Leg autotomy in a spider has minimal costs in competitive ability and development

A number of species have the ability to autotomize limbs voluntarily, but a nimals that have lost limbs often face substantial costs. We examined the f requency of leg loss and its effects on competitive ability and development in the spider Holocnemus pluchei (Araneae: Pholcidae), a family of spiders known for its readiness to autotomize legs. Leg loss was common in field p opulations, with 7.5% of all surveyed spiders missing at least one leg, mos t commonly one of the anterior pair. More spiders were missing multiple leg s than expected by chance, suggesting that leg loss events are not independ ent. Large adult spiders were missing legs more frequently than were small spiders. The competitive ability of injured males was tested in three conte xts. In the field, no effect of leg loss was found on the ability of spider s,to remain in webs into which they were introduced. In the laboratory, no effect of leg loss was found on the ability to fight with a single opponent over a prey, except that injured spiders were more likely to lose high-int ensity fights. There was no difference between intact and injured males in their ability to compete with three females for limited prey. Leg loss sign ificantly affected development time. The moult interval during the instar i n which the injury occurred increased by approximately 15%. However, the gr owth rate for injured spiders was slightly but not significantly faster in the instar following leg loss, and total development time of the two instar s together did not differ significantly between treatments. No spider showe d any signs of regeneration. We conclude that, although there were some sta tistically significant differences between intact and injured males, these are unlikely to have major impacts on fitness, in contrast to findings in o ther species. (C) 1999 The Association far the Study of Animal Behaviour.