Between-sex variation in running speed and a potential cost of leg autotomy in the wolf spider Pirata sedentarius

Leg autotomy in spiders is a relatively common occurrence, usually resulting from agonistic interactions with predators or conspecifics. While autotomy has immediate benefits, due to enhanced survival probability, it also potentially decreases future fitness. One possible cost of losing a leg is a reduction in burst running speed, which may affect prey capture and predator avoidance behaviors in wandering spiders. We examined sprint speed in intact and autotomized males and females of the wolf spider Pirata sedentarius from two stream banks in New York in an effort to determine if the sexes differed in either sprint speed or the potential cost of leg loss. Autotomy was fairly common in the field, with 18-22% of spiders missing at least one leg at our two sites. Males and females did not differ in frequency of leg loss. Females were larger than males (both in terms of mass and structural size) and ran significantly faster both before and after autotomy. Sprint speed was uncorrelated with body size (mass, carapace width or leg length) for males, while for females the only significant relationship was that between mass and pre-autotomy speed. Both sexes ran significantly faster when they had all legs compared to their speed after autotomy. We found no difference in speed between spiders which had lost a leg in the field and spiders from which we removed a leg in the laboratory or between intact spiders and spiders collected in the field with a leg missing. Overall, our results for P. sedentarius indicate that: (1) females are faster than males, (2) autotomy significantly reduces sprint speed in the lab for both sexes and (3) reductions in male sprint speed in the lab may result from a combination of autotomy and aging effects, while decreases in female speed are likely due primarily to autotomy.