Osmoregulation and water balance in the springhare (Pedetes capensis)

Springhares are large rodents that live in arid and semi-arid regions of Africa. We deprived springhares of water for periods of up to 7 days to determine what physiological adaptations, if any, enable them to survive in arid regions without drinking. During water deprivation, springhares lost up to 30% body weight and produced a mean maximum urine concentration of 2548 mosmol kg⁻¹ with a maximum of 3076 mosmol kg⁻¹ in an individual animal. Haematocrit and plasma sodium and potassium concentrations were well regulated throughout water deprivation at 47.5 ± 3.8% and 132.6 ± 7.4 mmol l⁻¹ and 3.5 ± 0.7 mmol l⁻¹, respectively, while plasma osmolality increased slightly from 293 ± 12.5 mosmol kg⁻¹ to 324 ± 7.3 mosmol kg⁻¹. Springhares thus appeared to be good osmoregulators and were able to maintain plasma volume during 7 days of water deprivation. In addition to the production of a relatively concentrated urine, water loss was limited by the lowered solute load and faecal water loss achieved by a reduction in food consumption and by the production of very dry faeces. These abilities, together with a favourable burrow microclimate and nocturnal activity pattern, enable them to survive in arid regions. Accepted: 8 September 1998     

Molecular phylogeny of the springhare, Pedetes capensis, based on mitochondrial DNA sequences

The phylogenetic position of the Pedetidae, represented by a single species Pedetes capensis, is controversial, reflecting in part the retention of both Hystricomorphous and Sciurognathous characteristics in this rodent. In an attempt to clarify the species evolutionary relationships, mtDNA gene sequences from 10 rodent species (representing seven families) were analyzed using phenetic, parsimony, and maximum-likelihood methods of phylogenetic inference; the rabbit, Oryctolagus cuniculus (Order Lagomorpha), and cow, Bos taurus (Order Artiodactyla), were used as outgroups. Investigation of 714 base pairs of the protein-coding cytochrome b gene indicate strong base bias at the third codon position with significant rate heterogeneity evident between the three structural domains of this gene. Similar analyses conducted on 816 base pairs of the 12S rRNA gene revealed a transversion bias in the loop sections of all taxa. The cytochrome b gene sequences proved useful in resolving associations between closely related species but failed to produce consistent tree topologies at the family level. In contrast, phylogenetic analysis of the 12S rRNA gene resulted in strong support for the clustering of Pedetidae/Heteromyidae/Geomyidae and Muridae in one clade to the exclusion of the Hystricidae/Thryonomyidae and Sciuridae, a finding which is concordant with studies of rodent fetal membranes as well as reproductive and other anatomical features.      

Ecology of Physaloptera capensis (Nematoda : Spiruroidea) infecting the Springhare Pedetes capensis (Mammalia) in Botswana

Incidence and intensity of the stomach nematode Physaloptera capensis in relation to the age, sex, reproductive status, physical condition, density and habitat of its host, the Springhare, were investigated in the Republic of Botswana (August 1971-August 1973). All data indicate that this nematode is a benign parasite of the Springhare. Infections were not randomly distributed within the Springhare population. Mean number of worms per Springhare was 83 and 34% of all Springhares were parasitized. Adults, females and lactating females showed significantly heavier infections than juveniles, males and non-lactating females, respectively. Infection was directly associated with the amount of grass cover in the Springhares' habitat but independent of the density and physical condition of Springhares. Possible causes of differences in rates of infection among Springhares of different age/reproductive classes and from populations of different density are mentioned. It is suggested that numbers of P. capensis may be regulated mainly by density-independent environmental factors operating upon rates of transmission.     

Reproductive ecology of the Springhaas Pedetes capensis in Botswana

The reproductive ecology of the Springhaas was studied in the Republic of Botswana (August 1971-August 1974). Springhaas were collected over 24 consecutive months (153 foetuses and 560 juveniles and adults). Springhaas are monotocous. There was no difference between the number of implantations in each uterine horn. Seventy-six per cent of adult females were pregnant, 46 % were lactating, and only 4 % were neither pregnant nor lactating. Neonates are confined to the burrow and totally dependent upon the mother until they attain a body weight of approximately 1.3 kg. The male to female ratio was 51:49, and the juvenile to adult ratio was 28:72. No seasonal peaks in reproductive effort were noted. The reproductive strategy of the Springhaas is considered. Predation is believed to be the primary mover in the evolution of the Springhaas reproductive strategy.     

Observations on the Leydig cells in the male East African spring hare (Pedetes surdaster larvalis).

The morphology of Leydig cells of the testis of sexually mature and sexually immature spring hares was studied. The cytoplasm of the Leydig of cells the sexually immature spring hares was packed with large lipid droplets leaving little space for the other organelles. Smooth endoplasmic reticulum was poorly developed and occasionally formed concentric layers of fenestrated cisterns around the large lipid droplets. The Leydig of cells the sexually mature spring hares were almost devoid of lipid droplets and their cytoplasm was occupied by abundant tubular smooth endoplasmic reticulum. Cells which shared characteristics with both immature Leydig cells and undifferentiated mesenchymal cells were observed in the limiting membrane of the seminiferous tubulus. These Leydig-like cells may play a role in the differentiation of Leydig cells in the spring hare.     

