Spatial variability in secondary metabolite production by the tropical redalga Portieria hornemannii

Apakaochtodenes A and B, which are halogenated monoterpenes and the major s econdary metabolites in Portieria hornemannii, are effective feeding deterr ents toward herbivorous reef fishes on Guam. A reciprocal transplant study was conducted to determine the relative importance of environmental versus genetic factors influencing site-to-site differences in the amount of apaka ochtodenes produced. The study sites were chosen for characteristically hig h (Anae Island) and low (Gun Beach) apakaochtodene levels. Algae collected from Anae Island and Gun Beach differed significantly in concentrations of apakaochtodene B at the start of the experiment, but by the end they had al most the same amount of the metabolite because the level had decreased in p lants at Anae Island. Additionally, algae from Anae Island had relatively h igh levels of apakaochtodene A (60-90% of apakaochtodene B concentration), whereas this compound was rarely detected in Gun Beach algae. Transplantati on to a different site had no significant effect on the levels of the apaka ochtodenes, other than a decrease in concentration that might have resulted from handling the algae. Our data indicate a strong site-to-site differenc e in apakaochtodene levels in P. hornemannii on Guam, notable interplant va riation in the levels of the compounds among thalli within the same site, a nd some evidence for temporal variation in levels of these compounds over a period of four weeks.