Predictors of Male and Female Tolerance to Insect Herbivory in Raphanus Raphanistrum

Abstract

Traits associated with plant tolerance to herbivory are often thought to be those involved in resource acquisition, e.g., root biomass, leaf area, and photosynthetic rate. Plant resistance traits, like concentrations of secondary compounds, can also be negatively associated with tolerance. Few studies have measured both ''tolerance'' and ''resistance'' traits in the same study to determine which are the best predictors of a plant's ability to tolerate insect damage. Here, we measured simultaneously a large suite of traits on damaged and undamaged siblings in 10 families of greenhouse-grown Raphanus raphanistrum plants. Traits measured were: leaf area, root biomass, shoot biomass, photosynthetic rate, trichome density, total glucosinolate concentration, flowering rate, petal size, total number of flowers, and total number of seeds. Pieris rapae larvae were used to damage plants to 50% leaf area removal. Using multiple regression, we examined which traits were the best predictors of tolerance. We considered both male tolerance (relative number of flowers produced by damaged and undamaged sibs) and female tolerance (relative number of seeds produced). We found that, generally, resistance traits were better predictors of both male and female tolerance than tolerance traits. Interestingly, we found that male and female tolerance were not correlated, and that male tolerance was significantly less variable than female tolerance. We also found that measurements of traits postdamage (induced state) were more informative than measurements on undamaged plants (constitutive state). Our results support the idea of a resistance/tolerance trade-off. In addition, our study suggests that there are conflicts in investment in male vs. female fitness after damage.

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

“…Male and female plant fitness of damaged and undamaged plants were equal by the end of the season (Strauss et al 2001). Resistance traits to insect herbivory (e.g., glucosinolate concentrations) were better predictors of male tolerance (relative numbers of flowers produced) and female tolerance (relative number of seeds produced) to herbivory, compared with resource acquisition traits, such as leaf area (Strauss et al 2003). Herbivory by P. rapae or spraying with the natural plant response elicitor, jasmonic acid, resulted in the induction of putatively defensive glucosinolates in wild radish (Agrawal 1999).…”

Nectar and Pollen Feeding by Insect Herbivores and Implications for Multitrophic Interactions

“…Floral herbivory may include damage to floral nectaries, stamen, or the ovary. As feeding on floral tissue commonly involves destruction of gametes, it often has a stronger direct impact on plant fitness than does foliar herbivory (118,149). Damage to the inflorescence may negatively affect the pollen quality as well as quantity (3) and may make the flower, the flowering plant, or even patches of flowering plants less attractive to pollinators (78).…”

Three‐Way Interactions among Mutualistic Mycorrhizal Fungi, Plants, and Plant Enemies: Hypotheses and Synthesis

“…2). This type of trade-off has been an implicit assumption in many of the discussions of plant defense theories (such as the optimal defense hypothesis [Rhoades 1979], the growth rate hypothesis [Coley et al 1985], and the growthdifferentiation balance hypothesis [Loomis 1932;Loomis 1953]) and has been empirically supported in several stud- ies (Fineblum and Rausher 1995;Stowe 1998;Fornoni et al 2003;Prittinen et al 2003;Strauss et al 2003; but see Mole 1994;Karban and Baldwin 1997). Plants associated with mycorrhizal fungi can use the additional resources to step off this trade-off plane described within many plant defense hypotheses and increase allocation to one or more axes (growth, defense, or tolerance) without decreasing allocation to any of the other axes ( fig.…”