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

Abstract

A number of species have the ability to autotomize limbs voluntarily, but animals that have lost limbs often face substantial costs. We examined the frequency of leg loss and its effects on competitive ability and development in the spiderHolocnemus pluchei(Araneae: Pholcidae), a family of spiders known for its readiness to autotomize legs. Leg loss was common in field populations, with 7.5% of all surveyed spiders missing at least one leg, most commonly one of the anterior pair. More spiders were missing multiple legs than expected by chance, suggesting that leg loss events are not independent. Large adult spiders were missing legs more frequently than were small spiders. The competitive ability of injured males was tested in three contexts. In the field, no effect of leg loss was found on the ability of spiders 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-intensity fights. There was no difference between intact and injured males in their ability to compete with three females for limited prey. Leg loss significantly affected development time. The moult interval during the instar in which the injury occurred increased by approximately 15%. However, the growth rate for injured spiders was slightly but not significantly faster in the instar following leg loss, and total development time of the two instars together did not differ significantly between treatments. No spider showed any signs of regeneration. We conclude that, although there were some statistically significant differences between intact and injured males, these are unlikely to have major impacts on fitness, in contrast to findings in other species.