Browsing by Author "Terblanche, John S."
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- ItemCold tolerance is unaffected by oxygen availability despite changes in anaerobic metabolism(Springer Nature, 2016) Boardman, Leigh; Sørensen, Jesper G.; Koštál, Vladimir; Šimek, Petr; Terblanche, John S.Insect cold tolerance depends on their ability to withstand or repair perturbations in cellular homeostasis caused by low temperature stress. Decreased oxygen availability (hypoxia) can interact with low temperature tolerance, often improving insect survival. One mechanism proposed for such responses is that whole-animal cold tolerance is set by a transition to anaerobic metabolism. Here, we provide a test of this hypothesis in an insect model system (Thaumatotibia leucotreta) by experimental manipulation of oxygen availability while measuring metabolic rate, critical thermal minimum (CTmin), supercooling point and changes in 43 metabolites in moth larvae at three key timepoints (before, during and after chill coma). Furthermore, we determined the critical oxygen partial pressure below which metabolic rate was suppressed (c. 4.5 kPa). Results showed that altering oxygen availability did not affect (non-lethal) CTmin nor (lethal) supercooling point. Metabolomic profiling revealed the upregulation of anaerobic metabolites and alterations in concentrations of citric acid cycle intermediates during and after chill coma exposure. Hypoxia exacerbated the anaerobic metabolite responses induced by low temperatures. These results suggest that cold tolerance of T. leucotreta larvae is not set by oxygen limitation, and that anaerobic metabolism in these larvae may contribute to their ability to survive in necrotic fruit.
- ItemComplex interactions between temperature and relative humidity on water balance of adult tsetse (Glossinidae, Diptera) : implications for climate change(Frontiers, 2011) Kleynhans, Elsje; Terblanche, John S.Insect water balance plays an important role in determining energy budgets, activity patterns, survival, and population dynamics and, hence, geographic distribution. Tsetse (Glossina spp.) are important vectors of human and animal disease occupying a wide range of habitats in Africa and are notable for their desiccation resistance in xeric environments. Here, we measure water balance and related traits [water loss rate (WLR), body water content (BWC), body lipid content (BLC) and body mass] in adult flies across a range of temperature (20–30°C) and relative humidity (0–99%) combinations in four tsetse species from both xeric and mesic habitats. WLRs were significantly affected by measurement under different temperature and relative humidity combinations, while BWC, BLC, and body mass were less affected. These results provide support for mass-independent inter- and intra-specific variation in WLRs and survival times. Furthermore, water balance responses to variation in temperature and relative humidity are complex in Glossina, and this response varies within and among species, subgroups, and ecotypes in terms of both magnitude of effects and the direction of change. Different effects of temperature and relative humidity within and among experimental conditions and species suggests cuticular permeability and saturation deficit are likely to be key factors in forecasting tsetse water balance responses to climate variability. This complicates potential forecasting of tsetse distribution in the face of climate change.
- ItemContaminant organisms recorded on plant product imports to South Africa 1994–2019(Springer Nature, 2021-03-16) Saccaggi, Davina L.; Arendse, Melanie; Wilson, John R. U.; Terblanche, John S.Biosecurity interception records are crucial data underlying efforts to predict and manage pest and pathogen introductions. Here we present a dataset containing information on imported plant products inspected by the South African Department of Agriculture’s laboratories between 1994 and 2019 and the contaminant organisms found on them. Samples were received from border inspectors as either propagation material (e.g. plants) or material for immediate use (e.g. fruit). Material for immediate use was further divided into two sample categories, depending on if contaminants were seen/suspected by the border official or not: intervention or audit samples. The final dataset consists of 25,279 records, of which 30% tested positive (i.e. had at least one contaminant) and 13% had multiple contaminants. Of the 13,731 recorded contaminants, fungi (41%), mites (37%) and insects (19%) were most common. This dataset provides insight into the suite of taxa transported along the plant import pathway and provides an important resource for analyses of contaminant organisms in international trade, which can inform strategies for risk assessment, pathway management and biosecurity protocols.
