Naked Mole Rat
Encyclopedia
The naked mole rat
(Heterocephalus glaber), also known as the sand puppy or desert mole rat, is a burrowing rodent
native to parts of East Africa
and the only species
currently classified in the genus
Heterocephalus. It is one of only two known eusocial
mammal
s (the other being the Damaraland mole rat
) and has a highly unusual set of physical traits that enables it to thrive in an otherwise harsh, underground environment, including a lack of pain sensation in its skin and a very low metabolism
.
The naked mole rat is well adapted for the limited availability of oxygen
within the tunnels that are its habitat: its lung
s are very small and its blood has a very strong affinity for oxygen, increasing the efficiency of oxygen uptake. It has a very low respiration and metabolic rate for an animal of its size, about 2/3 that of a mouse of the same size, thus using oxygen minimally. In long periods of hunger, such as a drought, its metabolic rate can be reduced by up to 25 percent.
The naked mole rat cannot generally regulate its body temperature in typical mammalian fashion, homeostasis
. They can overcome this via behavioral means to keep a constant temperature, as when cold, naked mole rats huddle together or bask in the shallow, more sun-warmed parts of their burrow systems. Conversely, when they get too hot, they retreat to the deeper, cooler parts of their tunnel system.
The skin of naked mole rats lacks a key neurotransmitter
called substance P
that is responsible in mammal
s for sending pain
signals to the central nervous system
. When naked mole rats are exposed to acid or capsaicin
, they feel no pain. When injected with Substance P, however, the pain signaling works as it does in other mammals, but only with capsaicin and not with the acids. This is proposed to be an adaptation to the animal living in high levels of carbon dioxide
due to poorly ventilated living spaces, which would cause acid to build up in their body tissues.
Naked mole rats' substance P deficiency has also been tied to their lack of the histamine-induced itching and scratching behavior typical to rodents.
, Kenya
, and Somalia
.
Clusters averaging 75 to 80 individuals live together in complex systems of burrows in arid African deserts. The tunnel systems built by naked mole rats can stretch up to two or three miles in cumulative length.
The naked mole rat is one of the two species of mammals that exhibit eusociality
. This eusocial structure, similar to that found in ant
s, termite
s, and some bee
s and wasp
s, is very rare among mammal
s. The Damaraland Mole Rat
(Cryptomys damarensis) is the only other eusocial mammal currently known.
Gestation is about 70 days. A litter typically ranges from three to twelve pups, but may be as large as 28. The average litter size is 11. In the wild, naked mole-rats usually breed once a year, if the litter survives. In captivity, they breed all year long and can produce a litter every 80 days. The young are born blind and weigh about 2 gram (0.0705479242102239 oz). The queen nurses them for the first month; after which the other members of the colony feed them feces
until they are old enough to eat solid food.
s, protecting the group from outside predators
. Workers are sterile when there is no new reproductive role to fill.
Naked mole rats feed primarily on very large tuber
s (weighing as much as 1000 times the body weight of a typical mole rat) that they find deep underground through their mining operations, but also eat their own feces (coprophagia
). A single tuber can provide a colony with a long-term source of food—lasting for months, or even years, as they eat the inside but leave the outside, allowing the tuber to regenerate. Symbiotic
bacteria
in their intestines ferment the fibres, allowing previously indigestible cellulose to be turned into volatile fatty acids.
, which prevents cell division once a group of cells reaches a certain size. Most mammals, including naked mole rats, have a gene called p27 which does a similar task, but prevents cellular reproduction at a much later point than p16 does. The combination of p16 and p27 in naked mole rats cells is a double barrier to cell proliferation. Hypersensitivity to contact inhibition
may be the reason for the cancer resistance of the naked mole rat.
.
Blesmol
The blesmols, also known as mole rats, or African mole-rats, are burrowing rodents of the family Bathyergidae. They represent a distinct evolution of a subterranean life among rodents much like the pocket gophers of North America, the tuco-tucos in South America, or the Spalacidae.- Distribution...
