Trophic Size Polyphenism in Lembadion Bullinum: Costs and Benefits of an Inducible Offense

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. Corresponding Editor: S. Nylin

Selective feeding behaviour of key free-living protists: avenues for continued study

“…Ingestion sensu strictu is limited by the morphological features of the predator, but unsuitable prey can be rejected (Stoecker et al 1995, Boenigk & Arndt 2000. To (partially) overcome such restrictions, a predator may have the capacity to enlarge its oral region (Kopp & Tollrian 2003a, 2003b or be adapted to digest cells extracellularly. However, in the case of radiolaria, feeding behaviour and diet are clearly related to skeletal morphology, and multi-segmented spumellarians ingest larger-sized prey compared to solitary spumellarians (Matsuoka 2007).…”

Evolutionary ecology of inducible morphological plasticity in predator–prey interaction: toward the practical links with population ecology

“…This approach has been instrumental in documenting the taxonomic prevalence of inducible defenses (Torllian and Harvell 1999;DeWitt and Scheiner 2004) and has shed considerable light on the adaptive value of trait plasticity (Lively 1986a,b;Kopp and Tollrian 2003a;Kishida and Nishimura 2005;Benard 2006). These insights have been further enhanced by studies of the role of inducible defenses in driving the evolution of geographic variation in prey phenotypes (Lively et al 2000;Trussell 2000a,b;Trussell and Smith 2000;Relyea 2002a;Trussell and Nicklin 2002;Laurila et al 2006;Kishida et al 2007) and the genetic basis of morphological plasticity via quantitative genetic (Relyea 2005a) and molecular genetic (Mori et al 2005(Mori et al , 2009) approaches.…”

Adaptive value of a predatory mouth-form in a dimorphic nematode

“…Previous analyses of polyphenisms have predicted fitness advantages by inferring costs and benefits of alternative forms [43][44][45][46]. In examples analogous to the predatory feeding dimorphism of P. pacificus, the densitydependent induction of predatory or cannibalistic morphs in ciliates [47,48], rotifers [49], Ambystoma salamanders [50][51][52] and spadefoot toads [6] have shown in particular how plasticity allows a rapid adaptive response that includes novel feeding strategies. However, the measurements of direct fitness that are required to test the adaptive value of alternative forms, specifically in the absence of heritable and environmental variation, are difficult to achieve in many systems.…”