Plant genetics predicts intra‐annual variation in phytochemistry and arthropod community structure

With the emerging field of community genetics, it is important to quantify the key mechanisms that link geneticsand community structure. We studied cottonwoods in common gardens and in natural stands and examined the potential for plantchemistry to be a primary mechanism linking plant geneticsand arthropodcommunities. If plantchemistry drives the relationship between plant geneticsand arthropod community structure, then several predictions followed. We would find (i) the strongest correlation between plant geneticcomposition and chemical composition; (ii) an intermediate correlation between plantchemical composition and arthropodcommunity composition; and (iii) the weakest relationship between plant geneticcomposition and arthropodcommunity composition. Our results supported our first prediction: plant geneticsand chemistry had the strongest correlation in the common garden and the wild. Our results largely supported our second prediction, but varied across space, seasonally, and according to arthropodfeeding group. Plantchemistry played a larger role in structuring common garden arthropodcommunities relative to wild communities, free-living arthropodsrelative to leaf and stem modifiers, and early-season relative to late-season arthropods. Our results did not support our last prediction, as host plant geneticswas at least as tightly linked to arthropod community structureas plantchemistry, if not more so. Our results demonstrate the consistency of the relationship between plant geneticsand biodiversity. Additionally, plantchemistry can be an important mechanism by which plant geneticsaffects arthropodcommunity composition, but other genetic-based factors are likely involved that remain to be measured.