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animals physiology temperature aestivation

What Do You Do When It's Too Hot to Move?

If there’s not enough ice cream in the world to cool you off, here are some tips from nature on coping with the heat!

According to the building manager, the lab I work in allegedly has air conditioning. I’ve searched all over the lab, but when temperatures in the northeastern US hit 95 degrees for the first time in June, I found absolutely no evidence of airflow and our south-facing windows were heating us up like a microwave. I tried to power through with an iced coffee, but by afternoon I was tired and headachey and wanted nothing more than to lie down and sleep. I eventually packed up and went to work from home, but I got curious about what animals without access to cold beverages and window fans do when it gets this dang hot.

Humans (and some other mammals like horses and monkeys) can sweat to cool off, lowering our body temperature through the evaporation of water from our skin. That’s a physiological response that we don’t have voluntary control over—and if you can somehow control sweating with your mind, definitely message me your secrets before my next conference presentation, please and thank you.

Apart from physiological responses (i.e. sweating) and options not available to your average animal (eating ice cream on the floor in front of the air conditioner), what behaviors keep animals cool in nature?

Option 1: pant!


Fig.1 Some hot animals (like these very good Dachshunds) pant to lower their body temperature. (Image via Luke Ma)

The panting response involves taking fast, shallow breaths that help speed evaporative heat loss and is used by both mammals and birds (both of which internally regulate their body temperatures). Most heat exchange during panting takes place in the mucus membrane lining of the nose, and special veins allow this cooler blood to absorb heat from blood that’s headed to the brain [1]. Panting lets animals literally keep a cool head by lowering the brain to an acceptable temperature even when it’s too hot to think.

Feasibility for me: low (I hyperventilated and also looked ridiculous. Not helpful).

Option 2: move!

Lizard hiding under rock


Fig. 2 When the heat gets to be too much, animals can move to a cooler environment. This lizard is just chillin’ under a rock. (Image via Mark Devine)

For ectotherms (animals that do not internally regulate their body temperatures), the environment plays a big role in how hot or cold you are. When it’s too hot, reptiles such as rock-dwelling lizards retreat to deep crevices. They prefer larger, thicker rocks that provide plenty of shade from the sun to wait out the hottest part of the day [2].

Feasibility for me: pretty effective, even though I’m not an ectotherm.

Option 3: aestivate!

27|50 1st place: Female Hazel Dormouse in torpor- Fraser Combe


Fig. 3 A female hazel dormouse in torpor. Gotta reduce energy output and keep that body temperature low! (Image via Fraser Combe)

When it’s just too hot, some animals have an even more extreme response up their sleeves: aestivation. Like hibernation, aestivation involves torpor, or an extended period of inactivity in which an animal’s metabolism goes way down [3]. Since metabolism (a.k.a., the general necessities of being alive, including converting food into energy and building and maintaining cells) generates heat, slowing down metabolism via torpor reduces both energy used and body heat produced. However, while hibernation is used to conserve energy through the winter, some animals use aestivation to lower their overall body temperatures when it’s too hot. A variety of mammals, birds, insects, and others aestivate when conditions are right.

Feasibility for me: sounds good, this will be my strategy for the next several months! Don’t try to rouse me from my torpor unless you have ice cream.

References:

  1. Robertshaw, D. “Mechanisms for the control of respiratory evaporative heat loss in panting animals.” Journal of Applied Physiology 101 (2006): 664-668

  2. Kearney, M. “Hot rocks and much-too-hot rocks: seasonal patterns of retreat-site selection by a nocturnal ectotherm.Journal of Thermal Biology 27 (2002): 205-218

  3. Geiser, F. “Aestivation in mammals and birds.” Aestivation: Molecular and Physiological Aspects (2009): 95-111.

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