Genome-Wide Comparative Analysis of Chemosensory Gene Families in Five Tsetse Fly Species

Abstract

For decades, odour-baited traps have been used for control of tsetse flies (Diptera; Glossinidae), vectors of African trypanosomes. However, differential responses to known attractants have been reported in different Glossina species, hindering establishment of a universal vector control tool. Availability of full genome sequences of five Glossina species offers an opportunity to compare their chemosensory repertoire and enhance our understanding of their biology in relation to chemosensation. Here, we identified and annotated the major chemosensory gene families in Glossina. We identified a total of 118, 115, 124, and 123 chemosensory genes in Glossina austeni, G. brevipalpis, G. f. fuscipes, G. pallidipes, respectively, relative to 127 reported in G. m. morsitans. Our results show that tsetse fly genomes have fewer chemosensory genes when compared to other dipterans such as Musca domestica (n>393), Drosophila melanogaster (n = 246) and Anopheles gambiae (n>247). We also found that Glossina chemosensory genes are dispersed across distantly located scaffolds in their respective genomes, in contrast to other insects like D. melanogaster whose genes occur in clusters. Further, Glossina appears to be devoid of sugar receptors and to have expanded CO2 associated receptors, potentially reflecting Glossina's obligate hematophagy and the need to detect hosts that may be out of sight. We also identified, in all species, homologs of Ir84a; a Drosophila-specific ionotropic receptor that promotes male courtship suggesting that this is a conserved trait in tsetse flies. Notably, our selection analysis revealed that a total of four gene loci (Gr21a, GluRIIA, Gr28b, and Obp83a) were under positive selection, which confers fitness advantage to species. These findings provide a platform for studies to further define the language of communication of tsetse with their environment, and influence development of novel approaches for control.

BdorOBP83a-2 Mediates Responses of the Oriental Fruit Fly to Semiochemicals

“…Phylogenetic analyses of the newly identified B. dorsalis OBPs were performed in conjunction with previously identified B. dorsalis OBPs and OBPs from other species, including 31 OBPs from B. dorsalis (Wu et al, 2015 ), 52 OBPs from D. melanogaster (Hekmat-Scafe et al, 2002 ; Vieira et al, 2007 ; Vieira and Rozas, 2011 ), 16 OBPs from Ceratitis capitata (Siciliano et al, 2014a ), 15 OBPs from Rhagoletis pomonella (Schwarz et al, 2009 ), 9 OBPs from Rhagoletis suavis (Ramsdell et al, 2010 ), Obp83a orthologs from G. m. morsitans (Liu et al, 2010 ; Macharia et al, 2016 ), Musca domestica (Scott et al, 2014 ), and Calliphora stygia (Leitch et al, 2015 ). After removal of signal peptide sequences, OBP amino acid sequences were aligned using MAFFT v6.935b (Katoh and Toh, 2010 ; Katoh and Standley, 2013 ) with the E-INS-i strategy, BLOSUM62 matrix, 1000 maxiterate and offset 0.…”

The Glossina Genome Cluster: Comparative Genomic Analysis of the Vectors of African Trypanosomes

“…Comparative analyses of genes responsible for perireceptor olfaction activities revealed high conservation of the repertoire among the six species. The genes appear to scatter across their respective genomes with only a few duplicates occurring in clusters [84]. Glossina species expanded loci that include Gr21a (responsible for CO 2 detection) [85], Or67d (mediates cis -vaccenyl acetate reception) and Obp83a, (thought to be olfactory specific) [86].…”

“…Glossina species expanded loci that include Gr21a (responsible for CO 2 detection) [85], Or67d (mediates cis -vaccenyl acetate reception) and Obp83a, (thought to be olfactory specific) [86]. The expanded loci suggest involvement of gene duplication and/or transposition in their emergence [84]. All six species lack sugar receptors likely as a result of tsetse’s streamlined blood-feeding behavior.…”

A nonrandom subset of olfactory genes is associated with host preference in the fruit flyDrosophila orena

“…; Macharia et al. ). These individual examples could represent genes that are important for the evolution of different preference traits.…”

“…; Macharia et al. ), and olfactory genes are commonly thought to evolve through positive natural selection (McBride and Arguello ; Whiteman and Pierce ; Sánchez‐Gracia et al. ; Lavagnino et al.…”