Cryptomys Hottentotus Pretoriae Research Articles

The Cost of Reproduction in a Cooperatively Breeding Mammal: Consequences of Seasonal Variation in Rainfall, Reproduction, and Reproductive Suppression.

Biological investments, such as reproduction, are influenced by both biotic and abiotic factors and their interactions. The trade-off between reproduction and survival has been well established. Seasonally breeding species, therefore, may exhibit variations in these trade-offs, but there is a dearth of knowledge concerning this. This study investigated the physiological cost of reproduction (measured through oxidative stress) across seasons in the cooperatively breeding highveld mole-rat (Cryptomys hottentotus pretoriae), one of the few seasonal breeding mole-rats. Oxidative stress indicates elevated reactive oxygen species (ROS) levels, which can overwhelm antioxidant defences resulting in damaged proteins, lipids and DNA, which overall can reduce longevity and compromise reproduction. Oxidative markers such as total oxidant status (TOS-measure of total peroxides present), total antioxidant capacity (TAC), oxidative stress index (OSI), and malondialdehyde (MDA) are utilised to measure oxidative stress. In this study, breeding and non-breeding male (NBM) and female mole-rats were captured during the dry season (breeding period) and wet season (non-breeding period). There was an apparent cost of reproduction in the highveld mole-rat; however, the seasonality pattern to the cost of reproduction varied between the sexes. Breeding females (BFs) had significantly higher MDA during the breeding period/dry season in comparison to the non-breeding period/wet season; this is possibly a consequence of bearing and nursing offspring. Contrastingly, breeding males (BMs) showed increased oxidative damage in the non-breeding/wet season compared to the breeding/dry season, possibly due to increased activities of protecting their mating rights for the next breeding/dry season, but this was not significant. Interestingly, during the non-breeding period/wet season, non-breeding females (NBFs) are released from their reproductive suppression, which resulted in increases in TOS and OSI, which again indicated that just the mere ability to be able to breed results in a cost (oxidative stress). Therefore we can speculate that highveld mole-rats exhibited seasonal variation in redox balance brought about by variation in abiotic variables (e.g., rainfall), physiology and behaviour. We conclude that physiological changes associated with reproduction are sufficient to induce significant acute oxidative stress in the plasma of female highveld mole-rats, which become alleviated following transition to the non-breeding season/wet period suggesting a possible hormetic effect.

Adult neurogenesis and its anatomical context in the hippocampus of three mole-rat species.

African mole-rats (family Bathyergidae) are small to medium sized, long-lived, and strictly subterranean rodents that became valuable animal models as a result of their longevity and diversity in social organization. The formation and integration of new hippocampal neurons in adult mammals (adult hippocampal neurogenesis, AHN) correlates negatively with age and positively with habitat complexity. Here we present quantitative data on AHN in wild-derived mole-rats of 1 year and older, and briefly describe its anatomical context including markers of neuronal function (calbindin and parvalbumin). Solitary Cape mole-rats (Georychus capensis), social highveld mole-rats (Cryptomys hottentotus pretoriae), and eusocial naked mole-rats (Heterocephalus glaber) were assessed. Compared to other rodents, the hippocampal formation in mole-rats is small, but shows a distinct cytoarchitecture in the dentate gyrus and CA1. Distributions of the calcium-binding proteins differ from those seen in rodents; e.g., calbindin in CA3 of naked mole-rats distributes similar to the pattern seen in early primate development, and calbindin staining extends into the stratum lacunosum-moleculare of Cape mole-rats. Proliferating cells and young neurons are found in low numbers in the hippocampus of all three mole-rat species. Resident granule cell numbers are low as well. Proliferating cells expressed as a percentage of resident granule cells are in the range of other rodents, while the percentage of young neurons is lower than that observed in surface dwelling rodents. Between mole-rat species, we observed no difference in the percentage of proliferating cells. The percentages of young neurons are high in social highveld and naked mole-rats, and low in solitary Cape mole-rats. The findings support that proliferation is regulated independently of average life expectancy and habitat. Instead, neuronal differentiation reflects species-specific demands, which appear lower in subterranean rodents.

