Geographical distribution, climatic variability and thermo-tolerance of Chagas disease vectors

Submitted by editor on 8 August 2015. Get the paper!
A fifth-instar nymph of the blood-sucking bug Triatoma infestans placed inside the respirometry chamber (photograph by Diana Martinez Llaser).

by Gerardo J. de la Vega and Pablo E. Schilman

Several climate-based hypotheses have been proposed to explain the relationship between geographic distribution limits and climatic conditions across species. The climate variability hypothesis (CVH) states that terrestrial organisms distributed in highly variable environments (e.g. high latitudes or altitudes) are adapted to withstand a broader range of climatic conditions than organisms in less variable environments (e.g. low latitudes or altitudes). Therefore, species at high latitudes (or altitudes) develop a broader thermo-tolerance range, thus becoming more extensively distributed than species at low latitudes (or altitudes).

In this study, we examine for the first time the range of thermotolerance in two Chagas disease vectors, i.e. Triatoma infestans from the southern South America and Rhodnius prolixus from the northern South America and Central America and address it´s relation with their geographic distribution limits to test the CVH.

We showed a greater temperature tolerance for T. infestans compared to R. prolixus supporting the CVH, and explain the southern limit distribution for both species in terms of physiological constraints by taking a correlative approach and thermal tolerance traits.

This study represents a unique attempt to link geographical distribution and physiological limitations in Chagas disease vectors. The macrophysiology approach used combining physiological experiments with modelling allows us to test the climatic variability hypothesis on these insect vectors that could explain their pattern distribution in agreement with Rapoport´s rule.

Relation between critical thermal limits (CTmax: horizontal and CTmin: vertical dashed lines) and extreme temperaturas for the distributions of the two triatomine species.