Browsing by Author "Nicolson, Sue W"

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    Energy and water balance in the lesser double-collared sunbird, Nectarinia chalybea
    (1999) Lotz, Christopher Neil; Nicolson, Sue W
    Nectarivores feed on aqueous sugar solutions, and their water balance is tightly linked to their energy balance. When nectar is dilute and energy demands are high, consumption of a large excess of preformed water is inevitable. Physiological implications of nectarivory for the lesser double-collared sunbird, Nectarinia chalybea, have been investigated here. Sunbirds consumed 2.7 times their body mass (8 g) per day when feeding on 0.4 M sucrose at an ambient temperature of 10°C, and excreted 87 % of the water. When feeding on 1.2 M sucrose at 30°C, sunbirds drank only 0.5 times their body mass of water daily. In view of the sometimes high flux of water, combined with the low electrolyte concentrations of nectar, sunbirds must be efficient at conserving ions to maintainelectrolyte balance. When 15 mM each of KCl and NaCI were included in a diet of 0.4 M sucrose, sunbirds precisely maintained electrolyte balance by increasing cation excretion from 2 to 17 mM. Considering the high preformed water content of dilute nectar, sunbirds may expend large amounts of energy warming their food to body temperature, which was measured as 42°C irrespective of diet. Modelling revealed that sunbirds feeding on dilute (0.4 M) sucrose at 18°C would use the same proportion of their daily energy intake (4 %) to warm their food as high-latitude aquatic endotherms feeding on fish or invertebrates just above freezing point. The evaporative water loss (and therefore evaporative heat loss) of N. chalybea increased as dietary sucrose concentration decreased (more than two-fold between 1.2 and 0.2 M).
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    Open Access
    Energy and water balance in the lesser double-collared sunbird, Nectarinia chalybea
    (1999) Lotz, Christopher Neil; Nicolson, Sue W
    Nectarivores feed on aqueous sugar solutions, and their water balance is tightly linked to their energy balance. When nectar is dilute and energy demands are high, consumption of a large excess of preformed water is inevitable. Physiological implications of nectarivory for the lesser double-collared sunbird, Nectarinia chalybea, have been investigated here. Sunbirds consumed 2.7 times their body mass (8 g) per day when feeding on 0.4 M sucrose at an ambient temperature of 10°C, and excreted 87 % of the water. When feeding on 1.2 M sucrose at 30°C, sunbirds drank only 0.5 times their body mass of water daily. In view of the sometimes high flux of water, combined with the low electrolyte concentrations of nectar, sunbirds must be efficient at conserving ions to maintainelectrolyte balance. When 15 mM each of KCl and NaCI were included in a diet of 0.4 M sucrose, sunbirds precisely maintained electrolyte balance by increasing cation excretion from 2 to 17 mM. Considering the high preformed water content of dilute nectar, sunbirds may expend large amounts of energy warming their food to body temperature, which was measured as 42°C irrespective of diet. Modelling revealed that sunbirds feeding on dilute (0.4 M) sucrose at 18°C would use the same proportion of their daily energy intake (4 %) to warm their food as high-latitude aquatic endotherms feeding on fish or invertebrates just above freezing point. The evaporative water loss (and therefore evaporative heat loss) of N. chalybea increased as dietary sucrose concentration decreased (more than two-fold between 1.2 and 0.2 M).
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    Life history and physiological ecology of the lizard, Cordylus Giganteus
    (1992) Van Wyk, Johannes H; Louw, Gideon; Turner, Scott; Nicolson, Sue W
    Cordylus giganteus is a large, terrestrial, viviparous lizard, endemic to the Highveld grasslands of South Africa. Its distribution is limited and its conservation status is vulnerable. Autopsy and mark-recapture methods were used to study the seasonal aspects of its reproductive cycle, diet, energy reserves, growth, population dynamics, daily activity and thermoregulation. Reproduction is distinctly seasonal in both sexes. Females may reproduce biennially. Vitellogenesis commenced in autumn (March), and continued through hibernation with ovulation in spring (October). Two or three young are born in autumn. A functional placenta is implicated. Seasonal steroid hormone profiles are presented. Males exhibit a postnuptial spermatogenetic cycle. Spermatogenesis commences in spring with peak spermiogenesis in autumn and testicular regression following in late autumn. Spermatozoa are stored in the epididymis and ductus deferens for seven to eight months. A bimodal plasma testosterone profile is reported, consistent with spermiogenesis in autumn and mating behaviour in spring. C. giganteus feeds during 8 months of the year and prefer Coleoptera as prey. Fat bodies are utilized for winter maintenance and reproduction. Hatchlings grow 20-30mm during the first year and maximum growth rates occur in summer. Males and females attain sexual maturity at about 165 mm SVL in the fourth year. Seasonal affects on growth rate resulted in poor fit by either logistic-by-length or von Bertalanffy models and a seasonal oscillating model was introduced. Adult males are smaller than females; head sizes are the same but allometric slopes differed significantly. Population size and structure remained stable in the study area. Densities ranged from 9 - 11 lizards/ha. The age structure is marked by the low relative abundance of juveniles. Survivorship during the first year varied among years. Mortality was highest during summer months rather than winter months. Average annual survival of adults 'was high, but varied with sex and years (ranged from 58%-80%). A life table yielded a net reproductive rate (Ro= 1) sufficient to sustain the population, if the reproductive life of an adult female is at least 12 years. Lizards remain in their burrows during winter. In summer, activity was bimodal on sunshine days but unimodal on cool overcast days. Body temperature is regulated by behavioural means (postural and orientation changes) and by shuttling to the cool burrow microclimate. The life history strategy corresponds partially to that of K-selection.