Natural Parasite Infection Affects the Tolerance but Not the Response to a Simulated Secondary Parasite Infection

Parasites deplete the resources of their host and can consequently affect the investment in competing traits (e.g. reproduction and immune defence). The immunocompetence handicap hypothesis posits that testosterone (T) mediates trade-offs between parasite defence and reproductive investment by suppressing immune function in male vertebrates while more recently a role for glucocorticoids (e.g. cortisol (C)) in resource allocation has been suggested. These hypotheses however, have not always found support in wild animals, possibly because most studies focus on a single parasite species, whereas infections with multiple parasites are the rule in nature. We measured body mass, T- and C-levels of wild male highveld mole-rats (Cryptomys hottentotus pretoriae) naturally uninfected or infected with a cestode (Mathevotaenia sp.) right after capture. Subsequently, we injected animals subcutaneously with a lipopolysaccharide (LPS) to simulate a bacterial infection and recorded changes in body mass, food intake, haematological parameters and hormone levels. As a control, animals were injected with saline. Natural infection neither affected initial body mass nor C-levels, whereas infected males had significantly reduced T-levels. We observed significant reductions in food intake, body mass and T in response to LPS but not saline while C increased. However, this response did not vary with infection status. In contrast, final body mass and some haematological parameters were significantly lowered in infected males. Our results suggest that naturally infected males are able to compensate for resource depletion by physiological adjustments. However, this leaves them less tolerant to the challenges of a secondary infection.

Heterothermy in two mole‐rat species subjected to interacting thermoregulatory challenges

Maintaining a high and constant body temperature (T(b) ) is often viewed as a fundamental benefit of endothermy, but variation in T(b) is likely the norm rather than an exception among endotherms. Thus, attempts to elucidate which factors cause T(b) of endotherms to deviate away from the T(b) that maximizes performance are becoming more common. One approach relies on an adaptive framework of thermoregulation, used for a long time to predict variation in T(b) of ectotherms, as a starting point to make predictions about the factors that should lead to thermoregulatory variation in endotherms. Here we test the predictions that when confronted with thermoregulatory challenges endotherms should (1) become more heterothermic, (2) lower their T(b) setpoint, and/or (3) increase behavioral thermoregulation (e.g., activity levels or social thermoregulation). We exposed two species of relatively homeothermic mole-rats to two such challenges: (a) ambient temperatures (T(a)) well below the thermoneutral zone and (b) increased heat loss caused by the removal of dorsal fur. In general, our results support the adaptive framework of endothermic thermoregulation with each species conforming to some of the predictions. For example, Mashona mole-rats (Fukomys darlingi) increased heterothermy as T(a) decreased, highveld mole-rats (Cryptomys hottentotus pretoriae) displayed lower T(b) 's after shaving, and both species increased behavioral thermoregulation as T(a) decreased. This suggests that there is some merit in extending the adaptive framework to endotherms. However, none of the three predictions we tested was supported under all experimental conditions, reiterating that attempts to determine universal factors causing variation in T(b) of endotherms may prove challenging.

The Role of Host Traits, Season and Group Size on Parasite Burdens in a Cooperative Mammal

The distribution of parasites among hosts is often characterised by a high degree of heterogeneity with a small number of hosts harbouring the majority of parasites. Such patterns of aggregation have been linked to variation in host exposure and susceptibility as well as parasite traits and environmental factors. Host exposure and susceptibility may differ with sexes, reproductive effort and group size. Furthermore, environmental factors may affect both the host and parasite directly and contribute to temporal heterogeneities in parasite loads. We investigated the contributions of host and parasite traits as well as season on parasite loads in highveld mole-rats (Cryptomys hottentotus pretoriae). This cooperative breeder exhibits a reproductive division of labour and animals live in colonies of varying sizes that procreate seasonally. Mole-rats were parasitised by lice, mites, cestodes and nematodes with mites (Androlaelaps sp.) and cestodes (Mathevotaenia sp.) being the dominant ecto- and endoparasites, respectively. Sex and reproductive status contributed little to the observed parasite prevalence and abundances possibly as a result of the shared burrow system. Clear seasonal patterns of parasite prevalence and abundance emerged with peaks in summer for mites and in winter for cestodes. Group size correlated negatively with mite abundance while it had no effect on cestode burdens and group membership affected infestation with both parasites. We propose that the mode of transmission as well as social factors constrain parasite propagation generating parasite patterns deviating from those commonly predicted.

