Corals
The reef-building corals that inhabit the warm, shallow waters of the tropics are perhaps the best-known example of a mutualism involving an animal, and in tropical marine environments, they are certainly one of the most significant. The enduring ability
- PDF / 988,379 Bytes
- 13 Pages / 439.37 x 666.14 pts Page_size
- 33 Downloads / 258 Views
Corals
8.1
The Case of Reef Building Corals: A Complex Association Between Animal, Algal, and Bacterial Components
The reef-building corals that inhabit the warm, shallow waters of the tropics are perhaps the best-known example of a mutualism involving an animal, and in tropical marine environments, they are certainly one of the most significant. The enduring ability of corals (Scleractinia) and coral reefs to attract public interest and their ecological and economic importance stands in stark contrast to our ignorance of many basic aspects of their biology. In part, the lack of understanding is a consequence of the complexity of the association, but the net result is that we are seriously underequipped to understand why coral reefs everywhere are in serious decline and to implement policies that might at least slow this process. Under the premise that the primary function of the immune system is to mediate host–microbe interactions, it follows that coexisting with a more complex microbiota requires a more functionally complex immune system, most likely with more components. In this context, it is interesting to compare the predicted innate immune repertoires of the coral Acropora with those of the sea anemone Nematostella and Hydra. This kind of comparison indicates that the numbers of pattern-recognition receptors, both for external molecules (Toll-like receptors, interleukin-1-like receptors, other transmembrane TIR proteins) and internal patterns (NBD proteins), are much greater in the coral than in the other cnidarians, and the diversity of domain combinations, particularly in the NBD proteins, is also greater. These characteristics are consistent with a requirement for more sophisticated control of host–microbial interactions in the coral than in other Cnidaria.
© Springer-Verlag Wien 2016 T.C.G. Bosch, D.J. Miller, The Holobiont Imperative: Perspectives from Early Emerging Animals, DOI 10.1007/978-3-7091-1896-2_8
99
100
8.2
8 Corals
Attempts to Generalize About Coral–Microbe Interactions Are Complicated by the Evolutionary and Physiological Diversity of Corals
As is well known, shallow water reef-building corals are an association between a coral animal and a photosynthetic dinoflagellate belonging to the genus Symbiodinium. The association is an obligate one, at least as far as the coral animal is concerned—although these corals can survive for a short period after losing their partners, they die if an association with Symbiodinium is not reestablished in short order. It is much less well known that the Scleractinia, the order to which reefbuilding corals belong, contains almost as many species (more than 47 % of the 1490 recognized species; Cairns et al. 1999; Cairns 2007) that do not host (and do not require) Symbiodinium. These “azooxanthellate” corals frequently inhabit deep waters, where light levels are often very low and are mostly, but not exclusively, solitary—some azooxanthellate species are colonial and form massive deep-water reefs (Fig. 8.1). For example, the largest known Lophelia r
Data Loading...
