Sublethal predation on Stylaria lacustris: a study of regenerative capabilities

Abstract

Research on predator–prey interaction has generally ignored the possibility of prey injury by predator. Although injured prey usually constitute a minor group in a population, sublethal predation can play an important role in some aquatic assemblages. In a laboratory experiment, I tested the effect of attack by larvae of the damselfly Ischnura elegans and tanyponid Clinotanypus nervosus on the oligochaete Stylaria lacustris. Predation by these insect larvae caused damage to the prey which then are able to escape and survive. More than 50% of the worms used in the experiment were damaged by C. nervosus. Results of predation by I. elegans larvae of different lengths showed that the number of damaged worms decreased with the length of predatory larvae. Small predators injured more worms than large ones, which killed and totally consumed most of the prey. Damage to S. lacustris usually involves the loss of anterior, posterior or both these fragments (middle part preserved). An analysis of the survival of worms revealed that individuals which lost anterior, posterior, or both fragments survived equally well as control ones, with the exception of worms that lost 70% of the body length posteriorly amputated. It should be noted that these worms were the least numerous in all worms damaged by predators. The laboratory experiment on the regenerative capability of S. lacustris showed that after amputation, all worms regenerated the lost structures and started to increase in length. The small individuals after amputation of both anterior and posterior fragments achieved their initial length in the course of the experiment. It is likely that the regenerative capability in S. lacustris is an adaptation to sublethal effects of predation, which seems to play an important role in littoral assemblages dominated by oligochaetes.