J Chem Ecol (2014) 40:313–314 DOI 10.1007/s10886-014-0415-3

COMMENTARY: REFLECTIONS ON 40 YEARS

Chemical Ecology: Body Odor, Behavior, and Body Building Marcel Dicke

Published online: 9 April 2014 # Springer Science+Business Media New York 2014 A major issue in ecology is to understand “decision making” of organisms. Decisions on e.g., whom to accept as a sexual partner, where to forage, and how to allocate time to different activities. These choices are reflected in behavioral responses and influence an organism’s Darwinian fitness, i.e., its contribution to the next generation in the form of building bodies that further carry the organism’s genes. Every organism, whether plant, animal, or microbe needs to make such “decisions”. The information used during decision making frequently consists of chemical cues emitted by individuals, i.e. an organism’s body odor. Thus, chemical ecology can be described as the science of body odor, behavior, and body building. Although Darwinian fitness is the accomplishment of an individual, this individual lives in a complex community consisting of conspecific and heterospecific organisms. Moreover, the individual and the community that it is part of are exposed to abiotic conditions that can decisively influence the reward of an individual’s decisions in terms of offspring production. The choices of an individual should, therefore, be the best decisions within such a community context within the abiotic context that the community lives in. An individual that makes the best decisions will build more bodies than its competitors and thus will contribute more to the next generation. The field of chemical ecology focusses on chemical cues that underlie the choices of individual organisms. It addresses the effects of chemical cues on interactions among organisms, integrating analytical chemistry and ecology. Moreover, because of the community context and the effects of abiotic conditions, the scope of chemical ecology is much wider. It includes the perception of the chemicals, the integration of their information with information on other intrinsic as well as extrinsic conditions, the behavioral responses elicited as a result, the effects of chemical cues within a multitrophic community context, the selective forces acting on emission and response to infochemicals etc. Thus, the science of chemical ecology is truly multidisciplinary as can be seen in the developments within the Journal of Chemical Ecology (JCE). Originally the research field focussed especially on the role of chemical cues in interactions between individual organisms. Initially with a strong focus on pheromones, but gradually with many contributions also on the role of chemical cues in interspecific interactions. I had the opportunity to see these developments early on. My personal interest in chemical ecology was triggered when I was an undergraduate student with an interest in ecology, biochemistry, and analytical chemistry, fields that were considerably separated in the 1970s and 1980s. After taking a full year of courses in chemistry, I was about to choose to specialize in either ecology or chemistry when Richard L. Jones, who spent a sabbatical at Leiden University (The Netherlands), gave a seminar on the role of chemical cues in the foraging behavior of parasitic wasps. He clearly showed the M. Dicke (*) Laboratory of Entomology, Wageningen University, 6700 EH Wageningen, The Netherlands e-mail: [email protected]

added value of combining the disciplines of chemistry and ecology to gain a more profound understanding of how parasitoids find their hosts. One of his papers on this topic was published in the first volume of the JCE (Lewis et al. 1975). His enthusiasm and outlook to the future of chemical ecology provided important input to my own decision process. The integration of insect behavior, parasitoid biology, and chemistry was exactly what I needed to resolve my split between the disciplines of chemistry and ecology. It made me decide to combine my interest in the ecology of parasitoid-host interactions and biological control of insects pests with my interest in biochemistry and analytical chemistry: I devoted my MSc thesis to the study of the chemical cues that were used by a parasitoid of Drosophila larvae during long-range and short-range foraging. Interestingly, the parasitoid’s foraging behavior was not only mediated by cues from the host but also from cues from the food of the host, i.e., yeasts. The results of that study were published in JCE, and this Msc thesis project was decisive for my career in chemical ecology. The involvement of microorganisms in interactions between macroorganisms became clear quite early in the lifetime of the JCE, for instance, with respect to the involvement of microorganisms in the chemical ecology of microbivores, the role of fungi in the biology of bark beetles, and in the foraging behavior of natural enemies of microbivores. Moreover, in other systems, it also became clear that the interactions between two individuals could be decisively influenced by a third organism, such as the production of herbivore-induced plant volatiles (HIPVs) that attract carnivorous enemies of herbivores. At present, it is commonly known that if one organism within a community emits a chemical cue, this represents public information that can be exploited by any member of the community. For instance, a moth’s sex pheromone can be exploited by egg parasitoids during host searching, and HIPVs can affect various organisms both above and belowground, such as herbivores, pollinators, predators, parasitoids, hyperparasitoids, and neighboring plants. Moreover, community members also may emit cues that mimic an information-conveying cue from another community member, e.g., orchids can emit a mimic of a pheromone of their bee pollinators. Therefore, one of the most difficult aspects of chemical ecology is to assess the costs and benefits of the emission of infochemicals: to do so, the costs and benefits of all interactions that result from its emission should be assessed. This requires an understanding of the consequences of its emission under natural conditions for reproductive success of the emitter, which is dependent on the interactions affected by the infochemical and on local community composition. Studies in this direction are now being conducted and they are based on knowledge related to different levels of biological integration, including molecular, physiological, behavioral, ecological, and evolutionary aspects. The Journal of Chemical Ecology has played an important role in shaping the field of chemical ecology, from the early days onwards. It has provided a platform for the integration of ecology and chemistry. Its very name clearly indicated that this was all about understanding ecology by addressing the underlying chemical basis. The initial focus on the

314 integration of ecology and chemistry was an important development that was later adopted by other journals as well. The JCE did not restrict itself to particular focal organisms, nor did it focus on particular levels of biological organization. In addition to the development towards addressing more complex systems that included more than two or three interacting organisms, an expansion towards more extensive mechanistic aspects, including protein synthesis and gene transcription also were covered by the journal. The JCE covers proximate and ultimate aspects, mechanistic and ecological aspects, individual interactions, and interactions within a community context. Although the focus is still more on proximate, mechanistic aspects of individual interactions, there are excellent opportunities to expand to addressing the role of infochemicals in more complex systems and to focus more on evolutionary aspects. The comprehensiveness of the field of chemical ecology represents an exciting challenge, especially as the field rapidly expands and includes new approaches to address outstanding questions. Bringing together authors from very different (sub)disciplines means that the journal provides a platform for integrative research approaches that are a prerequisite for tackling the complex questions that are associated with understanding the

J Chem Ecol (2014) 40:313–314 role of chemical information conveyance in shaping processes underlying the dynamics of ecological communities. During the past 40 years the Journal has been important for the development of chemical ecology. Further accommodating the dynamic interaction of different disciplines will be a rewarding challenge. For this to be successful, scientists from different (sub)disciplines should be willing to collaborate, and for this to be successful the chemistry between them must be right. When that is done, many more bodies of interesting scientific research will be built that can result in exciting new papers for the Journal of Chemical Ecology.

Reference Lewis WJ, Jones RL, Nordlund DA, Sparks AN (1975) Kairomones and their use for management of entomophagous Insects. I. Evaluation for increasing rates of parasitization by Trichogramma spp. in the field. J Chem Ecol 1:343–347

Chemical ecology: body odor, behavior, and body building.

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