How does rising atmospheric CO2 affect marine organisms?

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The Intracolonial Genetic Variability of Corals
Schweinsberg, M., Gonzalez Pech, R.A., Tollrian, R. and Lampert, K.P. 2014. Transfer of intracolonial genetic variability through gametes in Acropora hyacinthus corals. Coral Reefs 33: 77-87.

The authors report that in recent years an increasing number of studies have suggested that genetic inhomogeneity - the co-occurrence of different genotypes within the same organism - has been documented in a number of diverse types of marine life, such as red algae (Monro and Poore, 2009), sponges (Maldonado, 1998; Blanquer and Uriz, 2011), bryozoans (Hughes et al., 1992), hydroids (Shenk and Buss, 1991) and ascidians (Bishop and Sommerfeldt, 1999; Sommerfeldt et al., 2003), as well as within scleractinian corals (Frank et al., 1997; Barki et al., 2002; Amar et al., 2008; Puill-Stephan et al., 2009, 2012; Maier et al., 2012; Nozawa and Hirose 2011). However, they say that to this point in time, it has "remained unclear whether the intracolonial genetic variability of the adult coral is also present in the gametes."

What was done
In an attempt to obtain some clarity on the subject, Schweinsberg et al. explored the occurrence of intracolonial genetic variability in 14 mature colonies of the coral Acropora hyacinthus by focusing on eight microsatellite loci. This they did by placing a grid over each colony in advance of its spawning and collecting emerging egg/sperm bundles separately in each grid, after which the underlying tissues as well as the egg/sperm bundles were genotyped to determine whether different genotypes were present in each unique colony.

What was learned
In the words of the four researchers, "within the 14 mature colonies, we detected 10 colonies with more than one genotype (intracolonial genetic variability)." And they say that "four out of these 10 mature colonies showed a transfer of different genotypes via the eggs to the next generation," while "in two out of these four cases, we found additional alleles."

What it means
In discussing the significance of their findings, Schweinsberg et al. write that "an adaptive advantage of high levels of genetic diversity [such as they documented in the coral they studied] seems likely." And they thus go on to say that "it could be possible that under changing environmental conditions and the possibility that different genotypes within a colony spawn," this phenomenon "could be an advantage and allow sexual reproduction even in extreme isolation after, e.g., the coral population of the colony was mostly destroyed," which they describe as "a topic of very high interest in the ages of global warming and substantial reef loss." And so it is. And it is very encouraging, as it describes yet another way by which individual species of coral may maintain their viability in a CO2-enriched and warming world.

Amar, K.O., Chadwick, N.E. and Rinkevich, B. 2008. Coral kin aggregations exhibit mixed allogeneic reactions and enhanced fitness during early ontogeny. BMC Evolutionary Biology 8: 10.1186/1471-2148-8-126.

Barki, Y., Gateņo, D., Graur, D. and Rinkevich, B. 2002. Soft-coral natural chimerism: a window in ontogeny allows the creation of entities comprised of incongruous parts. Marine Ecology Progress Series 231: 91-99.

Bishop, J.D.D. and Sommerfeldt, A.D. 1999. Not like Botryllus: indiscriminate post-metamorphic fusion in a compound ascidian. Proceedings of the Royal Society B 266: 241-248.

Blanquer, A. and Uriz, M.-J. 2011. "Living together apart": the hidden genetic diversity of sponge populations. Molecular Biology and Evolution 28: 2435-2438.

Frank, U., Oren, U., Loya, Y. and Rinkevich, B. 1997. Alloimmune maturation in the coral Stylophora pistillata is achieved through three distinctive stages, 4 months post-metamorphosis. Proceedings of the Royal Society B 264: 99-104.

Hughes, T.P., Ayre, D., Connell, J.H. and Nifio, E. 1992. The evolutionary ecology of corals. Trends in Ecology and Evolution 7: 292-295.

Maier, E., Buckenmaier, A., Tollrian, R. and Nurnberger, B. 2012. Intracolonial genetic variation in the scleractinian coral Seriatopora hystrix. Coral Reefs 31: 505-517.

Maldonado, M. 1998. Do chimeric sponges have improved chances of survival? Marine Ecology Progress Series 164: 301-306.

Monro, K. and Poore, A.G.B. 2009. The evolvability of growth form in a clonal seaweed. Evolution 63: 3147-3157.

Nozawa, Y. and Hirose, M. 2011. When does the window close? The onset of allogeneic fusion 2-3 years post-settlement in the scleractinian coral, Echinophyllia aspera. Zoological Studies 50: 396.

Puill-Stephan, E., Willis, B., van Herwerden, L. and van Oppen, M. 2009. Chimerism in wild adult populations of the broadcast spawning coral Acropora millepora on the Great Barrier Reef. PLOS ONE 4: e7751.

Puill-Stephan, E., van Oppen, M.J.H., Pichavant-Rafini, K. and Willis, B.L. 2012. High potential for formation and persistence of chimeras following aggregated larval settlement in the broadcast spawning coral Acropora millepora. Proceedings of the Royal Society B 279: 699-708.

Shenk, M.A. and Buss, L.W. 1991. Ontogenetic changes in fusibility in the colonial hydroid Hydractinia symbiolongicarpus. Journal of Experimental Biology 257: 80-86.

Sommerfeldt, A.D., Bishop, J.D.D. and Wood, C.A. 2003. Intraclonal genetic variation: ecological and evolutionary aspects. Chimerism following fusion in a clonal ascidian (Urochordata). Biological Journal of the Linnean Society 79: 183-192.

Reviewed 7 May 2014