Reproductive incompatibility between Amblyomma maculatum (Acari: Ixodidae) group ticks from two disjunct geographical regions within the USA

Molecular characterisation of Amblyomma integrum circulating in southern India

Amblyomma integrum is a large gooseberry sized longirostrate tick (when fully repleted) found in India and Sri Lanka. In Kerala (India), this tick is commonly found in the forest and its fringe areas frequently infesting deer and hence it is locally known as "maan chellu / maanunny" (deer tick). In the present study, molecular characterisation and phylogenetic analysis of A. integrum collected from the area grazed by the sambar deer (Rusa unicolor) of Kerala, south India was performed using three molecular markers viz., the mitochondrial cytochrome c oxidase subunit 1 (COI), mitochondrial 16S ribosomal RNA, and nuclear 18S ribosomal RNA genes. Cytochrome c oxidase subunit 1 (COI) gene showed better resolving ability for elucidating the evolutionary relationship of A. integrum and identified two distinct clades, viz., A and B. The Tamil Nadu isolates of south India and Marayoor isolate 1 (from Idukki district of Kerala bordering with Tamil Nadu) belonged to clade A. Majority of Wayanad isolates from Kerala, occupied clade B. The intraspecific genetic distance among the A. integrum species ranged from 0.00 to 13.34%. Between clades A and B, the genetic distance observed was 11.49%. The clade B isolates were genetically close to A. geoemydae (GD: 1.22%). Morphological variations between the clades included darker exoskeletal coloration in clade A and distinct differences in the shape of basis capitulum. Further analysis using Assemble Species by Automatic Partitioning (ASAP) and Generalized Mixed Yule Coalescent (GMYC) provided additional insights. Assemble Species by Automatic Partitioning (ASAP) identified 26 Molecular Operational Taxonomic Units (MOTUs) at a threshold distance of 5.38%, supporting the species partition of A. integrum clade B. Generalized Mixed Yule Coalescent (GMYC) analysis retained the same species complex (A. integrum-geoemydae Complex) inferred from the ASAP analyses. It could be inferred from the present study that the A. integrum clades A and B could be two different putative pseudocryptic species.

New Identification Tools for the Nymphs of Three Amblyomma spp. Koch (Ixodida: Ixodidae) in South Texas

Taxonomic uncertainties and morphologic and molecular similarities may lead to incorrect or incomplete species identifications of immature ticks. This problem can be compounded when the diagnostic morphological features used are unreliable, unstable, or difficult to view. Our study attempts to sort out the similar morphologies of three Amblyomma spp. nymphs with partially overlapping geographic distributions in South Texas. Amblyomma americanum (L.), Amblyomma mixtum Koch, and Amblyomma tenellum Koch are three closely related species with similar nymphs and larvae. Previous attempts to morphologically distinguish among nymphs of these species have relied on difficult-to-observe and unreliable characters. Over the course of decades of routine diagnostic work with these ticks, we have observed and discovered consistent and useful morphologic features sufficient to practically distinguish among these nymphs. We confirmed our morphological studies with molecular genetic evidence (i.e., 12S mitochondrial genes), and we propose that practical, rapid morphological species-level identification of nymphs of the three named species is now possible with confidence.

Environmental Drivers of Gulf Coast Tick (Acari: Ixodidae) Range Expansion in the United States

In the United States, the Gulf Coast tick (Amblyomma maculatum Koch) is a species of growing medical and veterinary significance, serving as the primary vector of the pathogenic bacterium, Rickettsia parkeri (Rickettsiales: Rickettsiaceae), in humans and the apicomplexan parasite, Hepatozoon americanum, in canines. Ongoing reports of A. maculatum from locations outside its historically reported distribution in the southeastern United States suggest the possibility of current and continuing range expansion. Using an ecological niche modeling approach, we combined new occurrence records with high-resolution climate and land cover data to investigate environmental drivers of the current distribution of A. maculatum in the United States. We found that environmental suitability for A. maculatum varied regionally and was primarily driven by climatic factors such as annual temperature variation and seasonality of precipitation. We also found that presence of A. maculatum was associated with open habitat with minimal canopy cover. Our model predicts large areas beyond the current distribution of A. maculatum to be environmentally suitable, suggesting the possibility of future northward and westward range expansion. These predictions of environmental suitability may be used to identify areas at potential risk for establishment and to guide future surveillance of A. maculatum in the United States.

Extension of the distribution of Amblyomma triste Koch, 1844: Morphological and molecular confirmation of Morphotype I in Colombia

Ticks of the Amblyomma maculatum (Acari: Ixodidae) group are represented by three species: Amblyomma maculatum, Amblyomma tigrinum, and Amblyomma triste. This group is widely distributed throughout the Nearctic and Neotropical regions, from the United States of America (USA) to Argentina. They parasitize several vertebrates, including domestic mammals and humans. Nonetheless, the identification and distribution of the species within the group have been controversial but can be solved with integrative studies on their taxonomy and ecology. In Colombia, a Neotropical country from which up to 58 tick species have been reported, only Amblyomma maculatum Koch, 1844 (sensu stricto - s.s.) - morphotype II - has been molecularly confirmed. Here, specimens of the A. maculatum group from three departments of Colombia were examined by morphological and molecular analyses. The results confirmed the wide distribution of A. maculatum s.s. in Colombia. Furthermore, the presence of A. triste s.s. - morphotype I was confirmed for the first time at the molecular level, which broadens the distribution of this species in the American continent. Considering that both taxa are vectors of pathogens such as Rickettsia parkeri s.s., additional taxonomic, reproductive compatibility and niche distribution studies are needed, as well as the application of new molecular markers due to the controversial taxonomy. This will allow us to explore cryptic diversity within the recently established putative groups.