Analyzing plant defenses in nature

Abstract

A broad range of chemical plant defenses against herbivores has been studied extensively under laboratory conditions. In many of these cases there is still little understanding of their relevance in nature. In natural systems, functional analyses of plant traits are often complicated by an extreme variability, which affects the interaction with higher trophic levels. Successful analyses require consideration of the numerous sources of variation that potentially affect the plant trait of interest. In our recent study on wild lima bean (Phaseolus lunatus L.) in South Mexico, we applied an integrative approach combining analyses for quantitative correlations of cyanogenic potential (HCNp; the maximum amount of cyanide that can be released from a given tissue) and herbivory in the field with subsequent feeding trials under controlled conditions. This approach allowed us to causally explain the consequences of quantitative variation of HCNp on herbivore-plant interactions in nature and highlights the importance of combining data obtained in natural systems with analyses under controlled conditions.Analyzing plant defenses against herbivores in nature is often complicated by an extreme variability in multiple factors. Plant populations generally show high genetic variability resulting in substantial intraspecific variation of plant traits. 1 In addition to genotypic variability, phenotypic plasticity of plants is a source of variation. 2 At the level of individual plants, expression of defensive traits strongly depends on plant organ and ontogeny of plants or plant parts. Within an individual plant, it is quite common for reproductive structures and young leaves to be better chemically defended than older leaf tissues. To explain these within-plant variations of defenses, the optimal defense hypothesis (ODH) was formulated. Concerning the variability of chemical defenses of leaves, the ODH predicts that within the total foliage of a plant, young leaves make a larger contribution to plant fitness than old leaves as they have a higher potential photosynthetic value resulting from a longer expected life-time. [3][4][5] In addition, younger leaves are often more nutritious and thus more attractive to herbivores 6 and should consequently be better defended. 7 In this line, the basic assumption of the ODH is that three main factors-cost of defense, risk of attack and value of the respective plant organdetermine the investment in defensive secondary metabolites. 8,9 Thus, the higher the risk of a given plant tissue to be consumed by herbivores and the higher its value for plant fitness, the more energy should be allocated to its defense. 10,11 Beyond genotypic and ontogenetic variability of a given defense, potential co-variation with other defensive or nutritive traits expressed by the same plant individual can strongly affect its efficiency as defense against herbivores. 12,13 In addition to these endogenous sources of defensive variability, the expression of plant traits strongly depends on multiple external factors such ...

Genetic and environmental interactions determine plant defences against herbivores

“…In natural systems, analyses of plant responses to abiotic conditions at small and larger scales and analyses of the consequences of these responses for higher trophic levels are complicated by various factors (Ballhorn et al. 2009b).…”

“…Among these, overlapping effects of the plants’ genetic variability (i.e. genotypic variation), ontogenetic variability (variation depending on developmental stages of plants and/or specific plant organs) and phenotypic plasticity (here defined as variation depending on external factors) are major sources of variation that have to be considered – and separated – in functional analyses of plant traits (Schlichting & Pigliucci 1998; Busk & Møller 2002; Ballhorn, Kautz & Rakotoarivelo 2009c; Ballhorn et al. 2009b).…”

Cymbopogon Species; Ethnopharmacology, Phytochemistry and the Pharmacological Importance

“…The presence of secondary metabolites in plants is characterized by their ability to provide defenses against biotic and abiotic stress [1]. The mechanism of defense varies from plant to plant, their environmental conditions and climatic variations.…”

Distance and Sex Determine Host Plant Choice by Herbivorous Beetles

“…The factors that drive plant-herbivore interactions are complex and we are only beginning to understand their functional interplay in natural systems [1]. In addition to quantitative and qualitative variation in plant primary and secondary metabolites, the attractiveness of host plants to insect herbivores is influenced by multiple factors, such as the presence of phytopathogens, predators, parasitoids, soil biota, as well as of other conspecific and heterospecific herbivores [1]–[7].…”

“…In addition to quantitative and qualitative variation in plant primary and secondary metabolites, the attractiveness of host plants to insect herbivores is influenced by multiple factors, such as the presence of phytopathogens, predators, parasitoids, soil biota, as well as of other conspecific and heterospecific herbivores [1]–[7]. Furthermore, plant attractiveness is affected by microclimatic conditions, plant architecture, and abundance [2]–[5].…”