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The Olympia Oyster: Fighting Ocean Acidification Via Exaptation

Paper Reviewed
Waldbusser, G.G., Gray, M.W., Hales, B., Langdon, C.J., Haley, B.A., Gimenez, I., Smith, S.R., Brunner, E.L. and Hutchinson, G. 2016. Slow shell building, a possible trait for resistance to the effects of acute ocean acidification. Limnology and Oceanography 61: 1969-1983.

Exaptation describes a process by which an organism acquires a functional trait through natural selection or evolution, which later phenomenon is coopted to serve another function. It is important because of its potential to enhance environmental resilience resulting from either natural or human effects, including global warming and ocean acidification, which resilience was the subject of investigation in a recently published paper in the journal Limnology and Oceanography by Waldbusser et al. (2016).

Working with the Olympia oyster (Ostrea lurida), a brooding species native to the North American Pacific coast, the team of nine researchers examined this bivalve's response to various levels of ocean acidification by extracting fertilized eggs prior to shell development and then exposing the embryos to "a wide range of marine carbonate chemistry conditions" (pH values ranging from 7.39 to 8.29, PCO2 from 201 to 2539 µatm and Ωar from 0.35 to 6.43 µmol kg-1) during the initial shell building stage.

In the course of this experiment, the Olympia oyster broods internally fertilized eggs for about 10 days prior to their release as veliger larvae. As a result, shell development was slower than typical broadcast spawned larvae from other bivalve species. Thus, it was the thought of Waldbusser et al. that this "slower development (and thus slower calcification) may be a mechanism by which brooding indirectly provides increased resiliency to ocean acidification in marine invertebrates as seen in recent studies (Noisette et al., 2014; Lucey et al., 2015)," and which would serve as a possible example of exaptation. So was this found to be the case?

In the words of Waldbusser et al., "surprisingly, O. lurida showed no acute negative response to any ocean acidification treatments." And this observed lack of response in which slow shell building counteracts the negative effects of ocean acidification, they conclude, is indeed an example of exaptation.

Commenting further on these findings, the scientists note that "the possibility of coopting current traits for fitness has rarely been recognized in the ocean acidification literature." And their contribution to the topic suggests that "some [marine] organisms may already have traits that could provide fitness in a high CO2 world and thus may not require the long multi-generational time-scales needed for selection and development of new traits resulting directly from ocean acidification exposure. That being the case, we have yet another reason to temper the gloom and doom prognostications of ocean acidification alarmists.

References
Lucey, N.M., Lombardi, C., DeMarchi, L., Schulze, A., Gambi, C. and Calosi, P. 2015. To brood or not to brood: Are marine invertebrates that protect their offspring more resilient to ocean acidification? Science Reports 5: DOI:10.1038/srep12009.

Noisette, F., Comtet, T., Legrand, E., Bordeyne, F., Davoult, D. and Martin, S. 2014. Does encapsulation protect embryos from the effects of ocean acidification? The example of Crepidula fornicate. PLoS One 9: e93021.

Posted 9 March 2017