Phylogenetic analysis of ticks (Acari: Ixodida) using mitochondrial genomes and nuclear rRNA genes indicates that the genus Amblyomma is polyphyletic.

Our understanding of the phylogenetic relationships among tick lineages has been limited by the lack of resolution provided by the most commonly used phylogenetic markers. Mitochondrial genomes are increasingly used to address controversial phylogenetic relationships. To date, the complete mitochondrial genomes of eleven tick species have been sequenced; however, only three of these species are metastriate ticks, the most speciose lineage of ticks. In this study, we present the nucleotide sequences of the complete mitochondrial genomes of five more species of metastriate ticks: Amblyomma elaphense, Amblyomma fimbriatum, Amblyomma sphenodonti, Bothriocroton concolor and Bothriocroton undatum. We use complete mitochondrial genome sequences to address the phylogenetic placement of two morphologically 'primitive' species -Am. elaphense and Am. sphenodonti - with respect to the genus Amblyomma. Our analysis of these five mitochondrial genomes with the other eleven tick mitochondrial genomes, as well as analysis of nuclear rRNA genes, provides strong evidence that the genus Amblyomma is polyphyletic with the inclusion of Am. sphenodonti and Am. elaphense. A new genus or two new genera may be required to describe Am. sphenodonti and Am. elaphense. It is also possible that these two species are sisters to two established genera, Bothriocroton in the case of Am. sphenodonti, and Haemaphysalis in the case of Am. elaphense. However, other arrangements of these taxa cannot be excluded with the current data. Thus, while Am. sphenodonti and Am. elaphense do not belong in the genus Amblyomma, the phylogenetic placement of these two species cannot be resolved without more data from metastriate ticks, either greater sampling of mitochondrial genomes, or a large data set of nuclear genes.