Natural Selection on Blowfly Genomes and Transcriptomes

Abstract

Blowflies (Calliphoridae) are widely known for causing myiasis, an infestation of live tissues of vertebrates by dipterous larvae. Although many species in this family display this kind of parasitic feeding habit, some are actually saprophagous and others are facultative parasites, whose diet may rely on either living or decaying matter. Habits do not necessarily reflect phylogenetic relationships. Indeed, for each parasitic calliphorid there is at least one closely related species which has a saprophagous diet. It has been proposed that the ancestral state of feeding habit was saprophagous and it progressed into obligate parasitism as the clade evolved to its present state, and if that is true, parasitic myiasis must have arisen at least four times since the origin of Calliphoridae. The variety of habits and the unique evolutionary history of the clade both make Calliphoridae an interesting model for understanding the evolution of complex traits such as feeding behaviour. One approach to this issue is the search for molecular markers that provide information about the evolutionary transitions among habits in Calliphoridae phylogeny. Several calliphorid genomes and transcriptomes are publicly available, with which large scale analyses may be held. Both genomes and transcriptomes allow the study of coding regions and the occurrence of synonymous and non-synonymous mutations, therefore providing information on which genes are under positive selection, purifying selection or neutrally evolving, in a species or group of species. Also, genomes allow an even deeper analysis, for with them it is possible to study non-coding regions (which may contain sequences that regulate gene expression and therefore impact the phenotypes). All these publicly available sequences will be downloaded, and then protein coding regions will be analyzed by the calculation of the rate of non-synonymous and synonymous substitutions (dN/dS or É), whilst no-coding regions will be studied with the shared motif method (it allows the finding of regions of high local similarity - the shared motifs - between two DNA sequences regardless of their order, orientation or spacing). Such tools will be used aiming to find similarities and differences among species with each feeding habit to understand whether there are genetic convergences correlating to the phenotypic ones or if the independent parasitic behaviour origins are each underlain by different molecular bases. (AU)