Cyphoma gibbosum

Figure 1. C. gibbosum feeding on gorgonian coral. Source: rsmas.miami.edu

Morphology

The colorful appearance of C. gibbosum can be attributed to the mantle of the organism. Although it is capable of retraction if threatened, the mantle oftentimes completely encases the shell (Figure 2). Coloration of the mantle ranges from a white to cream base overlain with black-ringed orange spots (Figure 1). The bright coloration makes the diurnally active Flamingo Tongue conspicuous against the monochromatic backdrop of its gorgonian hosts (Rosenburg, 1989). Although this lack of camouflage may seem disadvantageous to the snail, aposematic coloration serves to warn predators of its toxicity, which is a result of prey toxin incorporation into the tissues. In comparison, the cream-colored shell, approximately 20-50mm in length and characterized by a transverse mid-shell ridge, is quite drab (Figure 3).

Reproduction and Life Cycle

As is common in gastropods, C. gibbosum has both a juvenile and adult stage in its life cycle. Unlike the bright coloration characteristic in adults, juvenile Flamingo Tongues have a bland color palate similar to their gorgonian hosts. It is unknown whether or not the juvenile stage is toxic, but the small size and developing shell would likely make aposematic coloration disadvantageous, as predatory tasting would likely result in injury or death to many (Rosenburg, 1989). The cryptic, nocturnal behavior exhibited by juveniles, as opposed to the diurnally active adults, also supports this theory.

C. gibbosum is dioecious and reproduces sexually. After copulation, females lay a transparent egg capsule on the bare stalk, established by persistent feeding in a localized area, of their gorgonian host. Approximately 10 days later, the eggs hatch, releasing up to 300 planktrophic larva into the surrounding waters. The larva are then dispersed via currents until settlement, after which they metamorphose into juveniles, and eventually progress to the adult stage (Rosenburg, 1989). The lifespan of these organisms is around two years, with the potential to reproduce monthly in coincidence with lunar cycles.

Feeding Behavior and Ecology

Flamingo Tongue snails are corallivores, specifically feeding upon a variety of gorgonian (soft coral) species. Using their radula, the snails scrape polyps from the corals. Dependent upon the damage left in their wake, ranging from a series of shallow grooves to stripped stalks, C. gibbosum is considered to exhibit either communalistic or parasitic symbiosis, respectively, with its host (Harvell and Suchanek, 1987) (Figure 4).

Figure 4. Superficial grazing (left) and stripping-style grazing (right) remnants of gorgonian species subject to C. gibbousm predation.

Source: Harvell and Suchanek, 1987

A study conducted by Burkepile and Hay evaluated the ecological role of predation on C. gibbosum by large fishes (2007). Results indicated that the frequency and extent of attack by C. gibbosum on gorgonian corals increased 8 times upon elimination of predatory fishes from the ecosystem (Figure 5). These findings stress the importance of policies which help maintain top-down control on corallivores in maintaining healthy coral reef ecosystems.

Figure 5. Graphs depicting the increased extent of grazing (left) and abundance of C. gibbosum on gorgonian hosts in caged (lack fish predators) and uncaged environments.

Source: Burkepile and Hay, 2007

Distribution Amongst Gorgonian Corals

Although C. gibbosum is known to utilize a variety of gorgonian corals as its host, there does appear to be a trend of selective preference. For instance, observational analyses of a reef in the US Virgin Islands identified the almost exclusive presence of C. gibbosum on B. asbestinum, as opposed to other gorgonian hosts inhabiting the area (Hazlett and Bach, 1982). Preference amongst a given species was also suggested by a transfer experiment within the same study. In these trials, four C. gibbosum were displaced from their current host gorgonian and moved to another unoccupied host of the same species. It should be noted that temporal distribution patterns showed a single host was never continuously occupied, as commonly occupied hosts were found baring no organisms for spans of multiple days. Within 24 hours all of the snails had left their new host and within 48 hours, returned to one of the four previously occupied hosts. One proposed explanation for this behavior may be selective preference of toxins within the host, as other studies have shown chemical variance within single species of gorgonians.

Contrary to the previous belief that biological pressures, such as local predator abundance, were the largely uncontested factor influencing the distribution of C. gibbosum amongst its gorgonian hosts, recent research suggests that there may be numerous contributing factors. Further experiments conducted on the US Virgin Island reef mentioned previously identified a positive correlation between percent occupancy (the number of days on which any C. gibbosum were found on a colony divided by the number of days surveyed) and the size of the host colony, with larger colonies boasting a greater percent occupancy (Hazlett and Bach, 1982). Percent occupancy also showed a negative correlation with distance to the nearest neighboring B. asbestinum colony, with more isolated colonies having a greater occupancy percentage. Although the latter may appear to signify possible territoriality of the snails, other studies showed that C. gibbosum are often aggregated in a small area, or even on an individual host (Lasker and Coffrath, 1988). This finding is furthered supported by research which has focused primarily on the gregariousness of C. gibbosum, which is thought to be a behavior exhibited to increase the effectiveness of their primary defensive mechanism, distastefulness (Gerhart, 1986). In addition to social interactions, wave surge intensity (Gerhart, 1989), predator avoidance (Lasker et al., 1988), and mating preferences (Nowlis, 1993) have also been proposed to influence C. Gibbosum distribution.

