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Biomedical subjects

S L Chown

Publications and source records attributed to S L Chown.

13 recordsLinked to original sources
PubMed2006

Gas exchange characteristics, metabolic rate and water loss of the Heelwalker, Karoophasma biedouwensis (Mantophasmatodea: Austrophasmatidae).

This study presents the first physiological information for a member of the wingless Mantophasmatodea, or Heelwalkers. This species shows cyclic gas exchange with no evidence of a Flutter period (more typical of discontinuous gas exchange in insects) and no indication that the spiracles are fully occluded during quiescent metabolism. Standard metabolic rate at 20 degrees C was 21.32+/-2.73 microl CO(2)h(-1) (mean+/-S.E.), with a Q(10) (10-25 degrees C) of 1.7. Increases in V()CO(2) associated with variation in mass and with trial temperature were modulated by an increase in burst period volume and a decline in cycle frequency. Total water loss rate, determined by infrared gas analysis, was 0.876+/-0.08 mg H(2)Oh(-1) (range 0.602-1.577, n=11) whilst cuticular water loss rate, estimated by linear regression of total water loss rate and metabolic rate, was 0.618+/-0.09 mg H(2)Oh(-1) (range 0.341-1.363, n=11). Respiratory water loss rate was therefore no more than 29% of the total rate of water loss. Both total water loss rate and estimated cuticular water loss rate were significantly repeatable, with intraclass correlation coefficients of 0.745 and 0.553, respectively.

Animals↗
PubMed2005

Inertia in physiological traits: Embryonopsis halticella caterpillars (Yponomeutidae) across the Antarctic Polar Frontal Zone.

Geographic variation is characteristic of many physiological traits at the population and species levels. However, several recent studies have suggested that population-level variation is either limited or that it is mostly a consequence of phenotypic plasticity. Here we show that there is considerable physiological inertia in cold hardiness, upper thermal tolerance limits and desiccation resistance in caterpillars of the sub-Antarctic moth Embryonopsis halticella Eaton, such that populations from two climatically different islands are physiologically very similar. Both populations are moderately chill tolerant, with no difference in the supercooling points of caterpillars (-17 to -20 degrees C). Within their host plants caterpillars of both populations freeze at substantially higher, and statistically equivalent temperatures (-9.5 to -11.5 degrees C). The populations also have similar upper lethal limits (38 degrees C), and survival times of dry conditions (6-170 h depending on mass). The previously inexplicably low freezing point of caterpillars at the climatically less severe Marion Island seems likely a consequence of physiological inertia given that the freezing point of caterpillars within their hosts is only a few degrees below absolute minima at the older, and colder, Heard Island. Lack of adaptive geographic variation in physiological traits has consequences for models of range limits, and highlights the importance of exploring phenotypic plasticity as a response to climatic variation.

Animals↗
PubMed2005

Temperature- and body mass-related variation in cyclic gas exchange characteristics and metabolic rate of seven weevil species: Broader implications.

The influence of temperature on metabolic rate and characteristics of the gas exchange patterns of flightless, sub-Antarctic Ectemnorhinus-group species from Heard and Marion islands was investigated. All of the species showed cyclic gas exchange with no Flutter period, indicating that these species are not characterized by discontinuous gas exchange cycles. Metabolic rate estimates were substantially lower in this study than in a previous one of a subset of the species, demonstrating that open-system respirometry methods provide more representative estimates of standard metabolic rate than do many closed-system methods. We recommend that the latter, and especially constant-pressure methods, either be abandoned for estimates of standard metabolic rate in insects, or have their outputs subject to careful scrutiny, given the wide availability of the former. V(.)CO(2) increase with an increase in temperature (range: 0-15 degrees C) was modulated by an increase in cycle frequency, but typically not by an increase in burst volume. Previous investigations of temperature-related changes in cyclic gas exchange (both cyclic and discontinuous) in several other insect species were therefore substantiated. Interspecific mass-scaling of metabolic rate (ca. 0.466-0.573, excluding and including phylogenetic non-independence, respectively) produced an exponent lower than 0.75 (but not distinguishable from it or from 0.67). The increase of metabolic rate with mass was modulated by an increase in burst volume and not by a change in cycle frequency, in keeping with investigations of species showing discontinuous gas exchange. These findings are discussed in the context of the emerging macrophysiological metabolic theory of ecology.

