A protocol for analysing thermal stress in insects using infrared thermography. (February 2016)

• Record Type: Journal Article
• Authors: Gallego, Belén; Verdú, José R.; Carrascal, Luis M.; Lobo, Jorge M.
• Is Part Of: Journal of thermal biology. Volume 56(2015)
• Page Start: 113
• Page End: 121
• Publication Date: 2016-02
• Subjects: CCR Chill coma range -- CCRR Chill coma recovery range -- CCRT Chill coma recovery temperature -- CCT Chill coma temperature -- CR Cooling rate -- CTmax Critical thermal maximum -- HCR Heat coma thermal range -- HR Heating rate -- HRT Heat regulation temperature -- HSR Heat stress range -- iHCR Differences in the area under the response curves of the model and living individuals for the heat coma range (HCR) -- iHSR Difference in the area under the response curves of the model and living individuals for the heat stress range (HSR) -- iSAR Differences in the area under the response curves of the model and living individuals for the supra-optimal activity range (SAR) -- iTR Differences in the area under the response curves of the model and living individuals for the thermoregulation range (TR) -- LLT Lower lethal temperature -- OAR Optimal activity range -- PLSR Partial least squares regression analysis -- rHCR Rate of increase in the body temperature per unit of time during the heat coma range (HCR) -- rHSR Rate of increase in the body temperature per unit of time during the heat stress range (HSR) -- rSAR Rate of increase in the body temperature per unit of time during the supra-optimal activity range (SAR) -- rTR Rate of increase in the body temperature per unit of time during the thermoregulation range (TR) -- SAR Supra-optimal activity range -- SCP Temperature at which individuals reached their supercooling point -- SST Start stress temperature -- TR Thermoregulation range -- ULT Upper lethal temperature; Body temperature -- Thermal limits -- Thermoregulation -- Partial least squares -- Jekelius; Thermobiology -- Periodicals; Temperature -- Periodicals; Biology -- Periodicals; Thermobiologie -- Périodiques; Thermobiology; Periodicals; 571.46
• DOI: 10.1016/j.jtherbio.2015.12.006
• Languages: English
• ISSNs: 0306-4565

Abstract

Abstract: The study of insect responses to thermal stress has involved a variety of protocols and methodologies that hamper the ability to compare results between studies. For that reason, the development of a protocol to standardize thermal assays is necessary. In this sense, infrared thermography solves some of the problems allowing us to take continuous temperature measurements without handling the individuals, an important fact in cold-blooded organisms like insects. Here, we present a working protocol based on infrared thermography to estimate both cold and heat thermal stress in insects. We analyse both the change in the body temperature of individuals and their behavioural response. In addition, we used partial least squares regression for the statistical analysis of our data, a technique that solves the problem of having a large number of variables and few individuals, allowing us to work with rare or endemic species. To test our protocol, we chose two species of congeneric, narrowly distributed dung beetles that are endemic to the southeastern part of the Iberian Peninsula. With our protocol we have obtained five variables in the response to cold and twelve in the response to heat. With this methodology we discriminate between the two flightless species of Jekelius through their thermal response. In response to cold, Jekelius hernandezi showed a higher rate of cooling and reached higher temperatures of stupor and haemolymph freezing than Jekelius punctatolineatus . Both species displayed similar thermoregulation ranges before reaching lethal body temperature with heat stress. Overall, we have demonstrated that infrared thermography is a suitable method to assess insect thermal responses with a high degree of sensitivity, allowing for the discrimination between closely related species. Highlights: A protocol to obtain thermal variables is presented using infrared thermography. A high number of variables can be obtained from a low number of insect specimens. Individuals are not necessarily killed. PLS regressions disentangle the effects of these correlated variables. Thermal responses of sympatric and closely related dung beetles are discerned.