New insights into the systematics of the Afrotropical Amblyomma marmoreum complex (Acari, Ixodidae) and a novel Rickettsia africae strain using morphological and metagenomic approaches

The Amblyomma marmoreum complex includes some Afrotropical species, such as Amblyomma sparsum, a three-host tick that parasitizes reptiles, birds, and mammals, and is a recognized vector of Ehrlichia ruminatum. However, the lack of morphological, genetic and ecological data on A. sparsum has caused considerable confusion in its identification among A. marmoreum complex members. In this study, we used microscopy and metagenomic approaches to analyze A. sparsum ticks collected from a puff adder snake (Bitis arietans) in southwest Senegal (an endemic rickettsioses area) in order to supplement previous morphological descriptions, provide novel genomic data for the A. marmoreum complex, and search for some associated spotted fever agent. Based on stereoscope and scanning electron microscopy (SEM) morphological evaluations, we provided high-quality images and new insights about punctation and enameling in the male of A. sparsum to facilitate identification for future studies. Additionally, the metagenomic approach allowed us assembly the complete mitochondrial genome of A. sparsum, as well as the nearly entire chromosome and complete plasmid sequences of a novel Rickettsia africae strain. Phylogenomic analyses showed a close relationship between A. sparsum and A. nuttalli for the first time and confirmed the position of A. sparsum within the A. marmoreum complex. Our results provide new insights into the systematic of A. sparsum and A. marmoreum complex, as well as the genetic diversity of R. africae in Afrotropical region. Future studies should consider the possibility that A. sparsum may be a competent vector for R. africae.