Genetic correlations in multi-species plant/herbivore interactions at multiple genetic scales: implications for eco-evolutionary dynamics

In plant/herbivore systems, elucidating the hierarchical genetic correlations that exist between enemies to a host plant (e.g., in the magnitude of damage) and determining how stable these effects are across environments is crucial for our understanding of potential eco-evolutionary dynamics in these systems. This sort of information would allow us to better know how plant populations have evolutionarily diverged in their phenotypic traits, which organisms are driving the evolutionary change and how rapid evolutionary change in one enemy or plant species can feedback to affect other herbivore and pathogen species showing genetically correlated responses to the host plant. Here, we investigate consistency in patterns of the genetic correlations within and among populations in preferences among multiple enemies for a globally planted species, Eucalyptus globulus, and explore how stable these genetically based correlations are across environments. We show plant enemies respond to underlying host genetic variation at two genetic hierarchical scales and that relationships between plant enemies are both independent and correlative. Our finding of a significant positive genetic correlation in damage to the host plant between a sawfly and a fungal leaf pathogen species suggests a potential indirect eco-evolutionary feedback loop mediated by the genetic correlation. We also demonstrate that among population divergence patterns are not constrained by within population correlations, and this decoupling between among and within population patterns suggests that diffuse relationships between two enemies are not constraining the evolutionary diversification in resistance of populations of their host plant. In addition, when genetic effects are present, there is clear stability in the genetic influences of this host tree on its enemies across trials. This indicates that in an eco-evolutionary dynamic setting, the strength and consistency of any selective force would be maintained across environments.