Giant Mole-rat Fukomys Mechowii Research Articles

Functional histology of the skin in the subterranean African giant mole-rat: thermal windows are determined solely by pelage characteristics.

Excavation of burrows is an extremely physically demanding activity producing a large amount of metabolic heat. Dissipation of its surplus is crucial to avoid the risk of overheating, but in subterranean mammals it is complicated due to the absence of notable body extremities and high humidity in their burrows. IR-thermography in a previous study on two species of African mole-rats revealed that body heat was dissipated mainly through the ventral body part, which is notably less furred. Here, we analyzed the dorsal and ventral skin morphology, to test if dermal characteristics could contribute to higher heat dissipation through the ventral body part. The thickness of the epidermis and dermis and the presence, extent and connectivity of fat tissue in the dermis were examined using routine histological methods, while vascular density was evaluated using fluorescent dye and confocal microscopy in the giant mole-rat Fukomys mechowii. As in other hitherto studied subterranean mammals, no subcutaneous adipose tissue was found. All examined skin characteristics were very similar for both dorsal and ventral regions: relative content of adipose tissue in the dermis (14.4 ± 3.7% dorsally and 11.0 ± 4.0% ventrally), connectivity of dermal fat (98.5 ± 2.8% and 95.5 ± 6.8%), vascular density (26.5 ± 3.3% and 22.7 ± 2.3%). Absence of large differences in measured characteristics between particular body regions indicates that the thermal windows are determined mainly by the pelage characteristics.

Audiograms of three subterranean rodent species (genus Fukomys) determined by auditory brainstem responses reveal extremely poor high-frequency hearing.

Life underground has shaped the auditory sense of subterranean mammals, shifting their hearing range to low frequencies. Mole-rats of the genus Fukomys have, however, been suggested to hear at frequencies up to 18.5 kHz, unusually high for a subterranean rodent. We present audiograms of three mole-rat species, Fukomys anselli, Fukomys micklemi and the giant mole-rat Fukomys mechowii, based on evoked auditory brainstem potentials. All species showed low sensitivity and restricted hearing ranges at 60 dB SPL extending from 125 Hz to 4 kHz (5 octaves) with most-sensitive hearing between 0.8 kHz and 1.4 kHz. The high-frequency cut-offs are the lowest found in mammals to date. In contrast to predictions from middle ear morphology, F. mechowii did not show higher sensitivity than F. anselli in the low-frequency range. These data suggest that the hearing range of Fukomys mole-rats is highly restricted to low frequencies and similar to that of other subterranean mammals.

Correction: Audiograms of three subterranean rodent species (genus Fukomys) determined by auditory brainstem responses reveal extremely poor high-frequency cut-offs.

ABSTRACT Life underground has shaped the auditory sense of subterranean mammals, shifting their hearing range to low frequencies. Mole-rats of the genus Fukomys have, however, been suggested to hear at frequencies up to 18.5 kHz, unusually high for a subterranean rodent. We present audiograms of three mole-rat species, Fukomys anselli, Fukomys micklemi and the giant mole-rat Fukomys mechowii, based on evoked auditory brainstem potentials. All species showed low sensitivity and restricted hearing ranges at 60 dB SPL extending from 125 Hz to 4 kHz (5 octaves) with most-sensitive hearing between 0.8 kHz and 1.4 kHz. The high-frequency cut-offs are the lowest found in mammals to date. In contrast to predictions from middle ear morphology, F. mechowii did not show higher sensitivity than F. anselli in the low-frequency range. These data suggest that the hearing range of Fukomys mole-rats is highly restricted to low frequencies and similar to that of other subterranean mammals.

Surprisingly low risk of overheating during digging in two subterranean rodents

Capacities for and constraints of heat dissipation are considered to be important factors governing maximum intensity and duration of physical activity. Subterranean mammals are endurance diggers, but because of lack of air currents in their burrows, high relative humidity and other physical constraints, the capacity of common mammalian cooling mechanisms underground is very limited. We analyzed surface and body core temperature changes after digging in soft and hard substrates in two species of African mole-rats (Bathyergidae, Rodentia); the social giant mole-rat Fukomys mechowii and the solitary silvery mole-rat Heliophobius argenteocinereus. As expected, we observed an increase of body core temperature in both species after digging in both substrates. Surprisingly, and contrary to our expectations, we observed remarkable decrease of mole-rats' surface temperature immediately after the end of the digging trials. This decrease was greater in soft and moister soil than that in hard and drier soil. Our results suggest that mole-rats may effectively avoid overheating in burrows by effective cooling while digging, especially in wet soil. This indicates that burrowing in soils moistened by rains could be easier than previously thought contributing thus to mole-rats success in challenging environment of subterranean burrows.