Prey Detoxification Mechanisms

The diet of C. gibbosum consists of a variety of chemically-defended gorgonian corals. In order to compensate for ingestion of toxins, consumer detoxification is critical to these animals. Recent toxicology research has identified the role of multiple glutathione S-transferases as an important detox mechanism suitable for a variety of gorgonian species (Paul et al, 2011). In C. gibbosum, these transferases are present in high concentrations and display constitutive expression. This is likely due to the continuous presence of high affinity substrates for these transferases present in consumed gorgonian tissues, which then need to be exported using associated multidrug resistance-associated protein (MRP) families (Whalen and Sotka et al, 2010). Although the expression extent is not significantly altered, the activity of the GST was found to vary according to diet allelochemical composition (Vrolijk and Targett, 1992). The primary biotransformation role of GSTs, as opposed to cytochrome P450, also has the potential to minimize production of intermediate compounds that may serve harmful to the snail. However, the role of diverse cytochrome P450 molecules found in these animals should not be dismissed, especially concerning their use in evolutionary contexts (Whalen and Starczak et al., 2010).

References

Burkepile, D. E., & Hay, M. E. (2007). Predator release of the gastropod Cyphoma gibbosum increases predation on gorgonian corals. Oecologia, 154(1), 167–173. https://doi.org/10.1007/s00442-007-0801-4

Gerhart, D. (1986). Gregariousness in the gorgonian-eating gastropod Cyphoma gibbosum: tests of several possible causes. Marine Ecology Progress Series, 31, 255–263. https://doi.org/10.3354/meps031255

Gerhart, D. J. (1989). Movements of the tropical gorgonian-eating gastropod Cyphoma gibbosum (Linnaeus): association with wave surge. Marine Behaviour and Physiology, 15(October), 207–215. https://doi.org/10.1080/10236248909378729

Harvell, C., & Suchanek, T. (1987). Partial predation on tropical gorgonians by Cyphoma gibbosum (Gastropoda). Marine Ecology Progress Series, 38, 37–44. https://doi.org/10.3354/meps038037

Hazlett Brian A.; Bach, C. E. (1982). Distribution pattern of the flamingo tongue shell (cyphoma gibbosum) on its gorgonian prey (briareum asbestinum). Marine Behaviour and Physiology, 8(4). https://doi.org/10.1080/10236248209387027

Lasker, H. R., Coffroth, M. A., & Fitzgerald, L. M. (1988). Foraging Patterns of Cyphoma gibbosum on Octocorals : the Roles of Host Choice and Feeding Preference. Biological Bulletin, 174(3), 254–266. https://doi.org/10.2307/1541952

Lasker, H. R., & Coffrath, M.A. (1988). Temporal and spatial variability among grazers: variability in the distribution of the gastropod Cyphoma gibbosum on octocorals. Marine Ecology Progress Series, 43, 285–295.

Nowlis, J. P. (1993). Mate- and Oviposition-Influenced Host Preferences in the Coral-Feeding Snail Cyphoma Gibbosum. Ecology, 74(7), 1959–1969.

Paul, V. J., Ritson-Williams, R., & Sharp, K. (2011). Marine chemical ecology in benthic environments. Natural Product Reports, 28(2), 345–387. https://doi.org/10.1039/c0np00040j

Rosenburg, G. (2010). Aposematism Evolves by Individual Selection: Evidence from Marine Gastropods with Pelagic Larvae. Evolution, 43(8), 1811–1813. http://www.jstor.org/stable/2409397.

Vrolijk, N., & Targett, N. (1992). Biotransformation enzymes in Cyphoma gibbosum (Gastropoda: Ovulidae)- implications for detoxification of gorgonian allelochemicals . Marine Ecology Progress Series, 88, 237–246. https://doi.org/10.3354/meps088237

Whalen, K. E., Sotka, E. E., Goldstone, J. V., & Hahn, M. E. (2010). The role of multixenobiotic transporters in predatory marine molluscs as counter-defense mechanisms against dietary allelochemicals. Comparative Biochemistry and Physiology - C Toxicology and Pharmacology, 152(3), 288–300. https://doi.org/10.1016/j.cbpc.2010.05.003

Whalen, K. E., Starczak, V. R., Nelson, D. R., Goldstone, J. V, & Hahn, M. E. (2010). Cytochrome P450 diversity and induction by gorgonian allelochemicals in the marine gastropod Cyphoma gibbosum. BMC Ecology, 10(1), 24. https://doi.org/10.1186/1472-6785-10-24