Abstract
Tsetse flies are responsible for the transmission of Trypanossoma sp. to vertebrate animals in Africa causing huge health issues and economic loss. The availability of the genome sequence of Glossina morsitans enabled the discovery of several genes related to medically important phenotypes and novel physiological features. However, a genome-wide scan for coding regions that underwent positive selection is still missing, which is surprising given the evolution of traits associated with the hematophagy in this lineage. In this study, we employed an experimental design that controlled for the rate of false positives and we performed a scan of 3,318 G. morsitans genes. We found 145 genes with significant historical signal of positive selection. These genes were categorized into 18 functional classes after careful manual annotation. Based on their attributed functions, we identified candidate genes related with feeding habits and embryonic development. When our results were contrasted with gene expression data, we confirmed that most genes that underwent adaptive molecular evolution were frequently expressed in organs associated with key physiological evolutionary innovations in the G. morsitans lineage, namely, the salivary gland, the midgut, fat body tissue, and in the spermatophore.
Highlights
The Glossinidae consists of an African family of flies known as tsetse, which are the vectors responsible for the transmission of Trypanossoma sp. to humans and other vertebrates
Because we aimed to identify genes related with hematophagy and embryogenesis evolving under positive selection exclusively in G. morsitans, our experimental design included D. melanogaster, the sisterlineage in which such traits are absent, in all orthologous groups analyzed
Using the branch-site test, we were able to identify 145 genes with at least one codon site evolving under positive selection exclusively in G. morsitans (Table S2)
Summary
The Glossinidae consists of an African family of flies known as tsetse, which are the vectors responsible for the transmission of Trypanossoma sp. to humans and other vertebrates. The Glossinidae consists of an African family of flies known as tsetse, which are the vectors responsible for the transmission of Trypanossoma sp. Trypanosomiasis is known as sleeping sickness, whereas a pathologic condition dubbednagana’ is reported in other vertebrates (Büscher et al, 2017). These flies are naturally distributed all over the rural areas of sub-Saharan Africa, being endemic to 36 territories, where approximately 70 million people are at risk (Simarro et al, 2012). In 2009, for the first time in 50 years, the number of new reports in humans dropped to < 10,000 cases, and this trend has been kept steady due to WHO efforts in committed areas (WHO, 2017a). The genome of the tsetse fly Glossina morsitans was finished in 2014 (International Glossina Genome Initiative, 2014), and subsequent works identified the function of a number of genes in this species (Benoit et al, 2014a,b, 2015, 2017; Christoffels et al, 2014)
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