Abstract
The combination of defensive traits leads to the evolution of ‘plant defense syndromes’ which should provide better protection against herbivores than individual traits on their own. Defense syndromes can be generally driven by plant phylogeny and/or biotic and abiotic factors. However, we lack a solid understanding of (i) the relative importance of shared evolution vs. convergence due to similar ecological conditions and (ii) the role of induced defense strategies in shaping defense syndromes. We investigate the relative roles of evolutionary and ecological factors shaping the deployment of pine defense syndromes including multiple constitutive and induced chemical defense traits. We performed a greenhouse experiment with seedlings of eighteen species of Pinaceae family, and measured plant growth rate, constitutive chemical defenses and their inducibility. Plant growth rate, but not phylogenetic relatedness, determined the deployment of two divergent syndromes. Slow-growing pine species living in harsh environments where tissue replacement is costly allocated more to constitutive defenses (energetically more costly to produce than induced). In contrast, fast-growing species living in resource-rich habitats had greater inducibility of their defenses, consistent with the theory of constitutive-induced defense trade-offs. This study contributes to a better understanding of evolutionary and ecological factors driving the deployment of defense syndromes.
Highlights
Most plant defense theories predict the occurrence of trade-offs between different types of anti-herbivore defenses [1,2]
We addressed three questions: (i) Are defensive phenotypes of pine species clustered into defensive syndromes that simultaneously include both constitutive and induced defensive traits? (ii) Are defensive syndromes driven by shared evolutionary history, or do unrelated plants converge on the same set of syndromes? And (iii) do plant growth rate shape pine defense syndromes? To address these questions, we used data from a previous greenhouse experiment with juveniles of eighteen species of Pinaceae family trees distributed across a broad range of environmental conditions in both Nearctic and Palearctic ranges [28,31]
Early growth rate of pine species included in Cluster B was nearly double that of pine species included in Cluster A (Fig 3)
Summary
Most plant defense theories predict the occurrence of trade-offs between different types of anti-herbivore defenses [1,2]. Recent studies have challenged this view and argue that, in order to cope with a wide range of herbivore species, plants optimize an arsenal of diverse traits in concert, including plant chemical and physical defenses, indirect defenses, plant nutritional quality and tolerance mechanisms [3,4,5,6,7,8,9,10]. Agrawal & Fishbein [3] extended the concept of animal behavioral syndromes [11] to plants and proposed that defense syndromes, defined as correlated suites of defensive traits covarying at the species or population level across environments, may be prevalent in nature.
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