A Noah's Ark strategy will fail. In the roughest sense, it is the conclusion of a first-class study that highlights which marine species can survive in a world where temperatures rise and the oceans become acidic.
Two-by-two, or even moderately medium-sized residues, may have little chance of continuing on a climate-changed planet. Instead of many species, "we need large populations," says Melissa Pespeni, a biologist at the University of Vermont, who led the new study of how hundreds of thousands of marine brushes responded to experiments where their seawater was either moderate or extremely acidic.
The study was published on June 11, 2019, in Progress of the Royal Society B.
Pespeni and her team were surprised to find that the rare variation in DNA of a small minority of urbins was very useful for survival. These rare genetic variants are "a bit like having a winter coat among fifty light jackets when the weather hits twenty below in Vermont," Pespeni says. "It's the gown that lets you survive." When the water conditions were made extremely acidic, these rare variants increased in the frequency of the larvae. These are the genes that allow the next generation of urchins to change how different proteins work – which they use to make their hard-but easily resolved shells and handle the acidity of their cells.
However, in order to maintain these rare variants in the population plus other necessary genetic variation that is more common and allows response to a number of acid levels in the water, many individuals require.
"The larger the population, the more rare variation you will have," says Reid Brennan, a postdoctoral researcher in Pespenis UVM lab and leading author of the new study. "If we lower the population sizes, we will get less food for evolution – and less chance of getting the rare genetic variation that may be beneficial."
In other words, some organisms can remain in a climate-changed world because they can change their physiology, think about sweating more. Some will be able to migrate, perhaps further north or up. But for many others, their only hope of development is rescued by the potential for change that is awaiting rare DNA stretches.
The purple sea urchins UVM team studied in their Vermont lab are part of natural populations ranging from Baja, California to Alaska. These spotted creatures are made of rocky reefs and kelp forests, and are a favorite snack of seaweeds – and an important species that creates life in tides and sub-tidal zones. Because of their huge numbers, geographical ranges, and the different conditions they live in, the ureans have high "standing genetic variation", the researchers note. This makes purple eggs likely to survive in the harsh future of a surrogate sea and good candidates to understand how marine creatures can adapt to rapidly changing conditions.
It is well understood that rising average global temperatures are a fundamental driver of the imminent extinction that meets one million or more species, as a recent UN report on biodiversity. But it's not just rising averages that matter. It can be the hottest or most acidic moments that test the boundaries of an organism and control its survival. And, as the UVM team writes, "the genetic mechanisms that allow rapid adaptation to extreme conditions have rarely been investigated."
Currency in the present sea
The new study used an innovative "single generation" experiment that began with twenty-five wild-caught adult urchins. Each woman produced about 200,000 eggs from which the researchers were able to extract DNA from pools of approximately 20,000 surviving larvae living in different water conditions. This very large number of individuals gave the researchers a clear idea that purple eggs have a genetic heritage that allows them to adapt to extremely acidic seawater. "This species of sea bass will be okay in the short term. They can react to these low pH conditions and develop the necessary genetic variation," says UVM's Reid Brennan. "As long as we do our part to protect their habitats and keep their populations large. "
But coming through the tough challenge of rapid climate change can come at a high cost. "It is hopeful that development will take place – and it is surprising and exciting that these rare variants play such a strong role," says Melissa Pespeni, assistant professor of UVM's biological department and expert on marine ecosystems. "This discovery has important implications for prolonged species start. These rare variants are a kind of currency that the ova need to spend," she says. "But they can only spend it once."
University of Vermont. Original written by Joshua E. Brown. .