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    Mating dynamics of South African forest millipedes : Centrobolus (Diplopoda: Pachybolidae)
    (1998) Cooper, Mark Ian; Telford, Steven; Nicolson, Sue W
    This study focuses on the mating dynamics of South African forest millipedes Centrobolus (Diplopoda: Spirobolida: Pachybolidae). The main objectives were to investigate the two most common mechanisms of sexual selection, sperm competition and cryptic female choice. The approach was to (1) quantify sexual dimorphism and find the selection pressures operating on the sexes, (2) determine the functional significance of male and female genitalia, (3) understand why there should be a conflict of sexual interests in prolonged copulations, and (4) resolve the mechanisms of sperm competition and cryptic female choice by comparing male mating strategies and sperm precedence to female mating strategies and sperm usage. All hypotheses tested in this thesis are centered on whether there is a conflict of interests between the sexes.
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    Pollen digestion in flower-feeding Scarabaeidae : protea beetles (Cetoniini) and monkey beetles (Hopliini)
    (2000) Johnson, Shelley; Nicolson, Sue W; Tets, Ian G van
    Beetles pollinate over 80% of all flowering plants and feed on the two most common floral rewards, nectar and pollen. Pollen is nutritionally very valuable, being a rich protein and carbohydrate source. However, the hard and highly resistant outer wall (exine) of the grain is an obstacle that pollen-feeders must overcome in order to benefit from the pollen's nutritious protoplasm. There are a variety of mechanisms that pollen-feeders may use to deal with the exine. Collembolans secrete exinase that breaks down the wall, but other pollen-feeders do not produce this enzyme. Pollen-feeders that are unable to ingest grains may either pierce the grain and suck out the contents (thrips and biting-flies) or cause the grain contents to leach out an imbibe the leachate (butterflies and the eucalupt nectar fly). Pollen-feeders that can ingest the grains (bees, syrphid flies, rodents, marsupials, bats and birds) may use osmotic shock, pseudo-germination, exudation, microbial digestion or enzyme penetration to gain access to the protoplasmic contents. Further study is needed to define the details of these methods and whether they are all in use.
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    Sex in southern african spirostreptida millipedes : mechanisms of sperm competition and cryptic female choice
    (1997) Barnett, Mandy; Telford, Steven; Nicolson, Sue W; Brown, Alec C
    Spirostreptida millipedes comprise three families, the Harpagophoridae, Spirostreptidae and Odontopygidae. They are polygynandrous. Males transfer sperm via species-specific accessory genitalia called gonopods, that comprise three components, two of which, the emote and telopodite, are involved in processes of sperm transfer. The emotes function to translocate ejaculates from the penes to the vulvae, where they are stored. A delay between insemination and fertilisation provides an arena for syn- and postcopulatory sexual competition. These operate at the gametic level via sperm competition and cryptic female choice. By combining studies of genital form and function with single and double mating experiments, this study elucidates these processes in some southern African Spirostreptida millipedes.
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    Water and energy balance in the Namib sand-dune lizard, Angolosaurus skoogi
    (1992) Clarke, Brian Craig; Louw, Gideon; Nicolson, Sue W
    The field metabolic rate (FMR) and water flux of the herbivorous Namib sand-dune lizard, Angolosaurus skoogi, was measured during the summer non-breeding period (early January) by means of doubly labelled water. FMR was about half that expected for a lizard of this size. Water flux and laboratory measured standard metabolic rates were, however, typical of other desert lizards. It thus appeared a priori that this species was behaviourally reducing metabolic costs through reduced activity. This generated questions with regard to the ecological and physiological significance of low FMRs. Is the reduction forced by intolerable environmental conditions or the need to stay in positive water and energy balance? Alternatively, is activity reduction voluntary and geared towards optimizing growth and storage, possibly in preparation for periods of physiological stress ? The research required to answer these questions forms the basis of this thesis. There has been much discussion about the evolutionary and ecological significance of growth rates. The consensus seems to be that, under most circumstances, animals are adapted in ways that maximize growth or optimize growth in relation to realistically attainable rates of gross energy intake. Animal behaviour may be influenced by factors unrelated to growth considerations such as starvation, involuntary hypo/hyperthermia, predator evasion and social interactions. These factors may be difficult to identify and isolate, making this hypothesis difficult to test. Previous studies on the biology of A. skoogi have shown that this species has a perennially available food source, a wide range of potential body temperatures at its disposal and a low predation risk. Social interaction appear to be confined to the breeding season. This species is thus a particularly suitable subject for a scope for growth optimization study.