Using information theory to decode network coevolution

Walking through a forest, you spot a colorful butterfly larva crawling and munching on a leaf—nothing unusual, just one scene in a calm ecological play. And yet, a massive “arms race” rages between plants and their herbivores (1, 2), spurred by information and misinformation transfer. Chemical signals play the role of communicators in a channel that joins each pair of interacting partners. The mechanisms that drive coevolution of these chemically mediated webs have been an active area of research, but a satisfactory theory has yet to be established. On page 1377 of this issue, Zu et al. (3) describe a new application of information theory to coevolutionary dynamics in animal-plant networks. Many scholars have explored the role of information in ecology and evolution (4) since the 1950s, in the wake of Claude Shannon's groundbreaking theory of information and communication (5). But the actual function of information, particularly in an evolutionary context, often has been obscured by insufficient data and the lack of a proper mapping of the links between information and fitness (6). Zu et al. made use of plants' secondary metabolism (which forms metabolites not involved in plant growth or development) to couple two bipartite networks, namely the animal-plant (AP) one (i.e., who eats what) and the plant–volatile organic compounds (PV) one [i.e., what volatile organic compounds (VOCs) plants generate]. The authors gathered data from a tropical dry forest; insect larvae were collected from leaves, and trophic interactions were confirmed in the laboratory. The VOC repertoire was retrieved from leaves in the field with a method that characterizes the chemical profile around each leaf.