Orexinergic neuron numbers in three species of African mole rats with rhythmic and arrhythmic chronotypes

In the present study, orexinergic cell bodies within the brains of rhythmic and arrhythmic circadian chronotypes from three species of African mole rat (Highveld mole rat—Cryptomys hottentotus pretoriae, Ansell's mole rat—Fukomys anselli and the Damaraland mole rat—Fukomys damarensis) were identified using immunohistochemistry for orexin-A. Immunopositive orexinergic (Orx+) cell bodies were stereologically assessed and absolute numbers of orexinergic cell bodies were determined for the distinct circadian chronotypes of each species of mole rat examined. The aim of the study was to investigate whether the absolute numbers of identified orexinergic neurons differs between distinct circadian chronotypes with the hypothesis of elevated hypothalamic orexinergic neurons in the arrhythmic chronotypes compared with the rhythmic chronotypes. We found statistically significant differences between the circadian chronotypes ofF. anselli, where the arrhythmic group had higher mean numbers of hypothalamic orexin neurons compared with the rhythmic group. These differences were observed when the raw data was compared and when the raw data was corrected for body mass (Mb) and brain mass (Mbr). For the two other species investigated, no significant differences were noted between the chronotypes, although a statistically significant difference was noted between all rhythmic and arrhythmic individuals of the current study when the counts of orexin neurons were corrected for Mb—the arrhythmic individuals had larger numbers of orexin cells.

Nuclear organization and morphology of cholinergic, putative catecholaminergic and serotonergic neurons in the brains of two species of African mole-rat

The distribution, morphology and nuclear subdivisions of the cholinergic, putative catecholaminergic and serotonergic systems within the brains of two species of African mole-rat (Cape dune mole-rat – Bathyergus suillus; highveld mole-rat – Cryptomys hottentotus pretoriae) were identified following immunohistochemistry for acetylcholinesterase, tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems by comparing those of the mole-rats to published studies of other rodents. The mole-rats used exhibit a major reduction of the visual system and live a subterranean lifestyle. These wild caught animals also have differing social systems, the Cape dune mole-rat is strictly solitary whereas the highveld mole-rat occurs in social familial units. While these differences, especially that of phenotype, may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in all three systems in the laboratory rat and other rodents had direct homologs in the brains of the mole-rats studied. There were no additional nuclei in the brains of the mole-rats that are not found in the laboratory rat or other rodents and vice versa. The mole-rats are phylogenetically distant from the laboratory rat, but are still part of the order Rodentia. We conclude that changes in the nuclear organization of the systems studied appear to demonstrate a form of constraint related to the phylogenetic level of the order.

An assessment of behavioural dominance in a social subterranean rodent, Cryptomys hottentotus pretoriae, using the cardinal dominance index method

The highveld mole-rat, Cryptomys hottentotus pretoriae, is a social bathyergid that exhibits a high reproductive skew and occurs in colonies of between 5 and 14 individuals. Behavioural dominance has previously been assessed in this species using an ordinal ranking procedure and it was found to possess a non-linear dominance hierarchy. The determination of dominance using ordinal ranking is often subjective and cannot deal with ties in rank. This study adapts an objective and robust cardinal assessment method to assign dominance indices to individuals. These indices are then ordered to assign a final rank to each individual within a colony. The non-linear, exponential decay model provided the best fit to data from average cardinal dominance index versus final rank and revealed that colonies contain a single behaviourally-dominant individual. However, final rank could not be predicted on the basis of body mass, sex or assumed reproductive status and is not always statistically significant due to the inherent variation. We propose that the cardinal method of dominance assessment, with the adaptations made in this study, be used in future dominance-related assessments for other bathyergids and social organisms in general.

An assessment of behavioural dominance in a social subterranean rodent, Cryptomys hottentotus pretoriae, using the cardinal dominance index method

The highveld mole-rat, Cryptomys hottentotus pretoriae, is a social bathyergid that exhibits a high reproductive skew and occurs in colonies of between 5 and 14 individuals. Behavioural dominance has previously been assessed in this species using an ordinal ranking procedure and it was found to possess a non-linear dominance hierarchy. The determination of dominance using ordinal ranking is often subjective and cannot deal with ties in rank. This study adapts an objective and robust cardinal assessment method to assign dominance indices to individuals. These indices are then ordered to assign a final rank to each individual within a colony. The non-linear, exponential decay model provided the best fit to data from average cardinal dominance index versus final rank and revealed that colonies contain a single behaviourally-dominant individual. However, final rank could not be predicted on the basis of body mass, sex or assumed reproductive status and is not always statistically significant due to the inherent variation. We propose that the cardinal method of dominance assessment, with the adaptations made in this study, be used in future dominance-related assessments for other bathyergids and social organisms in general.