(Heterocephalus glaber), also known as the sand puppy or desert mole rat, is a burrowing rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
native to parts of East Africa
East Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
and the only species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
currently classified in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Heterocephalus. It is one of only two known eusocial
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s (the other being the Damaraland mole rat
Damaraland Mole Rat
The Damaraland Mole Rat, or Damaraland blesmol is a burrowing rodent found in sub-Saharan Africa. Along with the smaller, less hairy Naked Mole Rat, it is one of only two known eusocial mammals....
) and has a highly unusual set of physical traits that enables it to thrive in an otherwise harsh, underground environment, including a lack of pain sensation in its skin and a very low metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
.
Physical description
Typical individuals are 8 to 10 cm (3.1 to 3.9 in) long and weigh 30 to 35 g (1.1 to 1.2 oz). Queens are larger and may weigh well over 50 grams (1.8 oz), the largest reaching 80 grams (2.8 oz). They are well-adapted to their underground existence. Their eyes are quite small, and their visual acuity is poor. Their legs are thin and short; however, they are highly adept at moving underground and can move backward as fast as they can move forward. Their large, protruding teeth are used to dig, and their lips are sealed just behind the teeth to prevent soil from filling their mouths while digging. They have little hair (hence the common name) and wrinkled pink or yellowish skin.The naked mole rat is well adapted for the limited availability of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
within the tunnels that are its habitat: its lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s are very small and its blood has a very strong affinity for oxygen, increasing the efficiency of oxygen uptake. It has a very low respiration and metabolic rate for an animal of its size, about 2/3 that of a mouse of the same size, thus using oxygen minimally. In long periods of hunger, such as a drought, its metabolic rate can be reduced by up to 25 percent.
The naked mole rat cannot generally regulate its body temperature in typical mammalian fashion, homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
. They can overcome this via behavioral means to keep a constant temperature, as when cold, naked mole rats huddle together or bask in the shallow, more sun-warmed parts of their burrow systems. Conversely, when they get too hot, they retreat to the deeper, cooler parts of their tunnel system.
The skin of naked mole rats lacks a key neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
called substance P
Substance P
In the field of neuroscience, substance P is a neuropeptide: an undecapeptide that functions as a neurotransmitter and as a neuromodulator. It belongs to the tachykinin neuropeptide family. Substance P and its closely related neuropeptide neurokinin A are produced from a polyprotein precursor...
that is responsible in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s for sending pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
signals to the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. When naked mole rats are exposed to acid or capsaicin
Capsaicin
Capsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...
, they feel no pain. When injected with Substance P, however, the pain signaling works as it does in other mammals, but only with capsaicin and not with the acids. This is proposed to be an adaptation to the animal living in high levels of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
due to poorly ventilated living spaces, which would cause acid to build up in their body tissues.
Naked mole rats' substance P deficiency has also been tied to their lack of the histamine-induced itching and scratching behavior typical to rodents.
Distribution and habitat
The naked mole rat is native to the drier parts of the tropical grasslands of East Africa, predominantly southern EthiopiaEthiopia
Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...
, Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
, and Somalia
Somalia
Somalia , officially the Somali Republic and formerly known as the Somali Democratic Republic under Socialist rule, is a country located in the Horn of Africa. Since the outbreak of the Somali Civil War in 1991 there has been no central government control over most of the country's territory...
.
Clusters averaging 75 to 80 individuals live together in complex systems of burrows in arid African deserts. The tunnel systems built by naked mole rats can stretch up to two or three miles in cumulative length.
Roles
There is dimorphism between the queen, her breeding males, and two kinds of workers. They have a complex social structure in which only one female (the queen) and one to three males reproduce, while the rest of the members of the colony function as workers. The queen and breeding males are able to breed at one year of age. Workers are sterile, with the smaller focusing on gathering food and maintaining the nest, while larger workers are more reactive in case of attack.The naked mole rat is one of the two species of mammals that exhibit eusociality
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
. This eusocial structure, similar to that found in ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s, termite
Termite
Termites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
s, and some bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s and wasp
Wasp
The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...
s, is very rare among mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. The Damaraland Mole Rat
Damaraland Mole Rat
The Damaraland Mole Rat, or Damaraland blesmol is a burrowing rodent found in sub-Saharan Africa. Along with the smaller, less hairy Naked Mole Rat, it is one of only two known eusocial mammals....
