Abstract
AbstractMutualisms exhibit extensive context-dependent genetic variation in fitness outcomes. However, the specific traits that underpin fitness variation in mutualisms remain understudied. Pinpointing fitness-associated traits in mutualisms is critical to understanding how mutualisms evolve, as well as identifying the mechanisms that maintain genetic variation for fitness in interacting populations. In this study, we quantified the contribution of host and symbiont genotypes to variation in resource exchange, use, and production traits measured in the host using the model mutualism between legumes and nitrogen fixing rhizobia as our study system. We predicted that plant genotype x rhizobia genotype (GxG) effects would be common to resource exchange traits because resource exchange is hypothesized to be governed by input from both interacting partners through bargaining. On the other hand, we predicted that plant genotype effects would be common to host resource use and production traits because these traits are indirectly related to the exchange of resources. Consistent with our prediction for resource exchange traits, but not our prediction for resource use and production traits, we found that rhizobia genotype and GxG effects were the most common sources of variation in the traits that we measured. The results of this study complement the commonly observed phenomenon of GxG effects for fitness by showing that numerous mutualism traits also exhibit GxG variation. Furthermore, they highlight the possibility that the exchange of resources as well as how partners use and produce traded resources can influence the evolution of mutualistic interactions. Future studies can now quantify the relationship between resource exchange, use and production traits and fitness (i.e. selection) to test the competing hypotheses proposed to explain the maintenance of fitness variation in mutualisms.
Publisher
Cold Spring Harbor Laboratory