Sequencing of complete mitochondrial genomes confirms synonymization of Hyalomma asiaticum asiaticum and kozlovi, and advances phylogenetic hypotheses for the Ixodidae

PLoS One. 2018 May 16;13(5):e0197524. doi: 10.1371/journal.pone.0197524. eCollection 2018.

Abstract

Phylogeny of hard ticks (Ixodidae) remains unresolved. Mitochondrial genomes (mitogenomes) are increasingly used to resolve phylogenetic controversies, but remain unavailable for the entire large Hyalomma genus. Hyalomma asiaticum is a parasitic tick distributed throughout the Asia. As a result of great morphological variability, two subspecies have been recognised historically; until a morphological data-based synonymization was proposed. However, this hypothesis was never tested using molecular data. Therefore, objectives of this study were to: 1. sequence the first Hyalomma mitogenome; 2. scrutinise the proposed synonymization using molecular data, i.e. complete mitogenomes of both subspecies: H. a. asiaticum and kozlovi; 3. conduct phylogenomic and comparative analyses of all available Ixodidae mitogenomes. Results corroborate the proposed synonymization: the two mitogenomes are almost identical (99.6%). Genomic features of both mitogenomes are standard for Metastriata; which includes the presence of two control regions and all three "Tick-Box" motifs. Gene order and strand distribution are perfectly conserved for the entire Metastriata group. Suspecting compositional biases, we conducted phylogenetic analyses (29 almost complete mitogenomes) using homogeneous and heterogeneous (CAT) models of substitution. The results were congruent, apart from the deep-level topology of prostriate ticks (Ixodes): the homogeneous model produced a monophyletic Ixodes, but the CAT model produced a paraphyletic Ixodes (and thereby Prostriata), divided into Australasian and non-Australasian clades. This topology implies that all metastriate ticks have evolved from the ancestor of the non-Australian branch of prostriate ticks. Metastriata was divided into three clades: 1. Amblyomminae and Rhipicephalinae (Rhipicephalus, Hyalomma, Dermacentor); 2. Haemaphysalinae and Bothriocrotoninae, plus Amblyomma sphenodonti; 3. Amblyomma elaphense, basal to all Metastriata. We conclude that mitogenomes have the potential to resolve the long-standing debate about the evolutionary history of ticks, but heterogeneous evolutionary models should be used to alleviate the effects of compositional heterogeneity on deep-level relationships.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • DNA, Mitochondrial / genetics*
  • Genome / genetics
  • Ixodidae / genetics*
  • Phylogeny
  • Sequence Analysis, DNA

Substances

  • DNA, Mitochondrial

Grants and funding

This study was supported by the China Agriculture Research System (CARS-39-15) and Special Fund for Agro-scientific Research in the Public Interest (Grant No. 201303037) (ZQL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.