Origin and evolutionary history of Culex pipiens complex mosquitoes

Abstract

The Culex pipiens complex is a group of closely related mosquito species with a markedly divergent array of physiological and behavioral traits despite little to no morphological differentiation. Even within the same species, there are behavioral ‘forms’ that are strikingly different in ecology and behavior such as host preference. The complex has a global distribution and is generally associated with humans, with key taxa serving as major vectors of pathogens such as West Nile fever or lymphatic filariasis. We know very little, however, about the origin and evolutionary history of the species and forms in the complex – when and where they originated and dispersed across the world. In Chapter 1, I synthesize the recent and historical literature on the origin and ecology of Culex pipiens sensu stricto and its enigmatic forms – pipiens and molestus. The synthesis of genetic and ecological studies spanning 100+ years clarifies a striking latitudinal gradient within the species and debunks the popularized idea that molestus originated in the London Underground system in situ within the past 200 years. In Chapter 2, I collect and sequence 800 Cx. pipiens complex mosquitoes from 46 countries across all six continents where they are known to occur – North America, South America, Europe, Africa, Asia, and Australia – to better understand their taxonomic status and evolutionary history. I clarify the phylogenetic relationships among members of the complex and provide genomic evidence for two ancestral lineages in sub-Saharan Africa. I again find little support for the in-situ evolution of molestus in the London Underground and instead present multiple lines of evidence suggesting that molestus evolved in Egypt or nearby areas of the Middle East. molestus likely diverged from nearby Mediterranean pipiens 2,000-10,000 years ago, suggesting that the rise of agriculture and civilization in the Middle East drove the evolution of the human-adapted ecotype. Together, this dissertation provides novel insights into the intricate evolutionary history and taxonomic status of this complex of mosquito vectors and has important implications for future public health efforts.