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Naked mole-rat

December 04, 2023

The naked mole-rat (Heterocephalus glaber), also known as the sand puppy,[6] is a burrowing rodent native to the Horn of Africa and parts of Kenya, notably in Somali regions. It is closely related to the blesmols and is the only species in the genus Heterocephalus.[7]

Naked mole-rat
Temporal range: 4.3–0 Ma
↓
Early Pliocene - Recent[1]
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Parvorder: Phiomorpha
Family: Heterocephalidae
Landry, 1957[4][5]
Genus: Heterocephalus
Rüppell, 1842[3]
Species:
H. glaber
Binomial name
Heterocephalus glaber
Distribution of the naked mole-rat
Various aged naked mole-rats.

The naked mole-rat exhibits a highly unusual set of physiological and behavioral traits that allow it to thrive in a harsh underground environment; most notably its being the only mammalian thermoconformer with an almost entirely ectothermic (cold-blooded) form of body temperature regulation,[8] as well as exhibiting a complex social structure split between reproductive and non-reproductive castes, making it and the closely related Damaraland mole-rat (Fukomys damarensis) the only widely recognized examples of eusociality (the highest classification of sociality) in mammals.[9][10] The naked mole-rat lacks pain sensitivity in its skin, and has very low metabolic and respiratory rates. It is also remarkable for its longevity and its resistance to cancer and oxygen deprivation.

While formerly considered to belong to the same family as other African mole-rats, Bathyergidae, more recent investigation places it in a separate family, Heterocephalidae.[5][11][12]

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, preventing soil from filling their mouths while digging.[13] About a quarter of their musculature is used in the closing of their jaws while they dig. They have little hair (hence the common name) and wrinkled pink or yellowish skin. They lack an insulating layer in the skin.

Physiology

Metabolism and respiration

The naked mole-rat is well adapted to the limited availability of oxygen within the tunnels of its typical habitat. It has underdeveloped lungs and its hemoglobin has a high affinity for oxygen, increasing the efficiency of oxygen uptake.[14][15][16] It has a very low respiration and metabolic rate for an animal of its size, about 70% that of a mouse, thus using oxygen minimally.[17] In response to long periods of hunger, its metabolic rate can be reduced by up to 25 percent.[15]

The naked mole-rat survives for at least 5 hours in air that contains only 5% oxygen; it does not show any significant signs of distress and continues normal activity. It can live in an atmosphere of 80% CO
2 and 20% oxygen. In zero-oxygen atmosphere, it can survive 18 minutes apparently without suffering any harm (but none survived a test of 30 minutes). During the anoxic period it loses consciousness, its heart rate drops from about 200 to 50 beats per minute, and breathing stops apart from sporadic breathing attempts. When deprived of oxygen, the animal uses fructose in its anaerobic glycolysis, producing lactic acid. This pathway is not inhibited by acidosis as happens with glycolysis of glucose.[15][16] As of 2017, it was not known how the naked mole-rat survives acidosis without tissue damage.[18]

Thermoregulation

The naked mole-rat does not regulate its body temperature in typical mammalian fashion. They are thermoconformers rather than thermoregulators in that, unlike other mammals, body temperature tracks ambient temperatures. However, it has also been claimed that "the Naked Mole-Rat has a distinct temperature and activity rhythm that is not coupled to environmental conditions."[19] The relationship between oxygen consumption and ambient temperature switches from a typical poikilothermic pattern to a homeothermic mode when temperature is at 29 °C or higher.[20] At lower temperatures, naked mole-rats can use behavioral thermoregulation. For example, cold naked mole-rats huddle together or seek shallow parts of the burrows that are warmed by the sun. Conversely, when they get too hot, naked mole-rats retreat to the deeper, cooler parts of the burrows.