- ItemDesiccation tolerance as a function of age, sex, humidity and temperature in adults of the African malaria vectors Anopheles arabiensis and Anopheles funestus(The Company of Biologists, 2014-09) Lyons, Candice L.; Coetzee, Maureen; Terblanche, John S.; Chown, Steven L.Adult mosquito survival is strongly temperature and moisture dependent. Few studies have investigated the interacting effects of these variables on adult survival and how this differs among the sexes and with age, despite the importance of such information for population dynamic models. For these reasons, the desiccation tolerance of Anopheles arabiensis Patton and Anopheles funestus Giles males and females of three different ages was assessed under three combinations of temperature and humidity. Females were more desiccation tolerant than males, surviving for longer periods than males under all experimental conditions. In addition, younger adults were more tolerant of desiccation than older groups. Both species showed reduced water loss rate (WLR) as the primary mechanism by which they tolerate desiccation. Although A. arabiensis is often considered to be the more arid-adapted of the two species, it showed lower survival times and higher WLR than A. funestus. The current information could improve population dynamic models of these vectors, given that adult survival information for such models is relatively sparse.
- ItemDivergent thermal specialisation of two South African entomopathogenic nematodes(PeerJ, 2015-07-02) Hill, Matthew P.; Malan, Antoinette P.; Terblanche, John S.Thermal physiology of entomopathogenic nematodes (EPN) is a critical aspect of field performance and fitness. Thermal limits for survival and activity, and the ability of these limits to adjust (i.e., show phenotypic flexibility) depending on recent thermal history, are generally poorly established, especially for non-model nematode species. Here we report the acute thermal limits for survival, and the thermal acclimation-related plasticity thereof for two key endemic South African EPN species, Steinernema yirgalemense and Heterorhabditis zealandica. Results including LT50 indicate S. yirgalemense (LT50 = 40.8 ± 0.3 ◦C) has greater high temperature tolerance than H. zealandica (LT50 = 36.7 ± 0.2 ◦C), but S. yirgalemense (LT50 = −2.4 ± 0 ◦C) has poorer low temperature tolerance in comparison to H. zealandica (LT50=−9.7±0.3 ◦C), suggesting these two EPN species occupy divergent thermal niches to one another. Acclimation had both negative and positive effects on temperature stress survival of both species, although the overall variation meant that many of these effects were non-significant. There was no indication of a consistent loss of plasticity with improved basal thermal tolerance for either species at upper lethal temperatures. At lower temperatures measured for H. zealandica, the 5 ◦C acclimation lowered survival until below−12.5 ◦C, where after it increased survival. Such results indicate that the thermal niche breadth of EPN species can differ significantly depending on recent thermal conditions, and should be characterized across a broad range of species to understand the evolution of thermal limits to performance and survival in this group.
- ItemEffects of within-generation thermal history on the flight performance of Ceratitis capitata : colder is better(The Company of Biologists, 2014-07) Esterhuizen, Nanike; Clusella-Trullas, Susana; Van Daalen, Corne E.; Schoombie, Ruben E.; Boardman, Leigh; Terblanche, John S.The influence of thermal history on temperature-dependent flight performance was investigated in an invasive agricultural pest insect, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at these temperatures (Ttest) as adults using a full-factorial study design. Major factors influencing flight performance included sex, body mass, Ttest and the interaction between Ttest and Tacc. Successful flight performance increased with increasing Ttest across all acclimation groups (from 10% at 15°C to 77% at 30°C). Although Tacc did not affect flight performance independently, it did have a significant interaction effect with Ttest. Multiple comparisons showed that flies which had been acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures, but warm-acclimated flies did not outperform cold-acclimated flies at warmer temperatures. This provides partial support for the ‘colder is better’ hypothesis. To explain these results, several flight-related traits were examined to determine whether Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase enzyme activity. Although significant effects of Tacc could be detected in several of the traits examined, with an emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any of these traits. Overall, these results are important for understanding dispersal physiology despite the fact that the mechanisms of acclimation-related changes in flight performance remain unresolved.
