Document type: article published in Science News
Author: Katarina Zimmer
Preview: Humans aren't the only animals with hot tempers. In 2016, ecologist Kristen Cecala and a colleague watched black-bellied salamanders(Desmognathus amphileucus) from Appalachian streams lunge at one another inside a lab incubator. The little animals - barely a hand's length - can be fiercely territorial, thrashing to bite their opponents or send them fleeing, says Cecala, of the University of the South in Sewanee, Tenn. "Salamander fight club," as Cecala calls the experiment, was set up to test how rising temperatures would affect the amphibians' behavior. Black-bellied salamanders, it turned out, were nearly four times as likely to act aggressively at 25° Celsius - much warmer than their stream habitats - compared with more natural conditions at 15° or 20° C.
And salamanders aren't alone in their raucous behavior. Studies show that many animals - monkeys, rats, mice, fish, ants - tend to get more aggressive at higher temperatures. As the planet warms due to climate change, rising temperatures could subtly affect some species' social structures and ecosystems. But the findings may also tell us something deeper about how heat affects animals physiologically - and potentially reveal clues to increased violence and crime among humans in hot weather. (...) In one 2024 study, freshwater biologist Erin Francispillai and her colleagues placed bluntnose minnows(Pimephales notatus) in tanks where temperatures fluctuated from 18° to 24° C within a day - a change that mimics similar conditions documented in streams that have lost shade due to deforestation. At higher temperatures, the small fish behaved more aggressively toward their shoalmates compared with fish kept at constant temperatures. (...) One possible explanation for this heat-aggression link in ectotherms is that warmth dials up the animals' metabolisms, using up more of their energy. This requires more calories, making animals more territorial and aggressive to secure food. (...)
By contrast, warm-blooded endotherms like mammals may be less sensitive to these effects, Francispillai says, because they can cool their bodies through sweating or panting, for instance. But the heat-aggression association has been documented in some monkeys, rats, mice and, according to Linnman's research, even dogs.
Even for endotherms, warmth boosts metabolic rates, and calorie loss may be exacerbated by the energy needed to cool their bodies, Francispillai says. When the priority is getting more calories, less energy may go toward maintaining social behaviors and regulating aggression, she speculates. Yet Linnman suggests that increased aggression could also arise from the discomfort that warm-blooded animals feel in hot weather. (...)
In humans, scientists debate the extent to which the aggression-heat relationship is due to biological effects of heat on behavior versus increased outdoor activities on hot days. But "as the heat-aggression correlation is consistent across multiple species, it suggests that simple 'sociological explanations' ... are not sufficient," Linnman says. (...)
