Phylogenetic and genetic population analyses of Amblyomma ovale (Parasitiformes: Ixodidae) from Brazil and Central America.

Amblyomma ovale is a widespread hard tick in Neotropics and it is an important vector of pathogens, particularly Rickettsia parkeri strain Atlantic rainforest, which causes a spotted fever illness in humans. Adult ticks primarily parasitize medium and large mammals, such as carnivores, while larvae and nymphs feed on small mammals and occasionally on birds. In Brazil, the species is found in all six major biomes (Amazon, Atlantic forest, Cerrado, Caatinga, Pantanal, Pampa), and is generally found in humid, forested areas. Despite its broad range, large-scale genetic studies have been lacking. This study analyzed the genetic diversity and population structure of A. ovale using five gene markers (four mitochondrial, one nuclear) in 57 specimens from Brazil (five biomes) plus Panama and Belize. High haplotype diversity was found for all markers, with numerous unique haplotypes and many biome-specific groupings. Phylogenetic analyses (maximum parsimony and maximum likelihood) revealed two major genetic clusters: one predominantly from Atlantic forest A region and another comprising samples from Atlantic forest B, other Brazilian biomes, and Central America. The nuclear marker (ITS2) exhibited low polymorphism and did not mirror mitochondrial patterns. This different pattern between mitochondrial and nuclear markers could be attributed to the over-resolution of mtDNA that can occur because the small inbreeding effective population size (Ne) of the mitochondrial genes may lead to coalescence of mtDNA lineages that are only temporarily isolated. Population genetic analyses (AMOVA and FST) revealed significant structuring among most regional populations, but no strong correlation between geographic and genetic distances (no isolation by distance). Neutrality tests indicated possible population expansion in the Atlantic forest B group. Overall, A. ovale exhibits high genetic diversity with some biome-linked clustering, especially between Atlantic forest subregions, as evidenced by mitochondrial markers. The tick's broad host range and high movement may reduce isolation, thereby maintaining gene flow across regions. Given the public health importance of A. ovale as a vector of spotted fever, understanding this genetic variation could inform disease ecology and risk in different biomes.