Ecological Genetics of an Induced Plant Defense Against Herbivores: Additive Genetic Variance and Costs of Phenotypic Plasticity

Abstract

Abstract. Adaptive phenotypic plasticity in chemical defense is thought to play a major role in plant-herbivore interactions. We investigated genetic variation for inducibility of defensive traits in wild radish plants and asked if the evolution of induction is constrained by costs of phenotypic plasticity. In a greenhouse experiment using paternal half-sibling families, we show additive genetic variation for plasticity in glucosinolate concentration. Genetic variation for glucosinolates was not detected in undamaged plants, but was significant following herbivory by a specialist herbivore, Pieris rapae. On average, damaged plants had 55% higher concentrations of glucosinolates compared to controls. In addition, we found significant narrow-sense heritabilities for leaf size, trichome number, flowering phenology, and lifetime fruit production. In a second experiment, we found evidence of genetic variation in induced plant resistance to P. rapae. Although overall there was little evidence for genetic correlations between the defensive and life-history traits we measured, we show that more plastic families had lower fitness than less plastic families in the absence of herbivory (i.e., evidence for genetic costs of plasticity). Thus, there is genetic variation for induction of defense in wild radish, and the evolution of inducibility may be constrained by costs of plasticity.

Constitutive and herbivore-inducible glucosinolate concentrations in oilseed rape (Brassica napus) leaves are not affected by Bt Cry1Ac insertion but change under elevated atmospheric CO2 and O3

“…The aliphatic GS concentration was generally low and seemed to be unaVected by elevated CO 2 . Possible changes in GS proWles under elevated CO 2 might have larger ecological impacts with respect to plant-insect interactions in the future, since glucosinolates seem to be subject to substantially high genetic variation in nature (Agrawal et al 2002). It is known that indolic GSs are herbivore-inducible (Bodnaryk 1992;Siemens and Mitchell-Olds 1998;Bartlet et al 1999) and this was also clearly reXected in the elevated 3IM-GS concentration following herbivory in Experiment 3 (acute O 3 ).…”

Effects of glucosinolate and myrosinase levels in Brassica juncea on a glucosinolate-sequestering herbivore – and vice versa

“…Most studies investigating induction responses of Brassicaceae to infestation with herbivores have demonstrated an increase of glucosinolates in damaged shoot or root tissue, particularly of indol glucosinolates (Agrawal 2000;Agrawal et al 2002;van Dam & Raaijmakers 2006). Also, increases of myrosinase transcripts and activities were found after induction with herbivore feeding or jasmonic acid treatment (Siemens & Mitchell-Olds 1998;Taipalensuu et al 1996;Taipalensuu et al 1997;Pontoppidan et al 2003).…”

Induced resistance in the indeterminate growth of aspen (Populus tremuloides)

“…Genetic variation in the induction response may be maintained by costs of plasticity, as the ability to respond chemically to defoliation may prevent the commitment of resources to growth and/or reproduction (Agrawal et al 2002).…”

“…Genetic variation in inducibility was demonstrated experimentally (Zangerl and Berenbaum 1990;van Dam and Vrieling 1994;Robison and Raffa 1997;Ruuhola et al 2001;Agrawal et al 2002), and plant defense theories predict environmental effects on induction (Coley et al 1985;Herms and Mattson 1992). According to these theories, plants adapted to high-nutrient environments are fast-growing, have low constitutive levels of resistance, and are more likely to show inducibility than slow-growing plants that have high constitutive levels of resistance and are common in resource-poor environments.…”