Data from: Standing genetic variation in host preference for mutualist microbial symbionts

Many models of mutualisms show that mutualisms are unstable if hosts lack
mechanisms enabling preferential associations with mutualistic symbiotic
partners over exploitative partners. Despite the theoretical importance of
mutualism-stabilizing mechanisms, we have little empirical evidence to
infer their evolutionary dynamics in response to exploitation by
non-beneficial partners. Using a model mutualism—the interaction between
legumes and nitrogen-fixing soil symbionts—we tested for quantitative
genetic variation in plant responses to mutualistic and exploitative
symbiotic rhizobia in controlled greenhouse conditions. We found
significant broad-sense heritability in a legume host's preferential
association with mutualistic over exploitative symbionts and selection to
reduce frequency of associations with exploitative partners. We failed to
detect evidence that selection will favour the loss of
mutualism-stabilizing mechanisms in the absence of exploitation, as we
found no evidence for a fitness cost to the host trait or indirect
selection on genetically correlated traits. Our results show that genetic
variation in the ability to preferentially reduce associations with an
exploitative partner exists within mutualisms and is under selection,
indicating that micro-evolutionary responses in mutualism-stabilizing
traits in the face of rapidly evolving mutualistic and exploitative
symbiotic bacteria can occur in natural host populations.