Abstract
Virtually all plants and animals, including humans, are home to symbiotic microorganisms. Symbiotic interactions can be neutral, harmful or have beneficial effects on the host organism. However, growing evidence suggests that microbial symbionts can evolve rapidly, resulting in drastic transitions along the parasite–mutualist continuum. In this Review, we integrate theoretical and empirical findings to discuss the mechanisms underpinning these evolutionary shifts, as well as the ecological drivers and why some host–microorganism interactions may be stuck at the end of the continuum. In addition to having biomedical consequences, understanding the dynamic life of microorganisms reveals how symbioses can shape an organism’s biology and the entire community, particularly in a changing world.
Highlights
Abstract | Virtually all plants and animals, including humans, are home to symbiotic microorganisms
In this Review, we integrate theoretical and empirical findings to discuss the mechanisms underpinning these evolutionary shifts, as well as the ecological drivers and why some host–microorganism interactions may be stuck at the end of the continuum
We focus the Review on eukaryotic host–microorganism symbi oses; we note that microbial interactions with mobile genetic elements (MGEs) can be analogous to sym bioses (Box 2) given the ability of these elements to confer beneficial traits and cause harm to bacterial hosts[37,38]
Summary
Abstract | Virtually all plants and animals, including humans, are home to symbiotic microorganisms. The genetic changes involved in microbial evolution are key contributors to the forma tion of mutualisms and parasitisms and their transitions along the symbiotic continuum. Through experimental evolution of the bacterial sym biont Parachlamydia acanthamoebae and its protist host Acanthamoeba sp., one study[46] observed an evolutionary shift of the microbial symbiont towards parasitism under horizontal transmission conditions.
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