Thermal limits of summer-collected Pardosa wolf spiders (Araneae: Lycosidae) from the Yukon Territory (Canada) and Greenland
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 °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 °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.
KeywordsEctotherm Supercooling point CTmax CTmin Pardosa Critical thermal limits
We would like to thank M. McFarlane, S. Turney, A.-S. Caron, A. Asmus, M. Skytte, T. Henrikson, M. Nielsen, B. Danielsen for collections in the field and C. Howard and A. Howard for logistical support. We would also like to thank DMI Is Centralen (Ice Patrol) for providing lodging and laboratory space in Greenland, and J. Aukema, J. Vanstone, D. Sweiger, and C. Cook of Western University for construction of “Freezy McFreezeface” (our Peltier temperature control device). Financial support was provided by a Northern Scientific Training Program grant to SEA, the Natural Sciences and Engineering Research Council of Canada (NSERC) via Discovery Grants to BJS and CMB, and a Northern Research Supplement to CMB, Western University via a strategic support grant to BJS, The Carlsberg Foundation (Grant CF14-0992) and Arctic Research Center at Aarhus University to TTH. Thanks to Joe Bowden and three anonymous referees for comments that improved the manuscript.
Funding was provided by Natural Sciences and Engineering Research Council of Canada, Northern Studies Training Program, The Carlsberg Foundation (Grant No. CF14-0992).
Compliance with ethical standards
Conflict of interest
There are no conflicts of interest to declare.
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