Signaling defenses with color: a meta-analysis of leaf color variation, palatability, and herbivore damage

Abstract

We investigated the impact of leaf color variation on herbivory, testing current hypotheses indicating that leaf color could influence herbivory through bottom-up control (by signaling leaf quality and defenses) or top-down control (by attracting predators). A comprehensive phylogenetic meta-analysis was conducted to assess the effects of leaf color on defense traits, leaf palatability, herbivore fitness, and herbivory. We show that nongreen leaves were better defended, less nutritive, and experienced less herbivory, leading to a reduction in herbivore fitness. Stronger effects of leaf color on herbivory were found in tropical plants, whereas lowered leaf quality in nongreen leaves was found in temperate plants. Increased leaf defense and reduction in insect fitness traits were observed in both temperate and tropical nongreen leaves. Our results indicate that leaf color plays a significant role in shaping plant defenses, leaf nutritive value, and herbivore fitness, ultimately modulating levels of herbivory. This suggests coordination between leaf color, defenses, and quality, which may be responsible for patterns of variation in herbivory and fitness-related traits in herbivores.

Keywords: delayed greening; herbivory; leaf color; leaf color polymorphism; red leaves.

Fig. 1

Conceptual models and predictions of the effects of leaf color on herbivory based on classical hypotheses aiming to explain intra‐ and interspecific variation in plant traits, including leaf defense and leaf quality, and insect traits associated with fitness. The response variables commonly evoked by authors to explain differences in herbivory levels in nongreen leaves are listed on the left. Arrows indicate either an increase (pointed up) or a decrease (pointed down) of such variables in nongreen, colored leaves.

Fig. 2

Phylogenetic reconstruction of plant species used in the meta‐analysis evaluating the effects of nongreen leaves on herbivory, leaf defenses, leaf quality, and insect traits associated with fitness. Icons denote the nongreen leaf type (e.g. red, purple, white) or pattern (e.g. green leaves with red margins) compared to green leaves within the same species.

Fig. 3

Overall effect sizes of leaf color on response variables associated with herbivory, herbivore fitness, leaf defenses, and leaf quality in plant species with nongreen leaves. Orchard plots indicate the mean overall effect with its associated 95% confidence interval (thick horizontal lines), the prediction confidence intervals around effect sizes (slim horizontal lines), and individual effect sizes weighed by their precision (1/SE). An overlap between confidence intervals and the dashed vertical lines indicates nonsignificant effects (k = number of independent comparisons).

Fig. 4

Effects sizes of leaf color on response variables associated with herbivory, insect traits associated with fitness, leaf defenses, and leaf quality in tropical and temperate regions. Orchard plots indicate the mean overall effect with its associated 95% confidence interval (thick horizontal lines), the prediction confidence intervals around effect sizes (slim horizontal lines), and individual effect sizes weighed by their precision (1/SE). An overlap between confidence intervals and the dashed vertical lines indicates nonsignificant effects (k = number of independent comparisons).