Ontogenetic consistency in oak defence syndromes

Abstract

Plant species allocate resources to multiple defensive traits simultaneously, often leading to so‐called defence syndromes (i.e. suites of traits that are co-expressed across several species). While reports of ontogenetic variation in plant defences are commonplace, no study to date has tested for ontogenetic shifts in defence syndromes, and we know little about the ecological and evolutionary drivers of variation in plant defence syndromes across ontogeny. We tested for ontogenetic variation in plant defence syndromes by measuring a suite of defensive and nutritional traits on saplings and adult trees of 29 oak (Quercus, Fagaceae) species distributed across Europe, North America, and Asia. In addition, we investigated if these syndromes exhibited a phylogenetic signal to elucidate the nature of their macro‐evolutionary variation, whether they were associated with levels of herbivore pressure and climatic conditions, and if any such evolutionary and ecological patterns were contingent on ontogeny. Our analyses revealed three distinct oak defence syndromes: the first included species with high defences, the second species with high defences and low nutrient levels, and the third species with high nutrients and thinner leaves. Interestingly, these defence syndromes remained virtually unchanged across the two ontogenetic stages sampled. In addition, our analyses indicated no evidence for a phylogenetic signal in oak syndromes, a result consistent across ontogenetic stages. Finally, with respect to ecological factors, we found no effect of climatic conditions on defences for either ontogenetic stage, whereas defence syndromes were associated with differing levels of herbivory in adults but not saplings suggesting an association between herbivore pressure and syndrome type that is contingent on ontogeny. Synthesis. Together, these findings indicate that defence syndromes remain remarkably consistent across oak ontogenetic stages, are evolutionarily labile, and while they appear unrelated to climate, they do appear to be associated with herbivory levels in an ontogenetic‐dependent manner. Overall, this study builds towards a better understanding of ecological and evolutionary factors underlying multivariate plant defensive phenotypes.

Predictability of Biotic Stress Structures Plant Defence Evolution

“…The adaptive value of ontogenetic changes in defence strategies matches patterns that act on longer-term scales of development (i.e. weeks to months for annuals, years for perennials) [59].…”

Elevational gradients in constitutive and induced oak defences based on individual traits and their correlated expression patterns

“…Although herbivory was absent or low in most cases for selected leaves, we estimated percent leaf area removed (mainly by miners and leaf chewers) prior to treatment application to account for pre‐existing herbivory as this may influence defence levels due to site‐specific induction. For this, we used the following scale: 0 = undamaged; 1 = 1–5% damaged; 2 = 6–10% damaged; 3 = 11–25% damaged; 4 = 26–50% damaged; 5 = 51–75% damaged; 6 = >75% damaged (Moreira et al 2020). We used the average value across leaves per plant for statistical analysis.…”

“…We identified four groups of phenolic compounds: flavonoids, ellagitannins and gallic acid derivates (‘hydrolysable tannins' hereafter), proanthocyanidins (‘condensed tannins' hereafter) and hydroxycinnamic acid precursors to lignins (‘lignins' hereafter). We quantified flavonoids as rutin equivalents, condensed tannins as catechin equivalents, hydrolysable tannins as gallic acid equivalents, and lignins as ferulic acid equivalents (Galmán et al 2019a, Moreira et al 2020). We achieved the quantification of these phenolic compounds by external calibration using the corresponding calibration curve at 0.25, 0.5, 1, 2 and 5 μg ml −1 for each of the four standards used (rutin, catechin, gallic acid and ferulic acid).…”

A roadmap for future research on insularity effects on plant–herbivore interactions

“…Research has shown that although plant defences are costly and that their redundancy can select against the expression or maintenance of multiple defences (Herms, 2002), in many cases plants express multiple defences simultaneously as a result of selection favouring the co‐expression of a broad array of traits to cope with multiple attacking herbivore species (Pellissier et al., 2016; Whitehead et al., 2021). Accordingly, this can result in so‐called defence syndromes (see Glossary; Agrawal & Fishbein, 2006; Moreira et al., 2020).…”