Phylogenomic study of hard ticks using transcriptome sequencing
Résumé
Hard ticks are vectors of numerous pathogens responsible for human and veterinary diseases. The Ixodes genus is distributed world‐wide and comprises several species that transmit the Lyme borreliosis agent (Borrelia sp.). This is the case of I. ricinus (in Europe) and I. scapularis (in the USA), two species for which complete genome projects have been undertaken. To better understand evolutionary patterns in this genus (for example how adaptations to different host species or host ranges evolved, and how fast did they change over evolutionary time), an accurate phylogeny of the whole group is needed. Yet, the phylogeny of the group was not completely resolved until recently. Points debated are for example the phylogenetic position of Australasian species (e.g. I. uriae, I. holocyclus), or at a very fine scale, the phylogenetic relationships between closely related species (e.g. in the I. ricinus / I. scapularis group). Using high output sequencing technology (RNA‐Seq), we investigated phylogenetic relationships in the group of hard ticks. Transcriptomes from 9 species in the Ixodes genus were sequenced using Illumina strand‐oriented, paired‐end sequencing. The new data sets produced by our group was combined whith data obtained from Genbank for two other Ixodes species as well as 10 non‐Ixodes tick species. We obtained de novo transcriptome assemblies for each species (21 in total), predicted their coding sequences and performed sequence comparisons among species. Single copy orthologs (SCO) were aligned. Maximum‐likelihood and Bayesian framework will then be used to reconstruct the species tree. We aim to provide thereby new insights on the evolutionnay history of ticks, producing a solid framework for further analyses of phylogeny and gene evolutionary patterns.