- ItemEnvironmental temperature alters the overall digestive energetics and differentially affects dietary protein and lipid use in a lizard(The Company of Biologists, 2019) Plasman, Melissa; McCue, Marshall D.; Reynoso, Vı́ctor Hugo; Terblanche, John S.; Clusella-Trullas, SusanaProcessing food (e.g. ingestion, digestion, assimilation) requires energy referred to as specific dynamic action (SDA) and is at least partially fuelled by oxidation of the nutrients (e.g. proteins and lipids) within the recently ingested meal. In ectotherms, environmental temperature can affect the magnitude and/or duration of the SDA, but is likely to also alter the mixture of nutrients that are oxidized to cover these costs. Here, we examined metabolic rate, gut passage time, assimilation efficiency and fuel use in the lizard Agama atra digesting cricket meals at three ecologically relevant temperatures (20, 25 and 32°C). Crickets were isotopically enriched with 13C-leucine or 13C-palmitic-acid tracers to distinguish between protein and lipid oxidation, respectively. Our results show that higher temperatures increased the magnitude of the SDA peak (by 318% between 32 and 20°C) and gut passage rate (63%), and decreased the duration of the SDA response (by 20% for males and 48% for females). Peak rate of dietary protein oxidation occurred sooner than peak lipid oxidation at all temperatures (70, 60 and 31 h earlier for 20, 25 and 32°C, respectively). Assimilation efficiency of proteins, but not lipids, was positively related to temperature. Interestingly, the SDA response exhibited a notable circadian rhythm. These results show that temperature has a pronounced effect on digestive energetics in A. atra, and that this effect differs between nutrient classes. Variation in environmental temperatures may thus alter the energy budget and nutrient reserves of these animals.
- ItemEvolutionary responses of discontinuous gas exchange in insects(National Academy of Sciences, 2007-05) White, Craig R.; Blackburn, Tim M.; Terblanche, John S.; Marais, Elrike; Gibernau, Marc; Chown, Steven L.The discontinuous gas-exchange cycles (DGCs) observed in many quiescent insects have been a cause of debate for decades, but no consensus on their evolutionary origin or adaptive significance has been achieved. Nevertheless, three main adaptive hypotheses have emerged: (i) the hygric hypothesis suggests that DGCs reduce respiratory water loss; (ii) the chthonic hypothesis suggests that DGCs facilitate gas exchange during environmental hypoxia, hypercapnia, or both; and (iii) the oxidative-damage hypothesis suggests that DGCs minimize oxidative tissue damage. However, most work conducted to date has been based on single-species investigations or nonphylogenetic comparative analyses of few species, despite calls for a strong-inference, phylogenetic approach. Here, we adopt such an approach by using 76 measurements of 40 wild-caught species to examine macrophysiological variation in DGC duration in insects. Potential patterns of trait variation are first identified on the basis of the explicit a priori predictions of each hypothesis, and the best phylogenetic generalized least-squares fit of the candidate models to the data is selected on the basis of Akaike's information criterion. We find a significant positive relationship between DGC duration and habitat temperature and an important interaction between habitat temperature and precipitation. This result supports the hygric hypothesis. We conclude that the DGCs of insects reduce respiratory water loss while ensuring adequate gas exchange. © 2007 by The National Academy of Sciences of the USA.
