Document: CHR-3-56-13

Cyclomorphosis in Daphnia cucullata - An adaptation against multipredator environments.

LAFORSCH, C.* and R.TOLLRIAN

Ludwig-Maximilians-Universität, München, Germany ¹

Abstract:
Cyclomorphosis in Daphnia cucullata has attracted the attention of scientists since the beginning of the last century. Although it is used as a textbook example of phenotypic plasticity, little is known about the proximate and ultimate factors of this phenomenon. Helmets from several daphnids have been induced with Chaoborus kairomones. However small cladocerans such as Daphnia cucullata are prey items for many invertebrate predators. Thus we tested the hypothesis that helmets offer protection in multipredator environments. Results from our induction experiments showed that chemical cues from Chaoborus flavicans, Leptodora kindtii, Cyclops sp. and Acari are proximate factors of cyclomorphosis in Daphnia cucullata. All the above were able to induce distinctly longer helmets and longer tail spines in Daphnia cucullata. Our predation experiments revealed that the induced morphological changes offered protection against each of the predators tested. In the experiment with Leptodora kindtii, helmeted daphnids greater than 600 m body length were less often eaten than the typical morph. Feeding trials with Cyclops sp. has achieved that even small induced Daphnia cucullata had a significant advantage. Direct observations of Chaoborus flavicans predation on the two different morphs indicate that there is a clear post- contact advantage for the intermediate and lager size classes of the helmeted morph. Our results imply that phenotypic plasticity in Daphnia cucullata has evolved as an adaptation against different kind of invertebrate predators.

Keywords: phenotypic plasticity, inducible defences, multipredator environments, Daphnia cucullata, invertebrate predators, Cyclomorphosis

This abstract is being presented at: 3:15 PM in session:
Oral Session #47: Zooplankton Ecology.