Pain insensitivity

 
Captive naked mole-rats huddling together

The skin of naked mole-rats lacks neurotransmitters in their cutaneous sensory fibers. As a result, the naked mole-rats feel no pain when they are exposed to acid or capsaicin. When they are injected with substance P, a type of neurotransmitter, the pain signaling works as it does in other mammals but only with capsaicin and not with 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.[21]

Naked mole-rats' substance P deficiency has also been tied to their lack of the histamine-induced itching and scratching behavior typical of rodents.[22]

Resistance to cancer

Naked mole-rats have a high resistance to tumours, although it is likely that they are not entirely immune to related disorders.[23] A potential mechanism that averts cancer is an "over-crowding" gene, p16, which prevents cell division once individual cells come into contact (known as "contact inhibition"). The cells of most mammals, including naked mole-rats, undergo contact inhibition via the gene p27 which prevents cellular reproduction at a much higher cell density than p16 does. The combination of p16 and p27 in naked mole-rat cells is a double barrier to uncontrolled cell proliferation, one of the hallmarks of cancer.[24]

In 2013, scientists reported that the reason naked mole-rats do not get cancer can be attributed to an "extremely high-molecular-mass hyaluronan" (HMW-HA) (a natural sugary substance), which is over "five times larger" than that in cancer-prone humans and cancer-susceptible laboratory animals.[25][26][27] The scientific report was published a month later as the cover story of the journal Nature.[28] A few months later, the same University of Rochester research team announced that naked mole-rats have ribosomes that produce extremely error-free proteins.[29][30] Because of both of these discoveries, the journal Science named the naked mole-rat "Vertebrate of the Year" for 2013.[31]

In 2016, a report was published that recorded the first ever discovered malignancies in two naked mole-rats, in two individuals.[23][32][33] However, both naked mole-rats were captive-born at zoos, and hence lived in an environment with 21% atmospheric oxygen compared to their natural 2–9%, which may have promoted tumorigenesis.[34]

The Golan Heights blind mole-rat (Spalax golani) and the Judean Mountains blind mole-rat (Spalax judaei) are also resistant to cancer, but by a different mechanism.[35]

In July 2023 a study reported the transference of the gene responsible for HMW-HA from a naked mole rat to mice leading to improved health and an approximate 4.4 percent increase in median lifespan for the mice.[36][37]

Longevity

Naked mole-rats can live longer than any other rodent, with lifespans in excess of 37 years; the next longest-lived rodent is the African porcupine at 28 years.[38][39] The mortality rate of the species does not increase with age, and thus does not conform to that of most mammals (as frequently defined by the Gompertz-Makeham law of mortality).[39] Naked mole-rats are highly resistant to cancer[40] and maintain healthy vascular function longer in their lifespan than shorter-living rats.[41]

The reason for their longevity is debated, but is thought to be related to their ability to substantially reduce their metabolism in response to adverse conditions, and so prevent aging-induced damage from oxidative stress. This has been referred to as "living their life in pulses".[42] Their longevity has also been attributed to "protein stability".[43] Because of their extraordinary longevity, an international effort was put into place to sequence the genome of the naked mole-rat.[44] A draft genome was made available in 2011[45][46][47] with an improved version released in 2014.[48] Its somatic number is 2n = 60.[7] Further transcriptome sequencing revealed that genes related to mitochondria and oxidation reduction are expressed more than they are in mice, which may contribute to their longevity.[49]

The DNA repair transcriptomes of the liver of humans, naked mole-rats and mice were compared.[50] The maximum lifespans of humans, naked mole-rats, and mice are respectively c. 120, 30 and 3 years. The longer-lived species, humans and naked mole-rats, expressed DNA repair genes, including core genes in several DNA repair pathways, at a higher level than did mice. In addition, several DNA repair pathways in humans and naked mole-rats were up-regulated compared with mice. These findings suggest that increased DNA repair facilitates greater longevity, and also are consistent with the DNA damage theory of aging.[51]

Size

Reproducing females become the dominant female, usually by founding new colonies, fighting for the dominant position, or taking over once the reproducing female dies. These reproducing females tend to have longer bodies than that of their non-reproducing counterparts of the same skull width. The measurements of females before they became reproductive and after show significant increases in body size. It is believed that this trait does not occur due to pre-existing morphological differences but to the actual attainment of the dominant female position.[52] As with the reproductive females, the reproductive males also appear to be larger than their non-reproducing counterparts but the difference is smaller than in females. These males also have visible outlines of the testes through the skin of their abdomens. Unlike the females, there are usually multiple reproducing males.[53]

Chronobiology

The naked mole-rat's subterranean habitat imposes constraints on its circadian rhythm.[54] Living in constant darkness, most individuals possess a free-running activity pattern and are active both day and night, sleeping for short periods several times in between.[54]

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.[55]

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 three to five kilometres (2–3 mi) in cumulative length.[56]

Roles

The naked mole-rat is the first mammal discovered to exhibit eusociality. The Damaraland mole-rat (Cryptomys damarensis) is the only other eusocial mammal currently known.

