Naked mole-rats (Heterocephalus glaber) are fascinating creatures with unique adaptations to their subterranean lifestyle. These small, nearly hairless rodents, native to the arid regions of eastern Africa, exhibit remarkable physiological and behavioral traits, including a diet and nutritional strategy tailored to their harsh environment. This article explores the dietary habits, nutritional requirements, and gut microbiome of naked mole-rats, highlighting how these factors contribute to their exceptional longevity and health.
Naked Mole-Rat Natural Habitat and Physical Characteristics
Naked mole-rats hail from the semiarid grassland habitats of Eastern Africa, specifically Somalia, Ethiopia, and Kenya. They are small, pink rodents with very little hair and an aptitude for digging tunnels. As the name suggests, these animals are small pink rodents with very little hair and an aptitude for digging tunnels. Naked mole-rats can be found in large burrow systems in eastern Africa.
These burrowing rodents eat the underground parts of plants, particularly the succulent tubers 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. The tunnels are about 1.5 inches (4 centimeters) in diameter. Some tunnels run just under the surface of the ground, while others can be up to 6.5 feet (2 meters) deep. There is a great deal of branching and interconnection of tunnels, with the result that a colony's total tunnel length can total up to 2.5 miles (4 kilometers). Tunnels connect nest chambers, toilet areas and food sources. Burrowing is the only way these animals find food, because they do not travel above ground.
Naked mole-rats may have a life span of 10-30 years. Maximum longevity in this species is as yet unknown; animals have been in human care for as long as 30 years. They have no external ears and they have tiny eyes, which make them virtually blind. Naked mole-rats live in complex underground burrow systems.
Primary Food Sources: Tubers and Roots
The diet of naked mole-rats primarily consists of the underground portions of plants, especially tubers, bulbs, and roots. When a group of mole-rats finds a large tuber (sometimes more than 1 foot in diameter), 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. They’ve learned to leave a portion of the tuber behind, so it can regrow, and they can harvest it again.
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In captivity, naked mole-rats are often fed a variety of root vegetables. The National Zoo provides them with a variety of root vegetables (turnip, beet, sweet potato, carrot), as well as corn, green beans, and leafy greens. Naked mole rats do not drink water and should never be given free-standing water. Naked mole-rats meet all their nutrient and water needs through an ad libitum supply of fruit and vegetables (bananas, apples, oranges, butternut squash, red bell pepper, romaine lettuce, cucumber, green beans, corn, carrots, and red garnet yams).
Water Acquisition
Through these plants, naked mole rats receive all of the fluids required to survive, so they don’t need to drink water. They obtain all the water they need through their food; they do not drink. Naked mole rats do not drink water and should never be given free-standing water.
Digestive Adaptations and Gut Microbiome
The diet of naked mole-rats is high in cellulose, a complex carbohydrate that is difficult to digest. To overcome this challenge, naked mole-rats have developed several digestive adaptations. Their high amounts of gut fauna assist in digesting the otherwise difficult to digest cellulose in their diet. Naked mole-rats have high densities of gut fauna that aid in digestion. Microbial fermentation resulted in higher SCFA concentrations on the carrot diet, with a 42% reduction in SCFA concentration on the sweet potato diet. Here, SCFA contributed 5.1% of daily energy expenditure and this increased 5.0-fold on the carrot diet.
Coprophagy
In addition to their specialized gut microbiome, naked mole-rats regularly engage in coprophagy, the practice of eating their own feces. As gross as this may sound, it ensures that the nutrients in their food don’t go to waste and are absorbed into their systems so they can spend less energy finding food. In addition to this, naked mole rats regularly eat their own poop in order to receive all possible nutrients from their food. Pups also eat feces provided for them on demand by the workers. This not only provides nutrition, it also inoculates their digestive system with beneficial gut fauna.
Gut Microbiota Composition
The gut microbiota of naked mole-rats is characterized by a unique composition, dominated by Firmicutes and Bacteroidetes. At phylum-level the gut microbiota of the long-lived naked mole-rat is largely dominated by Firmicutes (average relative abundance (rel.ab.), 40.8%) and Bacteroidetes (38.8%), followed by Spirochaetes (12.0%), Actinobacteria (2.7%), Proteobacteria (2.6%), Synergistetes (1.3%) and other phyla at rel.ab. < 0.1% (Supplementary Fig. 1).
