Giant Mole-rats Research Articles

Life expectancy, family constellation and stress in giant mole-rats (Fukomys mechowii).

Giant mole-rats (Fukomys mechowii) are remarkably long-lived subterranean rodents (maximum recorded lifespan as reported here greater than 26 years) that live in families with one reproductive pair (breeders) and their non-reproductive offspring (non-breeders). Previous studies have shown that breeders live on average approximately twice as long as non-breeders, a finding contradicting the classic trade-off between reproduction and lifespan. Because recent evidence points to the hypothalamic-pituitary-adrenal axis as playing an important role in shaping the pace of ageing in mole-rats, we analysed the influence of the social environment of giant mole-rats on intrafamilial aggression levels, indicators of long-term stress, and, ultimately, mortality. Behavioural data indicated that family constellation, especially the presence or the absence of parents, influences agonistic behaviour. As a measure of long-term stress, we established a non-invasive method of extracting and measuring cortisol from hair of giant mole-rats. Interestingly, orphaned non-breeders exhibited significantly lower levels of cortisol and lower mortality rates than did non-breeders living with both parents. Because hypercortisolism is harmful in the long-term, intrafamilial stress could help explain the earlier onset of senescence in non-breeders, resulting in a shorter lifespan. Our findings suggest that the social environment should be considered as a further factor in ageing studies involving group-living animals. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Middle Stone Age humans in high-altitude Africa

Paleoanthropology Recent archaeological research has produced evidence of the earliest human occupation of high-altitude habitats in the Andes and the Tibetan Plateau. Ossendorf et al. now present the oldest evidence of human settlement and adaptation to areas above 4000-meter elevation in Africa (see the Perspective by Aldenderfer). Their excavations at a rock shelter in the Bale Mountains of Ethiopia reveal obsidian artifacts and faunal remains, including abundant burnt bones, mostly of giant mole-rats. The findings reveal the environmental conditions and show how Late Pleistocene humans adapted to the harsh environments of these glaciated high-altitude African landscapes. Science , this issue p. [583][1]; see also p. [541][2] [1]: /lookup/doi/10.1126/science.aaw8942 [2]: /lookup/doi/10.1126/science.aay2334

Middle Stone Age foragers resided in high elevations of the glaciated Bale Mountains, Ethiopia

Studies of early human settlement in alpine environments provide insights into human physiological, genetic, and cultural adaptation potentials. Although Late and even Middle Pleistocene human presence has been recently documented on the Tibetan Plateau, little is known regarding the nature and context of early persistent human settlement in high elevations. Here, we report the earliest evidence of a prehistoric high-altitude residential site. Located in Africa's largest alpine ecosystem, the repeated occupation of Fincha Habera rock shelter is dated to 47 to 31 thousand years ago. The available resources in cold and glaciated environments included the exploitation of an endemic rodent as a key food source, and this played a pivotal role in facilitating the occupation of this site by Late Pleistocene hunter-gatherers.

Higher gene expression stability during aging in long-lived giant mole-rats than in short-lived rats.

Many aging-associated physiological changes are known to occur in short- and long-lived species with different trajectories. Emerging evidence suggests that numerous life history trait differences between species are based on interspecies variations in gene expression. Little information is available, however, about differences in transcriptome changes during aging between mammals with diverging lifespans. For this reason, we studied the transcriptomes of five tissue types and two age cohorts of two similarly sized rodent species with very different lifespans: laboratory rats (Rattus norvegicus) and giant mole-rats (Fukomys mechowii), with maximum lifespans of 3.8 and more than 20 years, respectively. Our findings show that giant mole-rats exhibit higher gene expression stability during aging than rats. Although well-known aging signatures were detected in all tissue types of rats, they were found in only one tissue type of giant mole-rats. Furthermore, many differentially expressed genes that were found in both species were regulated in opposite directions during aging. This suggests that expression changes which cause aging in short-lived species are counteracted in long-lived species. Taken together, we conclude that expression stability in giant mole rats (and potentially in African mole-rats in general) may be one key factor for their long and healthy life.

Chemical restraint of African mole-rats (Fukomys sp.) with a combination of ketamine and xylazine

