Browsing by Author "Clusella-Trullas, Susana"
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- ItemAll-in-one : physics, chemistry and ecology are essential fields to thermal ecologists(International Biogeography Society, 2018) Clusella-Trullas, SusanaThe book clearly targets principles that are essential for understanding the relationship between temperature and organisms and does not represent a book for applications on how to do measurements or complex tasks in thermal ecology. Principles of Thermal Ecology is a guiding book to get a solid knowledge of the building blocks that form the field of thermal ecology and does a brilliant job of achieving this. These building blocks and the relationships between physiology and ecology, as well as concepts that include larger scale patterns of life and diversity, will also be of great value to biogeographers and to wider audiences.
- ItemThe behavior-physiology nexus : behavioral and physiological compensation are relied on to different extents between seasons(University of Chicago Press Journals, 2015) Basson, Christine H.; Clusella-Trullas, SusanaEnvironmental variability occurring at different timescales can significantly reduce performance, resulting in evolutionary fitness costs. Shifts in thermoregulatory behavior, metabolism, and water loss via phenotypic plasticity can compensate for thermal variation, but the relative contribution of each mechanism and how they may influence each other are largely unknown. Here, we take an ecologically relevant experimental approach to dissect these potential responses at two temporal scales: weather transients and seasons. Using acclimation to cold, average, or warm conditions in summer and winter, we measure the direction and magnitude of plasticity of resting metabolic rate (RMR), water loss rate (WLR), and preferred body temperature (Tpref) in the lizard Cordylus oelofseni within and between seasons. In summer, lizards selected lower Tpref when acclimated to warm versus cold but had no plasticity of either RMR or WLR. By contrast, winter lizards showed partial compensation of RMR but no behavioral compensation. Between seasons, both behavioral and physiological shifts took place. By integrating ecological reality into laboratory assays, we demonstrate that behavioral and physiological responses of C. oelofseni can be contrasting, depending on the timescale investigated. Incorporating ecologically relevant scenarios and the plasticity of multiple traits is thus essential when attempting to forecast extinction risk to climate change.
- ItemCritical thermal limits depend on methodological context(Royal Society of Publishing, 2007) Terblanche, John S.; Deere, Jacques A.; Clusella-Trullas, Susana; Janion, Charlene; Chown, Steven L.A full-factorial study of the effects of rates of temperature change and start temperatures was undertaken for both upper and lower critical thermal limits (CTLs) using the tsetse fly, Glossina pallidipes. Results show that rates of temperature change and start temperatures have highly significant effects on CTLs, although the duration of the experiment also has a major effect. Contrary to a widely held expectation, slower rates of temperature change (i.e. longer experimental duration) resulted in poorer thermal tolerance at both high and low temperatures. Thus, across treatments, a negative relationship existed between duration and upper CTL while a positive relationship existed between duration and lower CTL. Most importantly, for predicting tsetse distribution, G. pallidipes suffer loss of function at less severe temperatures under the most ecologically relevant experimental conditions for upper (0.06°C min -1; 35°C start temperature) and lower CTL (0.06°C min -1; 24°C start temperature). This suggests that the functional thermal range of G. pallidipes in the wild may be much narrower than previously suspected, approximately 20-40°C, and highlights their sensitivity to even moderate temperature variation. These effects are explained by limited plasticity of CTLs in this species over short time scales. The results of the present study have broad implications for understanding temperature tolerance in these and other terrestrial arthropods. © 2007 The Royal Society.
- 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.
- ItemThe evolution of critical thermal limits of life on earth(Nature, 2021-02-19) Bennett, Joanne M.; Sunday, Jennifer; Calosi, Piero; Villalobos, Fabricio; Martinez, Brezo; Molina-Venegas, Rafae; Araujo, Miguel B.; Algar, Adam C.; Clusella-Trullas, Susana; Hawkins, Bradford A.; Keith, Sally A.; Kuhn, Ingolf; Rahbek, Carsten; Rodriguez, Laura; Singer, Alexander; Morales-Castilla, Ignacio; Olalla-Tarraga, Miguel AngelUnderstanding how species’ thermal limits have evolved across the tree of life is central to predicting species’ responses to climate change. Here, using experimentally-derived estimates of thermal tolerance limits for over 2000 terrestrial and aquatic species, we show that most of the variation in thermal tolerance can be attributed to a combination of adaptation to current climatic extremes, and the existence of evolutionary ‘attractors’ that reflect either boundaries or optima in thermal tolerance limits. Our results also reveal deep-time climate legacies in ectotherms, whereby orders that originated in cold paleoclimates have presently lower cold tolerance limits than those with warm thermal ancestry. Conversely, heat tolerance appears unrelated to climate ancestry. Cold tolerance has evolved more quickly than heat tolerance in endotherms and ectotherms. If the past tempo of evolution for upper thermal limits continues, adaptive responses in thermal limits will have limited potential to rescue the large majority of species given the unprecedented rate of contemporary climate change.