- ItemGas exchange patterns and water loss rates in the Table Mountain cockroach, Aptera fusca (Blattodea: Blaberidae)(Company of Biologists, 2013) Groenewald, Berlize; Bazelet, Corinna S.; Potter, C. Paige; Terblanche, John S.The importance of metabolic rate and/or spiracle modulation for saving respiratory water is contentious. One major explanation for gas exchange pattern variation in terrestrial insects is to effect a respiratory water loss (RWL) saving. To test this, we measured the rates of CO2 and H2O release (Embedded Image and Embedded Image, respectively) in a previously unstudied, mesic cockroach, Aptera fusca, and compared gas exchange and water loss parameters among the major gas exchange patterns (continuous, cyclic, discontinuous gas exchange) at a range of temperatures. Mean Embedded Image, Embedded Image and Embedded Image per unit Embedded Image did not differ among the gas exchange patterns at all temperatures (P>0.09). There was no significant association between temperature and gas exchange pattern type (P=0.63). Percentage of RWL (relative to total water loss) was typically low (9.79±1.84%) and did not differ significantly among gas exchange patterns at 15°C (P=0.26). The method of estimation had a large impact on the percentage of RWL, and of the three techniques investigated (traditional, regression and hyperoxic switch), the traditional method generally performed best. In many respects, A. fusca has typical gas exchange for what might be expected from other insects studied to date (e.g. Embedded Image, Embedded Image, RWL and cuticular water loss). However, we found for A. fusca that Embedded Image expressed as a function of metabolic rate was significantly higher than the expected consensus relationship for insects, suggesting it is under considerable pressure to save water. Despite this, we found no consistent evidence supporting the conclusion that transitions in pattern type yield reductions in RWL in this mesic cockroach.
- ItemGeographic variation and plasticity in climate stress resistance among southern African populations of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)(Nature Research, 2018-06-29) Weldon, Christopher W.; Nyamukondiwa, Casper; Karsten, Minette; Chown, Steven L.; Terblanche, John S.Traits of thermal sensitivity or performance are typically the focus of species distribution modelling. Among-population trait variation, trait plasticity, population connectedness and the possible climatic covariation thereof are seldom accounted for. Here, we examine multiple climate stress resistance traits, and the plasticity thereof, for a globally invasive agricultural pest insect, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also accounted for body size and population genetic connectivity among distinct populations from diverse bioclimatic regions across southern Africa. Desiccation resistance, starvation resistance, and critical thermal minimum (CTmin) and maximum (CTmax) of C. capitata varied between populations. For thermal tolerance traits, patterns of flexibility in response to thermal acclimation were suggestive of beneficial acclimation, but this was not the case for desiccation or starvation resistance. Population differences in measured traits were larger than those associated with acclimation, even though gene flow was high. Desiccation resistance was weakly but positively affected by growing degree-days. There was also a weak positive relationship between CTmin and temperature seasonality, but CTmax was weakly but negatively affected by the same bioclimatic variable. Our results suggest that the invasive potential of C. capitata may be supported by adaptation of tolerance traits to local bioclimatic conditions.
- ItemA hierarchy of factors influence discontinuous gas exchange in the grasshopper Paracinema tricolor (Orthoptera: Acrididae)(The Company of Biologists, 2014-07) Groenewald, Berlize; Chown, Steven L.; Terblanche, John S.The evolutionary origin and maintenance of discontinuous gas exchange (DGE) in tracheate arthropods are poorly understood and highly controversial. We investigated prioritization of abiotic factors in the gas exchange control cascade by examining oxygen, water and haemolymph pH regulation in the grasshopper Paracinema tricolor. Using a full-factorial design, grasshoppers were acclimated to hypoxic or hyperoxic (5% O2, 40% O2) gas conditions, or dehydrated or hydrated, whereafter their CO2 release was measured under a range of O2 and relative humidity (RH) conditions (5%, 21%, 40% O2 and 5%, 60%, 90% RH). DGE was significantly less common in grasshoppers acclimated to dehydrating conditions compared with the other acclimations (hypoxia, 98%; hyperoxia, 100%; hydrated, 100%; dehydrated, 67%). Acclimation to dehydrating conditions resulted in a significant decrease in haemolymph pH from 7.0±0.3 to 6.6±0.1 (mean ± s.d., P=0.018) and also significantly increased the open (O)-phase duration under 5% O2 treatment conditions (5% O2, 44.1±29.3 min; 40% O2, 15.8±8.0 min; 5% RH, 17.8±1.3 min; 60% RH, 24.0±9.7 min; 90% RH, 20.6±8.9 min). The observed acidosis could potentially explain the extension of the O-phase under low RH conditions, when it would perhaps seem more useful to reduce the O-phase to lower respiratory water loss. The results confirm that DGE occurrence and modulation are affected by multiple abiotic factors. A hierarchical framework for abiotic factors influencing DGE is proposed in which the following stressors are prioritized in decreasing order of importance: oxygen supply, CO2 excretion and pH modulation, oxidative damage protection and water savings.
