Overview
Distribution
Range Description
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Geographic Range
Naked mole-rats are found only in parts of Kenya, Ethiopia and Somalia.
Biogeographic Regions: ethiopian (Native )
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Physical Description
Morphology
Physical Description
Although, as their name indicates, naked mole-rats do not have fur, they are not completely hairless. They have sensory whiskers on their faces and on their tails (they move both backwards and forwards through their tunnel systems), and they have hairs between their toes that allow their feet to function as brooms with which they sweep soil. Their skin is pink and somewhat translucent on the underside and light purplish brown on their backs and tails. This countershading appears to be lost with advanced age. There is no sexual dimorphism between males and females. The queen and breeding males are generally among the heaviest individuals in a colony, and the queen is the longest individual. When a female becomes a queen she actually grows longer, even though she is already an adult, by increasing the distance between the vertebrae in her spine.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Average mass: 35 g.
Average basal metabolic rate: 0.128 W.
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Ecology
Habitat
Habitat and Ecology
can live in fine sand, pure gypsum, and laterite (Jarvis and Sherman 2002). The species is subterranean and eusocial, living in colonies averaging between 75 and 80 animals per colony (but may be as many as 290). The colonies are extended family groups, with overlapping generations. Reproduction is restricted to a single reproductive female, and at most three breeding males (usually one or two). Non-breeders (which are sociologically suppressed by aggressive behaviours of the dominant female) help care for and defend the reproductive animals and young. The non-breeding animals maintain and defense of the colony burrow system (Jarvis and Sherman 2002). The species has a gestation length of 66 to 74 days, after which between one and 28 young are born. Females can bear litters every 76 to 84 days, and wild females regularly bear more than 50 pups per year in four or five litters (Jarvis and Sherman 2002). In captivity, this is a relatively long-lived species; females lived to 23 years, and males to 28 years.
Systems
- Terrestrial
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Habitat
Naked mole-rats live underground in arid savannah and grasslands near the equator. Their population density is highest where their food plants are most abundant.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: savanna or grassland
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Trophic Strategy
Food Habits
These exclusively fossorial rodents eat the underground parts of plants, particularly the succulent tubers that are formed by many of the plant species that grow in arid areas. They obtain all the water they need through their food; they do not drink. In captivity they will readily consume sweet potatoes, various fruits, baby cereal and dog biscuits. When a group of mole-rats finds a large tuber (sometimes more than a foot in diameter) in the wild, they generally bore through it, eating mainly the interior flesh while leaving the thin epidermis intact. This behavior may allow the plant to remain healthy for some time, indeed even to continue growing, thereby providing a long-term food resource for the colony. This diet is high in cellulose, which is difficult to digest. Naked mole-rats have high densities of gut fauna that aid in digestion. They also regularly practice coprophagy, the reingestion of feces, which allows them to maximize their uptake of nutrients from their food.
Plant Foods: roots and tubers
Primary Diet: herbivore (Eats sap or other plant foods)
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Life History and Behavior
Behavior
Communication and Perception
The small eyes of these subterranian animals are nearly sightless. They also have small pinnae, but their hearing is acute, as evidenced by their large repertoire of social vocalizations. Their sense of smell is very important, and they are also very sensitive to vibrations in the ground and the movement of air currents.
Communication Channels: tactile ; acoustic ; chemical
Perception Channels: acoustic ; vibrations
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Life Expectancy
Lifespan/Longevity
A captive mole rat lived to at least 31 years in captivity. This life span is unprecedented among small rodents.
Range lifespan
Status: captivity: 31 (high) years.
Average lifespan
Status: captivity: 5.0 years.
Average lifespan
Status: captivity: 10.0 years.
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Lifespan, longevity, and ageing
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Reproduction
Reproduction
Only one female in a colony of naked mole-rats produces offspring; this female is called the queen. She mates with only a few of the colony's males, and these relationships can remain stable for many years. All other individuals in the colony aid in the queen's reproduction by caring for the pups, foraging for and providing food, and maintaining and defending the burrow system. These "workers" are physiologically capable of reproduction, but do not do so as long as they remain in the colony (which in most cases is their entire lives).