- ItemFirst finding of the parasitic fungus Hesperomyces virescens (Laboulbeniales) on native and invasive ladybirds (Coleoptera, Coccinellidae) in South Africa(EDP Sciences, 2016) Haelewaters, Danny; Minnaar, Ingrid A.; Clusella-Trullas, SusanaHesperomyces virescens is a fungal ectoparasite (Laboulbeniales) that infects adult ladybirds. Research has recently focused on this parasite due to the discovery of its prevalence on the globally invasive harlequin ladybird Harmonia axyridis and for its potential use in studies of co-evolution and pathogen spread. We collected adults from ten species of ladybirds in the Western Cape Province, South Africa, and screened for the presence of H. virescens. Infections with H. virescens were found in the samples of two species, H. axyridis and the native Cheilomenes propinqua. This marks the first record of H. virescens on H. axyridis from the African continent and the first record on Cheilomenes worldwide.
- ItemGlobTherm, a global database on thermal tolerances for aquatic and terrestrial organisms(Nature Research, 2018-03-13) Bennett, Joanne M.; Calosi, Piero; Clusella-Trullas, Susana; Martinez, Brezo; Sunday, Jennifer; Algar, Adam C.; Araujo, Miguel B.; Hawkins, Bradford A.; Keith, Sally; Kuhn, Ingolf; Rahbek, Carsten; Rodriguez, Laura; Singer, Alexander; Villalobos, Fabricio; Olalla-Tarraga, Miguel Angel; Morales-Castilla, IgnacioHow climate affects species distributions is a longstanding question receiving renewed interest owing to the need to predict the impacts of global warming on biodiversity. Is climate change forcing species to live near their critical thermal limits? Are these limits likely to change through natural selection? These and other important questions can be addressed with models relating geographical distributions of species with climate data, but inferences made with these models are highly contingent on non-climatic factors such as biotic interactions. Improved understanding of climate change effects on species will require extensive analysis of thermal physiological traits, but such data are both scarce and scattered. To overcome current limitations, we created the GlobTherm database. The database contains experimentally derived species’ thermal tolerance data currently comprising over 2,000 species of terrestrial, freshwater, intertidal and marine multicellular algae, plants, fungi, and animals. The GlobTherm database will be maintained and curated by iDiv with the aim to keep expanding it, and enable further investigations on the effects of climate on the distribution of life on Earth.
- ItemHigh metabolic and water-loss rates in caterpillar aggregations : evidence against the resource-conservation hypothesis(Company of Biologists, 2013) Schoombie, Ruben E.; Boardman, Leigh; Groenewald, Berlize; Glazier, Douglas S.; Van Daalen, Corne E.; Clusella-Trullas, Susana; Terblanche, John S.Several hypotheses have been proposed for explaining animal aggregation, including energy or water conservation. However, these physiological hypotheses have not been well investigated. Here, we report the effects of aggregation on metabolic (Embedded Image) and evaporative water-loss rates (Embedded Image) of the gregarious caterpillar Eutricha capensis, by comparing individuals and groups of individuals (N=10–100). Contrary to findings from previous physiological studies, we did not find an advantage to aggregation: unexpectedly, Embedded Image and Embedded Image did not decrease with increasing group size. Embedded Image and Embedded Image generally remained constant or increased in larger groups relative to individuals. The amount of water lost per unit of CO2 exchanged (Embedded Image: Embedded Image ratio) showed a marked increase in grouped caterpillars, particularly in larger groups. Other benefits of aggregation (e.g. reduced predation or increased growth rates) likely outweigh these potential costs, because individuals of E. capensis aggregate voluntarily despite no obvious energetic or hygric advantage, and other potentially confounding group effects (e.g. increased thermoregulatory advantage or whole-animal activity) are inconsequential. The results of this study provide an important exception to physiological studies reporting enhanced energy or water conservation in animal groups.
