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Supporting InformationData S1. Root colonization data used for genome-wide association mapping. All metrics reflect percent of root length colonized with arbuscular mycorrhizal fungi. Mean Colonization Rate (LS Mean) is the least squares mean of root colonization for each line (genotype) when corrected for spatial gradients in the greenhouse. Maximum Colonization is the highest colonization rate of the four biological replicates of each line. Range of Colonization represents the difference in colonization rate between the biological replicate with the highest colonization rate and the lowest colonization rate for each line. The Inclusion in GWAS column indicates the lines that were included in genome-wide association analysis, after 27 lines were excluded due to high residual heterozygosity.

Defense investment in plant reproductive structures is relatively understudied compared to the defense of vegetative organs. Here the evolution of chemical defenses in reproductive structures is examined in light of the optimal defense, apparency, and resource availability hypotheses within the genus Cornus using a phylogenetic comparative approach in relation to phenology and native habitat environmental data. METHODS: Individuals representing 25 Cornus species were tracked for reproductive phenology over a full growing season at the Arnold Arboretum of Harvard University. Floral, fruit, and leaf tissue was sampled to quantify defensive chemistry as well as fruit nutritional traits relevant to bird dispersal. Native habitat environmental characteristics were estimated using locality data from digitized herbarium records coupled with global soil and climate data sets. RESULTS: The evolution of later flowering was correlated with increased floral tannins, and the evolution of later fruiting was correlated with increased total phenolics. Leaves were found to contain the highest tannin activity, while inflorescences contained the highest total flavonoids. Multiple aspects of fruit defensive chemistry were correlated with fruit nutritional traits. Floral and fruit defensive chemistry were evolutionarily correlated with aspects of native habitat temperature, precipitation, and soil characteristics. CONCLUSIONS: Results provide tentative support for the apparency hypothesis with respect to both flower and fruit phenology, while relative concentrations of secondary metabolites across organs provide mixed support for the optimal defense hypothesis. The evolution of reproductive defense with native habitat provides, at best, mixed support for the resource availability hypothesis.

Premise As plant lineages diversify across environmental gradients, species are predicted to encounter divergent biotic pressures. This study investigated the evolution of volatile secondary metabolism across species of Helianthus. Methods Leaves and petals of 40 species of wild Helianthus were analyzed via gas chromatography–mass spectrometry to determine volatile secondary metabolite profiles. Results Across all species, 500 compounds were identified; 40% were sesquiterpenes, 18% monoterpenes, 3% diterpenes, 4% fatty acid derivatives, and 35% other compounds such as phenolics and small organic molecules. Qualitatively, annuals and species from more arid western climates had leaf compositions with a higher proportion of total monoterpenes, while erect perennials and species from more mesic eastern habitats contained a higher proportion of total sesquiterpenes. Among species, mass‐based leaf monoterpene and sesquiterpene abundance were identified as largely orthogonal axes of variation by principal component analysis. Profiles for leaves were not strongly correlated with those of petals. Conclusions Volatile metabolites were highly diverse among wild Helianthus, indicating the value of this genus as a model system and rich genetic resource. The independence of leaf and petal volatile profiles indicates a low level of phenotypic integration between vegetative and reproductive structures, implying vegetative defense and reproductive defense or pollinator attraction functions mediated by terpene profiles in these two organs can evolve without major trade‐offs. The major biosynthetic pathways for the major terpenes in wild Helianthus are already well described, providing a road map to deeper inquiry into the drivers of this diversity.