ObjectiveTo establish an accurate anaesthetic dose for chemical restraint of African mole-rats using ketamine and xylazine. Study designProspective nonrandomized laboratory study. AnimalsSixteen adult Ansell’s mole-rats (Fukomys anselli) and eight giant mole-rats (F. mechowii). MethodsFukomys anselli of different ages, sexes and reproductive status were systematically anaesthetized starting with an intramuscular injection of ketamine (2.5 mg kg−1) and increasing the doses in steps of 0.5 mg kg−1 until loss of the righting reflex (LRR) was observed. Xylazine was added to a constant dose of ketamine, starting at 0.5 mg kg−1 that was increased by 0.5 mg kg−1 in further trials. Once an effective combination was established and evaluated in F. anselli, it was also tested in F. mechowii. Heart and respiratory rates and rectal temperatures were measured during anaesthesia. anova for repeated measures and Student’s t-test were used to compare means. ResultsChemical restraint was accomplished at a dose of 6 mg kg−1 ketamine combined with 2.5 mg kg−1 xylazine. LRR lasted on average mean 56 ± SD 19 minutes (F. anselli) and 140 ± 41 minutes (F. mechowii). Loss of pedal withdrawal reflex (LPR) lasted for 20 ± 15 minutes (F. anselli) and for 29 ± 2 minutes (F. mechowii), respectively. All animals recovered satisfactorily. Heart and respiratory rates were stable during anaesthesia, but rectal temperature fell significantly in F. mechowii after losing the righting reflex (LRR) from T1 (32.6 ± 0.6 °C) to T3 (30.4 ± 0.9 °C). Conclusions and Clinical relevanceAfrican mole-rats (Bathyergidae) live in closed burrow systems under particular conditions (hypercapnia, hypoxia, stable temperature, humidity, darkness) and show several physiological adaptations. Injectable anaesthetics in the dose rates used in other rodents are not appropriate for use in these subterranean species. Here, a reliable protocol for chemical restraint is provided.

Burrow architecture, family composition and habitat characteristics of the largest social African mole-rat: the giant mole-rat constructs really giant burrow systems

Among African mole-rats, the giant mole-rat Fukomys mechowii is the largest social species. Despite several attempts to study a free-living population, information on its biology from natural habitats is very scarce. We mapped two neighbouring burrow systems of the giant mole-rat in a miombo woodland in Zambia. We provide information on the size and kin structure of the respective mole-rat families, architecture of their burrow systems, and characteristics of the food supply and soil around the two mapped and additional ten burrow systems. Both uncovered burrow systems were very large (total lengths, 2,245 and 743 m), making them the largest burrow systems ever mapped. Food resources around the additional ten burrow systems had a clumped distribution (standardized Morisita index of dispersion = 0.526), but a relatively high biomass (298 ± 455 g m−2). This, together with favourable soil conditions even in the advanced dry season (cone resistance, 328 ± 50 N m−2; soil density, 1.36 ± 0.06 g cm−3) indicates relatively hospitable ecological conditions. Both food supply and soil conditions were comparable with the conditions found in a miombo habitat of the solitary silvery mole-rat in Malawi. This suggests that there are no ecological constraints which would preclude the solitary life of a subterranean herbivore from the examined habitat. Microsatellite analysis supported the assumption that giant mole-rats live in monogamous multigenerational families with only one breeding pair of non-related animals and their offspring. The mean family size is consistent with previous findings on this species and comparable to that found in other Fukomys species studied thus far.

Extended Longevity of Reproductives Appears to be Common in Fukomys Mole-Rats (Rodentia, Bathyergidae)

African mole-rats (Bathyergidae, Rodentia) contain several social, cooperatively breeding species with low extrinsic mortality and unusually high longevity. All social bathyergids live in multigenerational families where reproduction is skewed towards a few breeding individuals. Most of their offspring remain as reproductively inactive “helpers” in their natal families, often for several years. This “reproductive subdivision” of mole-rat societies might be of interest for ageing research, as in at least one social bathyergid (Ansell's mole-rats Fukomys anselli), breeders have been shown to age significantly slower than non-breeders. These animals thus provide excellent conditions for studying the epigenetics of senescence by comparing divergent longevities within the same genotypes without the inescapable short-comings of inter-species comparisons. It has been claimed that many if not all social mole-rat species may have evolved similar ageing patterns, too. However, this remains unclear on account of the scarcity of reliable datasets on the subject. We therefore analyzed a 20-year breeding record of Giant mole-rats Fukomys mechowii, another social bathyergid species. We found that breeders indeed lived significantly longer than helpers (ca. 1.5–2.2fold depending on the sex), irrespective of social rank or other potentially confounding factors. Considering the phylogenetic positions of F. mechowii and F. anselli and unpublished data on a third Fukomys-species (F. damarensis) showing essentially the same pattern, it seems probable that the reversal of the classic trade-off between somatic maintenance and sexual reproduction is characteristic of the whole genus and hence of the vast majority of social mole-rats.

Behaviour and ecology of the Ethiopian wolf (Canis simensis) in a human-dominated landscape outside protected areas

The Ethiopian wolf (Canis simensis) is a very rare, endangered, endemic species surviving in isolated mountain pockets in the Ethiopian highlands, with nearly 50% of the global population living outside protected areas. In this paper we compare the ecology and behaviour of an Ethiopian wolf population living in Guassa, a communally managed area in the Central Highlands, with that of the Bale Mountains National Park in the Southern Highlands. Ethiopian wolves live at lower density in Guassa (0.2±0.05/km2) than in the Bale Mountains, but giant molerats (Tachyoryctes macrocephalus), the main prey for Ethiopian wolves in Bale Mountains, do not occur in the Central Highlands. Faecal analysis identified nine prey categories across wet and dry seasons common to both populations. In total, rodents accounted for 88% of prey volume in wolf diets. Home-range size was positively related to pack size (r2=0.85) and there was no difference in mean home-range sizes in both areas. In Guassa, however, wolves spent less time in the presence than in the absence of humans, but wolves spent similar amounts of time in the presence and absence of cattle. These findings suggest wolves can cope with, or adapt to, the presence of livestock and people in communally managed areas.

