Genomic and molecular evolutionary analyses of insects of economic and public health relevance

In 2015, the release of genomic resources of five Glossina species has facilitated comparative genomics analyses with the genome of G. m. morsitans (Attardo et al., 2014) and other Diptera genomes already available, providing additional information on vector competence, haematophagy, viviparity, as well as on species-specific genes involved in host seeking and vectorial capacity. In this framework, I firstly reconstructed the molecular phylogeny of the six species (G. morsitans, G. pallidipes, G. austeni, G. fuscipes, G. palpalis, G. brevipalpis) using a genome-wide set of orthologous genes. Our genomic phylogenetic analysis suggests that Morsitans, Palpalis and Fusca groups all show a monophyletic origin, with G. brevipalpis (Fusca group) being the most differentiated species. It is noteworthy that the phylogenetic relationships established by our analysis reflects the biological diversities exhibited by each of the Glossina group, such as the geographical distribution, the eco/ethological constrains, the degrees of vectorial capacity and the mating behavior. Based on this phylogeny, I used the molecular clock approach to derive the time of splitting among the Glossina groups and the included species. Orthologs genes derived from Musca domestica allowed us to date also the divergence between Musca and the Glossina genus at 209 Mya, in the Triassic period. The availability of genome sequences from six Glossina species provides unprecedented opportunities to study the evolution of reproductive traits relevant for interpreting the species differentiation. Indeed, reproduction is one of the fundamental processes influencing several aspects of insect’s life and it is often the target of control methods aiming at reducing the insect population size, particularly effective in reproductive systems similar to the one displayed by tsetse flies (Vreysen et al., 2000). I identified gene candidates for positive selection among those expressed in the male reproductive tissues, male accessory glands (MAGs) and testes. Our analysis was based on 2,563 genes selected from G. m. morsitans MAG- and testes-specific transcriptomes, because of their higher expression in MAG compared to testes, and vice versa. The analysis led to the identification of a number of genes candidate for positive selection. Interestingly, most of the identified genes remained uncharacterized. These “novel” genes putatively involved in species- or group-specific processes are particularly interesting for further evolutionary and applicative analyses. Considering the applicative potential of fast evolving and species-specific MAG sequences, I analyzed the regulatory elements responsible for the transcription of the 24 most highly transcribed accessory glands genes in G. m. morsitans. MAG-specific transcriptomic data revealed the presence of a transcription factor known as Paired. In silico analysis confirmed the transcription binding in the promoter region of most of the genes under study. The Paired transcription factor expression profile and protein localization have been demonstrated to be MAG-specific, thus suggesting a role in regulating the expression of MAG genes and, in turn, male reproduction. Its important role in reproduction is also confirmed by its sequence conservation among the six Glossina species analyzed. During my PhD studies, I have also been involved in the genome projects of two insect species: the Asian tiger mosquito Ae. albopictus and the medfly C. capitata. In the framework of the Ae. albopictus genome project (Italian strain), I have been involved in the determination of the genome size of the Fellini strain and, for both genomes, part of my research was dedicated to the manual curation and annotation of Odorant Binding Proteins (OBPs) and Odorant Receptor (OR) genes.