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High herbivore pressure favors constitutive over induced defense

View Article: PubMed Central - PubMed

ABSTRACT

Theoretical and empirical studies show that, when past or current herbivory is a reliable cue of future attack and defenses are costly, defenses can be induced only when needed and thereby permit investment in other functions such as growth or reproduction. Theory also states that, in environments where herbivory is constantly high, constitutive defenses should be favored. Here, we present data to support the second aspect of the induced resistance hypothesis. We examined herbivore‐induced responses for four species of Inga (Fabaceae), a common canopy tree in Neotropical forests. We quantified chemical defenses of expanding leaves, including phenolic, saponin and toxic amino acids, in experimental field treatments with and without caterpillars. Because young leaves lack fiber and are higher in protein than mature leaves, they typically lose >25% of their leaf area during the few weeks of expansion. We predicted that the high rates of attack would select for investment in constitutive defenses over induction. Our data show that chemical defenses were quite unresponsive to herbivory. We demonstrated that expanding leaves showed no or only small increases in investment in secondary metabolites, and no qualitative changes in the phenolic compound profile in response to herbivory. The proteinogenic amino acid tyrosine, which can be toxic at high concentrations, showed the greatest levels of induction. Synthesis: These results provide some of the first support for theoretical predictions that the evolution of induced vs. constitutive defenses depends on the risk of herbivory. In habitats with constant and high potential losses to herbivores, such as tropical rainforests, high investments in constitutive defenses are favored over induction.

No MeSH data available.


Heatmap comparison of the influence of light and herbivory on the metabolic profile of different Inga species (each row is a different plant). The top significant (ANOVA) features were selected to build the trees (each column is a feature). Ward linkage and Spearman distance algorithms were used. (A) Comparison of Inga marginata, I. multijuga, and I. pezizifera in gap and understory environments. (B) Comparison of Inga marginata, I. multijuga, and I. pezizifera with and without herbivory. No differences are observable between treatments, but species are clearly distinguished by their metabolite profile.
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ece32208-fig-0003: Heatmap comparison of the influence of light and herbivory on the metabolic profile of different Inga species (each row is a different plant). The top significant (ANOVA) features were selected to build the trees (each column is a feature). Ward linkage and Spearman distance algorithms were used. (A) Comparison of Inga marginata, I. multijuga, and I. pezizifera in gap and understory environments. (B) Comparison of Inga marginata, I. multijuga, and I. pezizifera with and without herbivory. No differences are observable between treatments, but species are clearly distinguished by their metabolite profile.

Mentions: For three species, we analyzed the qualitative composition of the fraction containing phenolic compounds using metabolomics (UPLC‐MS). The metabolome did not change in response to herbivore presence or light (Figs. 3, S9 and S10). That is, each of these Inga species had a unique combination of phenolic compounds or saponins (Figure S9A), but, overall, the presence and absence of those compounds did not change among herbivore treatments (Figs. 3B, S9B, and 10C, D).


High herbivore pressure favors constitutive over induced defense
Heatmap comparison of the influence of light and herbivory on the metabolic profile of different Inga species (each row is a different plant). The top significant (ANOVA) features were selected to build the trees (each column is a feature). Ward linkage and Spearman distance algorithms were used. (A) Comparison of Inga marginata, I. multijuga, and I. pezizifera in gap and understory environments. (B) Comparison of Inga marginata, I. multijuga, and I. pezizifera with and without herbivory. No differences are observable between treatments, but species are clearly distinguished by their metabolite profile.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016630&req=5

ece32208-fig-0003: Heatmap comparison of the influence of light and herbivory on the metabolic profile of different Inga species (each row is a different plant). The top significant (ANOVA) features were selected to build the trees (each column is a feature). Ward linkage and Spearman distance algorithms were used. (A) Comparison of Inga marginata, I. multijuga, and I. pezizifera in gap and understory environments. (B) Comparison of Inga marginata, I. multijuga, and I. pezizifera with and without herbivory. No differences are observable between treatments, but species are clearly distinguished by their metabolite profile.
Mentions: For three species, we analyzed the qualitative composition of the fraction containing phenolic compounds using metabolomics (UPLC‐MS). The metabolome did not change in response to herbivore presence or light (Figs. 3, S9 and S10). That is, each of these Inga species had a unique combination of phenolic compounds or saponins (Figure S9A), but, overall, the presence and absence of those compounds did not change among herbivore treatments (Figs. 3B, S9B, and 10C, D).

View Article: PubMed Central - PubMed

ABSTRACT

Theoretical and empirical studies show that, when past or current herbivory is a reliable cue of future attack and defenses are costly, defenses can be induced only when needed and thereby permit investment in other functions such as growth or reproduction. Theory also states that, in environments where herbivory is constantly high, constitutive defenses should be favored. Here, we present data to support the second aspect of the induced resistance hypothesis. We examined herbivore‐induced responses for four species of Inga (Fabaceae), a common canopy tree in Neotropical forests. We quantified chemical defenses of expanding leaves, including phenolic, saponin and toxic amino acids, in experimental field treatments with and without caterpillars. Because young leaves lack fiber and are higher in protein than mature leaves, they typically lose >25% of their leaf area during the few weeks of expansion. We predicted that the high rates of attack would select for investment in constitutive defenses over induction. Our data show that chemical defenses were quite unresponsive to herbivory. We demonstrated that expanding leaves showed no or only small increases in investment in secondary metabolites, and no qualitative changes in the phenolic compound profile in response to herbivory. The proteinogenic amino acid tyrosine, which can be toxic at high concentrations, showed the greatest levels of induction. Synthesis: These results provide some of the first support for theoretical predictions that the evolution of induced vs. constitutive defenses depends on the risk of herbivory. In habitats with constant and high potential losses to herbivores, such as tropical rainforests, high investments in constitutive defenses are favored over induction.

No MeSH data available.