PARENT SESSION
Oral Session #45: Herbivory: Effects on Plants. Presiding: T. Craig.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.

Variation in the chemical defenses of the red alga Delisea pulchra: causes and consequences.

WRIGHT, JEFF¹, DE NYS, ROCKY ¹, POORE, ALISTAIR¹, STEINBERG, PETER¹, ¹

ABSTRACT- Factors that affect quantitative variation in the chemical defenses of seaweeds, and the consequences of that variation for plants, are poorly understood. The red alga Delisea pulchra produces a range of biologically active non-polar secondary metabolites (furanones). Here, we present a series of experiments that examine environmental and genetic effects on variation in furanones, the effect of variation in furanones on consumption by herbivores, and the cost to plants in having high concentrations of furanones. Concentrations of furanones in plants vary greatly within and among populations and both environmental (UV light, nutrients, induction) and genetic factors affect this variation. In general, feeding by herbivores does not vary in response to variation in furanones with herbivores falling into two distinct groups: species that consume very little D. pulchra and are deterred by low levels of furanones, and species that consume and often prefer D. pulchra, and are undeterred by any naturally occurring furanone level. Thus, there is no obvious benefit to plants in terms of reduced herbivory to having high concentrations of furanones. This absence of a benefit is surprising as there are negative correlations between furanones and both plant mass and reproduction, suggesting a cost exists in having high concentrations of furanones. It may be that other natural enemies of D. pulchra, specifically bacteria, have been important in the evolution of furanones and the structural similarity of furanones to bacterial signalling molecules (AHLs) supports this.

KEY WORDS: herbivory, chemical defense, marine algae, furanones