PARENT SESSION
Contributed Oral Session 86: Herbivory: Genetic Variability in Insect - Plant Interactions
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Genetic variation and costs of chemical defense production and plasticity in a seaweed.

Pavia, Henrik¹, Toth, Gunilla^*,1, ¹ Göteborg University, Strömstad, Sweden

ABSTRACT- Phenotypic plasticity is the capacity of organisms to respond to environmental changes by expressing different (presumably adaptive) phenotypes, e.g. increased production of chemical defense metabolites by plants under herbivore attack (inducible defenses). The evolution of inducible (as opposed to constitutive) chemical defenses should be favored when defense chemicals are costly to produce, because plastic individuals will be able to use resources for growth and/or reproduction when herbivores are absent. However, evolution of optimal phenotypes may be constrained by costs associated with the ability to alter the phenotype, which are separate from costs associated with production of the new phenotype. Here we investigated the genetic variation and costs of chemical defense (phlorotannin) production and plasticity in a brown seaweed (Ascophyllum nodosum). Seaweed clones were grown in a common garden setting without herbivores for 4 months, and were then exposed to herbivorous gastropods in a 2-week induction experiment. The growth (used as a measure of fitness) and constitutive phlorotannin production varied significantly among seaweed individuals, and a significant negative genetic correlation between the two traits strongly indicated a cost of constitutive phlorotannin production. Furthermore, seaweed individuals differed significantly in their ability to induce a higher phlorotannin production in response to herbivore attack, and more plastic individuals had a lower fitness in the absence of herbivores, indicating a cost of phenotypic plasticity. Our results show that, although defense production can be costly, the evolution of inducible defenses may be constrained by costs of phenotypic plasticity.

Key words: cost, defense, plasticity, seaweed