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Amblyomma

Amblyomma, also known as the Bont Ticks, are a genus of hard ticks. Some are disease vectors, such as of Rocky Mountain spotted fever in United States or ehrlichiosis in Brazil.

This genus is the third largest in the family Ixodidae, after Ixodes and Haemaphysalis, with its species primarily occupying the torrid zones of all the continents. The centre of species diversity is on the American continent, where half of all the species occur. On this continent, Amblyomma species reach far beyond the torrid zone, up to the 40th parallel in the Northern Hemisphere, to the 50th parallel in the Southern Hemisphere, and even reaches the alpine zone of the Andes. They also occur in Eurasia, Africa and Australia.

Evolutionary history and systematics

Amblyomma is the largest genus in the Amblyocephalus lineage, and the only member of the Amblyomminae subfamily. Modelling suggests the most recent common ancestor (MRCA) of the Amblyocephalus originated approximately 48 million years ago, and the genus began to diversify approximately 37 ma. The Amblyomma MRCA likely evolved in a region between South America and Antarctica, lending credence to an out-of-Antarctica hypothesis for the genus' origin. A genetic divide in modern lineages between Australian Amblyomma and Amblyomma from the rest of the world supports the idea that the genus diverged in two directions out of Antarctica, with one lineage dispersing into Australian Gondwana, and another into South American Gondwana, at the end of the Eocene.

The genus has historically been large, and highly varied, morphologically, making circumscription criteria in accordance with genetic phylogenies difficult to define. Following the 2020 and 2024 excision of Africaniella and Cryptocroton species, respectively, Amblyomma is now monophyletic. Many species complexes remain unresolved, however. Additionally, most Amblyomma subgenera remain polyphyletic (Cernyomma, Anastosiella, Haemalastor, Xiphiastor, Adenopleura, Aponomma, and Dermiomma), with only Amblyomma (Amblyomma) and Amblyomma (Walkeriana) being monophyletic.

Description

Amblyomma species are medium to large, often ornamented ticks. They are subcircular to elliptical, with subpentagonal basis capituli and elongate mouthparts. Most species have eyes, except for those of the subgenus Amblyomma (Aponomma). Lateral grooves and festoons are usually distinct. Amblyomma ticks parasitise a wide range of vertebrates, except for amphibians.

The internal anatomy of Amblyomma species has been described in detail in a few species, including Amblyomma maculatum and Amblyomma variegatum.

Species

Fossil species

References