- ItemInteractions between controlled atmospheres and low temperature tolerance : a review of biochemical mechanisms(Frontiers Media, 2011-12-02) Boardman, Leigh; Sorensen, Jesper Givskov; Johnson, Shelley A.; Terblanche, John S.Controlled atmosphere treatments using carbon dioxide, oxygen, and/or nitrogen, together with controlled temperature and humidity, form an important method for post-harvest sterilization against insect-infested fruit. However, in insects, the cross tolerance and biochemical interactions between the various stresses of modified gas conditions and low temperature may either elicit or block standard stress responses which can potentiate (or limit) lethal low temperature exposure. Thus, the success of such treatments is sometimes erratic and does not always result in the desired pest mortality. This review focuses on the biochemical modes of action whereby controlled atmospheres affect insects low temperature tolerance, making them more (or occasionally, less) susceptible to cold sterilization. Insights into the integrated biochemical modes of action may be used together with the pests’ low temperature tolerance physiology to determine which treatments may be of value in post-harvest sterilization.
- ItemLearning to starve : impacts of food limitation beyond the stress period(The Company of Biologists, 2017) McCue, Marshall D.; Terblanche, John S.; Benoit, Joshua B.Starvation is common among wild animal populations, and many individuals experience repeated bouts of starvation over the course of their lives. Although much information has been gained through laboratory studies of acute starvation, little is known about how starvation affects an animal once food is again available (i.e. during the refeeding and recovery phases). Many animals exhibit a curious phenomenon – some seem to ‘get better’ at starving following exposure to one or more starvation events – by this we mean that they exhibit potentially adaptive responses, including reduced rates of mass loss, reduced metabolic rates, and lower costs of digestion. During subsequent refeedings they may also exhibit improved digestive efficiency and more rapid mass gain. Importantly, these responses can last until the next starvation bout or even be inherited and expressed in the subsequent generation. Currently, however, little is known about the molecular regulation and physiological mechanisms underlying these changes. Here, we identify areas of research that can fill in the most pressing knowledge gaps. In particular, we highlight how recently refined techniques (e.g. stable isotope tracers, quantitative magnetic resonance and thermal measurement) as well as next-generation sequencing approaches (e.g. RNA-seq, proteomics and holobiome sequencing) can address specific starvation-focused questions. We also describe outstanding unknowns ripe for future research regarding the timing and severity of starvation, and concerning the persistence of these responses and their interactions with other ecological stressors.
