Contributions to Zoology, 79 (2) – 2010Bastian T. Reijnen; Bert W. Hoeksema; Edmund Gittenberger: Host specificity and phylogenetic relationships among Atlantic Ovulidae (Mollusca: Gastropoda)
Discussion

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Associations

Reported host preferences of Cyphoma gibbosum (Bertsch, 1984; Lasker et al., 1988; Botero, 1990; Nowlis, 1993; Chiaponne et al., 2003) are partly confirmed and supplemented with new observations of associations of this species, showing once more that C. gibbosum is a generalist parasite (Table 2). Cymbovula acicularis turned out to be another generalist.

It remains unclear why 43% of the encountered alcyonacean species did not appear as hosts for ovulids at the time of our fieldwork (Table 3). It is known that Octocorallia may produce secondary metabolites as protection against predation (Ciereszko and Schneider, 1987; Chiaponne et al., 2003), but the effect of this defence strategy on ovulids is still largely unexplored. Other factors, such as the nutritional value of the corals (O’Neal and Pawlik, 2002) and the unpalatability of sclerites (Alstyne and Paul, 1992), may also influence host choices.

An overview of natural products produced by West Indian gorgonian octocorals reveals that many types of secondary metabolites are found. The largest class of metabolites encountered in Caribbean alcyonaceans are diterpenoids, followed by the sesquiterpenes (Rodriguez, 1995). For some of these compounds that are obtained from alcyonaceans, such as Erythropodium caribeorum, feeding experiments were performed, resulting in the observation that coral extracts are deterrent to fish. Also, crude extracts from the gorgonian Gorgonia ventalina, containing terpenoids, were used in feeding experiments with C. gibbosum. As a result, C. gibbosum consumed only 49% of an artificial diet containing terpenoids (Alstyne and Paul, 1992).

The sclerites of the gorgonian species that we found as hosts for Simnialena uniplicata and Cymbovula acicularis turned out to be relatively small. The sclerites of Gorgonia spp. and Pseudopterogorgia spp. have average sizes of 0.10 mm and 0.10-0.15 mm, respectively, whereas 0.30-1.00 mm is common for other Octocorallia species, like Eunicea and Pseudoplexaura species (Bayer, 1961). For Cyphoma gibbosum,however, the sclerites’ size seems to be irrelevant for host selection, since this species is found on corals containing either small or large sclerites. By analysing faecal pellets which all contained sclerites, we conclude that C. gibbosum at least ingests sclerites instead of eating around them.