Table 1.
A summary of the 28 ostensible “myths” of Braude et al. (2021) regarding naked mole-rat biology and our categorisation based upon available evidence. The origin of each myth is classified as (1) myths that are in headline form and hence represent oversimplifications or are of unknown provenance; (2) suppositions requiring more evidence; (3) former conclusions that have been revised in the scientific literature; and (4) differing interpretations of available evidence.
| Myth | Response | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Myth 1: naked mole-rats are hairless | Naked mole-rats do have a few hairs on their body, but they lack a fur coat. The sparse hairs are specialised sensory structures, similar to facial vibrissae. These hairs are nevertheless fundamentally different from pelage (hair or fur). | x | |||
| Myth 2: naked mole-rats are strictly subterranean and never go above ground | Naked mole-rats have been found above ground, although this is a very rare occurrence, and the cause and purpose of these rare events is unknown. There is no clear evidence that they forage, find mates, or disperse above ground. Rather, their rare appearances on the surface may be due to very rare dispersals or colony displacement from disturbed, breached, or flooded burrows. | x | x | x | |
| Myth 3: naked mole-rats have unusually long burrows | Irrespective of whether naked mole-rats in future studies remain the record holder for the longest burrow system among the social mole-rats, naked mole-rats have exceptionally long burrows for their body size and colony biomass. | x | |||
| Myth 4: naked mole-rats are the only poikilothermic mammals | This myth is predicated on two words - “only” and “poikilothermic”. Some other mole-rat species also show pronounced thermolability. Body temperature (Tb) of naked mole-rats, when given sufficient time to attain thermal equilibrium, closely tracks that of ambient temperature (Ta), being only slightly warmer than Ta. They nevertheless can and do employ endothermy, however this is ineffective at maintaining body temperature outside of a very narrow range of Ta. | x | x | ||
| Myth 5: naked mole-rats have uniquely low thyroid hormone levels | “Unique” is a perilous word, but naked mole-rats certainly have low free thyroxine (T4) levels. However, to date, neither triiodothyronine (T3) level nor the T4:T3 ratio have been reported in the peer-reviewed literature. | x | x | ||
| Myth 6: naked mole-rat burrows are hypoxic and hypercapnic | Measuring underground atmospheres without altering their composition is difficult. To date, oxygen and carbon dioxide levels have not been measured in nest chambers. Burrow composition, organisation, and animal density would suggest that naked mole-rats encounter a range of atmospheric conditions, including hypoxia and hypercapnia, in their daily routine. Also, numerous physiological traits demonstrate that naked mole-rats are extremely well-adapted to both hypoxic and hypercapnic conditions. | x | x | ||
| Myth 7: naked mole-rats are blind | The naked mole-rat visual system is degenerate, with significant atrophy of the structures required for visual image formation. Their visual cortex is primarily responsive to somatosensory inputs. However, some ancillary structures remain intact, and while they can detect changes in luminance, they cannot see images. | x | |||
| Myth 8: naked mole-rats have degenerated hearing |
Compared with surface-dwelling mammals, naked mole-rats have very restricted high-frequency hearing, high auditory thresholds, and very poor sound-localisation abilities. Questions remain about how their low-frequency hearing compares with that of related species. | x | x | ||
| Myth 9: naked mole-rats are the most vocal rodents because they live in large groups | Current evidence does not permit group size to be discounted as an important contributor to vocal complexity; it is likely to be one of several key evolutionary drivers that shaped the extensive range of the naked mole-rat’s vocal repertoire. | x | |||
| Myth 10: naked mole-rats feel no pain | This claim has no basis in the scientific literature. Naked mole-rats do respond to certain noxious stimuli (e.g. heat and mustard oil), but lack responses to others, such as acid and capsaicin. | x | |||
| Myth 11: naked mole-rats are the only eusocial mammals | The definition of the term ‘eusocial’ is controversial and has been extensively debated. Both naked and Damaraland mole-rats appear distinct from other species in that they have very high levels of skew in lifetime reproductive success, but solid evidence for task specialisation among workers is lacking. | x | x | x | x |
| Myth 12: colonies have castes of breeders and non-breeders, involving frequent workers, infrequent workers, non-workers, and dispersers | There is no disagreement about distinct reproductive division of labour, accompanied by some morphological specialisation in breeding queen naked mole-rats. However, there is no conclusive evidence of distinct worker and non-worker castes among non-breeding animals. | x | x | x | x |
