The first mammal shown to be eusocial, with one breeding queen and hundreds of sterile helpers (1981)
Jennifer Jarvis's paper in Science; the queen suppresses the others by shoving and by hormonal cues
Science · Biology
Naked mole-rat
Biology — mammals, eusociality and ageing
The naked mole-rat is a hairless, near-blind burrowing rodent of the Horn of Africa that breaks several of the rules of mammalian biology at once. It is eusocial, like an ant or a termite: a single breeding queen suppresses reproduction in a colony of up to three hundred non-breeding workers and soldiers, a pattern described in mammals for the first time by Jennifer Jarvis in 1981. It is effectively cold-blooded, keeping its temperature by moving around the burrow rather than by metabolism. It is almost never found with cancer, apparently thanks to an unusually large form of the sugar hyaluronan secreted by its cells. It feels no pain from acid or from chilli's capsaicin, it can survive eighteen minutes of total oxygen starvation by switching its metabolism to fructose, and it lives past thirty years with no measurable rise in its risk of death as it ages.
How to spot them
- ▸A hairless, wrinkled, almost blind rodent with protruding incisors that close outside its lips
- ▸The first mammal shown to be eusocial, with a single breeding queen and sterile workers
- ▸Effectively cold-blooded, and virtually never develops cancer
- ▸Survives eighteen minutes without oxygen by burning fructose
- ▸Lives past thirty years with no increase in mortality rate with age
Key facts
Its cells secrete a hyaluronan five times larger than a human's, and it almost never develops cancer (2013)
High-molecular-mass hyaluronan triggers early contact inhibition, reported in Nature
It survived eighteen minutes of total anoxia by switching its metabolism to fructose (2017)
Reported in Science; it accumulates fructose and metabolises it to lactate in the brain
It feels no pain from acid or from the capsaicin in chilli
Its pain fibres lack normal substance P signalling, and an amino-acid change tunes its sodium channels
Effectively cold-blooded: it regulates its temperature by moving around the burrow, not by metabolism
A thermoconformer, and unique among mammals in this
Its risk of death does not rise with age, defying the Gompertz law, and it can live past thirty (2018)
Ruby, Smith and Buffenstein, in eLife
Its protruding incisors close outside its lips so it can dig without eating soil
Roughly a quarter of its muscle mass is in the jaw, and it can move each incisor independently
Key ideas
- Eusociality in a mammal: reproduction is monopolised by one female, so the colony behaves like a superorganism. The likely drivers are the high cost of digging for scattered tubers in hard, arid soils, and the very high relatedness within a colony, which makes helping relatives breed a good genetic bargain.
- Negligible senescence: mortality that stays flat with age is not immortality — the animals still die — but it means age itself is not making death more likely, which is why the species is so heavily studied in ageing research.
Quick-fire facts
- •Heterocephalus glaber Rüppell, 1842; the only species in its genus, now usually given its own family, Heterocephalidae
- •Native to the dry grasslands of Ethiopia, Kenya and Somalia, living entirely underground in tunnel systems that can run for kilometres
- •About 8–10 cm long and 30–35 g; the queen lengthens her spine when she takes the throne, growing larger than her subjects
- •Colonies average around 75 animals and can exceed 290; the queen breeds with one to three males and may produce 900 pups in a lifetime
- •The Damaraland mole-rat, Fukomys damarensis, is the only other eusocial mammal
- •Its cancer resistance is attributed to very high-molecular-mass hyaluronan, over five times larger than the human form
- •It is insensitive to capsaicin and to acid-induced pain, an adaptation to the high carbon dioxide of a crowded burrow
- •Recorded lifespans exceed thirty years, several times that expected for a rodent of its size
- •Science named it 'Vertebrate of the Year' in 2013
- •Common misconception: it is neither a mole nor a rat, and it is not truly hairless — it has about a hundred fine sensory hairs used to feel its way in the dark
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Sources
- Xiao Tian et al., Nature 499 (2013) — High-molecular-mass hyaluronan mediates the cancer resistance of the naked mole rat
- Thomas J. Park et al., Science 356 (2017) — Fructose-driven glycolysis supports anoxia resistance in the naked mole-rat Eighteen minutes of anoxia survived; fructose metabolised to lactate
- J. Graham Ruby, Megan Smith and Rochelle Buffenstein, eLife 7 (2018) — Naked mole-rat mortality rates defy Gompertzian laws by not increasing with age