Plant ontogeny and chemical defence: older seedlings are better defended

Abstract

Although patterns of seedling selection by herbivores are strongly influenced by plant age and the expression of anti‐herbivore defence, it is unclear how these characteristics interact to influence seedling susceptibility to herbivory. We tracked ontogenetic changes in a range of secondary metabolites (total phenolics, alkaloids and cyanogenic glycosides) commonly associated with seedling defence for nine sympatric British grassland species. Although there was marked variation in concentrations of secondary metabolites between different species, we found a consistent increase in the deployment of phenolics, alkaloids and cyanogenics with seedling age for six of the seven dicotyledonous species examined. The two grass species by contrast exhibited low levels of secondary metabolites across all developmental stages, possibly due to an investment in structural (silica phytoliths) defence. Our results corroborate species‐specific patterns of seedling herbivory observed in field studies, and offer some explanation for the relatively high sensitivity to herbivore attack frequently observed for relatively young seedlings compared with their older conspecifics. Our results also support predictions made by the growth–differentiation balance hypothesis regarding ontogenetic changes in resource allocation to anti‐herbivore defence for a range of potential chemical defences and across a range of sympatric plant species presumably subject to broadly similar selective pressures at the regeneration stage.

Bidirectional Secretions from Glandular Trichomes of Pyrethrum Enable Immunization of Seedlings

“…Secondary metabolites from pyrethrum stored in trichomes or in leaves and seeds provide leaves and seeds with chemical protection against attacking insect herbivores and pathogens and potentially result in fitness benefits (Boege and Marquis, 2005;Elger et al, 2009;Yang et al, 2012). Chemical analysis of pyrethrum leaves and seeds showed that glandular trichomes present on the ovaries have a more complex composition than the glandular trichomes of leaves (Figure 3).…”

Arriving at the right time : a temporal perspective on above-belowground herbivore interactions

“…Nematode addition significantly reduced root biomass but only of plants at intermediate age three weeks after inoculation. This may be because young plants usually have a higher growth rate (Walters et al 1993) and old plants can better compensate loss to herbivory (Elger et al 2009), thereby mitigating or even counteracting the negative effects of root-feeding nematodes on root biomass.…”

“…As we could not relate the proportion of root P. penetrans to root N concentration over time (Regression analysis: R 2 = 0.04), our data suggest that other attributes in plant roots changed during plant development leading to the decreased proportion of P. penetrans in roots. One possibility may be that secondary chemicals may accumulate when roots age (Elger et al 2009;Quintero and Bowers 2012).…”

“…Plant age is frequently shown to affect a plant's adaptation to various environmental stresses (Boege and Marquis 2005) as it influences the plant's response in terms of induced defense (Quintero and Bowers 2011) and tolerance (Barton 2013) to stress. For example, defenses of young plants are often more easily inducible (Quintero and Bowers 2011) but young plants have lower tolerance (Elger et al 2009). …”

The Ecology of Extrafloral Nectar in Senna mexicana var. chapmanii

“…Investment in defensive traits should aim to maximize fitness benefits, while minimizing costs (McKey, 1974). As plants age the balance between costs and benefits may shift, and changes in the expression of defensive traits are predicted to occur (Elger et al, 2009). The effects of these ontogenetic variations on the dynamics of ant-plant interactions have only recently been explored (Boege and Marquis, 2005;Kwok and Laird, 2012;Quintero et al, 2013).…”