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Open Access Research

Inversion 2La is associated with enhanced desiccation resistance in Anopheles gambiae

Emilie M Gray1, Kyle AC Rocca1, Carlo Costantini2 and Nora J Besansky1*

Author Affiliations

1 Eck Institute for Global Health, Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA

2 Institut de Recherche pour le Développement (IRD), UR016, and Laboratoire de Recherche sur le Paludisme, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon

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Malaria Journal 2009, 8:215  doi:10.1186/1475-2875-8-215

Published: 21 September 2009

Abstract

Background

Anopheles gambiae, the principal vector of malignant malaria in Africa, occupies a wide range of habitats. Environmental flexibility may be conferred by a number of chromosomal inversions non-randomly associated with aridity, including 2La. The purpose of this study was to determine the physiological mechanisms associated with the 2La inversion that may result in the preferential survival of its carriers in hygrically-stressful environments.

Methods

Two homokaryotypic populations of A. gambiae (inverted 2La and standard 2L+a) were created from a parental laboratory colony polymorphic for 2La and standard for all other known inversions. Desiccation resistance, water, energy and dry mass of adult females of both populations were compared at several ages and following acclimation to a more arid environment.

Results

Females carrying 2La were significantly more resistant to desiccation than 2L+a females at emergence and four days post-emergence, for different reasons. Teneral 2La females had lower rates of water loss than their 2L+a counterparts, while at four days, 2La females had higher initial water content. No differences in desiccation resistance were found at eight days, with or without acclimation. However, acclimation resulted in both populations significantly reducing their rates of water loss and increasing their desiccation resistance. Acclimation had contrasting effects on the body characteristics of the two populations: 2La females boosted their glycogen stores and decreased lipids, whereas 2La females did the contrary.

Conclusion

Variation in rates of water loss and response to acclimation are associated with alternative arrangements of the 2La inversion. Understanding the mechanisms underlying these traits will help explain how inversion polymorphisms permit exploitation of a heterogeneous environment by this disease vector.