Damselfish In Distress Adapt To Warmer Waters

Within a few generations, damselfish can turn on genes that allow them to cope with heat. Joao Krajewski.

Coral reef fish adapt over a few generations to warmer temperatures, and key genes that allow them to do this have now been identified. The findings indicate that reef fish are ready to tackle one of the threats posed by climate change, but the authors of the study warn that their future may not be so bright on other fronts.

Spiny damselfish (Acanthochromis polyacanthus) are a common reef fish, easy to keep and study, making them “our lab rat,” according to Professor Philip Munday of the ARC Center for Coral Reef Research, Australia. Munday is the senior author of a study in Nature Climate Change, reporting on the responses of generations of damselfish when raised in waters several degrees higher than their natural habitat.

“Some fish have a remarkable capacity to adjust to higher water temperatures over a few generations of exposure,” said first author Dr Heather Veilleux. “But until now, how they do this has been a mystery.”

Veilleux and Munday identified 53 genes that play a part in allowing fish born in warmer environments to thrive compared to their parents and grandparents. “We found that shifts in energy production are key to maintaining performance at high temperatures,” said Veilleux.

This is not a case of natural selection weeding out the fish with unsuitable genes, Munday told IFLScience. “It’s plasticity, non-genetic inheritance,” he said. “It’s likely to be epigenetic, but parents can influence offspring in other ways, through hormones or proteins or food supply. One of the next things that we want to do is investigate the processes by which this occurs, looking for epigenetic marks such as DNA methylation.”

So far the ability to adapt has not been tested in other reef fish, but Munday thinks that it is likely to be common. “We would expect lots of variation in how much plasticity they have,” he told IFLScience. “Some species may be more adaptive than damselfish, others less.”

The problem, Munday warns, is that warmth is not the only threat that reef fish are facing. Munday was an author of a paper last year showing that reef fish do not adapt similarly to the effects of ocean acidification. Spiny damselfish born in acidic waters are unable to respond to the danger cues on which their species relies for survival in the wild, and over several generations Munday found that this doesn't improve, putting them in great danger in future.

Meanwhile, the debate goes on as to whether future spiny damsels will have coral homes to occupy. Munday says that corals are far more vulnerable to warming than fish because “Corals live right on the edge of their temperature preferences; even a couple of degrees can send them over.”

Non-adapted damselfish may struggle in warmer waters, but don’t respond with mass deaths like corals. Although some studies have found that corals are starting to adapt as temperatures rise, Munday says it is “an open question” as to whether they will be able to do this quickly enough to keep up with a warming world.

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