Meeting Abstract
Arachnids live in most terrestrial environments, but are underrepresented in thermal and environmental physiology datasets. As ectotherms, the activity of terrestrial arachnids is bounded by the critical thermal maximum (CTmax) and critical thermal minimum (CTmin). In Arctic and temperate climates, arachnids survive sub-freezing temperatures by either remaining unfrozen (freeze avoidant) or tolerating internal ice formation (freeze tolerant). In many arthropods, the thermal limits, and even cold tolerance strategy, are plastic. Here, we explore the thermal biology of a range of arachnids exposed to extreme conditions. We report that: The CTmin (mean= -3.6°C) and freezing temperature (supercooling point, SCP; mean= -6.9°C) are higher in the Beringian pseudoscorpion Wyochernes asiaticus (Yukon Territory) as compared to other small, high latitude ectotherms, as determined by previous studies. Whereas, the thermal limits (SCP and CTmax) of Arctic wolf spiders (Pardosa spp., Yukon Territory and Greenland; mean SCP= -5.4 to -8.0°C; mean CTmax=42.3 to 46.9°C) are also comparable to lower latitude ectotherms. These lower thermal limits are insufficient to allow arachnids to survive Arctic winters, therefore we tested for plasticity in the thermal limits. SCP and CTmax will change with acclimation in some Pardosa spp.; however, acclimation to low temperatures did not confer better low-temperature tolerance. Lastly, the temperate red velvet mite Allothrombium sp. is freeze-tolerant during winter. Thus, temperate and polar arachnids employ the full range of arthropod cold tolerance strategies.