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Compared to other mammals like mice and humans, the naked mole-rat microbiota exhibits an expanded relative contribution of families from the phylum Bacteroidetes, with a more pronounced inter-phylum diversity. Interestingly, bacteria of the family Bacteroidaceae, i.e. the most abundant Bacteroidetes member both in western humans, was not represented in the naked mole-rat. On the contrary, their Bacteroidetes fraction was composed mostly by Prevotellaceae, Paraprevotellaceae, Porphyromonadaceae and the recently identified family S24-7. This peculiar configuration, with the exception of the S24-7, resembles the one observed in the human rural population Hadza.
One notable feature of the naked mole-rat microbiota is the presence of Spirochaetaceae, particularly the genus Treponema. This genus was represented in the naked mole-rat microbiota by a diversified population (763 OTUs, related to around 20 different Treponema species), with an average diversity of ten Treponema species per individual at > 0.01%, and three species at > 1%. It is likely that Treponema, similar to the genus Prevotella, increases the ability of the naked mole-rat to digest and extract valuable nutrition from fibrous naturally occurring plants, of which both the naked mole-rat and the Hadza hunter-gatherers diet are enriched, since this genus includes proficient cellulose and xylan hydrolyzers.
Another interesting parallel is the presence of the family Mogibacteriaceae, which is also found in the microbiota of extremely aged humans (supercentenarians). Curiously, another feature of the naked mole-rat microbiota, i.e. the presence of the family Mogibacteriaceae (rel.ab. 0.8 ± 0.4%), offered a parallel with the microbiota of extremely aged humans (i.e. supercentenarians (105 + years old) in which this family was retrieved in similar amounts (0.6%) (Fig. 2)13. Naked mole-rat and supercentenarians are both models of healthy aging and, even if possessing completely different microbial ecosystems, the sharing of this small peculiarity is an interesting finding, possibly worth exploring in the future.
Furthermore, the naked mole-rat microbiota shows an appreciable abundance of bacterial families capable of utilizing sulfate, sulfite, or other sulfur-containing molecules as terminal electron acceptors for fermentative and/or respiratory metabolism.
Impact of Diet on Gut Microbiota
The composition of the gut microbiota in naked mole-rats can be influenced by dietary changes. A 2.4-fold increase in fibre and 2.5-fold decrease in starch content resulted in a decrease in caecal DM content (390 g/kg). A concomitant dramatic decline (by 93%) in ciliate protozoa with a corresponding 2-fold increase in bacteria also accompanied this change in diet. Fermentative efficiency as indicated by gas production was 2.6 times greater on a carrot diet than on sweet potato.
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Metabolic Adaptations and Longevity
Naked mole-rats exhibit a remarkably long lifespan compared to other rodents of similar size. This longevity is linked to their unique metabolic adaptations, including a low metabolic rate and the ability to survive in hypoxic conditions. Naked mole rats have the longest lifespan of any rodent, living up to 30 years in captivity - three times longer than standard lab mice. This may be due to the fact that they have the lowest metabolic rate of any mammal.
Metabolomic studies have revealed striking inter-species differences in amino acid, peptide, and lipid metabolites in naked mole-rats compared to mice. Low circulating levels of specific amino acids, particularly those linked to the methionine pathway, resemble those observed during fasting in hibernating ground squirrels and methionine-restricted rats. These data also concur with metabolome reports on long-lived mutant mice, including the Ames dwarf mice and calorically restricted mice, as well as fruit flies, and even show similarities to circulating metabolite differences observed in young human adults when compared to older humans.
Dietary Considerations in Captivity
When caring for naked mole-rats in captivity, it is important to provide a diet that mimics their natural food sources and meets their nutritional needs. The National Zoo often stuffs their diet into tunnels forcing the naked mole rats to excavate their food. Naked mole-rats are motivated to create a “nest” of materials such as hay, browse. or paper. This species has a strong instinct for chewing and should be given items such as sticks and clumps of hydrostone to chew.
An appropriate balance of calcium and phosphorus is important for long-term health in this species. They should eat foods high in complex carbohydrates rather than rapidly metabolized sugars. The teeth of naked mole rats should be monitored for malocclusion. Teeth may fall out in older animals.