Fitness trade-offs and the origins of endosymbiosis

Abstract

Endosymbiosis drives evolutionary innovation and underpins the function of diverse ecosystems. The mechanistic origins of symbioses, however, remain unclear, in part because early evolutionary events are obscured by subsequent evolution and genetic drift. This Essay highlights how experimental studies of facultative, host-switched, and synthetic symbioses are revealing the important role of fitness trade-offs between within-host and free-living niches during the early-stage evolution of new symbiotic associations. The mutational targets underpinning such trade-offs are commonly regulatory genes, such that single mutations have major phenotypic effects on multiple traits, thus enabling and reinforcing the transition to a symbiotic lifestyle.

Symbiosis: In search of a deeper understanding

“…In a related theme, Brockhurst and collaborators discuss the role of mutational decay and antagonistic pleiotropy as microbes shift from free-living forms to symbiotic forms that are strictly vertically transmitted and obligately dependent on hosts [8]. They also discuss how both selection and synthetic consortia experiments can be informative for understanding the forces that drive the early mutational changes underlying symbiotic interactions.…”