Plant sex and induced responses independently influence herbivore performance, natural enemies and aphid-tending ants
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- Mooney, K.A., Fremgen, A. & Petry, W.K. Arthropod-Plant Interactions (2012) 6: 553. doi:10.1007/s11829-012-9204-5
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Sex is an ecologically important form of genetic variation in dioecious plants, with males and females generally differing in constitutive resistance to herbivores. Yet little is known about sexual dimorphism with respect to induced or indirect defense, or whether sex-based differences are underlain by trade-offs among modes of defense. We compared male and female Valeriana edulis plants for constitutive and induced direct resistance to two herbivores, an early-season caterpillar and a late-season aphid, and for constitutive and induced indirect resistance in terms of abundance of natural enemies and aphid-tending ants. No sexual dimorphism was found in constitutive direct plant resistance, yet the sexes differed for constitutive indirect resistance, with 78 % more natural enemies and 117 % more ants present on females than males. Past feeding damage by caterpillars induced direct and indirect resistance in both males and females, increasing caterpillar development time by 26 % and the abundance of natural enemies by 147 %. Caterpillar feeding did not induce direct resistance with respect to caterpillar final mass or aphid performance. In all cases, there were no interactions between the effects of caterpillar damage and plant sex. In summary, plant sexual dimorphism and induced responses to herbivore damage independently influenced herbivore performance and the composition of arthropod communities at higher trophic levels.