- ItemThe metabolic costs of sexual signalling in the chirping katydid Plangia graminea (Serville) (Orthoptera: Tettigoniidae) are context dependent : cumulative costs add up fast(The Company of Biologists, 2017) Doubell, Marcee; Grant, Paul B. C.; Esterhuizen, Nanike; Bazelet, Corinna S.; Addison, Pia; Terblanche, John S.Katydids produce acoustic signals via stridulation, which they use to attract conspecific females for mating. However, direct estimates of the metabolic costs of calling to date have produced diverse cost estimates and are limited to only a handful of insect species. Therefore, in this study, we investigated the metabolic cost of calling in an unstudied sub-Saharan katydid, Plangia graminea. Using wild-caught animals, we measured katydid metabolic rate using standard flow-through respirometry while simultaneously recording the number of calls produced. Overall, the metabolic rate during calling in P. graminea males was 60% higher than the resting metabolic rate (0.443±0.056 versus 0.279±0.028 ml CO₂ h⁻ ¹ g⁻ ¹), although this was highly variable among individuals. Although individual call costs were relatively inexpensive (ranging from 0.02 to 5.4% increase in metabolic rate per call), the individuals with cheaper calls called more often and for longer than those with expensive calls, resulting in the former group having significantly greater cumulative costs over a standard amount of time (9.5 h). However, the metabolic costs of calling are context dependent because the amount of time spent calling greatly influenced these costs in our trials. A power law function described this relationship between cumulative cost (y) and percentage increase per call (x) (y=130.21x⁻¹˙⁰⁶⁸, R2=0.858). The choice of metric employed for estimating energy costs (i.e. how costs are expressed) also affects the outcome and any interpretation of costs of sexual signalling. For example, the absolute, relative and cumulative metabolic costs of calling yielded strongly divergent estimates, and any fitness implications depend on the organism's energy budget and the potential trade-offs in allocation of resources that are made as a direct consequence of increased calling effort.
- ItemOxygen safety margins set thermal limits in an insect model system(The Company of Biologists, 2015-03) Boardman, Leigh; Terblanche, John S.A mismatch between oxygen availability and metabolic demand may constrain thermal tolerance. While considerable support for this idea has been found in marine organisms, results from insects are equivocal and raise the possibility that mode of gas exchange, oxygen safety margins and the physico-chemical properties of the gas medium influence heat tolerance estimates. Here, we examined critical thermal maximum (CTmax) and aerobic scope under altered oxygen supply and in two life stages that varied in metabolic demand in Bombyx mori (Lepidoptera: Bombycidae). We also systematically examined the influence of changes in gas properties on CTmax. Larvae have a lower oxygen safety margin (higher critical oxygen partial pressure at which metabolism is suppressed relative to metabolic demand) and significantly higher CTmax under normoxia than pupae (53°C vs 50°C). Larvae, but not pupae, were oxygen limited with hypoxia (2.5 kPa) decreasing CTmax significantly from 53 to 51°C. Humidifying hypoxic air relieved the oxygen limitation effect on CTmax in larvae, whereas variation in other gas properties did not affect CTmax. Our data suggest that oxygen safety margins set thermal limits in air-breathing invertebrates and the magnitude of this effect potentially reconciles differences in oxygen limitation effects on thermal tolerance found among diverse taxa to date.
- ItemPhysiological mechanisms of dehydration tolerance contribute to the invasion potential of ceratitis capitata (Wiedemann) (Diptera: Tephritidae) relative to its less widely distributed congeners(BioMed Central, 2016) Weldon, Christopher W.; Boardman, Leigh; Marlin, Danica; Terblanche, John S.Background: The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is a highly invasive species now with an almost cosmopolitan distribution. Two other damaging, polyphagous and closely-related species, the marula fruit fly, Ceratitis cosyra (Walker), and the Natal fly, Ceratitis rosa Karsch, are not established outside of sub-Saharan Africa. In this study, adult water balance traits and nutritional body composition were measured in all three species at different temperatures and levels of relative humidity to determine whether tolerance of water stress may partially explain their distribution. Results: Adult C. capitata exhibited higher desiccation resistance than C. rosa but not C. cosyra. Desiccation resistance of C. capitata was associated with lower rates of water loss under hot and dry conditions, higher dehydration tolerance, and higher lipid reserves that were catabolised during water stress. In comparison with C. capitata, C. cosyra and C. rosa lost water at significantly higher rates under hot, dry conditions, and did not catabolise lipids or other sources of metabolic water during water stress. Conclusions: These results suggest that adult physiological traits permitting higher tolerance of water stress play a role in the success of C. capitata, particularly relative to C. rosa. The distribution of C. cosyra is likely determined by the interaction of temperature with water stress, as well as the availability of suitable hosts for larval development.