Hemoglobin–oxygen-affinity and acid-base properties of blood from the fossorial mole-rat, Cryptomys hottentotus pretoriae

Oxygen affinity and other hematological parameters in strictly subterranean mole-rats, Cryptomys hottentotus (subspecies pretoriae) were measured immediately upon capture and after 14-21 days in captivity. The pH, hematocrit, hemoglobin (Hb) concentration, blood oxygen content, 2,3 bisphosphoglycerate (2,3 BPG) concentration and oxygen dissociation curves (ODC), as well as tonometric measurements, were determined using whole blood. Additionally ODCs were also determined for stripped hemolysates of individual animals. Compared to other mammals, blood of freshly caught animals had low pH (7.32+/-0.22), elevated hematocrits (48.4+/-3.8 %) and significantly lower P50 values for whole blood (21.1+/-1.6 mm Hg at pH 7.4) than those reported for other similar-sized fossorial and terrestrial mammals. Blood carbon dioxide content (22.4+/-3.9 mMol L(-1)), hemoglobin concentration (1.9+/-0.15 mMol L(-1)), oxygen content (164.8+/-26 mL L(-1)), bicarbonate concentrations (22.5+/-3.5 mMol L(-1)) were within the range of values reported for similar-sized mammals. We conclude that high blood-oxygen affinity, low body temperature and possibly also high hematocrit enable C. h. pretoriae to maintain an adequate oxygen supply to the tissues in a potentially hypoxic burrow atmospheres, but that the blood of this species shows no exceptional CO2 sensitivity or buffering capacity.

Reproductive suppression in subordinate female highveld mole-rats ( Cryptomys hottentotus pretoriae): No role for endogenous opioid peptides

The influence of endogenous opioid peptides (EOPs) on plasma luteinizing hormone (LH) levels in subordinate female highveld mole-rats ( Cryptomys hottentotus pretoriae) was investigated to elucidate the physiological mechanisms responsible for inhibiting their gonadotropin-releasing hormone (GnRH) and/or LH release. The opioid antagonist naloxone was administered either alone or with GnRH. A single injection of naloxone failed to alter plasma LH levels in dominant reproductive females or in subordinate non-reproductive females in the presence or absence of their ovaries. Pituitary sensitivity to a GnRH challenge was not influenced by naloxone administered acutely or according to longer-term regimens in any of the treatment groups. The results suggest no role for EOPs at the level of the pituitary or hypothalamus in the socially induced infertility evident in non-reproductive female highveld mole-rats.

Relations between social status and the gonadotrophin‐releasing hormone system in females of two cooperatively breeding species of African mole‐rats, Cryptomys hottentotus hottentotus and Cryptomys hottentotus pretoriae: Neuroanatomical and neuroendocrinological studies

In common (Cryptomys hottentotus hottentotus) and highveld (Cryptomys hottentotus pretoriae) mole-rats, reproduction is subject to two forms of regulation in addition to incest avoidance. These are the only social bathyergids known to restrict breeding to a particular season; furthermore, subordinate members of their colonies show suppressed reproduction throughout the year. Females from both species were assessed and compared for social and seasonal effects on the gonadotrophin-releasing hormone (GnRH) system. GnRH-immunoreactive (ir) structures were visualized immunohistochemically; GnRH content was determined by radioimmunoassay. In both species, GnRH-ir cell bodies and processes are loosely distributed along the septopreopticoinfundibular continuum, with dense fiber aggregations in the region of the organum vasculosum of the lamina terminalis and median eminence. The two species differ in the rostrocaudal distribution of their GnRH-ir cell bodies. In highveld mole-rats, most of these cells are in the septal/preoptic area; in common mole-rats, more than half of them are in the mediobasal hypothalamus. Compared with common mole-rats, highveld mole-rats have a greater total number of GnRH-ir cell bodies, higher GnRH content, and more intense GnRH immunoreactivity in the median eminence. Within highveld colonies, the nonreproductive females have larger GnRH-ir cell bodies, more intense GnRH immunoreactivity in the median eminence, and higher GnRH content than the reproductive females; these findings suggest inhibited release of GnRH in the nonreproductive, subordinate females. In contrast, in common mole-rat females, neither status nor season appears to affect the investigated parameters of the GnRH system; this suggests a predominantly behavioral basis to their suppressed reproduction.