INDIVIDUAL ODOR SIMILARITIES WITHIN COLONIES AND ACROSS SPECIES OF CRYPTOMYS MOLE RATS

We studied similarities and differences in the qualities of individual odors across colonies and species of African eusocial mole rats using habituation techniques. Giant mole rats (Cryptomys mechowi) treated anogenital odors of 2 conspecifics from 1 colony as similar to each other and different from the odor of a conspecific from another colony, providing evidence for kinship odors. Subjects also discriminated between the subtle differences in the individual odors of familiar colony members. In another set of tests, mole rats from 3 species (C. mechowi, C. anselli, and C. kafuensis) treated anogenital odors of genetically closer heterospecifics as more similar to odors of conspecifics than to odors of less closely related heterospecifics. Thus, odor similarities paralleled genetic similarities as determined by the analysis of allozymic and karyotypic distances. The results demonstrate that similarities in individual odors covary with genetic similarities within colonies and across species. These similarities could provide a basis for different types of social recognition based on self-referent matching.

NATURAL HISTORY OF THE GIANT MOLE-RAT,CRYPTOMYS MECHOWI(RODENTIA: BATHYERGIDAE), FROM ZAMBIA

Abstract We present the 1st detailed field study on the giant mole-rat (Cryptomys mechowi), a eusocial subterranean bathyergid rodent from mesic areas of subequatorial central Africa. In Copperbelt Province, Zambia, we found giant mole-rats in a variety of habitats including agricultural fields, bushland, marshes, and forests. Soil types varied in hardness and air content, and varied vertically and horizontally. Burrow systems of single colonies were 0.2–2.5 ha. The diameter of burrows was about 8 cm, and the maximum depth was about 200 cm. Nests were found at an average depth of 91 cm (n = 8). Further characteristics of nests, food and defecation chambers, diet, helminth parasites, and commensals are described. Colony size ranged from 3 to >20 with a sex ratio of 1:1.2 (n = 65) in favor of females, with 8% juveniles, 39% subadults, and 53% adults. A significant sexual dimorphism was found in the body mass (345 g ± 95 SD in males versus 252 ± 34 g in females). A defined breeding season was not apparent. B...

Pituitary sensitivity to exogenous GnRH in giant Zambian mole-rats, Cryptomys mechowi (Rodentia: Bathyergidae): support for the ‘socially induced infertility continuum’

Pituitary sensitivity to exogenous GnRH in giant Zambian mole-rats, Cryptomys mechowi (Rodentia: Bathyergidae): support for the ‘socially induced infertility continuum’

The colony structure and social organization of the giant Zambian mole-rat, Cryptomys mechowi

Cryptomys mechowi is a social subterranean mole-rat which inhabits the mesic regions of south-eastern and central Africa. Giant mole-rats live in colonies of up to 11 animals in which reproduction is normally restricted to the largest male and female in the colony. In this preliminary study on a laboratory-reared colony, the non-reproductive members of the colony could not be placed into clearly defined, work-related groups based on body mass. The colony showed a work frequency related division of labour. Reproductive animals performed little work, 3-4% of the total work. The non-reproductive caste was divided into two groups based on the amount of burrow maintenance activity: those performing between 7-11% of total work and those ranging from 15-22% of total work. Male members of the colony tended to perform more work than the females. The dominance hierarchy of the colony was found to be nearly linear, with a value of 0.83 calculated from Landau's linearity index. The reproductive animals were the most dominant in their respective gender. Dominance was not age-related. However, non-reproductive males tended to be more dominant than non-reproductive females. Social organization within the giant Zambian mole-rat is compared with other southern African Cryptomys species in the light of the eusociality continuum.

SOME OBSERVATIONS ON THE GIANT MOLE-RAT TACHYORYCTES MACROCEPHALUS (RÜPPELL, 1842) (MAMMALIA RHIZOMYDAE) OF ETHIOPIA

SUMMARY The available material of the giant mole-rat Tachyoryctes macrocephalus (Ruppell, 1842) has been examined and compared with material of T. splendens (Ruppell, 1835) from Ethiopia, leading to a clearer understanding of the differences between them. T. macrocephalus is much larger, reaching a body weight of at least 900 g; most of its skull measurements are also larger, but its incisors are relatively and the interorbital width absolutely narrower than in T. splendens. Additional skull characters which separate the two races of T. macrocephalus confirm their status as subspecies. Observations were also made on the behaviour of a small colony of giant mole-rats, and on other aspects of their biology. Individuals spend up to 47 min gathering food and up to 18 min shovelling earth at the surface in a day; in total, the animals in the colony, probably six adults and one immature, were exposed at the surface for 165 and 178 min on 2 successive days. The food gathered included both grasses and dicotyledon...