Behavioral Ecology Advance Access originally published online on February 12, 2009
Behavioral Ecology 2009 20(2):251-257; doi:10.1093/beheco/arp014
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Living with the dead: when the body count rises, prey stick around
a UMR 1099 INRA-Agrocampus Ouest-Université Rennes I "Biologie des Organismes et des Populations appliquée à la Protection des Plantes" [BIO3P], 65 rue de Saint-Brieuc CS 84215, 35042 Rennes Cedex, France b UMR 1099 INRA-Agrocampus Ouest-Université Rennes I "Biologie des Organismes et des Populations appliquée à la Protection des Plantes" [BIO3P], 263 Av. du Général Leclerc CS 74205, 35042 Rennes Cedex, France
Address correspondence to Y. Outreman, Agrocampus Ouest, Laboratoire Ecologie et Sciences Phytosanitaires, 65 rue de Saint-Brieuc CS 84215, 35042 Rennes Cedex, France. E-mail: yannick.outreman{at}rennes.inra.fr.
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Abstract |
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Most terrestrial prey species are assumed to assess predation risk by detecting predators directly rather than using cues of previous attacks on conspecifics. However, such cues might represent valuable information, and prey can be expected to respond to the presence of congeners killed by enemies. Such cues are available in aphid colonies attacked by parasitic wasps because they do not remove parasitized hosts from the colony. Colonies are thus often a mixture of healthy, parasitized, and killed aphids, which corpses ("mummies") stay attached to the plant and can be encountered by live aphids. Aphids exhibit a dispersal polyphenism. Recent studies show that they produce more winged offspring when directly exposed to natural enemies or to alarm pheromone emitted by conspecifics. We hypothesized that aphids perceive the corpses of congeners killed by parasitoids and respond by increasing the production of winged morphs, but we surprisingly found the opposite. We determined the adaptive value of this response by analyzing the foraging behavior of parasitoids in aphid colonies with killed aphids ("mummies"). Parasitoid females responded to the presence of mummies by reducing both their time allocation and parasitism activity in the patch. The strategy of aphids to reduce emigration (i.e., they produce more wingless morphs when mummies are present) is adaptive because the presence of killed congeners reduces parasitoid pressure on colonies. This demonstrates that the remains of individuals killed by natural enemies can still have an ecological relevance in prey populations and that enemy-induced phenotypic plasticity depends on the type of predation cues.
Key words: aphids dispersal morph, "dead zone effect", killed congeners, parasitoids foraging behavior, phenotypic plasticity, predation risk cues.
Received 2 April 2008; revised 22 December 2008; accepted 12 January 2009.