Thermal limits of summer-collected Pardosa wolf spiders (Araneae: Lycosidae) from the Yukon Territory (Canada) and Greenland

摘要

Arctic and sub-Arctic terrestrial ectotherms contend with large daily and seasonal temperature ranges. However, there are few data available on the thermal biology of these high-latitude species, especially arachnids. We determined the lower and upper thermal limits of seven species of wolf spider from the genus Pardosa (Araneae: Lycosidae) collected in summer from the Yukon Territory (Canada) and Southern Greenland. None of these species survived freezing, and while spiderlings appeared freeze-avoidant, surviving to their supercooling point (SCP, the temperature at which they spontaneously freeze), chill-susceptible adults and juveniles died at temperatures above their SCP. The critical thermal minimum (CTmin, the lower temperature of activity) and SCP were very close (spiders continued moving until they freeze), and at - 5.4 to - 8.4 degrees C, are not substantially lower than those of lower-latitude species. The SCP of spiderlings was significantly lower than that of overwintering juveniles or adults, likely because of their small size. There was no systematic variation in SCP among collection sites, latitude, or species. Critical thermal maxima (CTmax) ranged from + 42.3 to + 46.8 degrees C, showed no systematic patterns of variation, and were also similar to those of lower-latitude relatives. Overall, heat tolerances of the Pardosa spp. were likely sufficient to tolerate even very warm Arctic summer temperatures, but cold tolerance is probably inadequate to survive winter conditions. We expect that seasonal thermal plasticity is necessary for overwintering in these species.