A Deep Sleep to Beat the Heat

a tenrec, a mammal with bristles, walks near a hollowed out log

Biological Strategy

Tenrecs

AskNature Team

Image: Robin Agarwal / Flickr / Some rights reserved

Maintain Homeostasis

When a living system is in homeostasis, it means that internal conditions are stable and relatively constant. For example, a human’s internal temperature is approximately 37 degrees Celsius (98.6 degrees Fahrenheit) unless there’s an illness. The human body maintains this temperature despite external ambient temperature. However, as with all physiological processes, maintaining homeostasis requires communication and coordination. So living systems have ways to detect changes from the norm, mechanisms to cause an adjustment, and negative feedback connections between the two. A desert lizard called the Gila monster offers a good example of maintaining homeostasis. The lizard goes from eating large meals to fasting for extended time periods. To maintain its blood sugar levels at a steady level, when food is scarce, its endocrine system releases a hormone that raises its blood sugar levels.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Tenrecs survive hot summer weather by entering a state of dormancy called estivation.

Image: Meghan Murphy, Smithsonian's National Zoo /

“Certain mammals are known to estivate. Perhaps the best-known examples are tenrecs – Madagascan insectivores related to hedgehogs. During the abnormally hot summer weather, they enter a state of inactivity resembling hibernation. Moreover, when outside temperatures plummet, they undergo true hibernation, becoming stiff and cold to the touch. This behavior has been noted on a number of occasions with captive zoo specimens of tenrecs maintained in countries with cooler average temperatures than that of their tropical Madagascan homeland.” (Shuker 2001:105)

“Prior to the start of the Austral winter (May to September) they eat more and lay down fat reserves within their bodies in order to hibernate, which they usually do in burrows with the entrance plugged with soil. The long-tailed or shrew tenrecs (Microgale) also store fat in their tails, and in Dobson’s shrew tenrec (Microgale dobsoni) the nomad weight of 1 1/2 ounces (46 g) is almost doubled by the fat stored for hibernation. Madagascan winters are quitter mild, and could be termed the cool, dry season rather than winter. In the highlands at 4,100 feet (1,250 m) the temperature averages 59° F (15° C) in the dry season, just a few degrees lower than summer levels, but the vegetation, and consequently the food supplies, suffer from lack of rain and the tenrecs become dormant in their burrows…Dormant tenrecs dug out of their burrows were cold to the touch, had a very low breathing rate, and had neither food in their stomach or feces in the intestine. Even when active the tenrecs have a variable body temperature that ranges from 75.2° F (24°C) to 95°F (35°C). This is considerable lower than other mammals, which average 98.6°F (37°C), and the tenrec shares with the sloths the title of the most cold-blooded mammal. The body temperature of hibernating tenrecs is usually just 1.8° F (1°C) above the ambient temperature…These tenrecs also experience a daily temperature range of several degrees between their active and rest periods during the spring and summer, and they also estivate during the hottest times of the year.” (Roots 2006: 191)

Last Updated September 14, 2016

References

Book

The Hidden Powers of Animals: Uncovering the Secrets of Nature

January 1, 1970 | Dr. Karl P. N. Shuker

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Reference

Book

Hibernation (Greenwood Guides to the Animal World)

February 24, 2021 | Clive Roots

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