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.
