Beyond Fermentation: Other Important Services Provided to Endothermic Herbivores by their Gut Microbiota

For decades, comparative biologists have recognized the importance of microbial partners in facilitating herbivory as a successful feeding strategy. Most of this success is attributed to the ability of gut microbes to digest recalcitrant dietary fiber and provides usable nutrients to their hosts. Gut microbes can also provide numerous other functions, such as vitamin synthesis, nitrogen recycling, and the detoxification of plant secondary compounds. Here, we review these microbial functions in herbivorous mammals and birds, highlighting studies that utilize recently developed metagenomic techniques. Several of these studies emphasize that microbial services are the product of interactions and exchanges within a complex microbial community, rather than the product of an individual member. Additionally, a number of these microbial functions are interdependent. For example, levels of dietary nitrogen or plant toxins can influence fiber digestibility. Further studies into the variety of microbial services provided to herbivorous hosts, and how these services might interact will broaden our understanding of host-microbe interactions.