Abstract
Ixodida are composed of hard (Ixodidae), soft (Argasidae) and the monotypic Nuttalliellidae (Nuttalliella namaqua) tick families. Nuclear 18S rRNA analysis suggested that N. namaqua was the closest extant relative to the last common ancestral tick lineage. The mitochondrial genomes of N. namaqua and Argas africolumbae were determined using next generation sequencing and de novo assembly to investigate this further. The latter was included since previous estimates on the divergence times of argasids lacked data for this major genus. Mitochondrial gene order for both was identical to that of the Argasidae and Prostriata. Bayesian analysis of the COI, Cytb, ND1, ND2 and ND4 genes confirmed the monophyly of ticks, the basal position of N. namaqua to the other tick families and the accepted systematic relationships of the other tick genera. Molecular clock estimates were derived for the divergence of the major tick lineages and supported previous estimates on the origins of ticks in the Carboniferous. N. namaqua larvae fed successfully on lizards and mice in a prolonged manner similar to many argasids and all ixodids. Excess blood meal-derived water was secreted via the salivary glands, similar to ixodids. We propose that this prolonged larval feeding style eventually gave rise to the long feeding periods that typify the single larval, nymphal and adult stages of ixodid ticks and the associated secretion of water via the salivary glands. Ancestral reconstruction of characters involved in blood-feeding indicates that most of the characteristics unique to either hard or soft tick families were present in the ancestral tick lineage.
Highlights
IntroductionThe Ixodida (ticks) are composed of three families, Argasidae (soft ticks ,200 species), Ixodidae (hard ticks ,700 species) and the monotypic Nuttalliellidae [1,2].Differentiation of the Argasidae and Ixodidae is uncomplicated based on biology and morphology
The Ixodida are composed of three families, Argasidae, Ixodidae and the monotypic Nuttalliellidae [1,2].Differentiation of the Argasidae and Ixodidae is uncomplicated based on biology and morphology
Given the basal position of N. namaqua to the other tick families [5], this suggested that the ancestral arthropod gene order was conserved in the last common ancestral tick lineage
Summary
The Ixodida (ticks) are composed of three families, Argasidae (soft ticks ,200 species), Ixodidae (hard ticks ,700 species) and the monotypic Nuttalliellidae [1,2].Differentiation of the Argasidae and Ixodidae is uncomplicated based on biology and morphology. Hard ticks of all life stages possess a sclerotized scutum, an apical located gnathostoma, feed for prolonged periods (several days to weeks) and ingest more than 1006 their body mass in blood [3,4]. Larvae possess a sclerotized scutum, while nymphs and adults have a semisclerotized pseudo-scutum and their mouthparts are located apically [5,6,7,8]. It differs from the other families in that nymphal and adult stages possess ball and socket leg joints and blood mealderived water is secreted via the Malpighian tubules [5,6,7]. Classification with regard to its relationship to the other tick families based on morphology and biology remains problematic [1]
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