Amblyomma quadricavum (Schulze, 1941) (Acari:Ixodidae): First Description of the Nymphal Stage and Phylogenetic Assessment of Its Taxonomic Status

The hard tick (Acari: Ixodidae) Amblyomma quadricavum (Schulze, 1941) is a parasite of snakes and is endemic to the Caribbean region. Morphological characters of this species, namely its rudimentary eye structures, have led to debate about its taxonomic status. The species was originally assigned to the genus Aponomma. However, with revisions of the genus Aponomma, and the recent creation of new genera created for some basal former-Aponomma, it has been suggested that perhaps Amblyomma quadricavum might be a close relative of Robertsicus elaphensis, the Trans-Pecos rat snake tick of the southwest United States and New Mexico, another eyeless former-Aponomma species that was recently assigned to a new genus. Herein, six molecular markers were used to analyze the taxonomic status of Amblyomma quadricavum: three mitochondrial genes (cytochrome c oxidase I [COI], 12S rDNA, and 16S rDNA) and three nuclear genes (internal transcribed spacer 2 [ITS2], 18S rDNA, and 28S rDNA). A concatenated tree of ITS2 and 12S rDNA datasets was created to increase the resolution of basal lineages. The phylogenetic results proved that Amblyomma quadricavum and Robertsicus elaphensis are not closely related. It was also supported that reptile parasitism evolved multiple times within Amblyomma. Additionally, the nymphal stage of Amblyomma quadricavum was described for the first time. Morphologically, Amblyomma quadricavum stood out as the only Caribbean endemic Amblyomma tick that is associated with snakes that has a rudimentary eye structure and is not ornamented