- ItemImpacts of invasive plants on animal diversity in South Africa : a synthesis(AOSIS Publishing, 2017) Clusella-Trullas, Susana; Garcia, Raquel A.Background: Increasing numbers of invasive alien plant (IAP) species are establishing around the globe and can have negative effects on resident animal species function and diversity. These impacts depend on a variety of factors, including the extent of invasion, the region and the taxonomic group affected. These context dependencies make extrapolations of IAP impacts on resident biota from region to region a substantial challenge. Objectives: Here, we synthesised data from studies that have examined the effects of IAPs on animal diversity in South Africa. Our focus is on ectothermic organisms (reptiles, amphibians and invertebrates). Method: We sourced relevant articles using keywords relating to (1) the effects of IAPs on species diversity (abundance, richness and composition), (2) the IAP and (3) the native ectotherm. We extracted the taxonomic and spatial coverage of IAPs and affected native species and assessed the extent of information given on potential mechanisms driving IAP impacts. Results: Across the 42 studies, IAPs had a decreasing or neutral effect on native animal abundance and richness and significantly changed species composition. This review highlighted the paucity of studies and the research deficits in taxonomic and geographic coverage and in the mechanisms underlying IAP impacts on ectotherms. Conclusion: By assessing the status of knowledge regarding the impacts of IAPs on resident animal species in South Africa, this study identifies information gaps and research priorities at the country level with a view to informing monitoring and conservation efforts, such as alien plant removal and control programmes, and ensuring that endemic terrestrial animal diversity is maintained.
- ItemInvestigating onychophoran gas exchange and water balance as a means to inform current controversies in arthropod physiology(The Company of Biologists, 2008-08) Clusella-Trullas, Susana; Chown, Steven L.Several controversies currently dominate the fields of arthropod metabolic rate, gas exchange and water balance, including the extent to which modulation of gas exchange reduces water loss, the origins of discontinuous gas exchange, the relationship between metabolic rate and life-history strategies, and the causes of Palaeozoic gigantism. In all of these areas, repeated calls have been made for the investigation of groups that might most inform the debates, especially of taxa in key phylogenetic positions. Here we respond to this call by investigating metabolic rate, respiratory water loss and critical oxygen partial pressure (Pc) in the onychophoran Peripatopsis capensis, a member of a group basal to the arthropods, and by synthesizing the available data on the Onychophora. The rate of carbon dioxide release (V̇ CO2) at 20°C in P. capensis is 0.043 ml CO2 h -1, in keeping with other onychophoran species; suggesting that low metabolic rates in some arthropod groups are derived. Continuous gas exchange suggests that more complex gas exchange patterns are also derived. Total water loss in P. capensis is 57 mg H2O h-1 at 20°C, similar to modern estimates for another onychophoran species. High relative respiratory water loss rates (∼34%; estimated using a regression technique) suggest that the basal condition in arthropods may be a high respiratory water loss rate. Relatively high Pc values (5-10% O2) suggest that substantial safety margins in insects are also a derived condition. Curling behaviour in P. capensis appears to be a strategy to lower energetic costs when resting, and the concomitant depression of water loss is a proximate consequence of this behaviour.
- ItemNiche shift and resource supplementation facilitate an amphibian range expansion(Wiley, 2019) Davies, Sarah J.; Hill, Matthew P.; McGeoch, Melodie A.; Clusella-Trullas, SusanaAim: To determine whether recent range expansion of small- bodied arboreal frogs, Hyperolius marmoratus Rapp, is accompanied by changes in species–environment re- lationships and whether its historical range was constrained by climate, availability of water bodies or topographic variables. We test if artificial water bodies in the novel range have facilitated niche shift by increasing available habitats for frog establishment. Location: Western Cape Province, South Africa, with reference to the broader spe- cies range in southeastern Africa. Methods: We build species distribution models using occurrence data from the his- torical and novel ranges and reciprocally project them to highlight areas of putative niche change. We test for niche shift through ordination- based approaches to disen- tangle how species–environment relationships may have altered and whether climate or landscape features (artificial water bodies and topography) are more strongly as- sociated with the identified change. We further decompose niche change into areas of expansion and unfilling to quantify niche shift and describe potential future spread. Results: We observed niche expansion into novel environmental space, with 21% of niche space in the invaded range composed of environments that were not occupied in the native range. We also observed 16% niche unfilling, signifying range disequilib- rium and potential for further spread. Mean annual precipitation and proximity to water bodies were more influential in models constructed in the novel range than in historical or combined range models, suggesting that presence of artificial water bodies in the landscape ameliorates novel range conditions. Together, these metrics suggest that range expansion may be ongoing based on climate and water body availability. Main conclusions: Our analyses identify a realised niche shift that has allowed painted reed frogs to occupy drier and more thermally variable habitats in their novel (invaded) range. This shift may be mediated by artificial water bodies that provide additional buffered habitats, a key resource supplement for these small- bodied tropi- cal frogs.
