Temporal variation in the production of four secondary metabolites in a colonial ascidian.

The ecological and applied importance of ascidian secondary metabolites is well reported, but little is known about temporal variation in the production of these compounds. Here, we examined seasonal variation in the production of the four main pyridoacridine alkaloids (shermilamine B, kuanoniamine D, and their deacetylated forms) of the purple morph of the ascidian Cystodytes sp. Five replicate samples were taken monthly from July 2004 to February 2006, and analyzed by high-performance liquid chromatography. Our results showed a high degree of intercolony variability in secondary metabolite concentration and a lack of statistically significant seasonal variation in the production of the four compounds. Minimum values, however, were consistently recorded over the studied years in late summer, after the reproductive period. These minima may be attributable to sexual exhaustion and seasonally varying biotic interactions or abiotic parameters.