The genus Cryptomys contains a number of social, subterranean rodents that are widely distributed throughout sub-Saharan Africa. Specimens of Cryptomys from 23 localities in south-west Zambia were karyotyped using a standard staining protocol. A minimum of five metaphases per specimen was scored for 2n and the fundamental number (NF) was determined in females. Nine new karyotypes, which may represent several new species, were identified: (1) 2n=42, NF=78 (Dongo, Southern Province); (2) 2n=44, NF=76 (Salujinga, North-western Province); (3) 2n=45, NF=78 (Lochinvar, Southern Province); (4) 2n=52, NF=86 (Chinyingi, North-western Province); (5) 2n=54, NF=78 (Monze, Southern Province); (6) 2n=56, NF=76 (Watopa, North-western Province); (7) 2n=58, NF=80 (Livingstone, Southern Province); (8) 2n=58, NF=86 (Senanga, Western Province); (9) 2n=60, NF=82 (Kataba, Western Province; type locality of C. damarensis micklemi). Contrary to previous reports, the specimens from Kataba and Senanga on the left bank of the Zambezi do not correspond to C. damarensis and should be considered a separate species: C. micklemi (as confirmed by molecular analyses; Ingram, Burda & Honeycutt, 2004). According to the karyotype, C. damarensis occurs only on the right bank of the Zambezi River in the Western Province. In contrast to the high karyotypic variability on the right bank of the Kafue River, it was found that C. anselli (2n=68) is widely distributed throughout the Central province on the left bank of the Kafue River. The resulting pattern of occurrence of the different karyotypes correlates well with the extant river system configuration that separates most karyotypes. We hypothesize that geomorphological changes and in particular river system dynamics in recent geological times have played an important role in the chromosomal diversification and may have provided opportunities for speciation to occur.

The highveld mole-rat Cryptomys hottentotus pretoriae is a social subterranean rodent that exhibits seasonal reproduction. Non-reproductive females remain anovulatory whilst in the confines of the natal colony. However, during the southern hemisphere summer, dispersal of non-reproductive females from the natal colony occurs with subsequent pairing with unrelated males. This study investigates whether the dispersing female highveld mole-rat is an induced or spontaneous ovulator. Eight non-reproductive females were removed from their natal colonies during the breeding season and housed individually for 5 weeks. Urine was collected every second day during the next 5 weeks of isolation. After this initial period, isolated females underwent one of three trials: two females were kept isolated without a male, three females were individually placed in chemical but not physical contact with unvasectomized males, while each of the remaining three females were allowed full contact with a vasectomized male. Urine was again collected every second day for a further 5 weeks, after which the females were killed. Both urinary progesterone profiles and histology of the ovaries revealed that the female highveld mole-rat is an induced ovulator. Females in physical contact with vasectomized males exhibited a significant increase in urinary progesterone concentration as well as the presence of corpora lutea in their ovaries, both indicative of ovulation. The act of coitus is necessary for ovulation to take place even though the males were not capable of fertilization. This is the first time induced ovulation has been shown in bathyergid rodents.

The foraging behaviour of captive colonies of the highveld mole-rat Cryptomys hottentotus pretoriae was investigated in an artificial soil-filled burrow system provided with four trays (patches) that varied in geophyte density and mass. An initial trial involving empty trays (only soil) revealed that there was no preference for any specific tray. There were no statistically significant preferences for excavating in any of the patches of different geophyte density. No preferences were evident for excavation in patches containing geophytes of different mass classes. Empty patches seemed to be preferred over patches containing geophytes when combinations of geophyte density/mass were investigated. The duration of handling and the rate of consumption of geophytes were recorded for 23 individuals of two mass classes. Handling time of geophytes was not related to mole-rat sex, but was strongly linked to mole-rat mass class. Handling time of geophytes was related to geophyte mass class. Small geophytes were less profitable to consume. These findings are considered in light of optimal foraging theory and the situation in the field. It was concluded that the mole-rats generally followed the qualitative predictions of optimal foraging theory, although falling short of being energy maximizers.