Spatial and Temporal Activity Patterns of the Free-Living Giant Mole-Rat (Fukomys mechowii), the Largest Social Bathyergid

Despite the considerable attention devoted to the biology of social species of African mole-rats (Bathyergidae, Rodentia), knowledge is lacking about their behaviour under natural conditions. We studied activity of the largest social bathyergid, the giant mole-rat Fukomys mechowii, in its natural habitat in Zambia using radio-telemetry. We radio-tracked six individuals during three continuous 72-h sessions. Five of these individuals, including a breeding male, belonged to a single family group; the remaining female was probably a solitary disperser. The non-breeders of the family were active (i.e. outside the nest) 5.8 hours per 24h-day with the activity split into 6.5 short bouts. The activity was more concentrated in the night hours, when the animals also travelled longer distances from the nest. The breeding male spent only 3.2 hours per day outside the nest, utilizing less than 20% of the whole family home range. The dispersing female displayed a much different activity pattern than the family members. Her 8.0 hours of outside-nest activity per day were split into 4.6 bouts which were twice as long as in the family non-breeders. Her activity peak in the late afternoon coincided with the temperature maximum in the depth of 10 cm (roughly the depth of the foraging tunnels). Our results suggest that the breeding individuals (at least males) contribute very little to the work of the family group. Nevertheless, the amount of an individual's activity and its daily pattern are probably flexible in this species and can be modified in response to actual environmental and social conditions.

Magnetic compass orientation in two strictly subterranean rodents: learned or species-specific innate directional preference?

Evidence for magnetoreception in mammals remains limited. Magnetic compass orientation or magnetic alignment has been conclusively demonstrated in only a handful of mammalian species. The functional properties and underlying mechanisms have been most thoroughly characterized in Ansell's mole-rat, Fukomys anselli, which is the species of choice due to its spontaneous drive to construct nests in the southeastern sector of a circular arena using the magnetic field azimuth as the primary orientation cue. Because of the remarkable consistency between experiments, it is generally believed that this directional preference is innate. To test the hypothesis that spontaneous southeastern directional preference is a shared, ancestral feature of all African mole-rats (Bathyergidae, Rodentia), we employed the same arena assay to study magnetic orientation in two other mole-rat species, the social giant mole-rat, Fukomys mechowii, and the solitary silvery mole-rat, Heliophobius argenteocinereus. Both species exhibited spontaneous western directional preference and deflected their directional preference according to shifts in the direction of magnetic north, clearly indicating that they were deriving directional information from the magnetic field. Because all of the experiments were performed in total darkness, our results strongly suggest that all African mole-rats use a light-independent magnetic compass for near-space orientation. However, the spontaneous directional preference is not common and may be either innate (but species-specific) or learned. We propose an experiment that should be performed to distinguish between these two alternatives.

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.

Control of ovulation in female giant mole‐rats Fukomys mechowii (Rodentia: Bathyergidae), and phylogenetic trends within the family

The giant mole-rat Fukomys mechowii is a cooperatively breeding, subterranean rodent inhabiting the Miombo woodland and savanna of south-central Africa, with reproduction occurring throughout the year. Across species within the family Bathyergidae, ovulation can be either induced by mating or spontaneous and the particular mechanism may correlate with patterns of seasonality, dispersal and opportunities for mating. We investigate the control of ovulation in F. mechowii, a species closely related to a spontaneously ovulating species but found in a habitat more typical of mole-rats with induced ovulation. Six wild-caught, non-reproductive females were removed from their natal colonies and non-invasively monitored for ovarian cyclicity by measuring urinary progesterone every 2 days, over 217 days. All six females had elevated progesterone profiles indicative of the luteal phase of the ovarian cycle, whether singly housed, separated from a male by a mesh screen (i.e. non-physical contact), or paired with a vasectomised male (full physical contact), although progesterone concentrations were significantly enhanced in the latter condition. Together with observations that male penile morphology is similar to other spontaneously ovulating bathyergids, these results strongly suggest that while ovarian cyclicity may occur spontaneously in F. mechowii, the presence of a male may have an additional stimulatory effect on ovulation. Comparative phylogenetic analysis revealed a positive correlation between seasonality in breeding and induced ovulation. Furthermore, a likelihood-based reconstruction suggests that induced ovulation is the ancestral state for the Bathyergidae and that this trait has been convergently lost in at least two lineages, giving rise to a spontaneous mode of ovulation.

