Figure 4.
Differences in herbivore-induced volatile (HIPV) emission between native and invasive plants and its effect on parasitoid attraction
(A) Total emission of HIPVs of invasive and native J. vulgaris genotypes originating from different ranges used in the parasitoid olfactometer experiment. One paired sample from NZ was lost. Values are means ± SE (n = 5 for AUS, n = 7 for NZ, n = 12 for WNA, and n = 25 for Europe). LMM, infestation: χ2(1) = 205.147, p < 0.001; origin: χ2(1) = 3.49, p = 0.062; range within origin: χ2(2) = 0.396, p = 0.82; infestation × origin: χ2(1) = 12.235, p < 0.001; range within origin × infestation: χ2(2) = 8.238, p = 0.013. Asterisks indicate significant differences between origin in infested plants; ∗∗∗p < 0.001; ns above the three invasive ranges represents no significant difference among the three invasive ranges. There were no differences between origin or among ranges in uninfested plants.
(B) Differences in total VOC emissions (after − before) between native and invasive regions. LMM, origin: χ2(1) = 18.936, p < 0.001; range within origin: χ2(2) = 1.801, p = 0.41. Asterisks indicate significant differences between origin; ∗∗∗p < 0.001; ns above the three invasive ranges represents no significant difference among the three invasive ranges.
(C and D) Parasitoid attraction.
(C) Number of females of C. popularis attracted to the odors of native J. vulgaris genotypes infested with 15-s instar T. jacobaeae versus uninfested native J. vulgaris genotypes.
(D) Number of females of C. popularis attracted to odors of native J. vulgaris infested with 15-s instar T. jacobaeae versus invasive J. vulgaris infested with 15-s instar T. jacobaeae from three ranges. Overall, 84% and 81% of the C. popularis parasitoids made a choice, respectively, in (C) and (D). GLMM with a Poisson error distribution: (C) origin: χ2(2) = 40.411, p < 0.001; (D) origin: χ2(2) = 114.003, p < 0.001; range within origin: χ2(2) = 0.125, p = 0.94. Different letters indicate significant differences among treatments at p < 0.05 with a Tukey post hoc test. ns above the three invasive ranges represents no significant difference among ranges.
(E) Proportion of females of the parasitoid C. popularis that chose the odor of native plants over invasive plants of J. vulgaris, both infested with 15-s instar of T. jacobaeae, plotted against the differences in the amounts of HIPVs produced between the native and invasive genotype of the same plant pair. Logistic regression (binomial GLM): χ2(1) = 11.449; p < 0.001. The solid line indicates the predictions from the model and the dotted lines the confidence intervals of the predictions.
See also Figures S1, S3, and S4 and Table S2.