When it comes to dealing with climate change, the old adage of “survival of the fittest” might also be the motto of the future. At least that’s the case with the small, but genetically complex, purple sea urchin.
A new study published in the Proceedings of the National Academy of Sciences found that purple sea urchins that were exposed to acidified ocean conditions similar to those that might exist in the future were able to undergo genetic changes that may help them survive.
Biologist Melissa Pespeni, of Indiana University Bloomington, led the experiment, explaining to TakePart, “We chose the purple sea urchin because they’re a really good developmental model organism. There’s been a genome sequence and there’s a lot of standing information about them even with respect to ocean acidification.”
What they found was that even though the exterior of the sea urchin larvae changed very little, their genetics were able to adapt to high CO2 conditions in a single life span.
“There are a few studies that have come out, but this is one of the first to actually measure genetic change in response to C02,” says Pespeni. “So from the genetic variability that exists out in nature, we wanted to know if they could use that variability to be able to effectively respond to the CO2 changes.”
Pespeni adds that they were mildly surprised at how quickly the urchin larvae evolved to their changing environment. “If there’s any organism we would expect to adapt to ocean acidification, it would be the purple sea urchin because they have evolved in a really variable environment,” she says.
“In the California ecosystem there’s a lot of upwelling of low PH waters already, so on a seasonal and even a daily basis, the purple sea urchins experience CO2 levels that are comparable to what will be experienced consistently in 2100. We thought they might have the genetic capacity to adapt just because they’re experiencing these environmental conditions on occasion already. But it was still kind of surprising how well they adapted and it makes us hopeful that we were actually able to measure genetic changes in such a short period of time.”
The experiment undertaken by Pespeni and her colleagues yielded results that were contrary to those reported in some previous studies which indicated that purple sea urchins and other shell-forming organisms might have trouble adapting to ocean acidification.
“The previous work that’s shown negative affects has been measuring the physiological responses,” explains Pespeni. “So changes in gene expression, an acute response in the moment, and measuring something negative. What we were measuring in contrast was genetic change through time, so which organisms survived depended on what genetic backgrounds they had. It may be that in physiological studies there’s a range of responses and a lot of natural variability—some are able to cope and some are not. What we were able to measure in our study was the ones that were able to cope, survived, and therefore resulted in genetic changes in the larvae pool.”
She adds, “It’s two different ways of looking at the same issue: A short-term physiological response at an individual level, and genetic changes that would carry over in evolutionary time. But that said, in a single generation, we still didn’t see the same negative consequences of the high C02 so that is a standing difference.”
“And the only thing we can think of in terms of differences in the rearing conditions is the larvae density—how the larvae were placed in the lab—and possibly some kind of technical details. For example, we had a paddle stirring the water, so there was much more natural water movement in the container versus no paddle movement.”
Pespeni notes that since this is the first time a study like this has been done, it needs to be replicated in other species to get a sense of what it is about the purple sea urchin that makes them adapt, or what it is about an organism in general that allows them to adapt.
“Purple sea urchins have a lot of things going for them,” says Pespeni. “They have more genetic variations in their populations than any creature that’s been measured to date— they have about a thousand times more genetic variations than humans—and they have really large population sizes which is a good characteristic for being able to harbor this genetic variability, and they experience these type of environmental conditions on a regular basis.”
“We need to test organisms that, for example, have small population sizes, low genetic variability, and don’t routinely experience these environmental conditions. It’s going to take replicating these sorts of studies in other species to figure out which characteristics make them able to respond.”
Hopefully that can happen soon and we’ll learn what other species can join the purple sea urchin in its blow-by-blow battle to keep up with climate change.