Abstract
Numerous prey organisms, including many rotifers, exhibit inducible defensive plasticity, such as spines, in response to predators. Here, we test the hypothesis that prey modify their defence response to different predator sizes with a bi-directional adjustment in spine length. First, we show experimentally, that large-sized predators induce a reduction in prey spine length. Second, we conducted a complementary field monitoring study showing that the spine length of the prey rotifer Keratella cochlearis changed in opposite directions, in response to the shift in dominance between small-sized and large-sized predators. Third, in order to test the generality of our novel findings, we conducted a meta-analysis covering a wide array of rotifer prey taxa, strengthening the conclusions from our experimental and field studies. Hence, by combining evidence from experiments and studies in the field with a meta-analysis, we, for the first time, demonstrate that rotifer prey distinguish between predators and adjust their protective spine length accordingly, i.e. rapidly adjust spine length to escape either below or above the dominant predator’s gape size window. In a broader perspective, our conclusions advance our knowledge on observed spatial and temporal variations in protective morphologies among prey organisms.
Highlights
Organisms in the wild simultaneously experience and handle a wide array of threats that may fluctuate in intensity both spatially and temporally
After exposure to the predator-conditioned medium for 12 days, the posterior spine length of K. cochlearis was significantly affected by kairomones from these predators
That large-sized predators induce a reduction in rotifer spine length
Summary
Organisms in the wild simultaneously experience and handle a wide array of threats that may fluctuate in intensity both spatially and temporally. On the other hand, constrained by their prey-size choices, for example by gape-size limitations and it has been repeatedly demonstrated that, in order to reduce the predation rate, prey respond by growing larger than the gape size limit of the predators[7, 8] It may be adaptive for a prey to escape from predation through avoiding the lower range of a predator’s gape size, this has rarely been demonstrated[9]. Growing longer spines may be adaptive towards small predators, they may instead be maladaptive when large predators dominate This suggests that it may be adaptive to develop longer spines when small predators dominate[10], reduced spine length should allow escaping from the optimal gape-size of larger predators. Based on a synthesis of these three approaches we demonstrate, for the first time, that the induction of protective spines in a common invertebrate prey is bi-directional and driven by the dominant predator
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