Résumé
The adaptation of species within the Anopheles gambiae complex to urban settings is of major interest for its potential implication in malaria transmission in cities in sub-Saharan Africa. This adaptation involves changes in their physiology, genetics and behavior, among others. During the last decades, a growing number of studies assessed Anopheles urban adaptation in Central Africa, but focused mainly on few cities located in forested areas. The objective of this thesis is to understand the evolution of Anopheles gambiae and Anopheles coluzzii populations in urban settings. To this end, we carried out an exhaustive larval sampling in four major cities of Central Africa: Libreville (Gabon), Douala (Cameroon), Brazzaville (Congo), and Bangui (CAR). We characterized the physical-chemical and ecological variables of 380 breeding sites and identified the presence of the different Anopheles species. Using an ecological modeling approach, we investigated the patterns of frequency variation of these Anopheles species within and across cities. Finally, we explored the genetic mechanisms associated with the presence of An. coluzzii in urban areas. Our study confirmed the capacity of An. gambiae and An. coluzzii to largely colonize Central Africa cities. Their presence across a variety of aquatic conditions revealed their environmental plasticity, a mirror of their ecological success in Africa. However, and despite their extensive presence in the four cities, these two species exhibit eco-geographical segregation. Environmental variables such as habitat, organic pollution, salinity, pH, presence or urban density, significantly influenced the frequency variation of urban larval habitats between An. coluzzii (predominant in coastal habitats) and An. gambiae (predominant in inland habitats). Despite the specific features of each city, we could predict the species frequency variation, revealing a common pattern in the adaptation to urban settings of both species in the four cities. Specifically, our research on the genetic mechanisms involved in the response to xenobiotic stress revealed a common response, independently of the aquatic pollutant origin. We then focused on genetic elements involved in this rapid adaptation, such as transposable elements. High-throughput genome sequencing of An. coluzzii samples from urban environments allowed capturing the diversity of transposable element families and their potential impact on the architecture and function of some genes involved in insecticide resistance and immune response. Overall, our work contributes significantly to improve the knowledge on the bio-ecology of urban vectors of human Plasmodium in Central Africa. We revealed the real malaria transmission threat linked to Anopheles extensive presence in the main cities of Central Africa. Moreover, we laid the foundations to understand the genetic signatures of this adaptation. Future research will carefully pay attention to behavioral and physiological changes that might affect the vectorial capacity of urban Anopheles in the scenario of rapid urbanization in Africa.