Synopsis

Nearly 75% of the world’s macroscopic biodiversity is tied up in the look between plants, herbivores, predators, and decomposers. In this context, the study of trophic interactions, involving plants, herbivores, and their predators or parasitoids represents a frontier in ecology, and this knowledge can be integrated in environmentally sound agricultural pest managements.

Over the last half century, complementary theories and hypotheses have been developed to try to explain the extraordinary variation in plant defensive strategies against herbivores, and, thanks to interdisciplinary interaction between ecologist, behaviorists, physiologist, and chemists, it has given rise to the body of work, collectively known as “plant defense theory”. Nowadays, advances in community phylogenetic and metabolomic analysis are the key components for refining plant defense theories at a novel frontier.

In (1964), Ehrlich and Raven, in their classic treatise defining “coevolution”, suggested that community evolution was “one of the still least understood aspects of population biology”.  Remarkably, they argued that it was time for the melding of community ecology, biochemical analysis, and macroevolutionary studies.  I would argue that only in the last few years, or perhaps only in the coming decade, will we be able to tackle this goal, and couple it with a better understanding of how complex interactions between plants and animal, and how do functional and defensive traits tradeoff in response to plant strategies and adaptations to different environments.

Below I outline my current and future contributions to the new coevolutionary synthesis:

1) Mechanistic chemical ecology occurs in a community context

My dissertation (awarded March 2006) at Neuchâtel University highlighted, for the first time, a belowground tritrophic interaction, between maize plants, an invasive root herbivore of agricultural fields and entomopathogenic nematodes. Thanks to international collaborations with the Max Planck Institute for Chemical Ecology in Jena (D), and CABInternational research center, I showed that herbivore-attacked plants release volatile cues in the soil that are used by predatory nematodes to locate insect hosts (Rasmann et al. 2005; Rasmann and Turlings 2007; Rasmann and Turlings 2008) .

2) Comparative biology is moving from description to experimental approaches

During my postdoctoral experience in the Agrawal lab at Cornell University I used phylogenetic, quantitative genetic and phyto-chemical analyses, coupled with behavioral assays to study the ecological importance and the evolution of chemical defenses in milkweed plants (Asclepias spp.), and their effect on herbivores and predators of the herbivores (e.g. Agrawal et al. 2009; Rasmann and Agrawal 2008; Rasmann and Agrawal 2011; Rasmann et al. 2009).

3) The same factors which mediate ecological interactions may play a role in adaptation and diversification.

Darwin’s paradox of closely related species being phenotypically similar (thus more likely to compete for the same resources), but distinct enough to co-occur in the same habitat, is still a tough nut to crack. We can study ecology mechanistically and diversification descriptively. Here my goal is to understand how they come together. To understand a community of coexisting plants and arthropods will thus need the knowledge of phylogenetic relatedness of plants and animals, and the mechanisms shaping their relationships.

At the University of Lausanne, I am currently studying the effect of radiation and adaptation into high altitudes on plant herbivore interactions and plant defenses. First results indicate that despite lower plant species richness in high altitudes, butterfly species tend to be more generalized in their host plant use, most likely due to a relaxation of plant resistance traits