- This web page was produced as an assignment for an undergraduate course at Davidson College -
Basic Biology and Habitat of the Naked Mole-Rat
Gray Lyons
The Naked Mole-Rat (Heterocephalus glaber) is a small mammal in the order Rodentia and the family Bathyergidae. The Naked Mole-Rat is morphologically characterized by its mostly hairless translucent skin and prominent incisor teeth. Naked Mole-Rats have some hair between their toes which they use to sweep dirt. It also has whiskers on both face and tail for navigating subterranean habitats as it is nearly sightless. The skin appears wrinkled because the Naked Mole-Rats are devoid of subcutaneous fat. Naked mole-rats are the only known poikilothermic mammals, that is, their body temperature is variable and related to ambient temperature. These animals have developed physiological mechanisms to withstand thermal variations, including the lack of cutaneous sweat glands, as well as behavioral mechanisms, such as burrowing and huddling (Yahav and Buffenstein, 1991).
The Naked Mole-Rat lives primarily under the arid African savannah grasslands in the region indicated in the map below, comprising parts of Kenya, Ethiopia, and Somalia. The animals live in colonies comprised of a complex burrow system. Their entire existence is spent in these burrows, without ever encroaching the surface. Since the burrows are discreet non-overlapping habitats, it may be said that the social spacing of the Naked Mole-Rat is that of a classical territory.
In a recent study, Naked Mole-Rats were observed in captivity for body temperature and oxygen consumption, thus indicating metabolic activity (Riccio and Goldman, 2000). On both parameters, the authors noticed regular circadian rhythms which coincided with a typical terrestrial twenty-four hour day. Moreover, when the naked mole-rats were given access to running wheels, exercise was observed most frequently during the day period. At first glance, the findings of this group are not especially notable - most species exhibit diurnal circadian rhythms. The effects of circadian rhythm on physiological function are particularly interesting, however, for the sub-terrestrial naked mole-rat (Riccio and Goldman, 2000).
Naked Mole-Rats are herbivorous and feed primarily on roots, tubers and corms. They do not drink water, rather they are hydrated by the food they consume. Naked Mole-Rats have been observed to engage in tuber boring - a practice whereby they pierce the skin of a root and eat a small hole through the root without consuming it entirely. They then will eat sporadically from the inside of the root without killing it - thereby forming a symbiotic relationship with the flora in their habitat. Moreover, eating from the inside of the bore toward the outside allows them to minimize the amount of the skin of the root that they must consume to get to the middle. To assist in digestion of these roots and tubers, Naked Mole-Rats have high levels of gut fauna which help break down the cellulose. Moreover, Naked Mole-Rats have been observed to engage in coprophagy, which is aids in digestion and maximize the absorption of nutrients.
Naked-Mole Rats occupy an uncommon niche due to their exclusively subterranean habitat. Although they are somewhat susceptible to predation by burrowing reptiles, they do not suffer from the high amounts of predation that plague other rodent species. Naked Mole-Rat colonies are believed to be exceptionally competitive. Although an intercolony encounter has never been observed in nature, those that have occurred in a laboratory setting are usually highly competitive. In this situation, Naked Mole-Rats will display aggressively and work to seal the opening between the two colonies. However, Naked Mole-Rats are most commonly known for their intracolony behavior, which is addressed in the next section, Eusociality and Reproduction in the Naked Mole-Rat.
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This web site was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2004