This eusocial structure of naked mole-rats is similar to that in ants, termites, and some bees and wasps.[57][58] Only one female (the queen) and one to three males reproduce, while the rest of the members of the colony function as workers.[59] The queen and breeding males are able to breed at one year of age. Workers are sterile,[58] with the smaller focusing on gathering food and maintaining the nest, while larger workers are more reactive in case of attack. The non-reproducing females appear to be reproductively suppressed, meaning the ovaries do not fully mature, and do not have the same levels of certain hormones as the reproducing females. On the other hand, there is little difference of hormone concentration between reproducing and non-reproducing males. In experiments where the reproductive female was removed or died, one of the non-reproducing females would take over and become sexually active. Non-reproducing members of the colony are involved in cooperative care of the pups produced by the reproducing female. This occurs through the workers keeping the pups from straying, foraging for food, grooming, contributing to extension of tunnels, and keeping them warm.[53]

 
Female mole-rat

Queen and gestation

The relationships between the queen and the breeding males may last for many years; other females are temporarily 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's body expands the space between the vertebrae in her backbone to become longer and ready to bear pups.[60]

Gestation is about 70 days. A litter typically ranges from three to twelve pups, but may be as large as twenty-eight. The average litter size is eleven.[61] 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.[62] The young are born blind and weigh about 2 grams (0.07 oz). The queen nurses them for the first month; after which the other members of the colony feed them fecal pap 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.[63] As in certain bee species, the workers are divided along a continuum of different worker-caste behaviors instead of discrete groups.[56] 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. There are two main types of worker, the "frequent workers" who frequently perform tasks such as foraging and nest building and "infrequent workers" that show role overlap with the "frequent workers" but perform at a much slower rate.[64] Workers are sterile when there is no new reproductive role to fill.

Dispersers

Inbreeding is a common phenomenon among naked mole-rats within a colony. Prolonged inbreeding is usually associated with lower fitness.[65] However, the discovery of a disperser role has revealed an outbreeding mechanism in addition to inbreeding avoidance.[66] Dispersers are morphologically, physiologically and behaviorally distinct from colony members and actively seek to leave their burrow when an escape opportunity presents itself.[66] These individuals are equipped with generous fat reserves for their journey.[66] Though they possess high levels of luteinizing hormone, dispersers are only interested in mating with individuals from foreign colonies rather than their own colony's queen.[66] They also show little interest in working cooperatively with colony members in their natal burrow.[66] Hence, the disperser morph is well-prepared to promote the exchange of individuals as well as genetic material between two otherwise separate colonies.[66]

Colonies

Colonies range in size from 20 to 300 individuals, with an average of 75.[67]

Female mate choice

Reproductively active female naked mole rats tend to associate with unfamiliar males (usually non-kin), whereas reproductively inactive females do not discriminate.[68] The preference of reproductively active females for unfamiliar males is interpreted as an adaptation for inbreeding avoidance. Inbreeding is avoided because it ordinarily leads to the expression of recessive deleterious alleles.[69]

Diet

 
A captive naked mole-rat eating

Naked mole-rats feed primarily on very large tubers (weighing as much as a thousand times the body weight of a typical mole-rat) that they find deep underground through their mining operations. A single tuber can provide a colony with a long-term source of food—lasting for months, or even years,[56] as they eat the inside but leave the outside, allowing the tuber to regenerate. Symbiotic bacteria in their intestines ferment the fibres, allowing otherwise indigestible cellulose to be turned into volatile fatty acids.[70]

Naked mole-rats sometimes also eat their own feces.[56] This may be part of their eusocial behavior and a means of sharing hormones from the queen.[71]

Predators

Naked mole rats are primarily preyed upon by snakes—especially the Rufous beaked snake and Kenyan sand boa—as well as various raptors. They are at their most vulnerable when constructing mounds and ejecting soil to the surface.[72]

