wildlife.•We experimentally generated an inescapable sub-lethal heatwave for nestling birds.•Heat bolstered growth but a battery of physiological responses were unaffected.•Behavior acclimated to heat, suggesting behavior is a front-line response to heat.•Organismal approaches are critical for interpreting the valence of heat's effects.