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Free keywords:
ciliates; cost-benefit analysis; demographic costs; feeding rate; gape-limited predator; inducible offense; Lembadion bullinum; phenotypic plasticity; population growth rate; predator-prey interaction; trophic size polyphenism
Abstract:
Trophic polyphenisms are examples of phenotypic plasticity where two or more morphs within a species exploit different food niches. In this context, induced traits that enhance feeding ability on certain prey types have been termed inducible offenses. Here, we describe a prey-induced continuous size polyphenism in the predatory ciliate Lembadion bullinum. Further to previous reports of "giant cannibals" in this species, we show that Lembadion is able to gradually adjust its size to the size of its prey. Large size acts as an inducible offense, since large morphs have an increased gape-size and can exploit a wider food range than small morphs. Despite-these benefits, large morphs reduce their size whenever small prey is available. This suggests that their fitness is governed by a trade-off. We experimentally demonstrate this trade-off by showing that, when offered small prey, large morphs achieve lower volume-specific feeding rates and lower maximal population growth rates than small morphs. Both results highlight that large morphs suffer demographic costs that make them inferior in small-prey environments. Consequently, inducible predator offenses may evolve as adaptations to situations where important prey characteristics vary with space or time.
