A transcriptome-based phylogenetic study of hard ticks (Ixodidae).

Area of Science:

• * Molecular Evolution
• * Systematics
• * Medical Entomology

Background:

• * Hard ticks (Ixodidae) are globally distributed and significant vectors of zoonotic diseases like Lyme disease.
• * Previous studies have unresolved evolutionary relationships within certain hard tick species and genera.
• * Understanding tick phylogeny is crucial for tracking disease transmission and developing control strategies.

Purpose of the Study:

• * To reconstruct the evolutionary relationships among hard tick species, particularly within the Ixodes genus.
• * To investigate evolutionary patterns and potential drivers of diversification in ticks.
• * To establish a robust phylogenetic framework for future tick research.

Main Methods:

• * Generated novel RNA-Seq datasets for nine Ixodes species.
• * Integrated new data with public datasets for 27 hard tick species, using soft ticks as an outgroup.
• * Assembled transcriptomes, predicted coding sequences, identified single copy orthologues (SCO), and reconstructed phylogenies using Maximum-likelihood and Bayesian frameworks for nuclear and mitochondrial genomes.

Main Results:

• * Confirmed the monophyly of the Ixodes genus and elucidated relationships among its sub-genera.
• * Identified an unexpected acceleration of substitutions in mitochondrial sequences of Prostriata.
• * Observed accelerated evolution in nuclear and mitochondrial genes of two Rhipicephalus species, linked to genome architecture and life-cycle changes.

Conclusions:

• * The study provides a well-resolved phylogeny for hard ticks, clarifying Ixodes relationships.
• * Discovered accelerated evolutionary rates in specific tick lineages, offering insights into their diversification.
• * This research serves as a foundational resource for studying tick evolution, host associations, and the emergence of tick-borne diseases.