Climate adaptation may be a family affair

A newfound ability of reef fish to adapt to shifting conditions over the course of two generations indicates they might be less vulnerable to climate change than previous research has suggested.

In a new study, young anemonefish (Amphiprion melanopus) exposed to elevated carbon dioxide levels and warmer water grew slowly, needed extra energy to perform normal bodily functions and died at higher rates. But they showed no adverse impacts if their parents had lived under the same conditions prior to breeding.

Recent research shows that young fish are particularly vulnerable to the decreases in water pH that are expected to occur over the next century as elevated CO₂ levels change the chemistry of the oceans (SN Online: 12/13/11). Zoologist Gabrielle Miller and her colleagues at James Cook University in Townsville, Australia, wanted to know what might happen if parents as well as hatchlings were exposed to such conditions.

The researchers exposed prebreeding adults to an environment representative of the Great Barrier Reef today or to water similar to what’s projected to develop in the oceans over the next 50 to 100 years: temperatures 1.5 to 3 degrees Celsius warmer and somewhat lower pH. After at least two months the adults were allowed to breed.

“We thought there might be some cost to the parents from this high CO₂,” says marine ecologist Philip Munday. The changed conditions might have sapped the parents’ energy or triggered stress reactions that led to smaller, less hardy babies. But 31 days after hatching, young anemonefish growing up under the experiment’s most extreme temperature and pH exhibited comparable in weight, length and survival to those raised in present-day conditions.

That outcome suggests “parents can precondition their offspring for the environment they’ll be born into,” says Hannes Baumann, a fish ecologist at Stony Brook University in New York who was not involved in the work. This idea, known as transgenerational plasticity, is “a type of adaptation without genetic change,” Baumann explains, “and has researchers all over the place scratching their heads.”

Hatchlings from all treatments emerged at about the same size and robustness, an observation that argues against the parental advantage reflecting some egg-nurturing effect, Miller’s team reports July 1 in Nature Climate Change.

Instead, the researchers say, it appears the parental benefit might be due to epigenetics — chemical alterations to portions of DNA that control gene activity. Pollution and other environmental factors can essentially introduce new on-off switches to affected genes. And emerging evidence, Munday notes, indicates that such epigenetic changes “can carry over between generations.” But he concedes his team currently lacks proof that epigenetics underlies the CO₂ accommodation.

Even if most reef fish can show climate accommodation, they “will still face serious problems as their habitat changes, such as from a loss of corals,” Munday cautions. This could jeopardize their access to both food and shelter.

“I think it’s great that folks who are studying ocean acidification are thinking about transgenerational plasticity and epigenetics,” says evolutionary biologist Stephan Munch with the National Marine Fisheries Service in Santa Cruz, Calif.

But the data on hatchlings’ accommodation to climate “is not unambiguously transgenerational,” he says. Fertilized eggs spent at least a week developing in their parents’ environment. Any accommodation, epigenetic or otherwise, might reflect direct effects of that environment on the young, he says — independent of their parents.