Microbes and animal olfactory communication: Where do we go from here?

We know that microbes contribute to the production of odors that some animals use to communicate, but how common is this phenomenon? Recent studies capitalizing on new molecular technologies are uncovering fascinating associations between microbes and odors of wild animals, but causality is difficult to ascertain. Fundamental questions about the nature of these unique host-microbe interactions also remain unanswered. For instance, do microbes benefit from signaling associations with hosts? How does microbial community structure influence signal production? How do hosts regulate microbes in order to generate appropriate signals? Here, we review the current state of knowledge on microbially produced signals in animals and discuss key research foci that can advance our understanding of microbial-based signaling in the animal world.