Watching fish adapt to climate change

Fish may be better able to cope with warming seas than previously assumed if the surprising results of experiments on a coral reef species apply more generally.

Timothy Ravasi and Michael Berumen of KAUST’s Division of Biological and Environmental Science and Engineering wondered how the common reef fish, Acanthochromis polyacanthus, would cope with the rises in water temperature that may result from climate change¹.

Collaborating with researchers from the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Australia, they compared the offspring of fish in two situations: “developmental” and “trans-generational”.  The former were reared in water that was either 1.5 or 3 degrees Celsuis warmer than the usual optimum temperature straight after hatching. The trans-generational group, however, consisted of fish whose parents had also been exposed to the higher temperatures from the time they had hatched.

Sufficient oxygen to meet energy demands, especially when active, is a challenge for fish in warmer waters. Specifically, higher temperatures reduce the fish’s “aerobic scope”: the difference between its resting and maximum metabolic rates.

Unsurprisingly, the aerobic scope of the “developmental” group fish, whose parents had not lived in warm waters, was significantly reduced. But surprisingly the trans-generational fish, whose parents had lived in warmer water, had a normal aerobic scope — they had acclimated to the temperature rise.

The team went on to look at the molecular mechanisms behind the acclimation. “The significance of this study is that we show the molecular changes that occur in these fish which enable them to adapt really fast — in just two generations,” says Ravasi.

The experiment is an example of non-genetic inheritance, a theory first proposed by Lamarck. One route for this is through epigenetic effects, Ravasi explains.

The KAUST team sequenced the transcriptomes (RNA) from cells in the fish’s livers to find which genes were being up- or down-regulated as a result of trans-generational exposure. Ravasi says they found 53 up- or down-regulated genes which are for pathways required by this particular fish to restore its aerobic scope. “Nearly two thirds of most highly up-regulated genes in the trans-generational group are concerned with lipid, protein and carbohydrate metabolism,” he adds.

Other up-regulated genes are involved in the immune and stress response, he explains, but surprisingly, heat-shock proteins were not affected. “This suggests that the mechanisms of long-term acclimation and short-term heat stress are different.” 

References

1. Veilleux, H. D., Ryu, T., Donelson, J. M., van Herwerden, L., Seridi, L. et al. Molecular processes of transgenerational acclimation to a warming ocean. Nature Climate Change 5, 1074–1078 (2015).| article