Genomic data reveal intense fish harvesting causes rapid evolution

Genomic data reveal intense fish harvesting causes rapid evolution
Juvenile Atlantic silversides (Menidia menidia) school in nearshore waters of Long Island Sound. Credit: Jacob Snyder

For the first time, scientists have unraveled genetic changes that cause rapid fish evolution due to intense harvesting—changes that previously had been invisible to researchers.

Over , many commercially harvested have grown slower and matured earlier, which can translate into lower yields and a reduced resilience to overexploitation. Scientists have long suspected rapid evolutionary change in fish is caused by intense harvest pressure.

"Most people think of evolution as a very slow process that unfolds over millennial time scales, but evolution can, in fact, happen very quickly," said lead author Nina Overgaard Therkildsen, professor of conservation genomics at Cornell University.

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

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

"Slower-growing fish will be smaller and escape the nets better, thereby having a higher chance of passing their genes on to the next generations. This way, fishing can cause rapid evolutionary change in growth rates and other traits," Therkildsen said. "We see many indications of this effect in wild , but no one has known what the underlying were."

Genomic data reveal intense fish harvesting causes rapid evolution
The evolved differences in adult size across fish from the three different harvest regimes. Credit: David Conover and Stephan Munch

Therkildsen and her colleagues took advantage of an influential experiment published in 2002. Six populations of Atlantic silversides, a fish that grows no bigger than 6 inches in length, had been subjected to intense harvesting in the lab. In two populations, the largest individuals were removed; in another two populations, the smallest individuals were removed; and in the final two populations, the fishing was random with respect to size.

After only four generations, the harvesting had led to an of an almost two-fold difference in adult size between the groups. Therkildsen and her team sequenced the full genome of almost 900 of these fish to examine the DNA-level changes responsible for these striking shifts.

The team identified hundreds of different genes across the genome that changed consistently between populations selected for fast and slow growth. They also observed large linked-blocks of genes that changed in concert, dramatically shifting the frequencies of hundreds of genes all at the same time.

Surprisingly, these large shifts only happened in some of the populations, according to the new paper. This means there were multiple genomic solutions for the fish in this experiment to get either larger or smaller.

Research like this can assess and improve humanity's understanding of "the speed, consequences and reversibility of complex adaptations as we continue to sculpt the evolutionary trajectories of the species around us," Therkildsen said.


Explore further

Fishing can cause slowly reversible changes in gene expression

More information: N.O. Therkildsen el al., "Contrasting genomic shifts underlie parallel phenotypic evolution in response to fishing," Science (2019). science.sciencemag.org/cgi/doi … 1126/science.aaw7271

C. Jorgensen el al., "Fishing for answers," Science (2019). science.sciencemag.org/cgi/doi … 1126/science.aay3158

Journal information: Science

Provided by Cornell University
Citation: Genomic data reveal intense fish harvesting causes rapid evolution (2019, August 1) retrieved 16 September 2019 from https://phys.org/news/2019-08-genomic-reveal-intense-fish-harvesting.html
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Aug 01, 2019
Fish evolve to avoid being caught by humans! That is certainly good news. Meanwhile, we know that bacteria evolve to avoid being killed by our antibiotics, and, one may hope, insects also evolve to resist insecticides.

Aug 01, 2019
Fish evolve to avoid being caught by humans! That is certainly good news. Meanwhile, we know that bacteria evolve to avoid being killed by our antibiotics, and, one may hope, insects also evolve to resist insecticides.


why any of this is a surprise is beyond me.

Aug 01, 2019
It had not occurred to me that fish would evolve to grow more slowly so as to escape nets. I supposed the fish were sitting ducks. Ha, I mean, you know, I thought they had no way to escape. So I am relieved to learn that they are "smart" enough to find ways to evade our rapacious human appetites. Eventually we will have to learn, too, to live sustainably on the planet. Which might require quite a small human population, I guess. Which in turn is hard to visualize.

Aug 01, 2019
Interesting, but pretty much obvious when you realize weeds have adapted to RoundUp, requiring more and more of it to be used to kill them. If weeds can do that, one would expect fish to evolve to escape nets, and the stronger the selection, the faster.

What's really interesting is that an animal can evolve in this few a number of generations. This is really about the evolution of the ability to evolve.

Aug 02, 2019
Researchers try to grow beef in the lab. I wonder if it wouldn't be easier and commercially more acceptable to grow fish meat in the lab. Fish are sold as canned fish, which is sometimes quite a messed up thing. And fish taste differently anyway. That'd free oceans from fishing too; and give us something to eat until we go for some bug munch.

What's really interesting is that an animal can evolve in this few a number of generations. This is really about the evolution of the ability to evolve.

Not necessarily surprising. If you take evolution as being static, i.e. just selection, this would work. Fish of all sizes existed but the larger ones were caught. The smaller ones survived and got similar fishlings, which would explain why there are more of those.

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