Light perception in two strictly subterranean rodents: life in the dark or blue?

BackgroundThe African mole-rats (Bathyergidae, Rodentia) are strictly subterranean, congenitally microphthalmic rodents that are hardly ever exposed to environmental light. Because of the lack of an overt behavioural reaction to light, they have long been considered to be blind. However, recent anatomical studies have suggested retention of basic visual capabilities. In this study, we employed behavioural tests to find out if two mole-rat species are able to discriminate between light and dark, if they are able to discriminate colours and, finally, if the presence of light in burrows provokes plugging behaviour, which is assumed to have a primarily anti-predatory function.Methodology/Principal FindingWe used a binary choice test to show that the silvery mole-rat Heliophobius argenteocinereus and the giant mole-rat Fukomys mechowii exhibit a clear photoavoidance response to full-spectrum (“white”), blue and green-yellow light, but no significant reaction to ultraviolet or red light during nest building. The mole-rats thus retain dark/light discrimination capabilities and a capacity to perceive short to medium-wavelength light in the photopic range of intensities. These findings further suggest that the mole-rat S opsin has its absorption maximum in the violet/blue part of the spectrum. The assay did not yield conclusive evidence regarding colour discrimination. To test the putative role of vision in bathyergid anti-predatory behaviour, we examined the reaction of mole-rats to the incidence of light in an artificial burrow system. The presence of light in the burrow effectively induced plugging of the illuminated tunnel.Conclusion/SignificanceOur findings suggest that the photopic vision is conserved and that low acuity residual vision plays an important role in predator avoidance and tunnel maintenance in the African mole-rats.

Field evidence for aseasonality of reproduction and colony size in the Afrotropical giant mole-rat Fukomys mechowii (Rodentia: Bathyergidae)

ABSTRACT The giant mole-rat, Fukomys mechowii is a cooperatively breeding subterranean mole-rat exhibiting a reproductive division of labour in which usually one, or occasionally two, females are responsible for procreation. In a field study that involved complete excavation of 32 burrow systems, mean colony size was 9.9 individuals (range 7–16). Pregnant reproductive females were found throughout the study period (September 2005 until June 2006), supporting preliminary evidence that reproduction occurs throughout the year. Of the 32 colonies sampled, 10 of 14 in which the reproductive female could be identified as pregnant contained a single reproductive female, while four had two females breeding simultaneously (plural breeding). The population sex ratio was skewed towards females at 1:1.46. Autopsy of pregnant reproductive females (n = 18) revealed that the production of two (10/18 pregnancies) or three (7/18) offspring was the norm, with one case of four embryos being present. These new data increase ...

Field evidence for aseasonality of reproduction and colony size in the Afrotropical giant mole-rat Fukomys mechowii (Rodentia: Bathyergidae)

The giant mole-rat, Fukomys mechowii is a cooperatively breeding subterranean mole-rat exhibiting a reproductive division of labour in which usually one, or occasionally two, females are responsible for procreation. In a field study that involved complete excavation of 32 burrow systems, mean colony size was 9.9 individuals (range 7–16). Pregnant reproductive females were found throughout the study period (September 2005 until June 2006), supporting preliminary evidence that reproduction occurs throughout the year. Of the 32 colonies sampled, 10 of 14 in which the reproductive female could be identified as pregnant contained a single reproductive female, while four had two females breeding simultaneously (plural breeding). The population sex ratio was skewed towards females at 1:1.46. Autopsy of pregnant reproductive females (n = 18) revealed that the production of two (10/18 pregnancies) or three (7/18) offspring was the norm, with one case of four embryos being present. These new data increase our fragmentary knowledge of the natural history of this little-studied species.

Encephalization of Bathyergidae and comparison of brain structure volumes between the Zambian mole-rat Fukomys anselli and the giant mole-rat Fukomys mechowii

Encephalization indices were calculated for Fukomys anselli and Fukomys mechowii by using interspecific allometric lines of Tenrecinae (recent Eutheria with the smallest brains) and average Rodentia to compare brain sizes independent of body size influence. These were contrasted with corresponding indices of other Bathyergidae and additionally with other rodents. The Bathyergidae species had indices within the variation of some Cricetidae and Muridae and thus do not differ in encephalization. F. anselli, however, had a clearly higher encephalization index than the sister species F. mechowii. The sizes of diverse structures were measured in the brains of these two species by help of the serial section method. No differences were found in relative composition. The lower encephalization of F. mechowii is discussed as a special phenomenon of gigantism during phylogenetic radiation which similarly was documented for other forms.