Costs of Induced Responses and Tolerance to Herbivory in Male and Female Fitness Components of Wild Radish

Abstract

Abstract.-Theory predicts that plant defensive traits are costly due to trade-offs between allocation to defense and growth and reproduction, Most previous studies of costs of plant defense focused on female fitness costs of constitutively expressed defenses. Consideration of alternative plant strategies, such as induced defenses and tolerance to herbivory, and multiple types of costs, including allocation to male reproductive function, may increase our ability to detect costs of plant defense against herbivores. In this study we measured male and female reproductive costs associated with induced responses and tolerance to herbivory in annual wild radish plants (Raphanus raphanistrum). We induced resistance in the plants by subjecting them to herbivory by Pieris rapae caterpillars. We also induced resistance in plants without leaf tissue removal using a natural chemical elicitor, jasmonic acid; in addition, we removed leaf tissue without inducing plant responses using manual clipping. Induced responses included increased concentrations of indole glucosinolates, which are putative defense compounds. Induced responses, in the absence of leaf tissue removal, reduced plant fitness when five fitness components were considered together; costs of induction were individually detected for time to first flower and number of pollen grains produced per flower. In this system, induced responses appear to impose a cost, although this cost may not have been detected had we only quantified the traditionally measured fitness components, growth and seed production. In the absence of induced responses, 50% leaf tissue removal, reduced plant fitness in three out of the five fitness components measured. Induced responses to herbivory and leaf tissue removal had additive effects on plant fitness. Although plant sibships varied greatly (49-136%) in their level of tolerance to herbivory, costs of tolerance were not detected, as we did not find a negative association between the ability to compensate for damage and plant fitness in the absence of damage. We suggest that consideration of alternative plant defense strategies and multiple costs will result in a broader understanding of the evolutionary ecology of plant defense.

Among-Population Variation in Tolerance to Larval Herbivory by Anthocharis cardamines in the Polyploid Herb Cardamine pratensis

“…Although artificial and natural damage often have similar effects on plant performance [34], studies have also shown that not all plants respond similarly to artificial damage compared to damage caused by herbivores [37], [38]. This could for example be due to the lack of induced plants responses caused by herbivore saliva [39] or the timing of damage [41].…”

“…Still, consumption of plant tissue by larvae may influence plants differently from damage by clipping [34], [37], [38]. For example prolonged exposure to larval saliva may trigger induced responses [39].…”

Differential Allocation of Constitutive and Induced Chemical Defenses in Pine Tree Juveniles: A Test of the Optimal Defense Theory

“…Other authors have assessed tissue fitness value by removing different plant tissues and measuring the impact on subsequent plant fitness [6], [12]. However, although removal of needles without apparent defensive responses have been used elsewhere, we think that removal of plant tissues in pine trees could induce herbivory signaling and provoke defensive responses, potentially leading to dramatic changes in the plant sink-source balance, carbon allocation and growth patterns [32]–[34]. This is of particular relevance given that our aim is to study constitutive and induced defenses, and could well lead to confounding results.…”

Variation and fitness costs for tolerance to different types of herbivore damage in Boechera stricta genotypes with contrasting glucosinolate structures

“…However, these studies simulate damage mainly through manual clipping, which may be a poor surrogate for genuine herbivory (Strauss & Agrawal, 1999). In addition, little is known about how different kinds of herbivore damage influence tolerance to herbivory across naturally varying genotypes (but see Agrawal et al ., 1999; Tiffin & Rausher, 1999; Pilson, 2000). However, to understand the evolution of tolerance, it is essential to determine whether conspecific genotypes show differential tolerance to herbivore damage.…”