Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Sinclair, Brent J.

Abstract

Temperate and high latitude terrestrial ecosystems have high thermal variability, and the ectotherms that inhabit these regions must have thermal tolerances that mirror these temperatures. However, the thermal limits of many high-latitude arachnids are unknown, as well as any underlying mechanisms of seasonal plasticity for any arachnid. The objective of my thesis is to measure the thermal tolerances of temperate, Arctic, and sub-Arctic arachnids, and identify if they have thermal plasticity, either seasonally or following acclimation. I collected the high-latitude pseudoscorpion Wyochernes asiaticus streamside from the Yukon Territory, where besides large thermal variability, they are also inundated with spring flooding. I also collected a variety of wolf spiders (Genus Pardosa) in the Yukon, Greenland, and Norway, where they are abundant and active on the tundra in the Arctic summer. In the lab, half of the of the air-exposed and low oxygen water-submerged pseudoscorpions survived for 17 days; showing that they are likely adapted to seasonal flooding. The pseudoscorpions and spiders I collected in the summer have thermal tolerances (the low and high temperatures at which activity stops) that range from -6°C in both pseudoscorpions and spiders, to 37.8°C (in pseudoscorpions) and 45°C (in spiders). Following 4°C-acclimation, the spiders did not show an ecologically significant change in their thermal tolerance breadths (Tbr, the difference between their low- and high-temperature tolerance), potentially because their Tbr is large enough to remain active during summer temperatures. I collected the temperate and freeze-tolerant red velvet mite in late fall, mid-winter, and early spring to compare their lower lethal temperature, and potential mechanisms associated with cold-tolerance. In mid-winter, the hemolymph osmolality and glycerol content increases, and water content decreases: all likely cryoprotectant mechanisms. Temperate red velvet mites show seasonal acclimatization resulting in freeze-tolerance, the first evidence of freeze-tolerance in microarthropods.

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