The Ontogeny of Plant Defense and Herbivory: Characterizing General Patterns Using Meta‐Analysis

Abstract

Defense against herbivores often changes dramatically as plants develop. Hypotheses based on allocation theory and herbivore selection patterns predict that defense should increase or decrease, respectively, across ontogeny, and previous research partly supports both predictions. Thus, it remains unclear which pattern is more common and what factors contribute to variability among studies. We conducted a meta-analysis of 116 published studies reporting ontogenetic patterns in plant defense traits and herbivory. Patterns varied depending on plant life form (woody, herbaceous, grass), type of herbivore (insect, mollusk, mammal), and type of defense trait (secondary chemistry, physical defense, tolerance). In woody plants, chemical defense increased during the seedling stage, followed by an increase in physical defenses during the vegetative juvenile stage. Mammalian herbivores showed a strong preference for mature compared to juvenile tissues in woody plants. Herbs experienced a significant increase in secondary chemistry across the entire ontogenetic trajectory, although the magnitude of increase was greatest during the seedling stage. Correspondingly, mollusks preferred young compared to older herbs. Future research investigating growth/defense trade-offs, allometry, herbivore selection patterns, and ecological costs would shed light on the mechanisms driving the ontogenetic patterns observed.

Tests of the coupled expression of latex and cardenolide plant defense in common milkweed (Asclepias syriaca)

“…Surprisingly few studies have followed ontogenetic trajectories of plant defense expression across multiple years. A recent meta-analysis found increasing investment in defensive chemistry across ontogenetic development for herbaceous plants, but this pattern was restricted to short term developmental changes, typically across the first year of growth (Barton and Koricheva 2010). A few other studies have followed insect attack on a cohort of plants across several years, but in these cases, the impact of changing plant phenotypes was unclear (e.g., Roininen et al 1993).…”

Temporal Changes in Allocation and Partitioning of New Carbon as 11C Elicited by Simulated Herbivory Suggest that Roots Shape Aboveground Responses in Arabidopsis

“…their ability to enhance the sink strength at the feeding site and out compete other plant sinks for resources; Larson and Whitham, 1997;Wool, 2004). While investigators have acknowledged different responses in defense chemistry and downstream effects on herbivores as plants enter their reproductive stage (Bazzaz et al, 1987;Zangerl and Bazzaz, 1992;Baldwin, 1998;Barton and Koricheva, 2010), there are no clear generalizations regarding the relationship between other naturally occurring competing sinks (young leaves and roots) and plant defense responses. Moreover, recent attempts to develop a conceptual model of changes made to plant resource allocation following herbivore attack that takes into account vascular architecture, tissue development, variation over time, and local environmental variation have been impeded by differences in temporal and spatial variation in responses and by the dependency of induction of local defense responses on other plant modules (Hanhimäki and Senn, 1992;Orians and Jones, 2001).…”

A comparison of plants and animals in their responses to risk of consumption

“…For example, seedlings are much less tolerant of partial consumption [48], and are predicted to err on the side of more defense, similar to animals. Indeed, a meta-analysis found that chemical defenses for woody plants increased during the seedling stage and decreased at later stages [49]. Similarly plants invest heavily in constitutive defense in tissues of high reproductive value (e.g., seeds) but have inducible defenses in leaves and roots, presumably reflecting the high cost of leaving valuable tissues undefended [50].…”