Ultrastructure of epididymal spermatozoa in three social African mole-rats of the genus Cryptomys (Rodentia: Bathyergidae): conservatism in sperm morphology

The morphology, size and three-dimensional structure of spermatozoa from three representatives of the genus Cryptomys were investigated. To date, there has been no study to either elucidate the morphological features or relative dimensions of spermatozoa in the genus Cryptomys specifically, or in the Bathyergidae as a whole. Semen samples were collected from the whole region of the epididymides, in one eusocial species, the Damaraland mole-rat, Cryptomys damarensis and two social subspecies the common mole-rat, Cryptomys hottentotus hottentotus and the highveld mole-rat, Cryptomys hottentotus pretoriae. Spermatozoa were processed using standard procedures for scanning electron microscopy (SEM). Whole sperm dimensions were measured and morphological characteristics documented. The results reveal a degree of conservation of morphological structure of the spermatozoa within the genus Cryptomys, with a slight plasticity in the size of some sperm components. Key words: Bathyergidae, spermatozoa, sperm morphology, scanning electron microscopy.

Characterization of Gonadotrophin‐Releasing Hormone Precursor cDNA in the Old World Mole‐Rat Cryptomys Hottentotus Pretoriae: High Degree of Identity with the New World Guinea Pig Sequence

Regulation of pituitary gonadotrophins by the decapeptide gonadotrophin-releasing hormone 1 (GnRH1) is crucial for the development and maintenance of reproductive functions. A common amino acid sequence for this decapeptide, designated as 'mammalian' GnRH, has been identified in all mammals thus far investigated with the exception of the guinea pig, in which there are two amino acid substitutions. Among hystricognath rodents, the members of the family Bathyergidae regulate reproduction in response to diverse cues. Thus, highveld mole-rats (Cryptomys hottentotus pretoriae) are social bathyergids in which breeding is restricted to a particular season in the dominant female, but continuously suppressed in subordinate colony members. Elucidation of reproductive control in these animals will be facilitated by characterization of their GnRH1 gene. A partial sequence of GnRH1 precursor cDNA was isolated and characterized. Comparative analysis revealed the highest degree of identity (86%) to guinea pig GnRH1 precursor mRNA. Nevertheless, the deduced amino acid sequence of the mole-rat decapeptide is identical to the 'mammalian' sequence rather than that of guinea pigs. Successful detection of GnRH1-synthesizing neurones using either a guinea pig GnRH1 riboprobe or an antibody against the 'mammalian' decapeptide is consistent with the guinea pig-like sequence for the precursor and the classic 'mammalian' form for the decapeptide. The high degree of identity in the GnRH1 precursor sequence between this Old World mole-rat and the New World guinea pig is consistent with the theory that caviomorphs and phiomorphs originated from a common ancestral line in the Palaeocene to mid Eocene, some 63-45 million years ago.

Fos expression in the suprachiasmatic nucleus in response to light stimulation in a solitary and social species of African mole-rat (family Bathyergidae)

Mole-rats are strictly subterranean rodents that are rarely exposed to environmental light. They are well adapted to their environment and have reduced eyes and a severely regressed visual system. It has been shown, however, that mole-rats do exhibit endogenous circadian rhythms that can be entrained, suggesting an intact and functional circadian system. To determine whether light is the entraining agent in these animals, Fos expression in response to light pulses at different circadian times was investigated to obtain phase response curves. Light is integrated effectively in the suprachiasmatic nucleus of the Cape mole-rat ( Georychus capensis), and Fos expression is gated according to the phase of the circadian clock. The Fos response in the Cape mole-rat was comparable to that of aboveground rodents. In contrast, the highveld mole-rat ( Cryptomys hottentotus pretoriae) was less sensitive to light and did not show a selective Fos response according to the phase of the circadian cycle. Social species appear to be less sensitive to light than their solitary counterparts, which compares well with results from locomotor activity studies.

