Ectotherms, such as insects, are susceptible to climate changes because their body temperature is not physiologically regulated. Forecasts indicate a worldwide temperature rise of 1.4-6 °C by 2100, and an increase in heatwave frequency is expected. This study investigated the effects of constant temperatures (CT; 27, 34, 39, 40 and 41 °C) and fluctuating temperature (FT; 27/34 °C: 12/12 h) on the survival, metabolic rate, locomotor activity, gas exchange pattern, heat loss and water content of the male Jamaican field cricket, Gryllus assimilis (Fabricius, 1775) (Orthoptera: Gryllidae). It was found that 39 °C was the estimated lethal temperature for 50% of the population and that 41 °C was considered the thermal limit, causing 100% mortality in 96 h. Furthermore, FT caused slightly higher mortality (8.9 ± 3.8%) than CT27 (0%) and CT34 (1.43 ± 1.43%). FT caused a greater increase in the metabolic rate and locomotor activity than CT27. It was found that G. assimilis males had a continuous gas exchange as a standard at CT27; however, CT34 changed the gas exchange pattern from continuous to cyclic in 27% of crickets. FT decreased heat loss in crickets more than CT34; however, no significant differences were found in locomotor activity and metabolic rate. In addition, no significant differences between CT27, CT34 and FT were observed in terms of water content, thus suggesting no difference in water loss. Thus, it is suggested that FT, despite involving a modest warming, increased the climate sensitivity of G. assimilis males and led to a change in their optimum temperature, pushing it beyond its usual thermal limits. However, higher mortality in FT compared to CT27 (control) and CT34 must be interpreted with caution. In addition, the risk of higher mortality of G. assimilis males is predicted, especially in South America, where this cricket is widely distributed.
Keywords: Climate change; Evaporative cool; Heat wave; Locomotor activity; VCO(2).
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