A Noah's Ark strategy will fail. In the roughest sense, this is the conclusion of a first-of-its-kind study that illuminates which marine species may have the ability to survive in a world where temperatures are rising and oceans are becoming acidic.
Two-by-two, or even moderately sized, remnants may have little chance to persist on a climate-changed planet. Instead, for many species, we will need large populations, "says Melissa Pespeni, a biologist at the University of Vermont, who led the new research examining how hundreds of thousands of sea urchin larvae responded to experiments where their seawater was made either moderately or
The study was published on June 1
Pespeni and her team were surprised to discover that rare variations in the DNA of a small minority of urchins were highly useful for survival. These rare genetic variants are "a bit like a winter coat amongst fifty lightweight jackets when weather hits twenty below in Vermont," Pespeni says. "It's that coat that lets you survive." When the water conditions have been made extremely acidic, these rare variants have increased in frequency in the larvae. These are the genes that let the next generation of urchins alter how different proteins function-like those they use to make their hard-but-easily-dissolved shells and manage acidity in their cells
But to maintain these rare variants in the population-plus other necessary genetic variation that is more common and allows for response to a range of acid levels in the water-requires many individuals
"The larger the population, the more rare variation you'll have," says Reid Brennan, and a post-doctoral researcher at Pespeni's UVM lab and lead author on the new study. "If we reduce population sizes, then we will have less fodder for evolution and less chance to have the rare genetic variation that might be beneficial."
In other words, some organisms might persist in a climate-changed world because they are able to change their physiology-think of sweating more; some will be able to migrate, perhaps farther north or upslope.
The purple sea urchins the UVM team studied in their Vermont lab has a portion of natural populations that stretch from Baja, California to Alaska. Found in rocky reefs and kelp forests, these prickly creatures are a favorite snack of sea otters and a key species in shaping life in the intertidal and subtidal zones. Because of their vast numbers, geographic range, and the varying conditions they live in, the urchins have a high "standing genetic variation," the scientists note. This makes purple urchins likely survivors in the harsh future of an acidified ocean – and good candidates for understanding how marine creatures can adapt to rapidly changing conditions
It is well understood that rising average global temperatures are a fundamental driver of imminent extinction faced by a million or more species-as a recent UN biodiversity report notes. But it's not just rising averages that matter. It may be the hottest or most acidic moments that test the body's limits and control its survival. And, as the UVM team writes, "the genetic mechanisms that allow rapid adaptation to extreme conditions have been rarely explored."
Currency in the current sea
-generation selection "experiment that began with twenty-five wild-caught adult urchins. Each female produced about 200,000 eggs from which scientists were able to extract DNA out of pools of about 20,000 surviving larvae that were living in different water conditions. This very large number of individuals gave the scientists a clear view that purple urchins possess a genetic heritage that allows them to adapt to extremely acidic ocean water. "These species of sea urchin are going to be okay in the short term, they can respond to these low pH conditions and have the necessary genetic variation to evolve," says Reid Brennan of UVM. "So long as we do our part to protect their habitats and keep their populations large."
But coming through the ferocious challenge of rapid climate change may come at a high cost. "It's hopeful that evolution will happen – and it's surprising and exciting that these rare variants play such a powerful role," says Melissa Pespeni, an assistant professor at the UVM's biology department and expert on ocean ecosystems. "This discovery has important implications for long-term species persistence. These rare variants are a kind of currency that urchins have to spend," she says. "But they can only spend it once."
Sea urchins cope with rising CO2 levels
Rare genetic variation and balanced polymorphisms are important for survival in global change conditions Proceedings of the Royal Society B rspb.royalsocietypublishing.or … .1098 / rspb.2019.0943
Why Noah's Ark Will not Work (2019, June 11)
retrieved 11 June 2019
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