sperm of this species can find the correct eggs. A similar function as recently been found for the chemicals concentrated in the eggs of Lobophytum crassum (Coll et al., 1995). Lobophytum crassum and L. compactum both contain isomers of cembranoid diterpenes in their eggs, (-)-epi-thunbergol and (-)-thunbergol respectively. These were shown to act as sperm attractants at very low concentrations, Since Lobophytum have separate male and female colonies, often separated by large distances, these attractants would play an important role during mass spawnings. Given these results it is not unreasonable to assume that the other egg specific compounds isolated from some ten other species of octocoral may also be sperm attractants (Coll et al., 1995).
One interesting observation is that the presence of secondary metabolites is highly variable. Concentrations can vary widely from species to species within a genus, and between genera (LaBarre, et al., 1986). The reproductive state also appears to play a role, with some chemicals only being present when eggs are present (Coll, et al, 1995; Sammarco and Coll, 1986). The geographic location also plays a role, with the same species showing varying levels of chemicals from one area to the next
(Harvell et al., 1993; Coll et al., 1995). Finally, Leone et al.(1995)
showed that moving colonies of Lobophytum compactum resulted in a significant increase in diterpenes, but this decreased after two months. Ongoing work at the University of Hawaii has also shown that many of the organisms that contain these defensive chemicals lose these chemicals when removed from the presence of predators (B. Carlson, pers. comm.).
Terpenes, diterpenes and other natural products of octocorals are attracting a great deal of attention and studies are now underway to investigate the possible uses of these compounds in medicine and industry. Many new natural marine products are discovered each year and they are often tested by researchers at the U.S. National Institute of Health, the U.S. National Cancer Institute and other organizations around the world. For those of you who would like to investigate these substances more closely or want to keep up-to-date on the latest findings we recommend reading The Journal of Natural Products as well as the annual reports by Dr. D. J. Faulkner published as the Natural Products Report each year.
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