- ItemUsing µCT in live larvae of a large wood-boring beetle to study tracheal oxygen supply during development(2021) Lehmann, P.; Javal, M.; Du Plessis, A.; Terblanche, J.S.How respiratory structures vary with, or are constrained by, an animal's environment is of central importance to diverse evolutionary and comparative physiology hypotheses. To date, quantifying insect respiratory structures and their variation has remained challenging due to their microscopic size, hence only a handful of species have been examined. Several methods for imaging insect respiratory systems are available, in many cases however, the analytical process is lethal, destructive, time consuming and labour intensive. Here, we explore and test a different approach to measuring tracheal volume using X-ray micro-tomography (mu CT) scanning (at 15 mu m resolution) on living, sedated larvae of the cerambycid beetle Cacosceles newmannii across a range of body sizes at two points in development. We provide novel data on resistance of the larvae to the radiation dose absorbed during mu CT scanning, repeatability of imaging analyses both within and between time-points and, structural tracheal trait differences provided by different image segmentation methods. By comparing how tracheal dimension (reflecting metabolic supply) and basal metabolic rate (reflecting metabolic demand) increase with mass, we show that tracheal oxygen supply capacity increases during development at a comparable, or even higher rate than metabolic demand. Given that abundant gas delivery capacity in the insect respiratory system may be costly (due to e.g. oxygen toxicity or space restrictions), there are probably balancing factors requiring such a capacity that are not linked to direct tissue oxygen demand and that have not been thoroughly elucidated to date, including CO2 efflux. Our study provides methodological insights and novel biological data on key issues in rapidly quantifying insect respiratory anatomy on live insects.
- ItemDNA barcoding for bio-surveillance of emerging pests and species identification in Afrotropical Prioninae (Coleoptera, Cerambycidae)(2021) Javal, M.; Terblanche, J.S.; Conlong, D.E.; Delahaye, N.; Grobbelaar, E.; Benoit, L.; Lopez-Vaamonde, C.; Haran, J.M.DNA barcoding has been succesfully used for bio-surveillance of forest and agricultural pests in temperate areas, but has few applications in the tropics and particulary in Africa. Cacosceles newmannii (Coleoptera: Cerambycidae) is a Prioninae species that is locally causing extensive damage in commercially-grown sugarcane in the KwaZulu-Natal Province in South Africa. Due to the risk of spread of this species to the rest of southern Africa and to other sugarcane growing regions, clear and easy identification of this pest is critical for monitoring and for phytosanitary services. The genus Cacosceles Newman, 1838 includes four species, most being very similar in morphology. The damaging stage of the species is the larva, which is inherently difficult to distinguish morphologically from other Cerambycidae species. A tool for rapid and reliable identification of this species was needed by plant protection and quarantine agencies to monitor its potential abundance and spread. Here, we provide newly-generated barcodes for C. newmannii that can be used to reliably identify any life stage, even by non-trained taxonomists. In addition, we compiled a curated DNA barcoding reference library for 70 specimens of 20 named species of Afrotropical Prioninae to evaluate DNA barcoding as a valid tool to identify them. We also assessed the level of deeply conspecific mitochondrial lineages. Sequences were assigned to 42 different Barcode Index Numbers (BINs), 28 of which were new to BOLD. Out of the 20 named species barcoded, 11 (52.4%) had their own unique Barcode Index Number (BIN). Eight species (38.1%) showed multiple BINs with no morphological differentiation. Amongst them, C. newmannii showed two highly divergent genetic clusters which co-occur sympatrically, but further investigation is required to test whether they could represent new cryptic species.
