Geographic variation in halogenated furanones from the red alga Delisea pulchra and associated herbivores and epiphytes

We examine patterns of quantitative variation in halogenated fuaranones, se condary metabolites of Delisea pulchra (Rhodophyta; Bonnemaisoniales), and how this relates to variation in local abundance of herbivores and epiphyte s. Fifteen populations of D. pulchra covering a distance of 650 km of tempe rate southeastern Australia were sampled. Concentrations of the 4 main fura nones in D. pulchra (Compounds 1 to 4) showed large variability but there w as no latitudinal trend to this variation. We found significant variation i n the concentrations of both total and individual furanones among locations , between summer and winter, and between different Life-history stages. Imp ortantly, the range of total furanone concentration among plants within loc ations was large, often varying by an order of magnitude or more. A total o f 5 species of herbivorous fish, 7 species of macroinvertebrate grazer and 6 groups of mesograzer (of varying taxonomic level) were found at the 15 lo cations. The abundance of both total macroinvertebrate grazers and total me sograzers known to consume D, pulchra varied significantly among locations. However, correlations between furanones and the abundance of macroinverteb rate grazers and mesograzers at the scale of location were all weak and non significant, as was the correlation between furanones and the abundance of epiphytes on D, pulchra. The large variability in concentrations of furanon es, and the absence of any positive relationships between furanones, herbiv ores and epiphytes, suggest that quantitative variation in furanones in D. pulchra is not driven by population-level selection or induction, but is mo re likely to be a result of small-scale variation in environmental factors such as nutrients and light, and genetic differences among individual plant s.