Microbial determinants of folivory in insects

Despite the ubiquity and seeming accessibility of plant leaves, obligate folivory poses a multitude of nutritional challenges that extend beyond the metabolic range of most animals. By engaging in a diverse array of interactions with symbiotic microbes, insects are able to exploit a diet defined by recalcitrant carbohydrates, noxious plant secondary compounds, and transient availability. This chapter explores the role of symbiont metabolic diversity in upgrading the nutritional ecology of folivorous insects. Diverse in form, many of the metabolic features of symbioses outlined here are nonetheless conserved in function, emphasizing the highly specific challenges associated with the exploitation of, and specialization on, leaves as a sole nutritional resource. Through the supplementation of essential digestive enzymes, or by extending the availability of a senescing ecological niche, symbiont contributions highlight the unique set of mutualistic factors that differentiate these interactions from other nutritional partnerships. In detailing the molecular and biochemical mechanisms that allow symbionts to elevate the adaptive and reproductive potential of their insect hosts, we emphasize the importance of the microbiome in spurring the evolution of leaf-feeding behavior. In light of their compositional simplicity and experimental tractability, many of the interactions detailed here underscore the importance of a metaorganismal approach towards understanding animal adaptation