Convergent evolution of signal-structure interfaces for maintaining symbioses.

• Partner fidelity is essential for establishing and maintaining symbioses. • Exchange of specific signals is one mechanism to ensure partner fidelity. • Signal-structure interfaces evolve to ensure fidelity when using non-specific signals. • Specialized structures for accommodating symbionts are widespread. • Signal-structure interfaces are common and may occur within the human microbiome. Symbiotic microbes are essential to the ecological success and evolutionary diversification of multicellular organisms. The establishment and stability of bipartite symbioses are shaped by mechanisms ensuring partner fidelity between host and symbiont. In this minireview, we demonstrate how the interface of chemical signals and host structures influences fidelity between legume root nodules and rhizobia, Hawaiian bobtail squid light organs and Allivibrio fischeri , and fungus-growing ant crypts and Pseudonocardia. Subsequently, we illustrate the morphological diversity and widespread phylogenetic distribution of specialized structures used by hosts to house microbial symbionts, indicating the importance of signal-structure interfaces across the history of multicellular life. These observations, and the insights garnered from well-studied bipartite associations, demonstrate the need to concentrate on the signal-structure interface in complex and multipartite systems, including the human microbiome. [ABSTRACT FROM AUTHOR]