Are there 16 species of brown dog ticks? Phylogenies from 60 entire mitochondrial genomes and 162 cox1 sequences reveal 16 species-level clades in the Rhipicephalus (Rhipicephalus) sanguineus group☆☆

The Rhipicephalus sanguineus group, the brown dog ticks, are cosmopolitan and doubtless the most important ticks of domestic dogs, clinically and economically. Despite four decades of taxonomic enquiry with nucleotide sequences and morphology, the taxonomy of the R. sanguineus group is confused, even chaotic. We provide 13 new mitochondrial (mt) genomes and internal transcribed spacer 2 (ITS2) sequences from nine localities in Australia, Israel and Japan. We inferred phylogenetic trees from 10 mt protein-coding genes (9,514 bp), as well as partial cox1, ITS2, 12S, and 16S rRNA genes, to resolve to common clades the >2,000 nucleotide sequences in GenBank from the R. sanguineus group. Then we applied three species delimitation protocols to 60 entire mt genomes (ca. 15,000 bp) and 162 partial cox1 sequences (472 bp): Automatic Barcode Gap discovery, Assemble Species by Automatic Partitioning, and Poisson Tree Process. We considered pairwise genetic differences and Tamura-Nei genetic distances among 60 entire mt genomes and 162 partial cox1 sequences. We found 16 species-level clades (clades A to P) that we hypothesise represent at least 16 species in the R. sanguineus group. These clades had intra-clade differences of <3.8% (entire mt genomes) and <5.1% (partial cox1) whereas the inter-clade differences were >7.7% (entire mt genomes) and >4.5% (partial cox1). We assigned the species names Rhipicephalus linnaei (Audouin, 1826), Rhipicephalus rutilus (Koch, 1844), Rhipicephalus secundus (Feldman-Muhsam, 1952) and R. sanguineus (Latreille, 1806) to clades A, C, D, and K, respectively. And we hypothesise that the names Rhipicephalus camicasi (Morel, Mouchet & Rodhain, 1976), Rhipicephalus turanicus (Pomerantsev, 1940), Rhipicephalus guilhoni (Morel & Vassilades, 1963), Rhipicephalus sulcatus (Neumann, 1908), Rhipicephalus rossicus (Yakimov & Kol-Yakimova, 1911), Rhipicephalus pumilio (Schulze, 1935) and Rhipicephalus pusillus (Gil Collado, 1936) apply to clades B, E, H, J, M, N and O, respectively. The newly described Rhipicephalus hibericus (Millán, Rodriguez-Pastor & Estrada-Peña, 2024) was genetically indistinguishable from R. sanguineus in clade K and thus is a synonym of R. sanguineus. We could not assign names to clades F (USA, Hungary), I (India, Pakistan), L (Nigeria), G (China, Kazakhstan), and P (Cameroon): some or all of these five clades may be new species in the R. sanguineus group. Our haplotype network of partial mt genes (cox1, cytb and nad2) revealed much genetic similarity among geographically distant populations of R. linnaei. This indicates recent dispersal, likely originating in Africa or the Middle East, since African populations were more genetically diverse than populations in other parts of the world.

The complete mitochondrial genome of Rhipicephalus haemaphysaloides and its phylogenetic analysis

We conducted an analysis of the complete mitochondrial genome of Rhipicephalus haemaphysaloides, a tick species known for transmitting various bacteria and viruses. The mitochondrial genome of R. haemaphysaloides has a length of 14,739 bp and consists of 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs), and 2 control regions. By utilizing the maximum likelihood method, we established the phylogenetic relationship among R. haemaphysaloides and other species within the Rhipicephalus genus of the Ixodidae family. This analysis revealed that R. haemaphysaloides and other Rhipicephalus species belong to the same clade, further affirming the taxonomic placement of R. haemaphysaloides within the Rhipicephalus genus. Furthermore, we compared the mitochondrial genomes of R. haemaphysaloides isolates from Changning, Yunnan Province, China, with isolates from Yangxin, Ganzhou, and Yingtan, Hubei Province, China. In summary, our investigation offers genetic proof endorsing the taxonomic categorization and phylogenetic placement of Ixodidae by assessing the entire mitochondrial genome of R. haemaphysaloides.

Detection of tick-borne bacterial DNA (Rickettsia sp.) in reptile ticks Amblyomma moreliae from New South Wales, Australia

Ticks are major arthropod vectors of disease, transmitting tick-borne pathogens during blood meal episodes. Rickettsia spp. and Borrelia spp. are two tick-borne pathogens of zoonotic concern previously identified in DNA isolates from the tick genera Amblyomma and Bothriocroton associated with reptilian hosts in Australia. Some reports suggest that these reptile ticks bite and attach to humans via accidental parasitism and transmit disease, with the tick Bothriocroton hydrosauri known to transmit Rickettsia honei or Flinders Island Spotted Fever Rickettsia to humans. This descriptive study aims to identify the ticks collected from wild reptiles submitted to veterinary clinics and captured by snake rescuers from New South Wales (NSW), Australia, and detect the presence of tick-borne bacterial DNA using quantitative polymerase chain reaction (qPCR) to detect Rickettsia spp. and Bartonella spp. and conventional nested-PCR to detect Borrelia spp. Morphological identification revealed ticks removed from one eastern blue-tongued lizard (Tiliqua scincoides scincoides) from North-Eastern NSW (Lismore), one eastern blue-tongued lizard from the Greater Sydney area (Canley Heights), one diamond python (Morelia spilota spilota) from the Greater Sydney area (Woronora Heights) and one red-bellied black snake (Pseudechis porphyriacus) from the Greater Sydney Area (Cronulla) in New South Wales were Amblyomma moreliae. No ticks were positive for Bartonella spp. and Borrelia spp. DNA using real-time PCR targeting ssrA gene and nested PCR targeting Borrelia-specific 16S rRNA gene, respectively. Real-time PCR targeting gltA, ompA, ompB and 17kDa gene of Rickettsia spp. revealed 14 out of 16 ticks were positive. The undescribed Rickettsia sp. DNA was identical to that previously recovered from reptile ticks in Australia and closely related to Rickettsia tamurae and Rickettsia monacensis, both of which are aetiologic pathogens of the Spotted Fever Group Rickettsiosis (SFGR). These results accentuate the ongoing need for increased study efforts to understand zoonotic potential of bacteria from reptile ticks and the tick-reptile-human relationship.