Mitochondrial DNA Phylogeography and Comparative Cytogenetics of the Springhare, Pedetes capensis (Mammalia: Rodentia)

Variation in mitochondrial DNA (mtDNA) was used together with comparative cytogenetics to examine the evolutionary history and taxonomic status of an African hystricomorphous rodent, the springhare Pedetes capensis. The mtDNA phylogeographic structure showed that the majority of the southern African populations (P. c. capensis) are characterized by unique but closely related maternal lineages. Based on restriction endonuclease fragment analysis, the east African populations (P. c. surdaster) appear more structured and are distinguished from those in southern Africa by an average sequence divergence of 5.52% (±1.4%). This marked divergence is concordant with results of the cytogenetic study. Specimens from southern Africa have 2n = 38, and those from east Africa 2n = 40. The change in diploid number is due to a single centric fusion. It is suggested that the closure of the Brachystegia or miombo woodland (20,000–10,000 B.P.), which delimits contemporary springhare ranges, may have been too recent to account for the accumulated genetic differences that distinguish these taxa. While rifting and associated habitat changes in east Africa can be invoked to explain genetic structure in this region, the southern African springhare populations, which have a high incidence of locality-specific haplotypes, show a shallow phylogeographic structure, in keeping with a relatively recent range expansion from smaller source populations. Given the magnitude of genetic, morphological, and ethological differences between the two geographic isolates, we believe that there is strong support for the elevation of the east African and southern African springhare populations to full species status, thus supporting earlier taxonomic treatments of this rodent.     

Metabolism and thermoregulation in the springhare (<Emphasis Type="Italic">Pedetes capensis</Emphasis>)

Springhares are large, nocturnally active, diurnally fossorial rodents that typically inhabit arid and semi-arid areas. This lifestyle means that they need to balance excessive heat loss when foraging at night against insufficient heat loss in a potentially warm, humid burrow and both of these against the need to minimize water turnover and energy requirements. In this study we investigated metabolism and thermoregulation in these animals. Basal metabolic rate averaged 8.62+/-1.37 J g(-1) h(-1) and minimum thermal conductance 0.386+/-0.062 J g(-1) h(-1) degrees C(-1). These were higher and lower than expected, respectively. This, along with a relatively low, lower critical temperature and broad thermal neutral zone indicate that springhares are physiologically well suited to the low night-time temperatures, which they typically encounter. Body temperatures were quite labile but springhares became hyperthermic at temperatures above 30 degrees C suggesting that they are poor thermoregulators at high temperatures. This is attributed to their seldom, if ever, encountering temperatures in this range. Insufficient heat loss under normal resting conditions does not appear to be a problem, as springhares inhabit deep burrows in which the temperature never exceeds the upper critical temperature. Excess heat generated during vigorous underground exercise is presumably stored and dissipated to the cool night air or the cooler soil when subsequently resting. Water turnover and energy expenditure are presumably adequately addressed by other physiological and behavioural characteristics.     

Electron microscopic study of the chorioallantoic placenta of the rock hyrax (Heterohyrax brucei)

The interhaemal membrane consisted of only two cellular elements: a single layer of cellular trophoblast and the fetal capillary endothelium. The hyrax is therefore one of the few mammals known to possess the cellular haemomonochorial type of placenta. The trophospongium was also cellular while the basal trophoblastic cells were strongly phagocytic. The giant multinucleate cells at the feto-maternal junction were ultrastructurally different from the trophoblast cells and showed no signs of degeneration. Their appearance suggests that they are of maternal rather than fetal origin.     

Muscle weights and succinic dehydrogenase distribution in the hind limb musculature of two rodents (Thryonomys gregorianus and Pedetes capensis) with different locomotory habits

The hind limb muscles of the spring hare (Pedetes capensis) were found to be relatively heavier than the hind limb muscles of the cane rat (Thryonomys gregorianus). The distribution of succine dehydrogenase activity was investigated in four of these muscles (m. gluteus superficialis, m.semimembranosus, m. biceps femoris and m.rectus femoris) from both animals. It was found that the spring hare had a higher proportion of low-activity fibres in all four muscles than the cane rat. All muscle fibre types were also smaller in diameter in the spring hare than the cane rat. These results are discussed in relation to the different locomotry habits of the two animals.     

A study in hystricomorph rodent relationships: the karyotypes of Thryonomys gregorianns, Pedetes capensis and Hystrix cristata

Karyotypes and G band patterns of Thryonomys gregorianus, Pedetes capensis and Hystrix cristata from Kenya are reported. Both Thryonomys and Pedetes have a diploid number of 40 but differ in the overall pattern of their karyotypes and by the presence of a marker chromosome in Thryonomys. The marker chromosome unites Thryonomys with the ctenodactylids. The karyotype of Hystrix cristata , with a diploid number of 60, bears some resemblance to the African bathyergids and Petromus but none to the erethizontids. The African hystricomorph-hystricognath rodents, with the exception of Pedetes , bear more resemblance to the South American caviomorphs than to any other group of rodents.