Morphologische Plastizität

The aim of this study was to reveal factors affiliated with morphological plasticity in Daphnia cucullata. This planktonic crustacean shows a seasonal variation in body shape that is commonly known as cyclomorphosis. Here I show that both predator-released chemicals and water-soluble “alarm” signals from wounded Daphnia can induce certain morphological features in Daphnia cucullata. Specifically, the inductive effect of the “alarm” signals is minute compared to the predator-exposed animals. Moreover, laboratory-generated small-scale turbulence was identified to be a proximate factor in cyclomorphosis. This special kind of turbulence is compared to turbulence evoked by the movement of other organisms. A distinct protective effect of the morphological traits against invertebrate predation was revealed as the likely ultimate factor of cyclomorphosis. Furthermore, a unique method of ultrasonic microscopy reveals “hidden” morphological plasticity in daphnids. The armor of predator-exposed animals is much stronger than that of those not exposed to predators. I developed a new SEM-preparation method to get detailed insight in ontogenesis in Daphnia. I detected morphological defenses in predator-chemical-induced Daphnia cucullata already in the last embryonic stage. Induction experiments on transgenerational effects in Daphnia cucullata show that defended mothers release offspring that are better defended than the descendants of unthreatened parents. Furthermore, daphnids could asses their actual predation risk by taking both predator and prey density into account. Thereafter the degree of a defense is adjusted to the individual hazard, thus saving unnecessary costs associated with the development of a particular defense. The combined results of this study indicate that cyclomorphosis in Daphnia cucullata has evolved as an adaptation to variable environments.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Ludwig-Maximilians-Universität

Year

2003

Author dc:creator

• Laforsch, Christian

Repository record source_url

https://edoc.ub.uni-muenchen.de/1632/

OAI identifier oai:identifier

oai:edoc.ub.uni-muenchen.de:1632