Biomedical subjects

C Jaco Klok

Publications and source records attributed to C Jaco Klok.

13 recordsLinked to original sources

PubMed2006

Discontinuous gas exchange in insects: a clarification of hypotheses and approaches.

Many adult and diapausing pupal insects exchange respiratory gases discontinuously in a three-phase discontinuous gas exchange cycle (DGC). We summarize the known biophysical characteristics of the DGC and describe current research on the role of convection and diffusion in the DGC, emphasizing control of respiratory water loss. We summarize the main theories for the evolutionary genesis (or, alternatively, nonadaptive genesis) of the DGC: reduction in respiratory water loss (the hygric hypothesis), optimizing gas exchange in hypoxic and hypercapnic environments (the chthonic hypothesis), the hybrid of these two (the chthonic-hygric hypothesis), reducing the toxic properties of oxygen (the oxidative damage hypothesis), the outcome of interactions between O(2) and CO(2) control set points (the emergent property hypothesis), and protection against parasitic invaders (the strolling arthropods hypothesis). We describe specific techniques that are being employed to measure respiratory water loss in the presence or absence of the DGC in an attempt to test the hygric hypothesis, such as the hyperoxic switch and H(2)O/CO(2) regression, and summarize specific areas of the field that are likely to be profitable directions for future research.

Animals↗

PubMed2006

Phenotypic plasticity and geographic variation in thermal tolerance and water loss of the tsetse Glossina pallidipes (Diptera: Glossinidae): implications for distribution modelling.

Using the tsetse, Glossina pallidipes, we show that physiologic plasticity (resulting from temperature acclimation) accounts for among-population variation in thermal tolerance and water loss rates. Critical thermal minimum (CT(Min)) was highly variable among populations, seasons, and acclimation treatments, and the full range of variation was 9.3 degrees C (maximum value = 3.1 x minimum). Water loss rate showed similar variation (max = 3.7 x min). In contrast, critical thermal maxima (CT(Max)) varied least among populations, seasons, and acclimation treatments, and the full range of variation was only approximately 1 degree C. Most of the variation among the four field populations could be accounted for by phenotypic plasticity, which in the case of CT(Min), develops within 5 days of temperature exposure and is lost rapidly on return to the original conditions. Limited variation in CT(Max) supports bioclimatic models that suggest tsetse are likely to show range contraction with warming from climate change.

Adaptation, Physiological↗

PubMed2005

Environmental physiology of three species of Collembola at Cape Hallett, North Victoria Land, Antarctica.

The environmental physiology of three speciesof Collembola: Cryptopygus cisantarcticus, Isotoma klovstadi (Isotomidae) and Friesea grisea (Neanuridae) was investigated from November 2002 to February 2003 at Cape Hallett, North Victoria Land, Antarctica. All three species were freeze avoiding, and while supercooling points were variable on seasonal and daily scales in I. klovstadi and C. cisantarcticus, they remained largely static in F. grisea. LT50 (temperature where 50% of animals are killed by cold) was -13.6, -19.1 and -19.8 degrees C for C. cisantarcticus, I. klovstadi and F. grisea, respectively. Upper lethal temperature was 34, 34 and 38 degrees C for C. cisantarcticus, I. klovstadi and F. grisea. Critical thermal minimum onset (the temperature where individuals entered chill coma) was ca. -7, -12 and -8 degrees C for C. cisantarcticus, I. klovstadi and F. grisea, and 25% of I. klovstadi individuals froze without entering chill coma. Critical thermal maximum (the onset of spasms at high temperature) was 30, 33 and 34 degrees C for C. cisantarcticus, I. klovstadi and F. grisea. Haemolymph osmolality was approximately 720 mOsm for C. cisantarcticus and 680 mOsm for I. klovstadi, and both species showed a moderate degree of thermal hysteresis, which persisted through the season. Desiccation resistance was measured as survival above silica gel, and the species survived in the rank order of C. cisantarcticus<< I. klovstadi = F. grisea. Desiccation resulted in an increase in haemolymph osmolality in I. klovstadi, and water was quickly regained by desiccation-stressed individuals that had access to liquid water, but not by individuals placed in high humidity, indicating that this species is unable to absorb atmospheric water vapour. SDS-PAGE did not suggest any strong patterns in protein synthesis either seasonally or in response to temperature or desiccation stress. Microclimate temperatures were measured at sites representative of collection sites for the three species. Microclimate temperatures were highly variable on a diurnal and weekly scale (the latter relating to weather patterns), but showed little overall variation across the summer season. Potentially lethal high and low temperatures were recorded at several sites, and it is suggested that these temperature extremes account for the observed restriction of the less-tolerant C. cisantarcticus at Cape Hallett. Together, these data significantly increase the current knowledge of the environmental physiology of Antarctic Collembola.

