Thermal performance of the Chagas disease vector, Triatoma infestans, under thermal variability

Vector-borne diseases (VBD) are particularly susceptible to climate change because most of the diseases' vectors are ectotherms, which themselves are susceptible to thermal changes. The Chagas disease is one neglected tropical disease caused by the protozoan parasite, Trypanosoma cruzi. One of the main vectors of the Chagas disease in South America is Triatoma infestans, a species traditionally considered to be restricted to domestic or peridomestic habitats, but sylvatic foci have also been described along its distribution. The infestation of wild individuals, together with the projections of environmental changes due to global warming, urge the need to understand the relationship between temperature and the vector's performance. Here, we evaluated the impact of temperature variability on the thermal response of T. infestans. We acclimated individuals to six thermal treatments for five weeks to then estimate their thermal performance curves (TPCs) by measuring the walking speed of the individuals. We found that the TPCs varied with thermal acclimation and body mass. Individuals acclimated to a low and variable ambient temperature (18 degrees C +/- 5 degrees C) exhibited lower performances than those individuals acclimated to an optimal temperature (27 degrees C +/- 0 degrees C); while those individuals acclimated to a low but constant temperature (18 degrees C +/- 0 degrees C) did not differ in their maximal performance from those at an optimal temperature. Additionally, thermal variability (i.e., +/- 5 degrees C) at a high temperature (30 degrees C) increased performance. These results evidenced the plastic response of T. infestans to thermal acclimation. This plastic response and the non-linear effect of thermal variability on the performance of T. infestans posit challenges when predicting changes in the vector's distribution range under climate change. Author summary The Chagas disease is transmitted by the infected feces of kissing bugs, such as Triatoma infestans, when it feeds on human blood. This species is an ectotherm and its physical activity level, behavior, and survival respond to environmental changes in temperature. Climate change predicts changes in environmental temperature and its variability. These changes may affect the distribution and survival of T. infestans, generating difficulties for eradication programs. Here, we evaluated the effects of temperature, and its variability on the performance of T. infestans' individuals maintained at or acclimated to six different temperatures, which capture the essence of climate change predictions regarding temperature (i.e., temperatures displaying changes in mean and in variance). We found that T. infestans exhibited a plastic response to thermal conditions, with individuals performing worse at a low mean temperature (18 degrees C) with variance (+/- 5 degrees C), while individuals acclimated to the same low temperature (18 degrees C) without variance (+/- 0 degrees C) performed as good as individuals acclimated to their optimal temperature (27 degrees C). Nevertheless, thermal variation at a high mean temperature (30 degrees C +/- 5 degrees C) increased performance. Thus, we concluded that the thermal variability affects the performance of this species, in a non-linear way. From our results, the difficulty to predict climate change effects on populations of T. infestans becomes evident, as well as the need to include putative thermal plasticity in future predictions.

Automated summary

Vector-borne diseases are vulnerable to climate change and the Chagas disease is transmitted by Triatoma infestans, one of the main vectors. Research found that the thermal performance of T. infestans is influenced by temperature acclimation and body mass, as well as the non-linear effect of thermal variability on their performance.