Cape Mole-rat Georychus Capensis Research Articles

Are southern African solitary mole-rats homeothermic or heterothermic under natural field conditions?

Abandoning of a stable body temperature (Tb), a phenomenon known as heterothermy, is an adaptation to cope mainly with a lack of food and water, especially in species inhabiting daily or seasonally variable environments. There is increasing evidence that African mammals avoid adverse conditions by heterothermy and eventually by entering torpor. Members of subterranean rodent family, the African mole-rats (Bathyergidae), are suitable candidates to study both phenomena, because of the diversity of their strategies in respect of maintaining stable Tb ranging from homeothermic species to a mammal with the most labile Tb, the naked mole-rat. Currently, there are field data on daily and seasonal Tb in one social species only and such information are lacking for any solitary mole-rat. In our study, we recorded yearly Tb in two solitary bathyergids, the Cape mole-rat Georychus capensis and the Cape dune mole-rat Bathyergus suillus from South Africa using intraperitoneally implanted dataloggers. Since this region is characterised by changing ecological characteristics, we expected either decreases of Tb within 24h indicating daily torpor and/or longer-term decreases of Tb, which would indicate multiday torpor. Although we found seasonally phase shifted low amplitude daily Tb cycles, we did not find any remarkable and regular daily and/or seasonal Tb deviations, likely showing an absence of torpor in both species. Due to absence of this energy saving mechanism, we may speculate that both species could be vulnerable to ongoing global climatic change.

Sleep in the Cape Mole Rat: A Short-Sleeping Subterranean Rodent

The Cape mole rat Georychus capensis is a solitary subterranean rodent found in the western and southern Cape of South Africa. This approximately 200-gram bathyergid rodent shows a nocturnal circadian rhythm, but sleep in this species is yet to be investigated. Using telemetric recordings of the electroencephalogram (EEG) and electromyogram (EMG) in conjunction with video recordings, we were able to show that the Cape mole rat, like all other rodents, has sleep periods composed of both rapid eye movement (REM) and slow-wave (non-REM) sleep. These mole rats spent on average 15.4 h awake, 7.1 h in non-REM sleep and 1.5 h in REM sleep each day. Cape mole rats sleep substantially less than other similarly sized terrestrial rodents but have a similar percentage of total sleep time occupied by REM sleep. In addition, the duration of both non-REM and REM sleep episodes was markedly shorter in the Cape mole rat than has been observed in terrestrial rodents. Interestingly, these features (total sleep time and episode duration) are similar to those observed in another subterranean bathyergid mole rat, i.e. Fukomys mechowii. Thus, there appears to be a bathyergid type of sleep amongst the rodents that may be related to their environment and the effect of this on their circadian rhythm. Investigating further species of bathyergid mole rats may fully define the emerging picture of sleep in these subterranean African rodents.

LH responses to single doses of exogenous GnRH in the Cape mole rat (Georychus capensis): the pituitary potential for opportunistic breeding

AbstractThe Cape mole rat Georychus capensis is a solitary mole rat that inhabits the winter rainfall region of the Western Cape Province of South Africa. Circulating basal concentrations of luteinizing hormone (LH) were found to be significantly higher in the breeding season in both sexes. During both the breeding and non‐breeding season, administration of exogenous gonadotropin‐releasing hormone (GnRH) increased circulatory LH levels. The magnitude of the LH response to an overdose of exogenous GnRH both in and out of the breeding season in males and females was not significantly different. Typically, seasonally breeding species exhibit a down‐regulation of the pituitary and reproductive functions out of the breeding season. It appears that there is no down‐regulation of GnRH receptors at the level of the pituitary out of the breeding season, because the pituitary responds to an exogenous GnRH challenge equally both in and out of the breeding period. The Cape mole rat exhibits the potential for opportunistic breeding out of the breeding period, provided that environmental factors are favourable. This finding questions whether this mole rat is actually a seasonal breeder or whether reproduction is hindered by the ecological constraint of the lack of opportunities to burrow and find mates at certain times of the year.

Do solitary, seismic signalling Cape mole‐rats (Georychus capensis) demonstrate spontaneous or induced ovulation?

AbstractThe Cape mole‐rat Georychus capensis is a solitary subterranean rodent that exhibits seasonal reproduction. This study set out to determine whether the female Cape mole‐rat is an induced or spontaneous ovulator. Eleven females were collected from the field just before the breeding season and housed individually. Urine was collected for 5 weeks. Females were subjected to one of three trials: housed separately without a male; allowed only non‐physical contact with unvasectomized males; placed in direct contact with four vasectomized males. Urine was collected for a further 5 weeks and urinary progesterone profiles established. Females housed in direct contact with males exhibited heightened progesterone concentrations and the presence of corpora lutea in their ovaries. The act of coitus seems to be necessary for ovulation to occur in the females even though males were not capable of fertilization.

Nutrition and burrowing energetics of the Cape mole-rat Georychus capensis.

At 22°C the resting oxygen consumption of G. capensis is 1.13±0.05 cm3O2·g-1·h-1 (mean± S.E.). In loose sandy soil the burrowing metabolic rate was approximately three times that of resting (3.41±0.19 cm3O2·g-1· h-1). Rate of oxygen consumption while burrowing bears a linear relationship with rate of burrowing. The equation of the regression line describing this relationship was used to construct a model for calculating energy expenditure of burrowing in free-living mole-rats. The diet of G. capensis consists of some green plant material and geophyte corms. The latter has a mean gross energy content of 16.36 kJ·g-1 dry weight. The digestibility coefficient for captive G. capensis fed on sweet potato, was 97.42±0.41%. Data collected from an excavated burrow system revealed that the total energetic cost of constructing the burrow amounted to 79% of the estimated digestible energy available from geophyte corms in the area. A food store in the same burrow system was sufficient to meet the maintenance requirements of an adult G. capensis, resting at 22°C, for approximately 80-85 days. Soil samples taken at random adjacent to the burrow contained corms with a mean estimated digestible energy value of 2084 kJ per m3 of soil. A comparison of energetic cost of burrowing and randomly available digestible energy in the field suggests that foraging patterns are not random.