Divergent and conserved elements comprise the chemoreceptive repertoire of the nonblood-feeding mosquito toxorhynchites amboinensis

Abstract

Many mosquito species serve as vectors of diseases such as malaria and yellow fever, wherein pathogen transmission is tightly associated with the reproductive requirement of taking vertebrate blood meals. Toxorhynchites is one of only three knownmosquito genera that does not host-seek and initiates egg development in the absence of a blood-derived protein bolus. These remarkable differencesmake Toxorhynchites an attractive comparative reference for under standing mosquito chemo sensation as it pertains to host-seeking.We performed deep transcriptome profiling of adult female Toxorhynchites amboinensis bodies, antennae and maxillary palps, and identified 25,084 protein-coding "genes" in the de novo assembly. Phylogenomic analysis of 4,266 single-copy "genes" from T. amboinensis, Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus robustly supported Ae. aegypti as the closest relativeof T. amboinensis, with the two species diverged approximately 40Ma.Weidentifieda large number of T. amboinensis chemosensory "genes," the majority of which have orthologsin other mosquitoes. Finally, cross-species expression analyses indicated that patterns of chemoreceptor transcript abundance were very similar for chemoreceptors that are conserved between T. amboinensis and Ae. aegypti, whereas T. amboinensis appeared deficient in the variety of expressed, lineage-specific chemoreceptors. Our transcriptome assembly of T. amboinensis represents the first comprehensive genomic resource for a nonblood-feeding mosquito and establishes a foundation for future comparative studies of blood-feeding and nonblood-feeding mosquitoes.We hypothesize that chemosensory genes that display discrete patterns of evolution and abundance between T. amboinensis and blood-feeding mosquitoes are likely to play critical roles in host-seeking and hence the vectorial capacity.