The fate of certain organisms will have an outsized impact on the world’s ecosystems, and E. huxleyi, a species of phytoplankton, is one of them. It’s hard to overstate the importance of phytoplankton; these tiny photosynthesizing drifters form the base of nearly all the ocean’s food webs, and are responsible for half of all photosynthetic activity on the planet. Specifically, E. huxleyi is a coccolithophore, a type of single-celled algae that makes up an important part of the ocean’s phytoplankton. The “coccoliths” that cover the cells are plates made of calcium carbonate, the same substance stony coral reefs are made of. Just as ocean acidification threatens the ability of corals to produce their reef-building calcium carbonate structures, it threatens to do the same for coccolithophores. The coccoliths themselves have their own ecological significance. When these calcium carbonate plates sink toward the ocean floor, they can push organic particles down with them, impacting the amount of organic matter that reaches the deep sea. Though individuals are only visible with a microscope, when conditions are right algal blooms can occur that can be seen from space because the coccoliths reflect light and change the seas to a beautiful milky blue.

E. huxlyei is both tiny and gigantic. Left: one individual under an SEM microscope (photo by Alison R. Taylor). Right: a bloom in the Barents Sea from space (photo from NASA).

Previous short-term studies have shown slower growth rates and lower levels of calcium carbonate production for E. huxleyi exposed to acidic (high carbon dioxide) conditions. Lead author Kai Lohbeck and his colleagues wanted to see if natural selection under acidic conditions could result in adaptations that would partially or fully restore growth and a calcification levels to normal.  Adapting to increasing ocean acidification is a race against time, but fortunately phytoplankton have very short generation times. The researchers took advantage of this and ran a year-long experiment that allowed for about 500 generations of asexual reproduction. They exposed populations of E. huxleyi to three different “selection conditions” — the conditions under which each population would be allowed to grow and reproduce, and to which they would have the chance to evolve adaptations. The selection conditions were: ambient (the control, which is our current level of carbon dioxide), medium (projected carbon dioxide levels for early next century), and high (higher than any projected carbon dioxide levels). At the end of the year-long experiment, the researchers tested all three “evolved” populations in their selection condition and in the control condition. Algae grown in the control condition were tested in all three conditions.

Not surprisingly, increased carbon dioxide conditions led to slower growth rates and calcium carbonate production than ambient conditions for all populations, even algae from the medium and high selection conditions. However, when tested in the acidic conditions, algae from the higher acidity selection conditions had significantly higher growth rates than those from ambient selection conditions, showing that natural selection had led to adaptations that partially restored growth rate. Similarly, in when tested in acidic conditions, algae that evolved in acidic conditions produced significantly higher amounts of calcium carbonate compared to controls grown under ambient conditions. This is particularly interesting because a common prediction was that during adaptation to acidification, coccolith formation would become too “costly” to maintain and would become reduced, through either genetic drift or direct selection against coccolith formation. This outcome would have major effects on ocean nutrient cycling, due to the role that coccoliths play in transporting organic particles to the ocean bottom, so it is encouraging to see indications against this possibility. The results of this study are especially exciting as they represent the first evidence for the potential for evolutionary adaptation to ocean acidification by a key phytoplankton species. Of course, the lab is not the field, and questions remain about how adaptation of E. huxleyi would play out in the ocean’s complex ecosystems.

It’s worth noting that in some respects this laboratory experiment is probably a conservative estimate for the adaptive capacity of E. huxleyi. Given a period longer than one year, populations grown in acidic conditions could possibly accrue more beneficial adaptations and fully recover the growth rates and calcium carbonate production levels seen under ambient conditions. The authors also note that genetic diversity of natural populations is far greater than the levels that were present in the experimental populations. E. huxleyi is also known to sexually reproduce, which would further increase genetic variation. That means that the E. huxleyi in the ocean right now have even better chances for adaptive evolution than what was demonstrated in the experiment.

Climate change and ocean acidification present many frightening unknowns for the future of ecology and evolution. Having experimental evidence that one key species has the capacity to quickly evolve adaptations to an acidic ocean is perhaps small comfort, but it’s something.

Lohbeck K.T., Riebesell U. & Reusch T.B.H. (2012). Adaptive evolution of a key phytoplankton species to ocean acidification, Nature Geoscience, 5 (5) 346-351. DOI: 10.1038/ngeo1441

This post has been submitted to the 2012 NESCent evolution blog contest.

Thor Hanson is a field biologist, a self-descriptor he uses often in the book. While not all readers will appreciate the distinction between ‘biologist’ and ‘field biologist,’ I think the subtle difference is apparent in his writing. He clearly has many of the hallmarks of the naturalists of an earlier era. He spends an ample amount of time outdoors in direct observation of animals, takes copious field notes, and has an inclination for hands-on exploration of anatomy and physiology. Reading about the University of Vermont’s field naturalist program, where he got his master’s, gives you a sense where he’s coming from. Though some of his projects in the “racoon shack” — his outdoor shed/office/workspace — remind me of the pursuits of a nature-obsessed ten-year-old, I think they are illustrative of an immediate joy in and curiosity about the natural world that is less evident in many other scientists and science writers.

While Hanson’s research extends across many fields and industries, he continually comes back to the work of evolutionary ornithologist Rick Prum and his research group at Yale. His fluidly written descriptions of Prum’s research programs were definitely the highlights of the book for me. Prum took a developmental approach to understanding feather evolution early on — his theory centers around the development and structure of feathers: they are tubes, not plates. The idea struck him while teaching:

“I was giving my class the standard scales-to-feathers theory, and by the end of the lecture I realized it didn’t make any sense. Feathers couldn’t have evolved that way!”

Neatly following Prum’s “eureka” moment, Hanson treats us to the exciting story of how the evidence to support Prum’s theory has come rolling in, mainly through massive fossil discoveries in the Yixian formation in China.

Hanson makes an interesting choice in including discussion of Alan Feduccia’s theories and his BAND (Birds Are Not Dinosaurs) group. To be clear, BAND members are not creationists — they are scientists in support of the theory that birds are more like second-cousins of theropod dinosaurs, rather than their direct descendants. However, given the abundant and continually growing evidence that birds did evolve from theropods, many in paleobiology find it frustrating that this still gets talked about, especially in popular media. Yet Hanson uses it to weave an engaging and important story about the scientific process, argumentation, and evidence. He notes:

“…continual reporting on the BAND’s minority viewpoint (in the interest of journalistic fairness) may be perpetuating a controversy that most scientists consider over and done with. But when I pressed him, Prum did admit that certain criticisms had helped refine his thinking, whatever the cost to his blood pressure.”

Feathers does something else that many popular science and nature books fail to do: it remains quite accessible to non-scientists throughout. Hanson never lets himself stray too far into the technical aspects of the science, and cultivates general interest by including extensive discussion of human interest in feathers instead of simply writing an ornithology book. Although his prose sometimes becomes somewhat awkward when he decides to cut a technical discussion short, I appreciate that he always does. Too many “popular” science books are only easily readable by people with some kind of science background. The book manages to be broad enough that scientists will learn something new, and restrained enough that non-scientists will understand and enjoy it.

Perhaps I particularly enjoyed Feathers because it was so personally relatable. I might have been a field biologist too, if I had ever really had the constitution for surviving Maine winters and African summers. For now, I am happy to sit back and read.

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