Animals↗

PubMed2005

The effects of acclimation on thermal tolerance, desiccation resistance and metabolic rate in Chirodica chalcoptera (Coleoptera: Chrysomelidae).

Despite much focus on species responses to environmental variation through space and time, many higher taxa and geographic areas remain poorly studied. We report the effects of temperature acclimation on thermal tolerance, desiccation rate and metabolic rate for adult Chirodica chalcoptera (Coleoptera: Chrysomelidae) collected from Protea nerifolia inflorescences in the Fynbos Biome in South Africa. After 7 days of acclimation at 12, 19 and 25 degrees C, critical thermal maxima (mean+/-s.e.: 41.8+/-0.2 degrees C in field-fresh beetles) showed less response (<1 degrees C change) to temperature acclimation than did the onset of the critical thermal minima (0.1+/-0.2, 1.0+/-0.2 and 2.3+/-0.2 degrees C, respectively). Freezing was lethal in C. chalcoptera (field-fresh SCP -14.6 degrees C) and these beetles also showed pre-freeze mortality. Survival of 2 h at -10.1 degrees C increased from 20% to 76% after a 2 h pre-exposure to -2 degrees C, indicating rapid cold hardening. Metabolic rate, measured at 25 degrees C and adjusted by ANCOVA for mass variation, did not differ between males and females (2.772+/-0.471 and 2.517+/-0.560 ml CO2 h(-1), respectively), but was higher in 25 degrees C-acclimated beetles relative to the field-fresh and 12 degrees C-acclimated beetles. Body water content and desiccation rate did not differ between males and females and did not respond significantly to acclimation. We place these data in the context of measured inflorescence and ambient temperatures, and predict that climate change for the region could have effects on this species, in turn possibly affecting local ecosystem functioning.

Acclimatization↗

PubMed2005

Temperature-dependence of metabolic rate in Glossina morsitans morsitans (Diptera, Glossinidae) does not vary with gender, age, feeding, pregnancy or acclimation.

While variation in metabolic rate at a single temperature can occur for a variety of reasons and the effect of temperature is well established in insects, within-generation variation of metabolic rate-temperature relationships has been relatively poorly explored. In this study, we investigate the effects of gender, age, feeding and pregnancy, as well as three acclimation temperatures (19, 24, 29 degrees C), on standard metabolic rate and its temperature-dependence within post-developmental (i.e. non-teneral) adult G. morsitans morsitans. Although most of the independent variables influenced metabolic rate at a single test temperature (P<0.001 in most cases), and cold-acclimation resulted in significant up-regulation of metabolic rate at all test temperatures relative to 24 and 29 degrees C acclimation (P<0.0001), mass-independent metabolic rate-temperature relationships were surprisingly invariant over all experimental groups (P>0.05 in all cases). Slopes of log10 metabolic rate (ml CO2h(-1)) against temperature ( degrees C) ranged from a minimum of 0.03035 (+/-S.E.=0.003) in young fasted females to a maximum of 0.03834 (+/-0.004) in mature fasted males. These findings have implications for predicting the metabolic responses of tsetse flies to short-term temperature variation and may also have applications for modelling tsetse population dynamics as a function of temperature.

Acclimatization↗

PubMed2005

Insect gas exchange patterns: a phylogenetic perspective.

Most investigations of insect gas exchange patterns and the hypotheses proposed to account for their evolution have been based either on small-scale, manipulative experiments, or comparisons of a few closely related species. Despite their potential utility, no explicit, phylogeny-based, broad-scale comparative studies of the evolution of gas exchange in insects have been undertaken. This may be due partly to the preponderance of information for the endopterygotes, and its scarcity for the apterygotes and exopterygotes. Here we undertake such a broad-scale study. Information on gas exchange patterns for the large majority of insects examined to date (eight orders, 99 species) is compiled, and new information on 19 exemplar species from a further ten orders, not previously represented in the literature (Archaeognatha, Zygentoma, Ephemeroptera, Odonata, Mantodea, Mantophasmatodea, Phasmatodea, Dermaptera, Neuroptera, Trichoptera), is provided. These data are then used in a formal, phylogeny-based parsimony analysis of the evolution of gas exchange patterns at the order level. Cyclic gas exchange is likely to be the ancestral gas exchange pattern at rest (recognizing that active individuals typically show continuous gas exchange), and discontinuous gas exchange probably originated independently a minimum of five times in the Insecta.

Animals↗

PubMed2004

Metabolic rate in the whip-spider, Damon annulatipes (Arachnida: Amblypygi).

