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Open Access Research

Thermal limits of wild and laboratory strains of two African malaria vector species, Anopheles arabiensis and Anopheles funestus

Candice L Lyons12*, Maureen Coetzee2, John S Terblanche3 and Steven L Chown14

Author Affiliations

1 Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa

2 Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa

3 Department of Conservation Ecology and Entomology, Stellenbosch University, Matieland, 7602, South Africa

4 Current address: School of Biological Sciences, Monash University, Victoria, 3800, Australia

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Malaria Journal 2012, 11:226  doi:10.1186/1475-2875-11-226

Published: 6 July 2012

Abstract

Background

Malaria affects large parts of the developing world and is responsible for almost 800,000 deaths annually. As climates change, concerns have arisen as to how this vector-borne disease will be impacted by changing rainfall patterns and warming temperatures. Despite the importance and controversy surrounding the impact of climate change on the potential spread of this disease, little information exists on the tolerances of several of the vector species themselves.

Methods

Using a ramping protocol (to assess critical thermal limits - CT) and plunge protocol (to assess lethal temperature limits - LT) information on the thermal tolerance of two of Africa’s important malaria vectors, Anopheles arabiensis and Anopheles funestus was collected. The effects of age, thermal acclimation treatment, sex and strain (laboratory versus wild adults) were investigated for CT determinations for each species. The effects of age and sex for adults and life stage (larvae, pupae, adults) were investigated for LT determinations.

Results

In both species, females are more tolerant to low and high temperatures than males; larvae and pupae have higher upper lethal limits than do adults. Thermal acclimation of adults has large effects in some instances but small effects in others. Younger adults tend to be more tolerant of low or high temperatures than older age groups. Long-standing laboratory colonies are sufficiently similar in thermal tolerance to field-collected animals to provide reasonable surrogates when making inferences about wild population responses. Differences between these two vectors in their thermal tolerances, especially in larvae and pupae, are plausibly a consequence of different habitat utilization.

Conclusions

Limited plasticity is characteristic of the adults of these vector species relative to others examined to date, suggesting limited scope for within-generation change in thermal tolerance. These findings and the greater tolerance of females to thermal extremes may have significant implications for future malaria transmission, especially in areas of current seasonal transmission and in areas on the boundaries of current vector distribution.

Keywords:
Culicidae; Laboratory adaptation; Phenotypic plasticity; Thermal biology; Tolerance limits