The Effects of Size, Sex, and Reproductive Condition on Thermal and Desiccation Stress in a Riparian Spider (Pirata Sedentarius, Araneae, Lycosidae)

Within a species, physiological tolerances and thermoregulatory behaviors may vary among ontogenetic stages or between sexes. Such different tolerances can strongly affect the ecology and life history of a species. In a laboratory study, we tested the hypothesis that Pirata sedentarius Montgomery 1904 is differentially susceptible to thermal/desiccation stress by size and sex. As predicted, male adults were more susceptible to thermal/desiccation stress than females. Unexpectedly, however, juvenile spiders survived longer under thermal/desiccation stress than adults. Furthermore, female adults without egg sacs displayed a trend toward higher thermal/desiccation tolerance than females carrying egg sacs. These results suggest that for P. sedentarius, microhabitat preferences and/or thermoregulatory behaviors may change over the course of development, and may vary between sexes and between females with and without egg sacs.