Conservation status

Naked mole-rats are not threatened. They are widespread and numerous in the drier regions of East Africa.[73]

The Photo Ark

A naked mole-rat living at the Lincoln Children's Zoo was the first animal to be photographed for the National Geographic project, The Photo Ark, which has the goal of photographing all species living in zoos and wildlife sanctuaries around the globe in order to inspire action to save wildlife.[74]

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Further reading

  • Ciszek, Deborah (1999). "Heterocephalus glaber, naked mole rat". Animal Diversity Web. Retrieved 22 January 2010.
  • . Brookfield Zoo. Archived from the original on 6 December 2010. Retrieved 22 January 2010.
  • "Naked Mole Rat". Chicago Zoological Society. Retrieved 26 April 2017.
  • Baskauf, Steve (2003). . Bioimages at Vanderbilt University. Archived from the original on 15 January 2009. Retrieved 22 January 2010.
  • Bryner, Jeanna (October 2006). "Naked Mole-rats Hold Clues to Human Aging". LiveScience. Retrieved 22 January 2010.
  • Sherman PW, Jarvis JU (November 2002). "Extraordinary life spans of naked mole-rats (Heterocephalus glaber)". Journal of Zoology. 258 (3): 307–311. doi:10.1017/S0952836902001437.
  • Shuster G, Sherman PW (1998). "Tool use by naked mole-rats". Animal Cognition. 1 (1): 71–74. doi:10.1007/s100710050009. S2CID 11671840.
  • Choi CQ (January 2008). "Strange Creature Immune to Pain". LiveScience. Retrieved 22 January 2010.
  • "Small Mammals (with a naked mole-rat webcam)". Smithsonian National Zoological Park. Retrieved 22 January 2010.

External links

 
Wikimedia Commons has media related to Naked Mole Rat.
 
Wikispecies has information related to Naked Mole Rat.