Phylogenetic relationships of the Amblyomma cajennense complex (Acari: Ixodidae) at mitogenomic resolution

The genus Amblyomma is the third most diverse in the number of species within the Ixodidae, with practically half of its species distributed in the Americas, though there are also species occurring in Africa, Asia, and Australia. Within the genus, there are several species complexes with veterinary and public health importance. The Amblyomma cajennense complex, in the Americas, is represented by six species with a wide distribution, from Texas to northern Argentina. We combined two sequencing techniques to generate complete mitogenomes of species belonging to the Amblyomma cajennense complex: genome skimming and long-range PCRs sequencing methods. Thus, we generated seven new mitochondrial genomes for all species of the Amblyomma cajennense complex, except for Amblyomma interandinum. Genetic distances between the mitogenomes corroborate the clear differentiation between the five species of the Amblyomma cajennense complex. The phylogenetic relationships of these species had previously been evaluated by combining partial nuclear and mitochondrial genes and here these relationships are corroborated with a more robust framework of data, which demonstrates that the conjunction of mitochondrial and nuclear partial genes can resolve close relationships when entire genes or genomes are unavailable. The gene order, structure, composition, and length are stable across these mitogenomes, and they share the general characteristics of Metastriata. Future studies should increase the number of available mitogenomes for this genus, especially for those species from the Indo-Pacific region and Africa, by means of a better understanding of their relationships and evolutionary process.

The “southeastern Europe” lineage of the brown dog tick Rhipicephalus sanguineus (sensu lato) identified as Rhipicephalus rutilus Koch, 1844: Comparison with holotype and generation of mitogenome reference from Israel

The brown dog tick Rhipicephalus sanguineus (sensu lato) in the southeastern Mediterranean region and the Middle East is difficult to identify due to the presence of multiple mitochondrial DNA haplogroup lineages. The purpose of this study was to clarify the identity of the "southeastern Europe" lineage of this tick species complex. Our research shows that female ticks of the "southeastern Europe" lineage correspond to the morphology of R. rutilus Koch, 1844 as found in type-material at the Museum für Naturkunde Berlin in Germany. We characterised the complete mitogenomes of R. rutilus, R. turanicus Pomerantsev, 1940 and Rhipicephalus sanguineus (Latreille, 1806) in order to improve our understanding of the phylogenetic relationships among species within the R. sanguineus (sensu lato) complex. The material associated with the morphology of R. rutilus was previously labelled as the "southeastern Europe" lineage and found in Israel and Egypt, including Lower Egypt and the Nile Delta, where the original type-material was collected. Based on the morphology, genetic identity, and geographical distribution of the species, we conclude that the name R. rutilus is correctly linked to the "southeastern Europe" lineage of R. sanguineus (sensu lato).

Rhipicephalus linnaei (Audouin, 1826) recognised as the "tropical lineage" of the brown dog tick Rhipicephalus sanguineus sensu lato: Neotype designation, redescription, and establishment of morphological and molecular reference

We re-describe the adult stages of Rhipicephalus linnaei (Audouin, 1826), and characterise its diagnostic molecular traits. A male R. linnaei collected in Esna City, Luxor Governorate, Egypt is designated as the neotype. Rhipicephalus linnaei is re-established as a valid tick name and removed from the synonymy list of Rhipicephalus sanguineus (Latreille, 1806). Rhipicephalus linnaei is most similar to R. sanguineus and Rhipicephalus camicasi Morel, Mouchet & Rodhain, 1976 because they share similar elongated comma-like spiracula that are narrowly visible dorsally, and the dorsal prolongation is narrower than the width of the adjacent festoon. The male of R. camicasi is distinguished from R. linnaei by the non-tapering caudal widening of the spiracula. The male of R. sanguineus is distinguished from R. linnaei by shorter extension that does not taper into a long narrow extension of the spiracula. The genital pore atrium of female R. linnaei is broadly U-shaped, while it is a narrower U-shape in R. sanguineus. The remaining species within the R. sanguineus species complex - Rhipicephalus sulcatus Neumann, 1908, Rhipicephalus turanicus Pomerantsev, 1940, Rhipicephalus guilhoni Morel & Vassilades, 1963, Rhipicephalus secundus Feldman-Muhsam, 1952 and Rhipicephalus afranicus Bakkes, 2020, all exhibit spiracula with the dorsal prolongation as wide as the adjacent festoon. The DNA sequence of R. linnaei is most closely related to R. guilhoni. The phylogenetic analysis of mitogenome (mtDNA) sequences including assembled mtDNA from whole genome sequencing of the neotype supports R. linnaei as a well-defined taxon when compared with DNA sequences of other species of the R. sanguineus species complex, in particular: R. sanguineus, R. turanicus, R. secundus and R. camicasi. Molecularly, R. linnaei belongs to the so-called R. sanguineus s.l. "tropical lineage" distributed globally including the Americas, Africa, Europe, Asia and is the only species from R. sanguineus species complex in Australia.