How plastic are upper thermal limits? A comparative study in tsetse (family: Glossinidae) and wider Diptera.

Critical thermal maximum (CT max) describes the upper thermal tolerance of an animal where biological functions start to fail. A period of acclimation can enhance CT max through plasticity, potentially buffering animals from extreme temperatures caused by climate change. Basal and acclimated CT max vary within and between species and may be explained by traits related to thermal physiology, such as body size and sex. Differences in CT max have not been established among species of tsetse fly (Glossina spp.), vectors of animal and human African trypanosomiasis. Here, we investigated basal CT max and its plasticity for five tsetse species following adult acclimation at constant 25 or 30 °C for five days. We then set our findings in context using a meta-analysis on 33 species of Diptera. We find that, of the five tsetse species considered, only Glossina palpalis gambiensis and Glossina brevipalpis exhibited plasticity of CT max , with an increase of 0.12 °C and 0.10 °C per 1 °C acclimation respectively. Within some species, higher basal CT max values were associated with larger body size and being female, while variation in plasticity (i.e., response to the acclimation temperature) could not be explained by sex or size. Our broader meta-analysis across Diptera revealed overall CT max plasticity of 0.06 °C per 1 °C acclimation, versus a similar 0.05 °C mean increase in tsetse. In contrast, there was greater CT max plasticity in males compared to females in Diptera. Our study highlights that CT max and its plasticity varies even among closely related species. Broader patterns across groups are not always reflected at a finer resolution; we thus emphasise the need for detailed experimental studies across a wide range of insect species to capture their capacity to cope with rapidly warming temperatures. • Thermal tolerance can inform how disease vectors will respond to climate change. • We compare the plasticity of critical thermal maximums (CT max) among five tsetse species. • Acclimation increased CT max in two of five species. • Larger body size and being female was related to higher basal CT max values. • Weak plasticity and small body size is likely to hinder tsetse in a warming world. [ABSTRACT FROM AUTHOR]