The evolutionary potential of symbiosis

Symbiosis is considered a source of evolutionary innovation. Example innovations that have evolved in symbioses include new organs, morphological adaptations, and metabolic abilities. However, it is unknown whether symbiosis is special with respect to generating innovation. In other words, does having a symbiotic partner tend to result in more innovation relative to not having a partner? Here, I argue that there are 2 gaps standing in the way of understanding the role of symbiosis in the evolution of innovation: (1) we have not rigorously quantified whether symbiosis tends to increase innovation and (2) we have not fully articulated evolutionary mechanisms that operate differently in symbiosis that could lead to more innovation. To overcome these gaps, I suggest that experimental evolution and comparative methods can be used to quantify whether symbiosis is a source of innovation. I then describe some unique features of symbiosis that promote (or hinder) the evolution of innovations through effects on evolvability. Measuring innovation and integrating concepts of evolvability into the study of symbiotic interactions will allow us to understand when and how symbiosis drives innovation.