| Myth 13: colonies have up to three male breeders (pashas) | Whilst copulation does not guarantee paternity, up to three male consorts have been reported, with evidence from both behavioural and genetic studies. It is not known if there could be more than three breeding males within a colony. | x | x | ||
| Myth 14: colonies have a single queen | Dual queening is well documented, but it is a very rare event both in captivity and in the wild. To date, there has been no recorded incidence of three or more reproductive females within a colony, and most colonies only have a single queen. | x | |||
| Myth 15: not all females can become queens | When isolated from a colony, most new pairs will breed. However, not all females appear capable of attaining and holding the dominant position of queen within a colony. | x | x | ||
| Myth 16: queens suppress workers with pheromones | Initial suggestion that pheromones “may” be involved in suppression was revised in the 1990s as behavioural contact between queen and non-breeders was recognised as key to reproductive suppression. To date, there is no conclusive evidence to suggest a role for pheromones in reproductive suppression. | x | x | ||
| Myth 17: queens shove workers to get them to work | Since the original paper proposing this, this idea has been debunked in multiple studies. | x | |||
| Myth 18: naked mole-rats never leave their natal colonies | Genetic evidence supports outbreeding as vital to the evolutionary ecology of the naked mole-rat. Some dispersal from the natal nest is thus required. | x | x | ||
| Myth 19: naked mole-rats are inbred | While facultative inbreeding does occur in captivity, it is rare in other social mole-rats. While early studies in the 1980s of a single population suggested extreme inbreeding, more recent studies reveal considerable heterozygosity in both wild and captive populations. | x | |||
| Myth 20: the GH/IGF axis is impaired in naked mole-rats | Substantial data support the premise that the GH/IGF axis is indeed dampened in this species. | x | x | x | |
| Myth 21: naked mole-rats are long-lived because they have low oxidative stress and damage | Although naked mole-rats have high levels of oxidative tissue damage, this manifests early in captive life and does not accumulate with age. This suggests that naked mole-rats can efficiently neutralise or repair oxidative damage. Production of reactive oxygen species and antioxidant expression vary among tissues. | x | x | x | |
| Myth 22: naked mole-rat cells do not display cellular senescence | While equivocal findings have been reported, it appears that naked mole-rat cells can undergo stress and oncogene-induced senescence in vitro. | x | |||
| Myth 23: naked mole-rats are immune to disease | Compared to other rodents in managed care, naked mole-rats have fewer documented diseases including age-related dysfunction (e.g. neurodegeneration, heart and kidney disease) and bacterial infections. Rare, lethal viral infections have been reported. | x | x | ||
| Myth 24: naked mole-rats do not get tumours or cancer | Although several cases of cancer have been identified in this species, the incidence of spontaneous neoplasia in naked mole-rats relative to other similarly sized mammals and even humans is extremely low. | x | |||
| Myth 25: naked mole-rats have extremely large hyaluronan | Naked mole-rat hyaluronan is larger than hyaluronan from several other mammals examined and has unusual material properties. Results may differ among research groups due to hyaluronan molecular weight being affected by the isolation procedure. | x | x | x | |
| Myth 26: naked mole-rat cells have early contact inhibition that prevents cancer |
Naked mole-rat cell growth is highly dependent upon tissue culture conditions, which can impede cell proliferation prior to confluence and exhibit contact inhibition properties. Under certain conditions (e.g. daily medium changes), cells grow to high density and show no signs of contact inhibition. | x | x | ||
| Myth 27: naked mole-rats are non-aging | Demographic data show no increased mortality risk as animals increase in age. Also, many physiological phenotypes show negligible age-related changes. These data support the premise of a non-ageing mammal and/or suggest that morbidities are likely compressed into the final years of life. | x | x | ||
| Myth 28: naked mole-rats are the single member of a taxonomic family | Whether the naked mole-rat is a single member of the family Heterocephalidae or a member of the family Bathyergidae that also includes other sub-Saharan mole-rats is controversial. The Sub-Saharan African mole-rats nevertheless appear to be a monophyletic group regardless of whether they are considered a single family or a superfamily. | x | x |