On the Origin of soft ticks (Parasitiformes, Ixodoidea, Argasidae)

Abstract

The origin of the common evolutionary branch of soft and hard ticks is dated to the later Permian, approximately coinciding with the Permian extinction, and divergence of the common branch of Ixodoidea into ancestral forms of Argasidae and Ixodidae occurred in the Triassic. Ancestors of the common branch of Ixodoidea (Ixodidae, Argasidae, Nuttalliellidae) were not bloodsucking arthropods and were closely related to modern representatives of Holothyridae. Bloodsucking and, later, temporary ectoparasitism had developed only after divergence of the main branches (Ixodidae, Argasidae and Nuttalliellidae), independently in each group. At early stages of the soft tick evolution, bloodsucking was a short-time process, long-time feeding had developed later in larvae and promoted dispersal of ticks. Maintenance of the short-time feeding can be explained by adaptation to dwelling in bird nests or in shelters visited by birds, and later, also in mammal burrows. Displacements of gnathosomе to the ventral side of idiosome hampered combing of a parasite from the host during short-time bloodsucking. Short-time feeding resulted in maintenance and development of coxal glands as the main organ for removal of superfluous liquid during bloodsucking. Adaptation to shelter habitats (nests, burrows, rock crevices, under dead tree cork, etc.) promoted development of polyphagia and adaptations for long-term starvation.