December 04, 2023
naked, mole, naked, mole, heterocephalus, glaber, also, known, sand, puppy, burrowing, rodent, native, horn, africa, parts, kenya, notably, somali, regions, closely, related, blesmols, only, species, genus, heterocephalus, temporal, range, preꞒ, early, pliocen. The naked mole rat Heterocephalus glaber also known as the sand puppy 6 is a burrowing rodent native to the Horn of Africa and parts of Kenya notably in Somali regions It is closely related to the blesmols and is the only species in the genus Heterocephalus 7 Naked mole ratTemporal range 4 3 0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Early Pliocene Recent 1 Conservation statusLeast Concern IUCN 3 1 2 Scientific classificationDomain EukaryotaKingdom AnimaliaPhylum ChordataClass MammaliaOrder RodentiaParvorder PhiomorphaFamily HeterocephalidaeLandry 1957 4 5 Genus HeterocephalusRuppell 1842 3 Species H glaberBinomial nameHeterocephalus glaberRuppell 1842 3 Distribution of the naked mole rat source source source source source source source Various aged naked mole rats The naked mole rat exhibits a highly unusual set of physiological and behavioral traits that allow it to thrive in a harsh underground environment most notably its being the only mammalian thermoconformer with an almost entirely ectothermic cold blooded form of body temperature regulation 8 as well as exhibiting a complex social structure split between reproductive and non reproductive castes making it and the closely related Damaraland mole rat Fukomys damarensis the only widely recognized examples of eusociality the highest classification of sociality in mammals 9 10 The naked mole rat lacks pain sensitivity in its skin and has very low metabolic and respiratory rates It is also remarkable for its longevity and its resistance to cancer and oxygen deprivation While formerly considered to belong to the same family as other African mole rats Bathyergidae more recent investigation places it in a separate family Heterocephalidae 5 11 12 Contents 1 Description 2 Physiology 2 1 Metabolism and respiration 2 2 Thermoregulation 2 3 Pain insensitivity 2 4 Resistance to cancer 2 5 Longevity 2 6 Size 2 7 Chronobiology 3 Ecology and behavior 3 1 Distribution and habitat 3 2 Roles 3 2 1 Queen and gestation 3 2 2 Workers 3 2 3 Dispersers 3 2 4 Colonies 3 3 Female mate choice 3 4 Diet 3 5 Predators 4 Conservation status 5 The Photo Ark 6 References 7 Further reading 8 External linksDescriptionTypical 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 preventing soil from filling their mouths while digging 13 About a quarter of their musculature is used in the closing of their jaws while they dig They have little hair hence the common name and wrinkled pink or yellowish skin They lack an insulating layer in the skin PhysiologyMetabolism and respiration The naked mole rat is well adapted to the limited availability of oxygen within the tunnels of its typical habitat It has underdeveloped lungs and its hemoglobin has a high affinity for oxygen increasing the efficiency of oxygen uptake 14 15 16 It has a very low respiration and metabolic rate for an animal of its size about 70 that of a mouse thus using oxygen minimally 17 In response to long periods of hunger its metabolic rate can be reduced by up to 25 percent 15 The naked mole rat survives for at least 5 hours in air that contains only 5 oxygen it does not show any significant signs of distress and continues normal activity It can live in an atmosphere of 80 CO2 and 20 oxygen In zero oxygen atmosphere it can survive 18 minutes apparently without suffering any harm but none survived a test of 30 minutes During the anoxic period it loses consciousness its heart rate drops from about 200 to 50 beats per minute and breathing stops apart from sporadic breathing attempts When deprived of oxygen the animal uses fructose in its anaerobic glycolysis producing lactic acid This pathway is not inhibited by acidosis as happens with glycolysis of glucose 15 16 As of 2017 it was not known how the naked mole rat survives acidosis without tissue damage 18 Thermoregulation The naked mole rat does not regulate its body temperature in typical mammalian fashion They are thermoconformers rather than thermoregulators in that unlike other mammals body temperature tracks ambient temperatures However it has also been claimed that the Naked Mole Rat has a distinct temperature and activity rhythm that is not coupled to environmental conditions 19 The relationship between oxygen consumption and ambient temperature switches from a typical poikilothermic pattern to a homeothermic mode when temperature is at 29 C or higher 20 At lower temperatures naked mole rats can use behavioral thermoregulation For example cold naked mole rats huddle together or seek shallow parts of the burrows that are warmed by the sun Conversely when they get too hot naked mole rats retreat to the deeper cooler parts of the burrows Pain insensitivity nbsp Captive naked mole rats huddling togetherThe skin of naked mole rats lacks neurotransmitters in their cutaneous sensory fibers As a result the naked mole rats feel no pain when they are exposed to acid or capsaicin When they are injected with substance P a type of neurotransmitter the pain signaling works as it does in other mammals but only with capsaicin and not with 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 21 Naked mole rats substance P deficiency has also been tied to their lack of the histamine induced itching and scratching behavior typical of rodents 22 Resistance to cancer Naked mole rats have a high resistance to tumours although it is likely that they are not entirely immune to related disorders 23 A potential mechanism that averts cancer is an over crowding gene p16 which prevents cell division once individual cells come into contact known as contact inhibition The cells of most mammals including naked mole rats undergo contact inhibition via the gene p27 which prevents cellular