Browsing by Author "Jarvis, J U M"

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    Aspects of the energetics and renal physiology of some African arid-adapted rodents
    (1984) Buffenstein, Rochelle; Jarvis, J U M
    The following aspects of physiological adaptation and resource usage were examined in several species of arid-adapted African rodents: The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in the North East African pigmy gerbil, gerbillus ppusillus; This gerbil did not strictly maintain homoeothermy and like most arid-adapted rodents had a reduced basal metabolic rate. When G. pusillus was maintained on an ad lib. food and water diet, its daily energy expenditure was similar to that predicted by mass. This increased to 116% of the expected allometric value when deprived of water. On a diet of air-dried millet seeds, increased kidney concentrating ability, reduced pulmocutaneous evaporation and a reduction in faecal water loss, were sufficient to impart virtual independence of exogenous water and the maintenance of a positive water balance. If food was restricted, G. pusillus utilized torpor to precisely balance energy expenditure with that available and so maintained a constant body mass. During torpor, assimilation efficiency was significantly reduced. The cost of maintaining coenothermia for the full duration of food processing would be prohibitive and it was estimated that it would have utilised approximately 50% of the daily energy available. The cost of employing torpor (0.5kJ.day-1) on the other hand was insignificant in comparison with the savings accrued by the use of torpor (32.25kJ. day -1). Parsimony of water loss with food restriction enabled the maintenance of a positive water balance during this period. The importance of micro-habitat in thermoregulation was investigated in Gerbillurus paeba, inhabiting the thermally stable confines of a plugged burrow, and in Aethomys namaquensis, a crevice dwelling rock rat. The rock rat, living in an environment characterized by large diet ranges, precisely controlled body temperature. It did this by compensating for its reduced basal metabolic rate, with a low rate of thermal conductance. Gerbillurus paeba tolerated a labile body temperature and used a high rate of thermal conductance to remove metabolic heat, for the high humidities it encountered in its milieu would impede the use of evaporative cooling. Daily energy expenditure of both Namib rodents. Was monitored when they were maintained on a low fibre food source (golden millet) and then when this was replaced with a high fibre food source (high-bulk bran). Aethomys namaquensis showed a DEE similar to that predicted by mass and this remained constant, irrespective of the food source or the presence or absence of water. The DEE of G. paeba was more variable. When water was freely available DEE was higher than that predicted by mass and was similar to that predicted for an insectivore of similar body mass. This might reflect its propensity towards an insectivorous diet. When water-stressed on a high fibre diet, DEE of G. paeba declined by half, suggesting that G. paeba employed torpor when conditions were stressful and when the quality of resources was reduced. On a low fibre diet, both species were able to maintain a positive water balance when deprived of water, showing similar reductions in water loss to that of G. pusillus. Low assimilation efficiency and the concomitant increase in faecal water loss precluded the maintenance of a positive water balance when they were fed a high fibre food source. Despite increased urine concentrations and reduced evaporative water loss both species succumbed to chronic water-deprivation. Daily water turnovers and urine concentrating ability was monitored in 17 species of African rodents from arid areas. In general, rodents belonging to the Cricetidae exhibited lower water turnovers and voided smaller volumes of urine at significantly greater concentrations than the murids. All these cricetid rodents were found to produce a crystalline precipitate of allantoin in their urine when water stressed. The quantities of crystalline allantoin excreted were far greater than that expected from purine catabolism and accounted for 30% of the total nitrogenous wastes of the cricetids when deprived of water. It was thought that the substantial quantities of allantoin excreted were responsible for the lower water turnover rates in the cricetids. It is suggested, therefore, when water is limiting, there is a shift in the nitrogen pathway from urea to allantoin, so conferring an eco-physiological advantage to these long term residents of the arid regions of Africa.
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    Demography and population dynamics of the striped fieldmouse, Rhabdomys pumilio, in alien Acacia vegetation on the Cape Flats, Cape Province, South Africa
    (1980) David, Jeremy Hugh Markham; Jarvis, J U M
    In view of the fact that the long-term study of small mammal populations in southern Africa has been largely neglected, this project was an attempt to document more accurately than has hitherto been the case in Africa, the population changes in a small rodent, the striped fieldmouse, Rhabdomys pumilio, over a relatively long period of time. It was felt that the usual field study of one or two years duration was insufficient to obtain reliable data on demographic parameters. This was because it was important to document the variability of population data and to have as large sample sizes as possible. The fieldmouse is an omnivore but mainly granivorous and the habitat chosen was favourable for the mice, being dominated by thickets of alien Acacia cyclops and A. saligna, which provided abundant food (seeds) all year round, as well as cover and shade. The study was conducted on the Cape Flats, an area of lowlying sand dunes, on the banks of the Kuils River. Livetrapping grids were established, consisting of parallel rows of trap stations, 10m apart. The overall size of the study area was 2,55ha with a total of 156 stations. This comprised a central control grid of 60 stations (0,45ha), which was first trapped in April 1972 and where regular monthly trapping for 4 consecutive days and nights was conducted from July 1972 through May 1977. This was surrounded on three sides by peripheral grid K of 96 stations arranged in three parallel rows (see Fig. 2). Trapping was conducted in 324. grid K from February 1975 through February 1976 in an attempt to detect dispersal of mice from the control grid. From March 1976 through May 1977 trapping was conducted in a third grid, experimental grid E, which was established in the north side of the old grid K. It comprised 60 stations (0,44ha), in which supplementary food was supplied in the form of commercial rat pellets. The effects of the extra food on the population of mice were compared with the control grid. The mice were readily captured in box-type aluminium Sherman livetraps and all mice caught were marked by toeclipping and released. A total of 2281 R. pumilio were marked and released during the five year study. In addition, over 860 specimens of R. pumilio were killtrapped for autopsy in the laboratory. These yielded information on reproduction, food habits and morphological characteristics - particularly skulls for age determination by tooth wear.