Animals↗
PubMed2004

Metabolic rate variation in Glossina pallidipes (Diptera: Glossinidae): gender, ageing and repeatability.

Despite the importance of metabolic rate in determining flight time of tsetse and in mediating the influence of abiotic variables on life history parameters (and hence abundance and distribution), metabolic rate measurements and their repeatability have not been widely assessed in these flies. We investigate age-related changes in standard metabolic rate (SMR) and its repeatability, using flow-through respirometry, for a variety of feeding, gender and pregnancy classes during early adult development in laboratory-reared individuals of the tsetse fly, Glossina pallidipes. Standard metabolic rate (144-635 microW) was generally within 22% of previous estimates, though lower than the values found using closed system respirometry. There was no significant difference between the genders, but metabolic rate increased consistently with age, probably owing to flight muscle development. Repeatability of metabolic rate was generally high (r=0.6-.09), but not in younger teneral adults and pregnant females (r approximately equal to 0.05-0.4). In these individuals, low repeatability values are a consequence of muscle or in utero larval development. Tsetse and other flies generally have a much higher metabolic rate, for a given size, than do other insect species investigated to date.

Aging↗
PubMed2002

Respiratory water loss in insects.

The contribution of respiratory transpiration to overall water loss in insects is contentious. Misgivings concerning the importance of this route of water loss have arisen largely as a consequence of work on discontinuous gas exchange cycles (DGC). Most studies have found that respiratory water loss constitutes only a small proportion of total water loss. Thus, it has been argued that modulation of metabolic rate and/or the components of the DGC is unlikely to constitute a fitness benefit. In contrast to these intraspecific studies, interspecific comparative data suggest that, at least in xeric species, respiratory transpiration is an important component of water loss. However, these arguments are confounded by several factors. In DGC-based studies, these include multiple effects of the experimental treatments, the absence of a null expectation for the contribution of respiratory to total water loss, and problems with the use of proportions as a way of assessing the importance of respiratory water loss. The interspecific studies are confounded by the likely significance of influences other than water conservation on metabolic rate, the absence of analyses of phylogenetic independent contrasts, and little information on behavioral differences between species. Future work should be based on a strong inference approach and designed in such a way that these problems can be resolved. Moreover, in the case of the DGC it should be recognized that several factors are likely to influence this gas exchange pattern, and that they probably act in concert, especially during dormancy.

Animals↗
PubMed2002

Physiological variation in insects: large-scale patterns and their implications.

In this paper we demonstrate how broad scale comparative physiology has an important role to play in informing a variety of assumptions made in macroecology. We do so by examining large-scale geographic variation in insect development, thermal tolerance and metabolic rate. From these studies, and those from the literature on insect water loss and thermoregulation, we show that there is often a bias to the geographic extent of available empirical data. Studies of cold hardiness are most usually undertaken at high latitudes, while investigations of upper thermal tolerances and water loss are most common in warm arid regions. Likewise, we demonstrate that much variation in insect physiological tolerances is partitioned at higher taxonomic levels, which has important implications for comparative physiology. Intriguingly, data on the full range of variables we review are available for only three species. We also show that, despite its importance, body size is regularly reported in only some kinds of investigations (metabolic rate, water loss rate), whereas in others (upper lethal temperature, cold hardiness, development) this variable is often ignored. In short, although large-scale comparative physiology can contribute considerable understanding to both physiology and ecology, there is much that remains to be done.

Animals↗
PubMed2001

The animal species-body size distribution of Marion Island.