reproduction at a much higher cell density than p16 does The combination of p16 and p27 in naked mole rat cells is a double barrier to uncontrolled cell proliferation one of the hallmarks of cancer 24 In 2013 scientists reported that the reason naked mole rats do not get cancer can be attributed to an extremely high molecular mass hyaluronan HMW HA a natural sugary substance which is over five times larger than that in cancer prone humans and cancer susceptible laboratory animals 25 26 27 The scientific report was published a month later as the cover story of the journal Nature 28 A few months later the same University of Rochester research team announced that naked mole rats have ribosomes that produce extremely error free proteins 29 30 Because of both of these discoveries the journal Science named the naked mole rat Vertebrate of the Year for 2013 31 In 2016 a report was published that recorded the first ever discovered malignancies in two naked mole rats in two individuals 23 32 33 However both naked mole rats were captive born at zoos and hence lived in an environment with 21 atmospheric oxygen compared to their natural 2 9 which may have promoted tumorigenesis 34 The Golan Heights blind mole rat Spalax golani and the Judean Mountains blind mole rat Spalax judaei are also resistant to cancer but by a different mechanism 35 In July 2023 a study reported the transference of the gene responsible for HMW HA from a naked mole rat to mice leading to improved health and an approximate 4 4 percent increase in median lifespan for the mice 36 37 Longevity Naked mole rats can live longer than any other rodent with lifespans in excess of 37 years the next longest lived rodent is the African porcupine at 28 years 38 39 The mortality rate of the species does not increase with age and thus does not conform to that of most mammals as frequently defined by the Gompertz Makeham law of mortality 39 Naked mole rats are highly resistant to cancer 40 and maintain healthy vascular function longer in their lifespan than shorter living rats 41 The reason for their longevity is debated but is thought to be related to their ability to substantially reduce their metabolism in response to adverse conditions and so prevent aging induced damage from oxidative stress This has been referred to as living their life in pulses 42 Their longevity has also been attributed to protein stability 43 Because of their extraordinary longevity an international effort was put into place to sequence the genome of the naked mole rat 44 A draft genome was made available in 2011 45 46 47 with an improved version released in 2014 48 Its somatic number is 2n 60 7 Further transcriptome sequencing revealed that genes related to mitochondria and oxidation reduction are expressed more than they are in mice which may contribute to their longevity 49 The DNA repair transcriptomes of the liver of humans naked mole rats and mice were compared 50 The maximum lifespans of humans naked mole rats and mice are respectively c 120 30 and 3 years The longer lived species humans and naked mole rats expressed DNA repair genes including core genes in several DNA repair pathways at a higher level than did mice In addition several DNA repair pathways in humans and naked mole rats were up regulated compared with mice These findings suggest that increased DNA repair facilitates greater longevity and also are consistent with the DNA damage theory of aging 51 Size Reproducing females become the dominant female usually by founding new colonies fighting for the dominant position or taking over once the reproducing female dies These reproducing females tend to have longer bodies than that of their non reproducing counterparts of the same skull width The measurements of females before they became reproductive and after show significant increases in body size It is believed that this trait does not occur due to pre existing morphological differences but to the actual attainment of the dominant female position 52 As with the reproductive females the reproductive males also appear to be larger than their non reproducing counterparts but the difference is smaller than in females These males also have visible outlines of the testes through the skin of their abdomens Unlike the females there are usually multiple reproducing males 53 Chronobiology The naked mole rat s subterranean habitat imposes constraints on its circadian rhythm 54 Living in constant darkness most individuals possess a free running activity pattern and are active both day and night sleeping for short periods several times in between 54 Ecology and behaviorDistribution 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 55 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 three to five kilometres 2 3 mi in cumulative length 56 Roles The naked mole rat is the first mammal discovered to exhibit eusociality The Damaraland mole rat Cryptomys damarensis is the only other eusocial mammal currently known This eusocial structure of naked mole rats is similar to that in ants termites and some bees and wasps 57 58 Only one female the queen and one to three males reproduce while the rest of the members of the colony function as workers 59 The queen and breeding males are able to breed at one year of age Workers are sterile 58 with the smaller focusing on gathering food and maintaining the nest while larger workers are more reactive in case of attack The non reproducing females appear to be reproductively suppressed meaning the ovaries do not fully mature and do not have the same levels of certain hormones as the reproducing females On the other hand there is little difference of hormone concentration between reproducing and non reproducing males In experiments where the reproductive female was removed or died one of the non reproducing females would take over and become sexually active Non reproducing members of the colony are involved in cooperative care of the pups produced by the reproducing