The highveld mole-rat, Cryptomys hottentous pretoriae is a social, subterranean, co-operative breeder with a high reproductive skew. The relationship between reproductive status and reproductive physiology in male highveld mole-rats was investigated. Testicular morphometrics, histological parameters, plasma testosterone concentrations and sperm motility parameters were studied in 31 males (14 reproductive and 17 non-reproductive males). Reproductive males were significantly larger than non-reproductive males, with testicular mass and volume corrected for body mass considerably larger for the reproductive males. Circulating plasma testosterone concentrations of reproductive males were not significantly higher than non-reproductive males (reproductive males 10.3±1.8 nmol l−1vs non-reproductive males 7.3±1.74 nmol l−1). Sperm motility parameters were measured, but no significant differences were found between reproductive and non-reproductive males. All 14 reproductive males had motile sperm, whereas 13 of the 17 (76%) of non-reproductive males possessed motile sperm. A typical ejaculate of a reproductive male contains 48.3% motile sperm characterized by a high percentage of flagellar defects, whereas the non-reproductive male has an ejaculate containing 45.6% motile sperm with a high percentage of head defects. It is apparent that non-reproductive males are not physiologically suppressed from reproducing. Moreover, the non-reproductive males are excluded from incestuous matings as a result of being the offspring of the reproductive female.

Non-reproductive female Damaraland mole-rats Cryptomys damarensis that were caught before a period of good rainfall (during which 90% of the average annual fell) (Group 1), exhibited a significantly lower pituitary sensitivity to gonadotrophin-releasing hormone compared to non-reproductive females (Group 2) caught in the same area, close to the end of the wet period. Group 2 were also significantly heavier than Group 1. Pituitary sensitivity was not significantly correlated to body mass within either group of females, nor within groups of reproductive males and non-reproductive males from a laboratory held colony. This suggests that rainfall may have resulted in the simultaneous, but unrelated, increase in pituitary sensitivity and body mass. Larger size and reduced sexual inhibition assist dispersal and the probability of successful independent reproduction, during periods when environmental constraints on dispersal are relaxed. These findings support the hypothesis that low rainfall may be an important constraint on dispersal and an important factor promoting the evolution of reproductive inhibition, and consequently eusociality, in this species.

Colonies of the Mashona mole-rat Cryptomys darlingi are founded from a single reproductive pair of animals that are genetically unrelated by descent. All non-reproductive animals are the progeny of the reproductive pair. Non-reproductive colony members do not seem to be suppressed from reproduction at the level of the pituitary. In colonies in which the reproductive female is removed or dies, there is strict incest avoidance and the colony remains reproductively quiescent. Reinstatement of sexual activity in a queenless colony may be brought about in the laboratory by the introduction of unfamiliar and unrelated adult males. In the queenless colony under study, there was a marked change in the dominance hierarchy with an increase in Landau's index of linearity from 0.61 to 1.0 on the introduction of two unrelated males. The two new males became the most dominant within the colony. All previously non-reproductive females exhibited heightened urinary oestradiol 17β and progesterone concentrations on the introduction of the males. However, it was only the older and most dominant non-reproductive female that became the new reproductive female and produced a litter of three pups 70 days after the initial introduction.

The highveld mole-rat Cryptomys hottentotus pretoriae exhibits an extreme reproductive division of labour. Reproduction in this seasonally breeding social mole-rat is restricted to a breeding pair. The non-reproductive females seem to be physiologically suppressed from reproducing, whereas the non-reproductive males are restricted from sexual activity through incest avoidance. Circulating basal concentrations of luteinizing hormone (LH) between reproductive and non-reproductive females were not significantly different, yet the response to an exogenous gonadotrophin-releasing hormone (GnRH) challenge was significantly lower in non-reproductive females when compared to reproductive females. The mean basal LH concentration in non-reproductive females was not significantly different in and out of the breeding season. However, the magnitude of the LH response in non-reproductive females out of the breeding season was greater than in the breeding season. The ovaries of reproductive females showed little change with respect to season. However, reproductive females had enhanced follicular activity in comparison to their non-reproductive counterparts. This suggests that non-reproductive females are under stricter control from the reproductive female when she is pregnant. The tropical African mole-rats exhibit a continuum of socially induced infertility with differing social species inhabiting regions of varying degrees of aridity. In this spectrum, a predominantly behavioural repression is found amongst non-reproductive females in social mesic-adapted species, whereas a strictly physiological suppression is operative amongst non-reproductive females in arid-adapted social species. Here we show that the mesic-adapted highveld mole-rat does not fit this trend in that the non-reproductive females seem to be physiologically suppressed. We discuss this in light of the seasonality of breeding and the ecological constraints that may operate during times of drought.