Body size is one of the most significant features of animals. Not only is it correlated with many life history and ecological traits, but it also may influence the abundance of species within, and their membership of, assemblages. Understanding of the latter processes is frequently based on a comparison of model outcomes with the frequency of species of different body mass within natural assemblages. Consequently, the form of these frequency distributions has been much debated. Empirical data usually concern taxonomically delineated groups, such as classes or orders, whereas the processes ultimately apply to whole assemblages. Here, we report the most complete animal species-body size distribution to date for those free-living species breeding on sub-Antarctic Marion Island and using the terrestrial environment. Extending over 15 orders of magnitude of variation in body mass, this distribution is bimodal, with separate peaks for invertebrates and vertebrates. Under logarithmic transformation, the distribution for vertebrates is not significantly skewed, whereas that for invertebrates is right-skewed. Contrary to expectation based on a fractal or pseudofractal environmental structure, the decline in the richness of species at the smallest body sizes is a real effect and not a consequence of unrecorded species or of species introductions to the island. The scarcity of small species might well be a consequence of their large geographic ranges.

Animals↗
PubMed2000

Thermal tolerance, climatic variability and latitude.

The greater latitudinal extents of occurrence of species towards higher latitudes has been attributed to the broadening of physiological tolerances with latitude as a result of increases in climatic variation. While there is some support for such patterns in climate, the physiological tolerances of species across large latitudinal gradients have seldom been assessed. Here we report findings for insects based on published upper and lower lethal temperature data. The upper thermal limits show little geographical variation. In contrast, the lower bounds of supercooling points and lower lethal temperatures do indeed decline with latitude. However, this is not the case for the upper bounds, leading to an increase in the variation in lower lethal limits with latitude. These results provide some support for the physiological tolerance assumption associated with Rapoport's rule, but highlight the need for coupled data on species tolerances and range size.

Adaptation, Physiological↗
PubMed2000

Feeding patterns of immature stages of Hyalomma truncatum and Hyalomma marginatum rufipes on different hosts.

In this study we examine the feeding patterns of immature stages of Hyalomma truncatum and Hyalomma marginatum rufipes ticks on different hosts. Larvae of H. truncatum developed through a three-host pattern on two species of field mice, Rhabdomys pumilio and Lemniscomys rosalia. On guinea-pigs, both Hyalomma species followed a mixed two-host and three-host pattern, with the latter route being preferred, since more than 70% of the fully fed larvae dropped off from their hosts. H. truncatum was a two-host tick on rabbits. Larvae of H. marginatum rufipes did not prefer R. pumilio and L. rosalia as hosts. On guinea-pigs, H. marginatum rufipes immatures showed a mixed two-host and three-host pattern with a bias towards the three-host life cycle, since approximately 58% of the fully fed larvae dropped off. On rabbits, H. marginatum rufipes was exclusively a two-host tick. Mean engorgement weights and blood quantities ingested by H. truncatum nymphs that developed through a three-host pattern on mice were significantly higher (p < 0.0001) than for those that developed through a two-host pattern on guinea-pigs and rabbits. For H. marginatum rufipes, there were no significant differences (p > 0.05) between engorgement weights of nymphs that developed through two-host and three-host patterns. However, there were significant differences (p < 0.0001) in blood quantities ingested by nymphs of this tick species following feeding on different hosts.

Animals↗
PubMed2000

Discontinuous gas exchange cycles in aphodius fossor (Scarabaeidae): a test of hypotheses concerning origins and mechanisms.

