Document: MIC-3-56-20
Prey-induced size polymorphism in a ciliate predator.
KOPP, M.* 1 and R.TOLLRIAN 2
Max-Planck-Institute for Limnology, Ploen, Germany 1
Ludwig-Maximilian University, Munich, Germany 2
Abstract:
Food dependent size polymorphism in the predacious hymenostome ciliate Lembadion bullinum was assesed. In addition, morphological counter-reaction of a predator to inducible prey defenses was observed. When Lembadion was cultured with various prey ciliates,cell size was positively correlated with the size of the respective prey. Mean cell volume varied by about a factor of 2.5. Large prey could only be swallowed by large morphs of the predator. However, when confronted with a mixture of prey Lembadion always adjusted its size to that of the smallest prey species. To find the reason for this close correlation to the size of the smallest available prey, we measured short term feeding rates and long term growth rates under various conditions. The results show that small predators were more efficient in capturing small prey. In addition, when fed with small prey, small predators attained higher population growth rates than large predators. Lembadion also increased in size when one of its prey species, Euplotes octocarinatus, developed an inducible morphological defense ('winged morph'). The enlarged predators were better able to capture the defended prey. We conclude that the size polymorphism of Lembadion is an adaptation to maximize this predator's hunting efficiency (attack coefficient) under various feeding regimes. When small prey was present, small morphs of the predator were favored because large cell sizes were associated with demographic costs. Finally, the observation that Lembadion reacted plastically to morphological changes of Euplotes may lead to the hypothesis that this plasticity evolved as a coevolutionary adaptation to inducible defenses of its prey.
Keywords: coevolution, inducible defenses, phenotypic plasticity, predation, size polymorphism
This abstract is being presented at: 3:45 PM in session:
Oral Session #11: Trophic Cascades.