Conspecific alarm cues induce an alternative reproductive strategy in aquatic oligochaetes

Although strategies that increase the survival of a predator attack have been widely observed, the strategy of altering reproductive effort under predation threats has not been well documented. A switch to sexual reproduction or an increased asexual reproductive rate may be inducible antipredator strategies in animals that are capable of both asexual and sexual reproduction. The results of laboratory experiments with two oligochaete species, Stylaria lacustris (L.) and Nais christinae Kasprzak, indicated that an increased asexual reproductive rate, a less typical strategy in response to alarm cues from conspecifics, is employed by the Naididae worms. The oligochaetes of both species exposed to conspecific cues also used the additional strategy of increased length at fission and consequently the increased length of parental worms and descendants after fission. The increase in body length appears to be beneficial in the case of sublethal predation by invertebrates. The similar life history changes observed in these two oligochaete species may be a universal adaptation against diverse predators that are abundant in the littoral zone.