It has been suggested that discontinuous gas exchange cycles (DGCs) in insects evolved in response to hypoxic and/or hypercapnic environments, and that the flutter phase of the DGC is predominantly diffusive. We tested these hypotheses by examining the rate of CO(2) release at a declining series of oxygen partial pressures in adults of Aphodius fossor, an inhabitant of moist to wet dung pats that can have low oxygen and high carbon dioxide concentrations. This mesic species showed a pronounced DGC, but progressively abandoned it when exposed to declining oxygen concentrations. That is, in response to a reduction in oxygen concentration, the closed phase declined in length and eventually disappeared, the flutter phase declined in length, while the flutter phase rate of CO(2) release increased, the open phase peak rate of CO(2) release declined and DGC frequency increased. Nonetheless, overall CO(2) release rate remained virtually unchanged. Thus, it appears that the flutter phase in A. fossor has a significant convective component. In addition, in response to declining oxygen concentrations, the spiracles are opened for prolonged periods to increase gas exchange. This behaviour is unlikely to incur a significant water loss penalty in the moist habitats in which A. fossor lives. Given the switch to continuous ventilation by A. fossor under hypoxic conditions, we conclude that current adaptive explanations for the DGC are inadequate. Rather, the DGC may be the default state of a system regulated by two interacting feedback loops when demands are absent.

Animals↗
PubMedDate not supplied

Discontinuous gas-exchange cycles in Scarabaeus dung beetles (Coleoptera: Scarabaeidae): mass-scaling and temperature dependence.

Although discontinuous gas exchange cycles (DGC) are known from many insects, the effects of body size and temperature on DGC have not been widely examined. Here, these effects are investigated in five Scarabaeus dung beetle species from mesic and xeric habitats. The investigation tests two hypotheses: that previous estimates of the scaling exponents for the DGC and its characteristics are more broadly applicable to insects, and that, in response to temperature, both DGC frequency and the quantity of CO2 emitted during the open (O) phase (O-phase emission volume) are modulated. Like previous workers, we find that V&d2;co2 scaled as mass0.968 and that O-phase emission volume scaled as mass0.833. However, temperature-associated increases in .Vco2 (Q10's of 2.19-2.65) were modulated mostly by increases in DGC frequency since O-phase volumes remained constant across temperature. Flutter (F)-phase and O-phase durations were closely coupled to DGC duration, although the relationship between closed (C)-phase duration and DGC duration was less pronounced. We show that ventilation phase coefficients, previously considered a measure of the proportional duration of each phase of the DGC, calculated from the slopes of these relationships are a measure of change in phase duration with change in DGC duration and not a measure of the way in which total DGC duration is apportioned among phases. We suggest that proportions be used to estimate the contribution of each of the phases to the total duration of the DGC.

Animals↗
PubMedDate not supplied

The influence of habitat and altitude on oxygen uptake in sub-Antarctic weevils.

Whole-organism oxygen uptake rate and its temperature sensitivity (determined using regression analyses and estimates of Q10) were examined in six closely related weevil species (Palirhoeus eatoni, Bothrometopus randi, Bothrometopus elongatus, Bothrometopus parvulus, Ectemnorhinus similis, and Ectemnorhinus marioni) from sub-Antarctic Marion Island over a short time period and using the same methods. Bothrometopus elongatus, B. parvulus, and the two Ectemnorhinus species have populations at both high and low elevations, and pairwise comparisons of these species were made. Regressions of the log of oxygen uptake rate on temperature and Q10 values revealed that the Ectemnorhinus species have a significantly greater thermal sensitivity than do species in the genera Bothrometopus and Palirhoeus. This may be considered an adaptation of the former to their moist lowland habitats and the requirements of angiosperm-feeding in E. similis. It is argued that elevated oxygen uptake rates and reduced slopes of the regression of the log of oxygen uptake rate on temperature in species and populations from high altitudes compared with those from low elevations provide evidence for metabolic cold adaptation. In addition, it seems likely that elevated oxygen uptake rates and their reduced thermal sensitivity within the genera Bothrometopus and Palirhoeus are an adaptation to the cold Neogene environments they evolved in. However, because data on the more basal taxa in the Ectemnorhinus group of weevils are not available, this temperature compensation could not be attributed conclusively to adaptation. Q10's of the lowland populations of all the species were negatively correlated with body water content, and it is suggested that the low temperature sensitivity of metabolism in P. eatoni and the Bothrometopus species may also be due to constraints imposed on them by their dry habitats.

Altitude↗