Abstract
Studies have identified chemicals within the stony coral genus Montipora that have significant biological activities. For example, Montiporic acids A and B and other compounds have been isolated from the adult tissue and eggs of Montipora spp. and have displayed antimicrobial activity and cytotoxicity in cultured cells. The ecological role of these toxic compounds is currently unclear. This study examines the role these toxins play in reproduction. Toxins were found in the eggs and larvae of the coral Montipora capitata. Releasing these toxins by crushing both the eggs and larvae resulted in irreversible inhibition of photosynthesis in endogenous and exogenous zooxanthellae within minutes. Moreover, these toxins were stable, as frozen storage of eggs and larvae did not affect toxicity. Photosynthetic competency of Porites compressa zooxanthellae treated with either frozen or fresh, crushed eggs was inhibited similarly (P > 0.05, ANCOVA). Addition of toxic eggs plugs to live P. compressa fragments caused complete tissue necrosis under the exposed area on the fragments within 1 week. Small volumes of M. capitata crushed eggs added to sperm suspensions reduced in vitro fertilization success by killing the sperm. After 30 min, untreated sperm maintained 90 ± 1.9% SEM motility while those treated with crushed eggs were rendered immotile, 4 ± 1.4% SEM. Flow cytometry indicated membrane disruption of the immotile sperm. Fertilization success using untreated sperm was 79 ± 4% SEM, whereas the success rate dropped significantly after exposure to the crushed eggs, 1.3 ± 0% SEM. Unlike the eggs and the larvae, M. capitata sperm did not reduce the photosynthetic competency of P. compressa zooxanthellae, suggesting the sperm was nontoxic. The identity of the toxins, cellular mechanism of action, advantage of the toxins for M. capitata and their role on the reef are still unknown.
Highlights
Adaptation is a key component to species survival
Even though the times to inhibition were slightly different, it was concluded that damaged eggs and larvae were both capable of inhibiting or damaging endogenous zooxanthellae within minutes, and that the toxins persisted in the larvae prior to settlement
When the adult tissue of six species of soft and stony adult coral were tested in the Red Sea, only soft corals exhibited antimicrobial activity [23]
Summary
The field of marine chemical ecology continues to unravel the complex ecological functions of marine natural products These compounds feature heavily in predator–prey interactions, trophic cascades, competition, prey capture, reproduction, and larval recruitment, and have added to ecological theory [1]. Competition for space is an important ecological process on coral reefs, and Pawlik et al [2] found that sponge compounds may stress corals by adversely influencing their symbiotic zooxanthellae. Allelopathy is one such adaptation where natural chemical defenses, such as toxins, inhibit the growth of another cell. Montipora [11] is the second largest genus in the family Acroporidae and has a cosmopolitan distribution [12], so if these adaptations are shared by many of the species within the genus, it could have broad implications for survival and adaptation on reefs around the world
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