Scientists Discover 'Weirdness' in Animals' Ability to Control Body Heat for Survival

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Scientists Discover 'Weirdness' in Animals' Ability to Control Body Heat for Survival

In a world where stability often seems paramount, cutting-edge scientific research is revealing extraordinary capabilities within the animal kingdom that challenge our conventional biological understanding. While we often assume mammals and birds maintain a constant internal body temperature – a state known as homeothermy – a growing body of evidence suggests many species employ a far more flexible strategy: heterothermy. This remarkable ability allows animals to dramatically alter their internal temperature, fluctuating it for minutes, hours, or even weeks at a time. This physiological plasticity provides a crucial survival advantage, enabling them to endure extreme environmental challenges such as severe storms, floods, and predator threats, moving beyond our baseline assumptions about animal physiology.

Historically, the capacity for stable body temperature was considered a defining characteristic of endotherms like mammals and birds. However, early explorations, such as those by British physician-scientist Charles Blagden in 1774, hinted at unusual phenomena. Blagden famously subjected himself to environments exceeding 93°C (200°F), yet remarkably maintained his core body temperature around 37°C (98°F), astonishing his contemporaries and hinting at a deeper complexity in thermal regulation.

Today, while homeothermy remains prevalent, the exceptions are becoming increasingly significant and scientifically compelling. The fat-tailed dwarf lemur, for instance, can exhibit body temperature fluctuations of nearly 25°C (45°F) within a single day. These dramatic shifts are not mere anomalies but sophisticated survival mechanisms finely tuned to environmental pressures.

Heterothermy, the capacity to vary body temperature, is an evolutionary strategy gaining substantial recognition. "Because we’re homeotherms, we assume all mammals work the way we do," explains Danielle Levesque, a mammalian ecophysiologist at the University of Maine. However, recent technological advancements, particularly in tracking small animals and monitoring their metabolic rates in the wild, have unveiled what Levesque terms "a lot more weirdness." This technological leap is enabling researchers to observe and understand these less conventional physiological adaptations in unprecedented detail.

One of the most extreme and well-studied forms of heterothermy is classic hibernation. This strategy is primarily employed to conserve energy during the harsh, prolonged winters of the Northern Hemisphere. Animals entering hibernation undergo periods of "deep torpor," characterized by a significant slowdown of metabolic processes and a drastic drop in body temperature, sometimes nearing freezing point. Yet, this profound state represents just one end of a broad spectrum of thermal regulation strategies.

Scientists now propose that many mammals can utilize shorter episodes of "shallow torpor." This is loosely defined as a less drastic reduction in metabolism and smaller fluctuations in body temperature, deployed as environmental conditions necessitate. This suggests that torpor serves a wider range of functions than previously understood. Comparative physiologist Fritz Geiser of the University of New England in Australia notes, "It’s extremely complicated. It’s much more interesting than homeothermy."

The adaptability of heterothermy is vividly illustrated by Australian eastern long-eared bats. Research conducted by bat biologist Mari Aas Fjelldal, using miniature transmitters to record skin temperatures of 37 wild bats, revealed that these animals adjust their torpor use based on daily weather fluctuations. While they predictably entered torpor more during cold spells, they also increased torpor frequency in response to rain and wind. Fjelldal and colleagues reported in *Oecologia* (2021) that this behavior is logical: wind and rain increase the energetic cost of flying – a significant challenge for tiny bats weighing less than a small candy bar – and make foraging for insects more difficult and energy-intensive.

Even more striking are reports of pregnant hoary bats entering torpor during unpredictable spring storms. This physiological maneuver effectively pauses their pregnancies. "It means that they can, to some degree, actually decide a bit when to give birth," Fjelldal explains, "which is really handy when you’re living in an environment that can be quite harsh in the spring." Given that producing milk is metabolically expensive, delaying birth until food resources are more reliably available offers a distinct survival advantage for both mother and offspring.

Other species, like the sugar glider – a small, pink-nosed marsupial that glides using skin membranes – rarely engage in torpor but can leverage it during severe weather emergencies. During a Category 1 cyclone event with winds near 100 km/h and substantial rainfall, sugar gliders were observed remaining in their tree hollows, with many entering torpor. Their body temperature dropped from a typical 34.5°C (94.1°F) to an average of approximately 19°C (66°F), according to findings by Geiser and colleagues.

Similarly, in a laboratory setting, researchers documented an unusual period of multi-day torpor in a golden spiny mouse following an accidental flooding event, with its body temperature reaching a low of about 24°C (75°F).

This flexible utilization of torpor allows heterotherms to "wait out" catastrophic events. In contrast, homeothermic species, unable to readily reduce their metabolic demands for food and water, may be less resilient to such extreme conditions. "Maybe there’s no food, maybe no water, it may be really warm," notes ecophysiologist Julia Nowack of Liverpool John Moores University, a co-author on the sugar glider study. She emphasizes that torpor, particularly in tropical environments, can be triggered by "lots of different things."

Beyond environmental pressures, threats such as predation can also prompt animals to enter torpor. The edible dormouse, for example, sometimes utilizes extended periods of torpor in early spring to navigate times of food scarcity.

These fascinating adaptations underscore the ongoing discoveries in animal survival strategies. The study of heterothermy not only deepens our understanding of evolutionary biology but also offers potential insights into resilience and adaptation in the face of escalating environmental challenges.

Ekhbary News Agency