Mating System: eusocial
The duration of gestation is approximately 70 days. A queen can produce a new litter every 80 days, and can have up to 5 litters per year. Pups generally weigh less than 2 g at birth. The number of pups per litter is quite variable. The average is about 12, with a maximum of 27. The queen nurses the pups for about 4 weeks, although they may begin eating solid food at as early as 2 weeks of age. Pups also eat feces that are provided for them on demand by the workers. This not only provides nutrition, it also inoculates their digestive system with beneficial gut fauna.
Pups begin performing work behaviors (digging, sweeping, carrying, etc.) at the age of 3 to 4 weeks. Maturation rate is variable, but in general juveniles are physiologically capable of reproduction by the age of one year.
Breeding interval: Queen naked mole rats can have up to 5 litters each year.
Breeding season: Naked mole rats breed throughout the year.
Range number of offspring: 27 (high) .
Average number of offspring: 12.
Average gestation period: 70 days.
Average weaning age: 4 weeks.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous
Average birth mass: 2 g.
Average gestation period: 70 days.
Average number of offspring: 7.
Average age at sexual or reproductive maturity (female)
Sex: female: 228 days.
Naked mole rat queens nurse their young until they are 4 weeks old. The entire colony help to protect and provide for the young.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)
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Conservation
Conservation Status
IUCN Red List Assessment
Red List Category
Red List Criteria
Version
Year Assessed
Assessor/s
Reviewer/s
Justification
History
- 2004Least Concern
- 1996Lower Risk/least concern
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Conservation Status
Although this unique animal has a limited geographic distribution, it can be quite numerous where it does occur.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
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Trends
Population
Population Trend
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Threats
Threats
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Management
Conservation Actions
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Relevance to Humans and Ecosystems
Benefits
Economic Importance for Humans: Negative
If a naked mole-rat colony finds a farmer's crop, it can quickly destroy much of the yield by eating the roots of the plants. They are a problem especially for sweet potato farmers.
Negative Impacts: crop pest
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Economic Importance for Humans: Positive
In the United States naked mole-rats are becoming very popular in zoos and in the popular press. The fascination that people tend to have for them makes them an excellent educational tool, since they provide an outstanding example of some of the myriad ways in which animals have adapted to exploit various environments.
Positive Impacts: ecotourism ; research and education
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Wikipedia
Naked mole rat
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 mammals (the other being the Damaraland mole rat) and has a highly unusual set of physical traits that enables it to thrive in a harsh, underground environment, including a lack of pain sensation in its skin and a very low metabolism.
Contents |
Physical description
Typical individuals are 8 to 10 cm (3 to 4 in) long and weigh 30 to 35 grams (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 within the tunnels that are its habitat: its lungs 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 mammals 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 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.[2]
Naked mole rats' substance P deficiency has also been tied to their lack of the histamine-induced itching and scratching behavior typical to rodents.[3]
Ecology and behavior
Distribution and habitat
The naked mole rat is native to the drier parts of the tropical grasslands of East Africa, predominantly southern Ethiopia, 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.[4]
Roles
There is dimorphism between the queen, her breeding males, and two kind 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. This eusocial social structure, similar to that found in ants, termites, and some bees and wasps, is very rare among mammals. The Damaraland Mole Rat (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, others 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.
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.[5] 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.[6] The young are born blind and weigh about 2 grams (0.071 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.
- Workers
Smaller workers focus on acquiring food and maintaining tunnels, while the larger workers are more reactive in case of attacks.[7] As in certain bee species, the workers are divided along a continuum of different worker-caste behaviors instead of discrete groups.[4] Some function primarily as tunnellers, expanding the large network of tunnels within the burrow system, and some primarily as soldiers, protecting the group from outside predators. Workers are sterile when there is no new reproductive role to fill.
