Cold-hardiness in the Antarctic tick, Ixodes uriae.
Ixodes uriae White (Ixodidae, Acarina) is the predominant tick on the Antarctic peninsula.This species has a circumpolar distribution in both hemispheres and is associated with or known to parasitize 48 species of seabirds. Large colonies of 1,000 or more individuals of all life stages were found beneath rocks on the periphery of penguin rookeries near Palmer Station, Anvers Island. All life stages (egg, larva, nymph and adult) were intolerant of freezing. Engorged nymphs and larvae had supercooling points between -18 and -20 C. Eggs had the lowest supercooling points (-28.7 C) white adults had the highest values (from -7 to -13 C). Acclimation to temperatures between -12 and +25 C for 2 weeks had no effect on the supercooling point of engorged immobile nymphs. Desiccation of engorged nymphs to 80% of their initial weight resulted in no change in supercooling points or glycerol levels. In January, engorged nymphs enter a state of apolysis and lose mobility. Correlated with this change is an increase in cold tolerance as evidenced by a decrease in supercooling points from -11.5 to -19.5 C. This species exhibits the greatest range of thermal tolerance, from -30 to 40 C, reported for any Antarctic terrestrial arthropod. Except for a short period associated with feeding, I. uriae remains in a permanent state of cold-hardiness throughout the year.