Genomic data reveal intense fish harvesting causes rapid evolution

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Genomic data reveal intense fish harvesting causes rapid evolution

For the first time, scientists have elucidated genetic changes that lead to rapid changes in fish due to fishing intensity - changes that were previously invisible to researchers.

In recent decades, many commercial fish have grown more slowly and matured earlier, which can result in lower yields and less resistance to overfishing. Scientists have long suspected that rapid evolutionary changes in fish are caused by intense harvesting pressure.

"Most people think evolution is a very slow process that takes place over millennia of time, but evolution can, in fact, happen very quickly," said Nina Overgaard Therkildsen, Professor of Conservation Genomics at Cornell University.

The article "Contrasting Genomic Shifts Underlie Parallel Phenotypic Evolution in Response to Fishing" was published in Science.

In highly exploited fish stocks, fishing almost always targets the largest individuals.

"Slower-growing fish will be smaller and will escape better from nets, increasing the chances of passing on their genes to future generations. In this way, the fishery can bring about rapid changes in the evolution of growth rates and other characteristics," said Therkildsen. "We see a lot of evidence of this effect in wild fish stocks, but no one knew what the underlying genetic changes were."

Therkildsen and his colleagues benefited from an influential experiment published in 2002. Six populations of Atlantic speed bumps, a fish that does not exceed 6 inches in length, have been intensively harvested in the laboratory. In two populations, the larger individuals were removed; in two other populations, the smaller individuals were removed; and in the latter two populations, fishing was random in size.

After only four generations, the harvest had led to an evolution of an almost double adult size difference between the groups. Therkildsen and his team sequenced the entire genome of nearly 900 of these fish to examine the DNA changes responsible for these striking changes.

The team identified hundreds of different genes across the genome that have changed constantly between populations selected for rapid and slow growth. They also observed large linked blocks of genes that changed together, significantly altering the frequency of hundreds of genes at the same time.

Surprisingly, these major changes have only occurred in some populations, according to the new document. This means that there were multiple genomic solutions to make the fish in this experiment bigger or smaller.

Such research can assess human impacts and improve humanity's understanding of "the speed, consequences and reversibility of complex adaptations as we continue to shape the evolutionary trajectories of the species around us," Therkildsen said.