RELATIVE AGE AND REPRODUCTIVE STATUS IN CRYPTOMYS HOTTENTOTUS PRETORIAE (RODENTIA: BATHYERGIDAE) FROM SOUTH AFRICA

The degree of molar eruption and wear were used to assign individuals of the social highveld mole-rat (Cryptomys hottentotus pretoriae) from South Africa into 9 relative age classes. Reproductive animals were found to be the oldest and heaviest members of colonies. Cranial morphometric analysis of 4 geographically disparate populations in South Africa generally showed lack of sexual dimorphism in cranial characteristics, but revealed 2 distinct groupings among the 9 relative age classes. The 1st grouping comprised individuals of age classes 1–4, which were all nonreproductive animals and considered to represent a combination of juveniles and subadults. The 2nd grouping included individuals of age classes 7–9, which included reproductive animals. Individuals of age classes 5 and 6, however, were largely intermediate, with some individuals included among both the younger and older age classes, but only a few of these animals were reproductive. These groupings suggest that if age classes are visualized as demarcating sections of variable and unknown length on a hypothetical growth curve, then individuals of age classes 5 and 6 appear to fall at a point on the curve just before it begins to stabilize. These results, together with a proposed microsatellite study, have the potential to provide additional tools to improve our current understanding of social structuring within colonies of the highveld mole-rat.

Is the highveld mole‐rat Cryptomys hottentotus pretoriae (Rodentia: Bathyergidae) an induced or spontaneous ovulator?

AbstractThe 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.

Circadian rhythms of locomotor activity in solitary and social species of African mole-rats (family: Bathyergidae).

Mole-rats are strictly subterranean and hardly, if ever, come into contact with external light. As a result, their classical visual system is severely regressed and the circadian system proportionally expanded. The family Bathyergidae presents a unique opportunity to study the circadian system in the absence of the classical visual system in a range of species. Daily patterns of activity were studied in the laboratory under constant temperature but variable lighting regimes in individually housed animals from 3 species of mole-rat exhibiting markedly different degrees of sociality. All 3 species possessed individuals that exhibited endogenous circadian rhythms under constant darkness that entrained to a light-dark cycle. In the solitary species, Georychus capensis, 9 animals exhibited greater activity during the dark phase of the light cycle, while 2 individuals expressed more activity in the light phase of the light cycle. In the social, Cryptomys hottentotus pretoriae, 5 animals displayed the majority of their activity during the dark phase of the light cycle and the remaining 2 exhibited more activity during the light phase of the light cycle. Finally in the eusocial Cryptomys damarensis, 6 animals displayed more activity during the light phase of the light cycle, and the other 2 animals displayed more activity during the dark phase of the light cycle. Since all three mole-rat species are able to entrain their locomotor activity to an external light source, light must reach the SCN, suggesting a functional circadian clock. In comparison to the solitary species, the 2 social species display a markedly poorer response to light in all aspects. Thus, in parallel with the sociality continuum, there exists a continuum of sensitivity of the circadian clock to light.

Foraging in the subterranean social highveld mole‐rat (Cryptomys hottentotus pretoriae): an investigation into mass‐dependent geophyte use and foraging patterns

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 reproductive biology and postnatal development of the highveld mole-rat, Cryptomys hottentotus pretoriae(Rodentia: Bathyergidae)

The highveld mole rat, Cryptomys hottentotus pretoriae, occurs in the summer rainfall grasslands of northern South Africa. It is a colonial bathyergid in which reproduction is restricted to a single female. Courtship and copulation are initiated by the male mole rat. Copulation is prolonged and involves multiple bouts of intromission. The gestation length is 63 66 days (n = 2). Newborn pups are altricial and the litter sizes small, averaging 1.6 ± 0.8 (n = 6). The pups are small 2 2.5 cm in length and hairless at birth. They begin to eat solids at day 14 ± 1.6 and are fully weaned after 33 days. Sibling sibling sparring occurs at day 40. The growth rate of the highveld mole rat is best described by the Gompertz model. The growth rate for a period of 318 days ranged from 0.23 0.39 g/day. The males had a growth rate spanning 0.36 0.39 g/day, whereas the female was 0.23 g/day. The reproductive biology of the highveld mole rat is compared with that of other southern and central African Cryptomys.