- ItemSex-specific effects of wind on the flight decisions of a sexually dimorphic soaring bird(John Wiley & Sons Ltd., 2020) Clay, Thomas A.; Joo, Rocio; Weimerskirch, Henri; Phillips, Richard A.; Den Ouden, Olivier; Basille, Mathieu; Clusella-Trullas, Susana; Assink, Jelle D.; Patrick, Samantha C.In a highly dynamic airspace, flying animals are predicted to adjust foraging behaviour to variable wind conditions to minimize movement costs. Sexual size dimorphism is widespread in wild animal populations, and for large soaring birds which rely on favourable winds for energy-efficient flight, differences in morphology, wing loading and associated flight capabilities may lead males and females to respond differently to wind. However, the interaction between wind and sex has not been comprehensively tested. We investigated, in a large sexually dimorphic seabird which predominantly uses dynamic soaring flight, whether flight decisions are modulated to variation in winds over extended foraging trips, and whether males and females differ. Using GPS loggers we tracked 385 incubation foraging trips of wandering albatrossesDiomedea exulans, for which males arec. 20% larger than females, from two major populations (Crozet and South Georgia). Hidden Markov models were used to characterize behavioural states-directed flight, area-restricted search (ARS) and resting-and model the probability of transitioning between states in response to wind speed and relative direction, and sex. Wind speed and relative direction were important predictors of state transitioning. Birds were much more likely to take off (i.e. switch from rest to flight) in stronger headwinds, and as wind speeds increased, to be in directed flight rather than ARS. Males from Crozet but not South Georgia experienced stronger winds than females, and males from both populations were more likely to take-off in windier conditions. Albatrosses appear to deploy an energy-saving strategy by modulating taking-off, their most energetically expensive behaviour, to favourable wind conditions. The behaviour of males, which have higher wing loading requiring faster speeds for gliding flight, was influenced to a greater degree by wind than females. As such, our results indicate that variation in flight performance drives sex differences in time-activity budgets and may lead the sexes to exploit regions with different wind regimes.
- ItemSpatial scale, topography and thermoregulatory behaviour interact when modelling species’ thermal niches(Nordic Society Oikos, 2019) Barton, Madeleine G.; Clusella-Trullas, Susana; Terblanche, John S.The spatial scale at which climate and species’ occupancy data are gathered, and the resolution at which ecological models are run, can strongly influence predictions of species performance and distributions. Running model simulations at coarse rather than fine spatial resolutions, for example, can determine if a model accurately predicts the distribution of a species. The impacts of spatial scale on a model’s accuracy are particularly pronounced across mountainous terrain. Understanding how these discrepancies arise requires a modelling approach in which the underlying processes that determine a species’ distribution are explicitly described. Here we use a process-based model to explore how spatial resolution, topography and behaviour alter predictions of a species thermal niche, which in turn constrains its survival and geographic distribution. The model incorporates biophysical equations to predict the operative temperature (Te), thermal-dependent performance and survival of a typical insect, with a complex life-cycle, in its microclimate. We run this model with geographic data from a mountainous terrain in South Africa using climate data at three spatial resolutions. We also explore how behavioural thermoregulation affects predictions of a species performance and survival by allowing the animal to select the optimum thermal location within each coarse-grid cell. At the regional level, coarse-resolution models predicted lower Te at low elevations and higher Te at high elevations than models run at fine resolutions. These differences were more prominent on steep, north-facing slopes. The discrepancies in Te in turn affected estimates of the species thermal niche. The modelling framework revealed how spatial resolution and topography influence predictions of species distribution models, including the potential impacts of climate change. These systematic biases must be accounted for when interpreting the outputs of future modelling studies, particularly when species distributions are predicted to shift from uniform to topographically heterogeneous landscapes.
- 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 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.