Dry savannahs of West Africa are characterised by the occurrence of two contrasting environmental seasons: a dry season, with important daily fluctuations in air temperature and significant decrease of the relative humidity, and a rainy season, during which temperature fluctuations flatten and water ponds are refilled.

 

 

 

 

 

 

 

 

The alternation of these two distinct seasons has a strong impact on the life cycle of many insect species, including mosquitoes. In particular, malarial mosquito densities have been found to follow the pace of breeding-site dynamics (i.e., water ponds). Hence, the pattern of malaria transmission is highly seasonal, and transmission mainly occurs during the rainy season when mosquito densities are the highest. Thus, in dry savannahs of West Africa, the malarial mosquitoes Anopheles coluzzii and An. gambiae swarm during the rainy season but almost disappear at the onset of the dry season.

 

Interestingly, the ecological and physiological bases enhancing the survival of these insects during the desiccating conditions of the dry season remain unknown, and hard to understand with field studies. Therefore, I conduct experimental and comparative studies to analyse the physiological and morphological plasticity of female An. coluzzii and An. gambiae mosquitoes in response to the environmental conditions of the dry season. Metabolomic, proteomic, morphometric and gas exchange analyses highlighted a wide range of responses to the dry season conditions in these species, and enables distinguishing the two considered species. Differences were also observed between populations of the An. coluzzii mosquitoes from distinct habitats.

 

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Accordingly, I showed that the young females of An. gambiae seem characterised by higher dispersal abilities. By contrast, in An. coluzzii females, the increasing amounts of osmoprotectants and metabolites involved in cuticle permeability suggest increased desiccation resistance at the onset of the dry season.

 

 

 

 

 

 

 

 

 

These new results contribute improving our understanding of the seasonal population dynamics of anopheline mosquitoes in West Africa. This work also opens new research perspectives in our understanding of the survival strategies of these malarial vectors during the unsuitable environmental conditions of the dry season.