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    A functional morphological study of limb regression in some Southern African species of Scincidae (Reptilia : Sauria)
    (1979) Leonard, Cecil John; Jarvis, J U M
    How and why did limblessness evolve in certain skinks? These questions are explored in certain species of the Scincidae (from southern Africa) that vary in the degree of limb reduction. This regression series consists of Mabuya capensis (with normal, pentadactyle limbs), Riopa sundevallii (with miniaturized, pentadactyle limbs), three species of the genus Scelotes (bipes, gronovii and brevipes - with vestigial hindlimbs varying in the degree of degeneration) and, finally, Acontias meleagris(without any trace of limbs). The osteology and the myology of the locomotor apparatus are described for all members of this regression series with special reference to the axial system which has in the past received but scant attention compared with the appendicular apparatus. Qualitative and morphometric data are used to construct morphoclines that are correlated with limb reduction. Numerous morphological trends and tendencies support the conclusion that the axial system hypertrophies as the appendages degenerate. The patterns of locomotion are also described for all members of the regression series. Furthermore, an ethocline, that links the limbed and limbless extremes, is postulated. Even in quadrupedal skinks the dominant appendicular system may be assisted by axial flexures that increase stride length. As limbs degenerate, appendicular progression is phased out while axial progression increases in importance.
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    Population genetic structuring in the common mole-rat, Cryptomys hottentotus hottentotus
    (2002) Bishop, Jacqueline M; Jarvis, J U M; O'Ryan, C
    This thesis addresses the population genetic consequences of divergent social structure and dispersal regimes in two study populations of the common mole-rat Cryptomys hottentotus hottentotus. Aspects relating to the relationship between, gene flow and genetic variation, the roles of mutation and drift in promoting genetic structuring, and the role of genetic parentage in the species' mating system were investigated using a suite of cryptomys-specific microsatellite markers. C. h. hottentotus is a social species living in colonies of 2-14 individuals, permanently inhabiting a network of burrows. The species is a co-operative whose colonies are composed of a breeding pair, their offspring and a number of potentially unrelated individuals. C. h. hottentotus is an obligate outbreeder whose offspring delay dispersal and the opportunities for independent reproduction until both social and ecological conditions are favourable. The species is widely distributed across South Africa from extreme arid regions where low rainfall restricts dispersal for much of the year, to highly mesic areas where dispersal is facilitated all year round. In response to varying ecological constraints on dispersal, the species displays differential degrees of social elaboration across its range. This appears to be in response to the high energetic costs of burrowing and the low probability of locating geophyte clumps in increasingly arid environments.
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    Pup ontogeny and factors influencing behavioural and morphological variation in naked mole-rats, Heterocephalus glaber (Rodentia, Bathyergidae)
    (1996) O'Riain, Justin; Jarvis, J U M
    A long term behavioural study was undertaken on laboratory-reared naked mole-rats. The main objective of the study was to provide a detailed qualitative and quantitative description of the behavioural and morphological development of naked mole-rats from birth through to adulthood. This study laid an empirical foundation for the subsequent testing of hypotheses pertaining to within and between colony conflict as well as for a study on the existence of a rare dispersal phenotype within colonies.
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    A study of hair characteristics of forty-two species of South African Muridae and the taxonomic application of these characteristics as definitive criteria.
    (1975) Keogh, Hillary Joan; Jarvis, J U M
    In this study cuticular scale patterns, groove size and hair measurements have been used as definitive criteria in identification of 42 species of the family Muridae. Keys for the use in identification have been made and detailed descriptions of the hairs of each species, together with micrographs of gelatin imprints and scanning electron micrographs are presented. The taxonomic and practical uses of this method are discussed. It has been found that the cuticular scale pattern on hairs of South African Murid species studied shows a remarkable specific constancy.
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    The trend towards sociality in three species of southern African mole-rats (Bathyergidae) : causes and consequences
    (1988) Bennett, Nigel Charles; Jarvis, J U M
    Three species of southern African mole-rats, possessing a wide range of social organisation were used to investigate the trend towards increasing sociality occurring in species inhabiting increasingly arid environments. The strictly solitary Georychus capensis, the weakly social Cryptomys hottentotus hottentotus and the highly social Cryptomys damarensis were chosen for this investigation and my findings are compared, where possible, with the eusocial Heterocephalus glaber. The level of social organisation exhibited by a particular mole-rat species appears to be dependent upon a number of physical factors as well as on the food resource distribution, its nutritional properties and its availability. Thus the soil moisture content, the annual rainfall pattern and the wear upon the extrabuccal incisors limit the amount of burrowing which can be undertaken by a single mole-rat, both on a daily and seasonal basis. These factors together with the size, distribution, digestible energy and fibre content of the geophytes on which they feed and nearest-neighbour distances occurring between the belowground portions of the geophytes, may be crucial in determining whether a habitat is suitable for solitary or colonial mole-rats.