Metabolic rate estimates as well as a measure of their repeatability and response to laboratory acclimation are provided for the amblypygid Damon annulatipes (Wood). This species (mean +/- S.E. mass: 640+/-66 mg) shows continuous gas exchange, as might be expected from its possession of book lungs, and at 21 degrees C has a metabolic rate of 30.22+/-2.87 microl CO2 h(-1) (approximately 229.6+/-21.8 microW, R.Q. = 0.72). The intraclass correlation coefficient (r=0.74-0.89) indicated substantial repeatability in metabolic rate which did not change with laboratory acclimation over a period of 2 weeks. By contrast, absolute metabolic rate declined by c. 16-33%, although this was not a consequence of changes in mass (which were non-significant over the same period). Rather, it appears that a reduction in overall stress or activity in the laboratory might have been responsible for the decline in mass-independent metabolic rate. At the intraspecific level, metabolic rate scaled as microW = 342 M(0.857), where mass is in grams. Metabolic rates of this species are in keeping with its sedentary behaviour such that for a given body size they are lower than those of most arthropods (spiders and insects), higher than the very sedentary ticks, and equivalent to scorpions. These findings have implications for the understanding of the evolution of metabolic rates in arthropods.

Adaptation, Physiological↗

PubMed2004

Metabolism of the sub-Antarctic caterpillar Pringleophaga marioni during cooling, freezing and thawing.

Although general models of the processes involved in insect survival of freezing exist, there have been few studies directly investigating physiological processes during cooling, freezing and thawing, without which these models remain hypothetical. Here, we use open-flow respirometry to investigate the metabolism of the freeze-tolerant sub-Antarctic caterpillar Pringleophaga marioni Viette (Lepidoptera: Tineidae) during cooling, freezing and thawing and to compare animals exposed to non-lethal (-5.8 degrees C) and lethal (-6.0 degrees C, after which caterpillars are moribund for several days, and -18 degrees C, after which caterpillars are completely unresponsive) freezing stress. We found a large decrease in metabolic rate (that is not associated with freezing) at -0.6+/-0.1 degrees C and calculated a Q10 of 2.14 x 10(3) at this breakpoint. This breakpoint is coincident with the critical thermal minimum (CTmin) and is hypothesised to be a metabolic manifestation of the latter, possibly a failure of the Na+/K(+)-ATPase pump. This provides a plausible link between processes at the cellular level and observations of the action of the CTmin at tissue and whole-organism levels. Caterpillars froze at -4.6+/-0.1 degrees C and had detectable metabolism when frozen. Post-thaw, metabolic rates were lower than pre-freezing measurements. Post-thaw metabolic rates did not differ between temperatures that did and did not kill the caterpillars, which suggests that mortality may be a result of a breakdown in processes at the organismal, rather than cellular, level of organisation.

Animals↗

PubMed2004

Upper thermal tolerance and oxygen limitation in terrestrial arthropods.

The hypothesis of oxygen limitation of thermal tolerance proposes that critical temperatures are set by a transition to anaerobic metabolism, and that upper and lower tolerances are therefore coupled. Moreover, this hypothesis has been dubbed a unifying general principle and extended from marine to terrestrial ectotherms. By contrast, in insects the upper and lower limits are decoupled, suggesting that the oxygen limitation hypothesis might not be as general as proposed. However, no direct tests of this hypothesis or its predictions have been undertaken in terrestrial species. We use a terrestrial isopod (Armadillidium vulgare) and a tenebrionid beetle (Gonocephalum simplex) to test the prediction that thermal tolerance should vary with oxygen partial pressure. Whilst in the isopod critical thermal maximum declined with declining oxygen concentration, this was not the case in the beetle. Efficient oxygen delivery via a tracheal system makes oxygen limitation of thermal tolerance, at a whole organism level, unlikely in insects. By contrast, oxygen limitation of thermal tolerances is expected to apply to species, like the isopod, in which the circulatory system contributes significantly to oxygen delivery. Because insects dominate terrestrial systems, oxygen limitation of thermal tolerance cannot be considered pervasive in this habitat, although it is a characteristic of marine species.

Adaptation, Physiological↗

PubMed2003

Diurnal variation in supercooling points of three species of Collembola from Cape Hallett, Antarctica.