- ItemPredictable patterns of trait mismatches between interacting plants and insects(BioMed Central, 2010-07) Anderson, Bruce; Terblanche, John S.; Ellis, Allan G.Background: There are few predictions about the directionality or extent of morphological trait (mis)matches between interacting organisms. We review and analyse studies on morphological trait complementarity (e.g. floral tube length versus insect mouthpart length) at the population and species level. Results: Plants have consistently more exaggerated morphological traits than insects at high trait magnitudes and in some cases less exaggerated traits than insects at smaller trait magnitudes. This result held at the population level, as well as for phylogenetically adjusted analyses at the species-level and for both pollination and host-parasite interactions, perhaps suggesting a general pattern. Across communities, the degree of trait mismatch between one specialist plant and its more generalized pollinator was related to the level of pollinator specialization at each site; the observed pattern supports the "life-dinner principle" of selection acting more strongly on species with more at stake in the interaction. Similarly, plant mating system also affected the degree of trait correspondence because selfing reduces the reliance on pollinators and is analogous to pollination generalization. Conclusions: Our analyses suggest that there are predictable "winners" and "losers" of evolutionary arms races and the results of this study highlight the fact that breeding system and the degree of specialization can influence the outcome.
- ItemThe speed and metabolic cost of digesting a blood meal depends on temperature in a major disease vector(The Company of Biologists Ltd, 2016) McCue, Marshall D.; Boardman, Leigh; Clusella-Trullas, Susana; Kleynhans, Elsje; Terblanche, John S.The energetics of processing a meal is crucial for understanding energy budgets of animals in the wild. Given that digestion and its associated costs may be dependent on environmental conditions, it is necessary to obtain a better understanding of these costs under diverse conditions and identify resulting behavioural or physiological trade-offs. This study examines the speed and metabolic costs – in cumulative, absolute and relative energetic terms – of processing a bloodmeal for a major zoonotic disease vector, the tsetse fly Glossina brevipalpis, across a range of ecologically relevant temperatures (25, 30 and 35°C). Respirometry showed that flies used less energy digesting meals faster at higher temperatures but that their starvation tolerance was reduced, supporting the prediction that warmer temperatures are optimal for bloodmeal digestion while cooler temperatures should be preferred for unfed or post-absorptive flies. 13C-Breath testing revealed that the flies oxidized dietary glucose and amino acids within the first couple of hours of feeding and overall oxidized more dietary nutrients at the cooler temperatures, supporting the premise that warmer digestion temperatures are preferred because they maximize speed and minimize costs. An independent test of these predictions using a thermal gradient confirmed that recently fed flies selected warmer temperatures and then selected cooler temperatures as they became post-absorptive, presumably to maximize starvation resistance. Collectively these results suggest there are at least two thermal optima in a given population at any time and flies switch dynamically between optima throughout feeding cycles.
