Summary of the findings of Piculell et al. , showing the measured fitness components of two maternal half-sib families of bishop pine plants (M18 and M19, measured as relative growth rate and root length) and two full-sib families of its mycorrhizal fungus (132 and 133, measured as the number of roots of the host that are inoculated) under four different environments. The height of each symbol is proportional to the measured performance value. The performance of both partners in the interaction varies depending on both the lineage of partner they are interacting with and the environment. This is most clearly seen for fungal performance in field soil, where the number of host roots inoculated varies by an order of magnitude.