- Colonies
Colonies range in size from 20 to 300 individuals, averaging 75 individuals.[8]
Diet
Naked mole rats feed primarily on very large tubers (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).[4] A single tuber can provide a colony with a long-term source of food—lasting for months, or even years,[4] as they eat the inside but leave the outside, allowing the tuber to regenerate. Symbiotic bacteria in their intestines ferment the fibres, allowing previously indigestable 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.[9] 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 summed up as "They're living their life in pulses."[10] Because of their extraordinary longevity, an international effort was put into place to sequence the genome of the naked mole rat.[11]
Resistance to cancer
Naked mole rats appear to have a high resistance to cancer; cancer has never been observed in them. The mechanism that stunts cancer is a gene called p16, known as an "over-crowding" gene, which prevents the creation of new cells 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 creates a double-layered barrier that prevents the formation of cancer cells.[12] Hypersensitivity to contact inhibition may be the reason for the cancer resistance of the naked mole-rat. [13]
Conservation status
Naked mole rats are not threatened. Despite their tough living conditions, they are widespread and numerous in the drier regions of East Africa.
References
- ^ Maree, S. & Faulkes, C. (2008). Heterocephalus glaber. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 5 January 2009.
- ^ Park, Thomas J.; et al. (2008). "Selective Inflammatory Pain Insensitivity in the African Naked Mole-Rat (Heterocephalus glaber)". PLoS Biology 6 (1): e13. doi:10.1371/journal.pbio.0060013. PMID 18232734.
- ^ St John Smith, E; Blass, GR; Lewin, GR; Park, TJ (2010). "Absence of histamine-induced itch in the African naked mole-rat and "rescue" by Substance P.". Molecular pain 6 (1): 29. doi:10.1186/1744-8069-6-29. PMID 20497578. PMC 2886013. http://www.molecularpain.com/content/6/1/29.
- ^ a b c d Dawkins, Richard (1976). The Selfish Gene. Oxford University Press. ISBN 0-19-286092-5.
- ^ Counting mole-rat mammaries and hungry pups, biologists explain why naked rodents break the rules, Roger Segelken, Cornell News, August 9, 1999
- ^ Ross Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Westport, Conn: Greenwood Press. ISBN 0-313-33922-8.
- ^ Rebecca Morelle (2010, May 5th). "Meet the 'sabre-toothed sausage'". BBC News. http://news.bbc.co.uk/2/hi/science_and_environment/10088502.stm.
- ^ The Naked Truth About Mole-Rats, Jill Locantore, Smithsonian Zoogoer, May/June 2002
- ^ Buffenstein R, Jarvis JU (May 2002). "The naked mole rat—a new record for the oldest living rodent". Sci Aging Knowledge Environ 2002 (21): pe7. doi:10.1126/sageke.2002.21.pe7. PMID 14602989. http://sageke.sciencemag.org/cgi/pmidlookup?view=long&pmid=14602989.
- ^ "Ugly Duckling Mole Rats Might Hold Key To Longevity". Sciencedaily.com. 2007-10-16. http://www.sciencedaily.com/releases/2007/10/071015225336.htm. Retrieved 2009-03-11.
- ^ "Proposal to Sequence an Organism of Unique Interest for Research on Aging: Heterocephalus glaber, the Naked Mole-Rat". Genomics.senescence.info. http://genomics.senescence.info/sequencing/heterocephalus.html. Retrieved 2009-04-30.
- ^ "Naked Mole Rat Wins the War on Cancer: Jocelyn Kaiser". AAAS. 26 October 2009. http://sciencenow.sciencemag.org/cgi/content/full/2009/1026/2. Retrieved 27 October 2009.
- ^ Seluanov A, Hine C, Azpurua J, Feigenson M, Bozzella M, Mao Z, Catania KC, Gorbunova V (2009). "Hypersensitivity to contact inhibition provides a clue to cancer resistance of naked mole-rat" (HTML). Proc Natl Acad Sci U S A 106 (46): 19352–7. doi:10.1073/pnas.0905252106. PMID 19858485. PMC 2780760. http://www.pnas.org/content/106/46/19352.long.
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