- ItemThermal limits of wild and laboratory strains of two African malaria vector species, Anopheles arabiensis and Anopheles funestus(BioMed Central, 2012-07) Lyons, Candice L.; Coetzee, Maureen; Terblanche, John S.; Chown, Steven L.Abstract Background Malaria affects large parts of the developing world and is responsible for almost 800,000 deaths annually. As climates change, concerns have arisen as to how this vector-borne disease will be impacted by changing rainfall patterns and warming temperatures. Despite the importance and controversy surrounding the impact of climate change on the potential spread of this disease, little information exists on the tolerances of several of the vector species themselves. Methods Using a ramping protocol (to assess critical thermal limits - CT) and plunge protocol (to assess lethal temperature limits - LT) information on the thermal tolerance of two of Africa’s important malaria vectors, Anopheles arabiensis and Anopheles funestus was collected. The effects of age, thermal acclimation treatment, sex and strain (laboratory versus wild adults) were investigated for CT determinations for each species. The effects of age and sex for adults and life stage (larvae, pupae, adults) were investigated for LT determinations. Results In both species, females are more tolerant to low and high temperatures than males; larvae and pupae have higher upper lethal limits than do adults. Thermal acclimation of adults has large effects in some instances but small effects in others. Younger adults tend to be more tolerant of low or high temperatures than older age groups. Long-standing laboratory colonies are sufficiently similar in thermal tolerance to field-collected animals to provide reasonable surrogates when making inferences about wild population responses. Differences between these two vectors in their thermal tolerances, especially in larvae and pupae, are plausibly a consequence of different habitat utilization. Conclusions Limited plasticity is characteristic of the adults of these vector species relative to others examined to date, suggesting limited scope for within-generation change in thermal tolerance. These findings and the greater tolerance of females to thermal extremes may have significant implications for future malaria transmission, especially in areas of current seasonal transmission and in areas on the boundaries of current vector distribution.
- ItemThermal tolerance in a south-east African population of the tsetse fly Glossina pallidipes (Diptera, Glossinidae) : implications for forecasting climate change impacts(2008-01) Terblanche, John S.; Clusella-Trullas, Susana; Deere, Jacques A.; Chown, Steven L.For tsetse (Glossina spp.), the vectors of human and animal trypanosomiases, the physiological mechanisms linking variation in population dynamics with changing weather conditions have not been well established. Here, we investigate high- and low-temperature tolerance in terms of activity limits and survival in a natural population of adult Glossina pallidipes from eastern Zambia. Due to increased interest in chilling flies for handling and aerial dispersal in sterile insect technique control and eradication programmes, we also provide further detailed investigation of low-temperature responses. In wild-caught G. pallidipes, the probability of survival for 50% of the population at low-temperatures was at 3.7, 8.9 and 9.6 °C (95% CIs: ±1.5 °C) for 1, 2 and 3 h treatments, respectively. At high temperatures, it was estimated that treatments at 37.9, 36.2 and 35.6 °C (95% CIs: ±0.5 °C) would yield 50% population survival for 1, 2 and 3 h, respectively. Significant effects of time and temperature were detected at both temperature extremes (GLZ, p<0.05 in all cases) although a time-temperature interaction was only detected at high temperatures (p<0.0001). We synthesized data from four other Kenyan populations and found that upper critical thermal limits showed little variation among populations and laboratory treatments (range: 43.9-45.0 °C; 0.25 °C/min heating rate), although reduction to more ecologically relevant heating rates (0.06 °C/min) reduce these values significantly from ∼44.4 to 40.6 °C, thereby providing a causal explanation for why tsetse distribution may be high-temperature limited. By contrast, low-temperature limits showed substantial variation among populations and acclimation treatments (range: 4.5-13.8 °C; 0.25 °C/min), indicating high levels of inter-population variability. Ecologically relevant cooling rates (0.06 °C/min) suggest tsetses are likely to experience chill coma temperatures under natural conditions (∼20-21 °C). The results from acute hardening experiments in the Zambian population demonstrate limited ability to improve low-temperature tolerance over short (hourly) timescales after non-lethal pre-treatments. In flies which survived chilling, recovery times were non-linear with plateaus between 2-6 and 8-12 °C. Survival times ranged between 4 and 36 h and did not vary between flies which had undergone chill coma by comparison with flies which had not, even after factoring body condition into the analyses (p>0.5 in all cases). However, flies with low chill coma values had the highest body water and fat content, indicating that when energy reserves are depleted, low-temperature tolerance may be compromised. Overall, these results suggest that physiological mechanisms may provide insight into tsetse population dynamics, hence distribution and abundance, and support a general prediction for reduced geographic distribution under future climate warming scenarios. © 2007 Elsevier Ltd. All rights reserved.