(Cryptomys damarensis) is the only other eusocial mammal currently known.
Queen and gestation
The relationships between the queen and the breeding males may last for many years; other females are temporally sterile. Queens live from 13 to 18 years, and are extremely hostile to other females behaving like queens, or producing hormones for becoming queens. When the queen dies, another female takes her place, sometimes after a violent struggle with her competitors. Once established, the new queen stretches the space between the vertebrae in her backbone to become longer and ready to bear pups.Gestation is about 70 days. A litter typically ranges from three to twelve pups, but may be as large as 28. The average litter size is 11. In the wild, naked mole-rats usually breed once a year, if the litter survives. In captivity, they breed all year long and can produce a litter every 80 days. The young are born blind and weigh about 2 gram (0.0705479242102239 oz). The queen nurses them for the first month; after which the other members of the colony feed them feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
until they are old enough to eat solid food.
Workers
Smaller workers focus on acquiring food and maintaining tunnels, while the larger workers are more reactive in case of attacks. As in certain bee species, the workers are divided along a continuum of different worker-caste behaviors instead of discrete groups. Some function primarily as tunnellers, expanding the large network of tunnels within the burrow system, and some primarily as soldierSoldier
A soldier is a member of the land component of national armed forces; whereas a soldier hired for service in a foreign army would be termed a mercenary...
s, protecting the group from outside predators
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. Workers are sterile when there is no new reproductive role to fill.
Diet
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
s (weighing as much as 1000 times the body weight of a typical mole rat) that they find deep underground through their mining operations, but also eat their own feces (coprophagia
Coprophagia
Coprophagia or coprophagy is the consumption of feces, from the Greek κόπρος copros and φαγεῖν phagein . Many animal species practice coprophagia as a matter of course; other species do not normally consume feces but may do so under unusual conditions...
). A single tuber can provide a colony with a long-term source of food—lasting for months, or even years, as they eat the inside but leave the outside, allowing the tuber to regenerate. Symbiotic
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
in their intestines ferment the fibres, allowing previously indigestible cellulose to be turned into volatile fatty acids.
Longevity
The naked mole rat is also of interest because it is extraordinarily long-lived for a rodent of its size (up to 28 years) and holds the record for the longest living rodent. The reason for their longevity is debated, but is thought to be related to the fact that they can substantially reduce their metabolism during hard times, and so prevent oxidative damage. This has been referred to as "living their life in pulses." Because of their extraordinary longevity, an international effort was put into place to sequence the genome of the naked mole rat. A draft genome was made available in 2011.Resistance to cancer
Naked mole rats appear to have a high resistance to cancer; cancer has never been observed in them. A potential mechanism that averts cancer is an "over-crowding" gene, p16P16 (gene)
Cyclin-dependent kinase inhibitor 2A, also known as multiple tumor suppressor 1 , is a tumor suppressor protein, that in humans is encoded by the CDKN2A gene...
, which prevents cell division once a group of cells reaches a certain size. Most mammals, including naked mole rats, have a gene called p27 which does a similar task, but prevents cellular reproduction at a much later point than p16 does. The combination of p16 and p27 in naked mole rats cells is a double barrier to cell proliferation. Hypersensitivity to contact inhibition
Contact inhibition
Contact inhibition is the natural process of arresting cell growth when two or more cells come into contact with each other. Oncologists use this property to distinguish between normal and cancerous cells....
may be the reason for the cancer resistance of the naked mole rat.
Conservation status
Naked mole rats are not threatened. Despite their tough living conditions, they are widespread and numerous in the drier regions of East AfricaEast Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
.