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Facing multiple predators - phenotypic integration in multiple antipredator traits

Final Report Summary - INTERATING DEFENCES (Facing multiple predators - phenotypic integration in multiple antipredator traits)

Phenotypic plasticity, the flexibility that animals and plants show in the face of varying environments, remains a central theme in ecology, evolution and developmental biology. It is incorporated across scales in our explanation of the causes and consequences of variation among and between species2. Predator induced phenotypic plasticity is a popular and exciting form of plasticity highlighted by ecologists, evolutionary biologists and developmental biologists. An emerging question in research on predator induced plasticity is how prey integrate their response to multiple predator threats, within a seasons and across morphological and life history traits. We examined the integration of predator induced behavioural, morphological and life history traits to spatial variation from multiple sources of predation risk in the classic system of water fleas (Cladocera) and its array of predators (predatory fish and phantom midge larvae (Chaoborus spec.)). The main objectives were : (i) within-and-between-predator-regimes, to test the hypothesis that predators of different size selectivity will generate different tradeHoffs among a suite of life historical and morphological traits. Studying plastic responses in the solitary presence of different predator species, we develop a picture of the integrated strategy of each preyHpredator combination, genetic variability (crossHclone) in this strategy and variation along the prey body size and predator hunting mode gradient. (ii) under-multiple-predator-regimes., to evaluate how prey responds to multiple predator pressure. We tested the hypothesis that multiple predators induce additive effects on trait integration. The alternatives are that multiple predators that induce different responses in multiple traits will produce phenotypes that are not the sum of the reactions to each predator but represent either a generalised phenotype being intermediately effective, a phenotype ineffective to multiple predators or a phenotype being only effective against the most dangerous predator.

Results show that the solitary presence of either predatory fish or Chaoborus increased integration measured as the overall number of partial correlations (Fig. 1). In absence of any predator, two independent character modules exist with traits being able to change independently across modules, however, dependent changes occurring within modules. The increase of threat of predation by density predatory fish and Chaoborus let vanish these modules and resulted in an overall higher integration (increase in number of partial correlations). This indicates that the presence of single predator types increase levels of trait integration enabling prey to react to the threat of predation in a combined multiple trait manner. However, the simultaneous presence of both predators differing in sizeHselectivity does not increase the level of integration but lead to new trait modules (Fig. 1). The presence of two predators with opposing selective direction (predatory fish selecting for small and Chaoborus selecting for large individuals) let daphnids decrease the level of integration and form new character modules. This provides evidence that the threat of multiple predators is not a sum of the reactions to each predator but rather a product of specific environmental combinations by e.g. predators.