Daily changes in microclimate temperature and supercooling point (SCP) of Collembola were measured during summer at Cape Hallett, North Victoria Land, Antarctica. Isotoma klovstadi and Cryptopygus cisantarcticus (Isotomidae) showed bimodal SCP distributions, predominantly in the high group during the day and in the low group during the night. There were no concurrent diurnal changes in water content or haemolymph osmolality. By contrast, Friesea grisea (Neanuridae) had a unimodal distribution of SCPs that was invariant between daytime and nighttime. Isotoma klovstadi collected foraging on moss had uniformly high SCPs, which shifted towards the low group when the animals were starved for 2-8 h. When I. klovstadi was acclimated for five days with lichen or algae, SCPs were higher than if they were supplied with moss, while those that were starved (with free water or 100% relative humidity) displayed a trimodal SCP distribution. A variety of pre-treatments, including cold, heat, desiccation and slow cooling were ineffective at inducing SCP shifts in C. cisantarcticus or I. klovstadi. It is postulated that behavioural avoidance of low temperatures by vertical migration may be key in I. klovstadi's short-term survival of nighttime temperatures. These data suggest that the full range of thermal responses of Antarctic Collembola is yet to be elucidated.

Acclimatization↗

PubMed2002

Discontinuous gas-exchange in centipedes and its convergent evolution in tracheated arthropods.

We have examined the gas-exchange characteristics of five southern African centipede species from three orders. Two scolopendromorph species exhibit discontinuous gas-exchange cycles (DGCs) identical to those recorded for several insect and chelicerate species. Another scolopendromorph and a lithobiomorph species exhibit weak periodic patterns, and a scutigermorph species shows continuous gas exchange. A crucial component for DGCs in tracheated arthropods is the presence of occludible spiracles. However, on the basis of studies of temperate centipedes, most recent invertebrate biology texts hold the view that centipedes, as a group, cannot close their spiracles. Using flow-through normoxic and normoxic-anoxic-normoxic respirometry and electron microscopy, we conclusively demonstrate that at least one of the scolopendromorph species, Cormocephalus morsitans L., can close its spiracles fully, thus accounting for its DGCs. Homologies in spiracular structure and DGCs suggest that several other tracheated arthropod taxa probably have this ability too and that DGCs have evolved convergently at least four times in the Arthropoda. Spiracular closure and discontinuous gas-exchange cycles are probably more widespread in arthropods than has previously been suspected.

Animals↗

PubMed1997

Critical thermal limits, temperature tolerance and water balance of a sub-Antarctic caterpillar, Pringleophaga marioni (Lepidoptera: Tineidae).

Thermal tolerance, supercooling point, water balance and osmoregulatory ability of Pringleophaga marioni Viette (Lepidoptera: Tineidae) are investigated in this study. Field-fresh larvae had a mean CT(Min) (cold stupor) of -0.6 degrees C and a mean CT(Max) (heat coma) of 38.7 degrees C. The mean supercooling point of field-fresh individuals was -5.0 degrees C. Caterpillars showed 100% survival of freezing to -6.5 degrees C, but at -12 degrees C mortality rose to 100%. Survival of a 30h exposure to -6.0 degrees C was 80%, but declined to 30% in the 6-12h interval at -7.5 degrees C. No caterpillars survived for longer than 12h at -9.0 degrees C. Survival of high temperatures (35 degrees C and above) was poor. Tolerance of water loss (46% of fresh mass) and rates of water loss (1% fresh massh(-1)) were similar to those found in other mesic insects. P. marioni larvae were incapable of metabolizing lipids to replenish lost water and showed no haemolymph osmoregulatory ability. It is suggested that the preponderance of freeze tolerance in high-latitude southern hemisphere species may be associated with their occurrence in moist habitats, and that the "freeze tolerance" category be re-examined in the light of the range of strategies adopted by such arthropods.

Journal Article↗

PubMedDate not supplied

Water-balance characteristics respond to changes in body size in subantarctic weevils.

Several environmental factors leading to size-dependent mortality influence insect body size. Few investigations have been concerned with the ways in which the mechanisms underlying variation in water-balance characteristics evolve in response to changes in body size that occur independently of water-balance requirements. Using an explicitly phylogenetic analysis, we show how body size has changed over time in the Ectemnorhinus group of weevils and how water-balance characteristics have evolved in response to this change and changes in habitat use. The basal species in the group are all large bodied and from moist environments. In response to a change in resource availability, there was a marked decline in size within the group. Despite the reduction in water content and dehydration tolerance that this meant, evolution of low whole-animal water-loss rates and high tolerance of dehydration resulted in conservation of desiccation resistance. The return to moist habitats in the group resulted in a reduction in dehydration tolerance and an increase in water-loss rate. Thus, dehydration tolerance and water-loss rate respond rapidly both when there is selection for water conservation and when this requirement is relaxed. Future laboratory selection experiments might usefully explore both directions of water-balance evolution.

Animals↗