A total of 104 Damaraland mole-rats was collected in 1988, 1990, 1991 and 1993 from an open water canal in the Otjiwarongo district of Namibia. The mole-rats were apparently dispersing above ground when they fell in and drowned; they had travelled at least 20 m in distance from their natal burrow systems. The dispersing mole-rats of both sexes were significantly larger than 73 animals trapped from a nearby control population. Sequential tooth wear and eruption patterns showed that dispersers were adult animals. There was a bias towards male mole-rats dispersing. Furthermore, in years with lower rainfall (< 300 mm) it was found that dispersal became even more male biased. Eighty per cent of males and 40% of female dispersers showed signs of reproductive readiness, with more males than females being ready to breed. Thus it appears that, in these otherwise totally subterranean mammals, at least one form of dispersal occurs, above ground, and that adult mole-rats are the principal dispersers.

The highveld mole-rat Cryptomys hottentotus pretoriae occurs in the summer rainfall region of the highveld of South Africa. It lives in colonies of up to 10 individuals, in which reproduction is limited to one to two of the largest males and the largest female in the colony. Of three field captured colonies, the mean colony size was 10 ± 0 animals with a mean biomass of 900 ± 147 g. The study colony had a sex ratio of 1.5:1 in favour of males.

The social hierarchy of the highveld mole-rat is non-linear and has a value of 0.3 calculated from Landau's linearity index. Dominance was negatively correlated with capture order.

Histological examination of the gonads of reproductively active and sexually quiescent members of both sexes of two colonies provides further support of there being a single reproductive male and female responsible for procreation in the colony.

The non-reproductives of both sexes appear to be important in burrow maintenance activity and in foraging for geophytes upon which the mole-rats feed. The non-reproductive members of the colony cannot be subdivided into different worker groups based on body mass. The available evidence suggests that the highveld mole-rat is a transiently social species, at one extreme of a sociality continuum in the genus Cryptomys. The position of this subspecies in respect to the sociality continuum is discussed.

Crytomys damarensis is a eusocial subterranean rodent occurring in colonies in which a sole reproductive female and one to two males are involved in procreation; the remaining colony members are non-reproductive. Within each sex the reproductive animals are usually the largest and most dominant animals.

The dominance hierarchy of a young colony consisting of a founding reproductive pair of genetically unrelated animals and the first three successive litters, comprising 12 offspring, from this pair had a non-linear dominance hierarchy, h = 0.32. Dominance was found to be correlated positively to body mass as well as to the age of the animal. A subsequent study, which followed the incorporation of two subsequent litters and growth of the first three litters, and comprised 15 offspring, revealed that the dominance hierarchy had attained linearity, h = 0.9. Dominance was again positively correlated with the age and body mass of respective colony members. In both studies there was no clear relationship between dominance and sex within the colony.

The relationship between body mass and burrow-maintenance activity revealed that frequent workers in the colony had a greater mean body mass than infrequent workers. It is suggested that in establishing colonies, the older, stronger and hence larger animals may constitute the initial workforce. In addition the colony exhibits frequency-related work determination into frequent and infrequent workers. Gender was found to play no role in the frequency of work associated with burrow maintenance.

The social organization and temporal changes with recruitment are discussed in the light of events occurring in the field.

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.