female This occurs through the workers keeping the pups from straying foraging for food grooming contributing to extension of tunnels and keeping them warm 53 nbsp Female mole ratQueen and gestation The relationships between the queen and the breeding males may last for many years other females are temporarily 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 s body expands the space between the vertebrae in her backbone to become longer and ready to bear pups 60 Gestation is about 70 days A litter typically ranges from three to twelve pups but may be as large as twenty eight The average litter size is eleven 61 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 62 The young are born blind and weigh about 2 grams 0 07 oz The queen nurses them for the first month after which the other members of the colony feed them fecal pap 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 63 As in certain bee species the workers are divided along a continuum of different worker caste behaviors instead of discrete groups 56 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 There are two main types of worker the frequent workers who frequently perform tasks such as foraging and nest building and infrequent workers that show role overlap with the frequent workers but perform at a much slower rate 64 Workers are sterile when there is no new reproductive role to fill Dispersers Inbreeding is a common phenomenon among naked mole rats within a colony Prolonged inbreeding is usually associated with lower fitness 65 However the discovery of a disperser role has revealed an outbreeding mechanism in addition to inbreeding avoidance 66 Dispersers are morphologically physiologically and behaviorally distinct from colony members and actively seek to leave their burrow when an escape opportunity presents itself 66 These individuals are equipped with generous fat reserves for their journey 66 Though they possess high levels of luteinizing hormone dispersers are only interested in mating with individuals from foreign colonies rather than their own colony s queen 66 They also show little interest in working cooperatively with colony members in their natal burrow 66 Hence the disperser morph is well prepared to promote the exchange of individuals as well as genetic material between two otherwise separate colonies 66 Colonies Colonies range in size from 20 to 300 individuals with an average of 75 67 Female mate choice Reproductively active female naked mole rats tend to associate with unfamiliar males usually non kin whereas reproductively inactive females do not discriminate 68 The preference of reproductively active females for unfamiliar males is interpreted as an adaptation for inbreeding avoidance Inbreeding is avoided because it ordinarily leads to the expression of recessive deleterious alleles 69 Diet nbsp A captive naked mole rat eatingNaked mole rats feed primarily on very large tubers weighing as much as a thousand times the body weight of a typical mole rat that they find deep underground through their mining operations A single tuber can provide a colony with a long term source of food lasting for months or even years 56 as they eat the inside but leave the outside allowing the tuber to regenerate Symbiotic bacteria in their intestines ferment the fibres allowing otherwise indigestible cellulose to be turned into volatile fatty acids 70 Naked mole rats sometimes also eat their own feces 56 This may be part of their eusocial behavior and a means of sharing hormones from the queen 71 Predators Naked mole rats are primarily preyed upon by snakes especially the Rufous beaked snake and Kenyan sand boa as well as various raptors They are at their most vulnerable when constructing mounds and ejecting soil to the surface 72 Conservation statusNaked mole rats are not threatened They are widespread and numerous in the drier regions of East 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28852094 Reardon Sara 20 October 2015 Poo turns naked mole rats into better babysitters Nature doi 10 1038 nature 2015 18606 S2CID 181362727 Mammals of Africa Volume III Bloomsbury Natural History February 2013 p 670 ISBN 9781408122570 International Union for Conservation of Nature Red List Heterocephalus Glaber listed as least concern Biga Leo Adam April 10 2018 Nature photographer Joel Sartore taking cue from Noah with his National Geographic Photo Ark Thereader com The Reader Archived from the original on June 16 2018 Retrieved June 16 2018 Further readingCiszek Deborah 1999 Heterocephalus glaber naked mole rat Animal Diversity Web Retrieved 22 January 2010 Heterocephalus glaber Cooperation is Key Brookfield Zoo Archived from the original on 6 December 2010 Retrieved 22 January 2010 Naked Mole Rat Chicago Zoological Society Retrieved 26 April 2017 Baskauf Steve 2003 Naked mole rat Heterocephalus glaber images Bioimages at Vanderbilt University Archived from the original on 15 January 2009 Retrieved 22 January 2010 Bryner Jeanna October 2006 Naked Mole rats Hold Clues to Human Aging LiveScience Retrieved 22 January 2010 Sherman PW Jarvis JU November 2002 Extraordinary life spans of naked mole rats Heterocephalus glaber Journal of Zoology 258 3 307 311 doi 10 1017 S0952836902001437 Shuster G Sherman PW 1998 Tool use by naked mole rats Animal Cognition 1 1 71 74 doi 10 1007 s100710050009 S2CID 11671840 Choi CQ January 2008 Strange Creature Immune to Pain LiveScience Retrieved 22 January 2010 Small Mammals with a naked mole rat webcam Smithsonian National Zoological Park Retrieved 22 January 2010 External links nbsp Wikimedia Commons has media related to Naked Mole Rat nbsp Wikispecies has information related to Naked Mole Rat View the hetGla2 genome assembly in the UCSC Genome Browser Portals nbsp Mammals nbsp Animals nbsp Biology nbsp Africa Retrieved from https en wikipedia org w index php title Naked mole rat amp oldid 1188168104, wikipedia, wiki, book, 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