- ItemLow-temperature physiology of climatically distinct south African populations of the biological control agent Neochetina eichhorniae(2021) Rogers, D.J.; Terblanche, J.S.; Owen, C.A.1. Neochetina eichhorniae is the most widely established biocontrol agent on water hyacinth populations around South Africa. However, some N. eichhorniae populations have failed to adequately control their host population, specifically those exposed to cold conditions. 2. The aim of this study was to determine whether two climatically distinct populations of N. eichhorniae in South Africa differ in their low-temperature physiology, which tests whether local-climate adaptation has occurred. 3. We estimated weevil CTmin, LLT50, SCP, and SCP mortality using standard approaches. Contrary to expectation based on climatic thermal profiles at the two sites, weevils from the warm locality ((mean ± SE) CTmin = 5.0 °C ± 0.2, LLT50 = −11.3 °C ± 0.03, SCP = −15.8 °C ± 0.6) were able to maintain activity and tolerate colder temperatures than the weevils from the colder site (CTmin = 6.0 °C ± 0.5, LLT50 = −10.1 °C ± 0.1, SCP = −12.9 °C ± 0.8). 4. These contradictory outcomes are likely explained by the poor nutrient quality of the plants at the cold site, driving low-temperature performance variation that overrode any macroclimate variation among sites. The cold site weevils may also have adapted to survive wide-temperature variability, rather than perform well under very cold conditions. In contrast, the mass-reared population of insects from the warm site has likely adapted to the consistent conditions that they experience over many years in confinement.
- ItemAcross-stage consequences of thermal stress have trait-specific effects and limited fitness costs in the harlequin ladybird, Harmonia axyridis.(2020) Shinner, R.; Terblanche, J.S.; Clusella-Trullas, S.The fitness consequences of thermal plasticity of functional traits of insects, and the life stages at which these responses manifest, remain a subject of much debate. Here, we examine whether a short-term exposure to cold, medium or warm fluctuating temperature regimes during development (larval or adult) affects adult performance, thermal tolerance and fitness of the globally invasive harlequin ladybird Harmonia axyridis. We found plastic responses of a metric of heat stress resistance—critical thermal maximum—and of preferred body temperature after adult temperature exposure, but not in other traits measured. By contrast, exposure of larval stages resulted in plasticity of adult walking performance (height and breadth of the curve) but not tolerance or preference. We found distinct fitness responses between larval and adult treatments, but a composite fitness index revealed negligible effects on reproductive output. These results suggest that the drivers underlying the plasticity of temperature tolerance and temperature selection are different to those shaping the plasticity of walking speed. By testing specific predictions based on current theory of developmental and reversible plasticity, this study contributes novel data to plastic responses of behaviour, stress resistance and fitness to temperature exposure across life stages and thus, provides insights to the broader evolutionary and ecological significance of these responses.
- ItemWater deprivation drives intraspecific variability in lizard heat tolerance(2020) Herrando-Perez, S.; Belliure, J.; Ferri-Yanez, F.; van den Burg, M.P.; Beukema, W.; Araujo, M.B.; Terblanche, J.S.; Vieites, D.R.Quantifying intraspecific variation in heat tolerance is critical to understand how species respond to climate change. In a previous study, we recorded variability in critical thermal maxima (CTmax) by 3 degrees C among populations of small Iberian lizard species, which could substantially influence predictions of climate-driven activity restriction. Here, we undertake experiments to examine whether we could reproduce similar levels of heat-tolerance variability in response to water deficit. We hypothesized that deprivation of drinking water should increase variability in CTmax between populations more than deprivation of food under the theoretical expectation that the variation of the more limiting resource must trigger stronger variation in physiological performance. We measured CTmax after manipulating availability of live prey and drinking water in two populations of an arid and a mesic lizard species from the Iberian Peninsula. We quantified a mean CTmax across all studied lizards of 44.2 degrees C +/- 0.2 SE for the arid species and 41.7 degrees C +/- 0.3 SE for the mesic species. Using multimodel inference, we found that water deprivation (combined with food supply) caused population differences in CTmax by 3 to 4 degrees C which were two to three times wider than population differences due to food deprivation (combined with water supply) or to food and water provision. To highlight the need for more thermo-hydroregulatory research, we examined bias in research effort towards thermal versus hydric environmental effects on heat tolerance through a systematic literature review. We show that environmental temperature has been used five times more frequently than precipitation in ecological studies of heat tolerance of terrestrial species. Studies linking thermal tolerance of ectotherms to the interplay of air temperature and water availability are needed in the face of projected increases in aridity and drought in the 21st century, because the balance of body temperature and water resources are functionally interlinked.