Preferred Temperatures of Two Species of Lycosid Spiders, Pardosa sierra and P. ramulosa1

Abstract

Pardosa sierra Banks and P. ramulosa (MacCook) were tested for their preferred temperatures in a temperature gradient, at 43% relative humidity. Tests were conducted on the spiders within 3 days of capture, and duplicate trials were carried out on cold-acclimated spiders kept at 7°C for 20 days. Both species were divided into 4 groups; unsexed immatures, adult males, adult females without egg sacs, and females with egg sacs. The mean preferred temperatures for nonacclimated P. sierra and P. ramulosa were 33.8 and 26.3°C, respectively. Acclimation to 7°C had no significant effect on the thermal preferences of these spiders. In both species, the immatures selected lower temperatures than did the males, which in turn selected lower temperatures than did the females. The females with egg sacs had the highest preferred temperatures in both species. This feature may be due to a behavioral mechanism which allows the eggs and spiderlings in the egg sacs to be exposed to an incubation temperature which may be necessary for their proper development. There were significant differences between the selected temperatures of both species in each of the groups, under both nonacclimated and acclimated conditions.