Assisted evolution

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Climate change creates such a huge problem for corals and other organisms because it is happening incredibly fast in comparison with the normal rate of environmental change. In theory, corals should be able to adapt to the temperature changes expected with RCP 8.5, but on their own they are unlikely to do so fast enough to avoid extinction. As described below, assisted evolution techniques [1] seek to speed up the natural acclimation and adaptation processes so that corals can keep up with the rate of climate change. They are similar to those used in selective breeding of plants and animals for agriculture and other commercial uses.

  • Stressing corals with warm temperatures can induce epigenetic changes which acclimate the corals and increase their future tolerance to those stresses. This may be able to carry over to future generations.
  • A coral's response to higher temperatures may depend to a large degree on its microbiome, particularly the zooxanthellae that live in their tissues and provide them with most of their food. The zooxanthellae established on a reef can be manipulated by providing larval corals with more heat tolerant strains (adult corals do not seem to be able to acquire new strains of zooxanthellae).
  • Corals can be crossed with others (including, in some cases, corals of other species) and selected for their ability to tolerate heat. Similarly, corals which have naturally adapted to the warm waters of a low latitude location can be transplanted to cooler waters containing other corals of the same species. If the corals from the warm location are more heat tolerant due to their genes (for which there is some evidence [2]), this will increase the availability of such heat tolerant genes in the local gene pool.
  • Mutations can be induced in zooxanthellae strains to modify their genetic code and create new strains (zooxanthellae reproduce asexually, so this is the only way they can evolve). This could be used to select for zooxanthellae that provide more heat tolerance for their host corals.

Assisted evolution seems like it would synergize well with the other techniques described in this wiki, which focus on locally modifying the environment to be more suitable for corals. There are about 800 species of hard corals alone [3], and to preserve reef biodiversity many of these need a place in the reefs of the future. Evolving all of these species in the short time frame of climate change under RCP 8.5 seems risky and difficult. Modifying the environment around a reef only works on a local scale, but affects all species living there. If there were enough such reefs, they would provide a stopgap for preserving healthy, intact reefs while assisted evolution proceeds.

Dealing with the effects of ocean acidification may also be another area for synergy with other techniques. Under RCP 8.5, aragonite saturation state is expected to drop to levels lower than that experienced by virtually all corals living today. It's difficult to say how well corals will be able to adapt to these conditions without technological assistance.

References

  1. Madeleine J. H. van Oppen, James K. Oliver, Hollie M. Putnam, Ruth D. Gates, Building coral reef resilience through assisted evolution, PNAS vol. 112 | no. 8 | 2307–2313 (2015)
  2. Groves B. Dixon, Sarah W. Davies, Galina V. Aglyamova, Eli Meyer, Line K. Bay, Mikhail V. Matz, Genomic determinants of coral heat tolerance across latitudes, Science 348 (6242), 1460-1462 (2015)
  3. https://oceanservice.noaa.gov/education/kits/corals/coral07_importance.html