Targets of rapid evolution in the culex pipiens complex proteome and insect sex determination cascade
Creators: name: Price, Dana C.
Publisher: name: No Publisher Supplied
Year: 2015

description: The ecology of arthropod disease vectors can greatly influence their vectorial capacity and thus both duration and severity of arboviral disease outbreaks.  Elucidating the genetic factors that influence these ecological characteristics is key in developing mitigation strategies.    In Chapter 1, I report the results of a transcriptomic comparison between feral and domestic forms of the northern house mosquito, Culex pipiens forms pipiens and molestus.  By examining the rate of nonsynonymous amino acid substitution between orthologous protein pairs, I define fast and slowly evolving genes and gene families that highlight the genetic variability in these two mosquito taxa.  The results implicate genes involved in olfaction, digestion and immunity as likely constituents of the genetic component driving the dramatic differences in behavior and physiology so important to understand.    In Chapter 2, I examine the mosaicism present within the genome of Culex pipiens pallens, a putative hybrid mosquito resulting from a cross between Culex pipiens and Culex quinquefasciatus.  Using a phylogenomic analysis, I quantify shared ancestry between Cx. pipiens pallens gene sequences and those of either putative parental genome.  Additionally, I identify genes and gene ontologies that show evidence of evolving at accelerated evolutionary rates among East Asian Culex species by calculating per-gene rates of peptide evolution, and identifying lineages with differential rates of evolution to examine how Cx. pipiens pallens has utilized and modified parental genes to exploit its environment and persist as a species.  My results show that Cx. pipiens pallens and Cx. quinquefasciatus share a greater degree of phylogenetic affiliation and lower protein divergence than either do with Cx. pipiens form molestus, and that the genetic component of the Cx. pipiens pallens proteome assigned to Cx. pipiens contains genes that function in energy metabolism, cell cycle / signaling, and redox reactions; the genes assigned to Cx. quinquefasciatus are enriched in lipid transport function and extracellular scavenging / innate immunity.    In Chapters 3 and 4, I select a fast-evolving gene of interest, doublesex, from the analysis performed in Chapter 1 and describe its evolution within the Culex pipiens complex, and in all hexapods.  Doublesex controls the somatic sexual fate of Drosophila melanogaster and may function thusly in many metazoans, including the malaria mosquito Anopheles gambiae and the dengue and yellow fever vector Aedes aegypti.  In these insects, upstream genetic signaling mechanisms regulate the splicing of the dsx transcript to produce sex-specific peptide isoforms that ultimately differentiate male and female insects.  This conserved function makes dsx a prime target for sterile insect technique (SIT) research.  Here I provide a full-length gene sequence, with sex-specific splicing, regulatory and evolutionary analyses of the doublesex gene from the southern house mosquito Culex quinquefasciatus.  I show that Cxqdsx maintains characters possibly derived in the Culicine mosquitoes and present in the Aedes aegypti dsx gene, and retains presumably ancestral qualities present in Anopheles gambiae (Angdsx).  Interestingly, the cis-regulated splicing of Cxqdsx does not appear to follow either currently described mosquito model; each of the three mosquito genera maintain unique regulatory mechanisms.  Additionally, using public sequence databases, I show doublesex to be ubiquitous in the hexapods and likely to have been present in the last common ancestor (LCA) of the group as a sex-specifically spliced multiple-copy gene.