Multiple predator defence strategies in Daphnia pulex and their relation to native habitat

Abstract

Daphnia may respond with an array of anti-predator defences (behavioural, morphological and life history) to a chemical cue (kairomone) exuded by its predators: fish and Chaoborus. Given the wide array of potential responses, it is an interesting question whether anti-predator defences are coupled or independent of each other. Since anti-predator responses are costly and even possessing the genetic information to respond to a certain predator might involve a cost, clones may only react to predators they co-occur with in nature. In this study, we provide evidence for an uncoupling of responses by Daphnia pulex in several anti-predator defences against Chaoborus. We were unable to detect a correlation between behavioural (migration), morphological (neck-spine induction) and life history [growth rate, neonate size and size at first reproduction (SFR)] responses. Furthermore, anti-predator responses did not always comply with what is commonly believed. We found that Daphnia clones can migrate up or down when exposed to fish or Chaoborus kairomone and that population growth rate, neonate size and SFR can increase or decrease in response to Chaoborus kairomone. We also show patterns in anti-predator defences that seem to relate to the habitat from which clones were derived. Daphnia clones that were collected in habitats with Chaoborus as the dominant predator tended to react strongly to Chaoboms kairomone by migrating upward and producing neck-spines. The migration behaviour against fish kairomone in these clones was often an unexpected upward migration. The Daphnia clone that co-existed with fish predators showed a downward migration in the presence offish as well as Chaoborus kairomone. Clones that had occurred with either both or no predators had mixed responses. We sometimes found an upward migration in combination with smaller body size as a response to Chaoborus kairomone. This may be interpreted as a behavioural defence against Chaoborus and a life-history defence against fish. Daphnia seem not to exhibit defence behaviour against predators they do not co-occur with. It might be costly for Daphnia to maintain genetic information to respond to these predators and protect that information from genetic drift.