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| Source: Wikipedia Commons |
Range and Habitat
Naked Mole rats are found chiefly in Africa, throughout Somalia, Ethiopia, and a large portion of eastern Kenya. Their range extends as far south as the Tsavo West National Park and is thought to be much wider than what is currently known. Naked mole rats live in arid environments with high temperatures and low and irregular rainfall patterns. (1) They live underground their entire lives and only appear when they are unearthing soil at a “volcano” shaped mound. The ground they inhabit is extremely hard—so hard it is difficult to dig with a shovel in. (2)
Physical Description
The naked mole rat is often described as looking like a bratwurst with legs and a tail. It is only about 4 or 5 inches long, with the exception of the “queen” who is typically larger. When she takes the queen role, her body length increases by 30% and she adds bone to her vertebral column to assist in carrying large litters. Their eyes are tiny little specks on the head, and the ears are pinholes. The incisor teeth grow through the skin of the mouth, making them permanently external. Naked mole rats are not truly naked as their name suggests. They have a fine scattering of whiskers covering their bodies. (2)
Physiology
Uniquely, naked mole rats are insensitive to acid-induced pain, resistant to cancer, and long-lived for a small mammal—up to 30 years. They seem to be resistant to typical signs of aging. The queen does not experience menopause. Blood vessels and muscle structure remain in good condition their entire lives. Additionally, naked mole rats can repair mitochondrial damage in their cells. In humans, this kind of damage is a factor in ailments such as senility and heart failure. (3) They are the only known “cold-blooded” mammals on earth. They are well adapted to a life exclusively underground. Their bodies are shaped to be very aerodynamic. The tail is short and nearly hairless like the rest of the body. Uniquely, they use their teeth to “dig” soil—not their forelimbs like other burrowers. In a sense, they gnaw their way through the ground. To achieve this, their lips close behind of their incisors. This prevents dirt from entering the mouth. Their feet are only used in sweeping soil. Their eyes only sense the extremes of light and dark—thus explaining why they are so small. The whiskers covering their bodies aid in sensing their underground surroundings. They use their sense of smell to identify one another and when two meet in a tunnel, the older mole rat gets to pass over top of the younger. They have very loose skin allowing them to turn into sharp tunnels and squeeze through small spaces. (4) The naked mole rat gut contains a mixture of microorganisms that help breakdown their high cellulose diet. They have an enlarged cecum to enable this digestion, like other rodents. (5)
Behavior
Naked mole rats can travel as fast backwards as they can forwards. They dig in groups almost like a conveyor with one at the front gnawing at the dirt and the rest sweeping the dirt to the surface. (2) The majority of the burrow consists of a labyrinth of shallow foraging tunnels stretching over 4 km. The communal nesting and toilet chambers are safely nestled much deeper underground—upwards of 5 feet beneath the surface. (5) Naked mole rats are never found alone. They survive in colonies. The average colony size is 80 individuals. A single reproductive female and several reproductive males exist within the colony. All the other mole rats are workers. On average the queen will have a litter of 18 pups. She is groomed and fed by other workers. (2) When the young are being weaned, they eat the feces of adults to infect their guts with the microorganisms necessary for digesting root vegetables—known as Coprophagia. (5) This cooperation is evolutionarily convergent with that of bees, wasps and ants. Ecological factors force them to work together as well as have a sense of kinship—the colony is one big family and the workers are helping raise and defend brothers and sisters. The mole rats defend against predators in groups by attacking with their teeth. (2) They have about 17 or 18 different vocalizations which sound like birds twittering. (3) Naked mole rats feed on large tubers. These don’t give off any smells and the mole rats cannot see them. By burrowing blindly over large distances, they come across the tubers by pure chance. Once they find one it can last the colony for up to a month. (2)
Ecology
Naked mole rats, due to their exclusively underground behavior, do not interact with other species normally. A few species of snakes occasionally prey upon mole-rats—provided that they find them in the tunnel system and manage to get past a mob of attacking mole rats. (5)
Evolutionary History
H. glaber is thought to have evolved separately at an early stage from the rest of the African mole-rats. Their divergence is estimated to be between 40 and 48 million years ago or 33-35 million years ago depending on the molecular clock calibration. The Bathyergidae family (African mole rats) is inferred to have originated in the Eocene, but the earliest known fossils have only been Miocene aged. Bathyergids are considered members of Hystricognathi, based on their lower jaw and inner ear morphology, Bathyergids have unusual masticatory muscle structure. Hystricognathi have an enlarged infraorbital foramen with zygomaticomandibularis muscle attaching to the rostrum. However, the Bathyergidae infraorbital is small and no masticatory musculature attaches to rostrum. Additonally, molecular analyses support close evolutionary association with Thryonomyidae (cane-rats) and Petromuridae (dassie rat). Some have even placed the naked mole rat in it’s own subfamily, Heterocephalinae. (6)
Resources
1. Maree, S., and C. Faulkes. "Heterocephalus glaber." The IUCN Red List of Threatened Species. Version 2014.2.
6.Cox, Philip G, and Chris G Faulkes. "Digital Dissection Of The Masticatory Muscles Of The Naked Mole-Rat, Heterocephalus glaber (Mammalia, Rodentia)." Peerj 2.(2014): e448. MEDLINE with Full Text. Web. 2 Dec. 2014.
Naked Molerat. Photograph. Wikimedia.org. Web. 1 Dec. 2014.
<http://upload.wikimedia.org/wikipedia/commons/thumb/8/83/Naked_Molerat_001.jpg/1024px-Naked_Molerat_001.jpg>.
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