halitschke et al 2008

halitschke et al 2008 - Ecology Letters, (2008) 11: 2434...

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LETTER Shared signals – Ô alarm calls Õ from plants increase apparency to herbivores and their enemies in nature Rayko Halitschke, 1 Johan A. Stenberg, 2 Danny Kessler, 3 Andre ´ Kessler 1 and Ian T. Baldwin 3 * 1 Department of Ecology and Evolutionary Biology, Cornell University, E443 Corson Hall, 14853 Ithaca, NY, USA 2 Department of Ecology and Environmental Science, Umea ˚ University, SE-90187 Umea ˚, Sweden 3 Department of Molecular Ecology, Max-Planck-Institute for Chemical Ecology, Hans- Kno ¨ ll-Str. 8, DE-07745 Jena, Germany * Correspondence: E-mail: baldwin@ice.mpg.de Abstract The attraction of natural enemies of herbivores by volatile organic compounds as an induced indirect defence has been studied in several plant systems. The evidence for their defensive function originates mainly from laboratory studies with trained parasitoids and predators; the defensive function of these emissions for plants in natural settings has been rarely demonstrated. In native populations and laboratory Y-tube choice experiments with transgenic Nicotiana attenuata plants unable to release particular volatiles, we demonstrate that predatory bugs use terpenoids and green leaf volatiles (GLVs) to locate their prey on herbivore-attacked plants. By attracting predators with volatile signals, this native plant reduces its herbivore load – demonstrating the defensive function of herbivore-induced volatile emissions. However, plants producing GLVs are also damaged more by flea beetles. The implications of these conflicting ecological effects for the evolution of induced volatile emissions and for the development of sustainable agricultural practices are discussed. Keywords cis - a -bergamotene, Epitrix hirtipennis , flea beetle, Geocoris pallens , kairomone, Manduca sexta , predation, tritrophic interaction. Ecology Letters (2008) 11: 24–34 INTRODUCTION Plants use both direct and indirect defences to protect themselves against herbivore attack, and the genes that mediate these defences are rapidly being elucidated in model plant systems (Gatehouse 2002). However, our understand- ing of whether these traits function as defences in plants Õ natural environments has not kept pace. A recent example is the discovery (Kappers et al. 2005; Schnee et al. 2006) of genes involved in the biosynthesis of herbivore-induced (HI) volatile organic compound (VOC) emissions that attract natural enemies to plants attacked by herbivores and thereby function as an induced indirect defence: a volatile Ô alarm call Õ (Dicke & Sabelis 1988). Fitness bene±ts have been demonstrated for maize (Hoballah & Turlings 2001) and Arabidopsis thaliana (van Loon et al. 2000) plants infested by parasitized herbivores compared with plants attacked by non-parasitized herbivores, suggesting a ±tness-increasing effect of a VOC-mediated attraction of parasitoids. For the majority of the studied systems, these bene±cial effects of HI-VOCs remain to be demonstrated under natural conditions outside of well-controlled laboratory experiments with trained predators and parasitoids. De Moraes et al.
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halitschke et al 2008 - Ecology Letters, (2008) 11: 2434...

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