Thorny skates come in sizes of “snacks” and “party”: after a century of speculation, scientists know why now

When Jeff Neebone was a university student in 2002, his research included marine mysteries that have been baffling curious scientists for the past 20 years. The mystery involved thorny skates in the North Atlantic. In some of the range, individuals of this type are offered in two different sizes regardless of gender, and no one could understand why. At the time, neither of them were able to kneel.

In a recent study, Kneebone and researchers at the Florida Museum of Natural History say they have finally found the answer. This study has been published in the journal Nature Communications.

People were aware of the inconsistency in the size of thorny skates for almost a century, but it became very important since the 1970s when numbers in the 1970s were rushing. The cause of the decline was thought to be overfished by humans, and the solution was simple. In 2003, a strict US fishing moratorium was introduced for spiny skates and another species of baldora skates.

“The Baldo skates have rebounded to the point where they are allowed to be harvested again, but for some reason, despite 20 years of protection, the thorny skates remain low,” said Kneebone, who currently works as a senior Ocean Life scientist for Ocean Life at the New England Aquarium.

Research data collected by the National Marine and Atmospheric Administration shows that thorny skating has fallen by 80 to 95% in some areas, particularly in the Bay of Maine, and is also causing minorities to suffer from Canadian waters from the Scosia shelves.

There is a large distribution of thorny skates. They can be found from South Carolina to the Arctic and east through Scotland, Norway and Russia. In the Arctic and European ranges, thorny skates come in one size. It is the coexistence of large and small varieties along the coast of North America.

“We couldn’t understand what the deal with these skates was,” said Gavin Naylor, a research co-author who is director of the Florida Shark Research Program at the Florida Museum of Natural History. Scientists tried to study the troublesome skate DNA to see if there was a difference between large and small sizes, but came out empty-handed.

“The larger shapes are twice the size and take 11 years to reach adulthood. The smaller shapes are mature by the age of six. They have to be genetically different.”

Naylor thought he might be able to crack the code.

The idea was simple. Previous studies have attempted to answer the question by analyzing several short DNA sequences taken from a small number of spiny skates. It was a good strategy, Naylor reasoned, but it was short since the researchers had not yet processed enough DNA.

Instead, what was needed was a gene capture approach. It is a labor-intensive method that allows researchers to collect DNA sequence data from thousands of sequences across an organism’s genome, and is a term used to describe DNA stored in the nucleus of a cell. Most importantly, they do this for hundreds of spiny skates.

He put that word into the science community, and people sent teams with over 600 tissue samples collected in most of the Northern Hemisphere. He prepared for the costly to proceed with the lab work.

The Covid-19 pandemic hit and subsequent restrictions were set, making it impossible to carry out work in a wide range of in-person labs, leaving the project indefinitely hibernation.

Shannon Corrigan, one of Naylor’s postdoctoral researchers at the time, gathered salvage missions. If gene captured DNA could not be collected from hundreds of spiny skates, you could sequence the entire genome of four or five people. This will significantly reduce the amount of face-to-face work.

It was a dangerous plan. There was a small chance they could find what they were looking for by sequencing the genome, and they only had enough funds to do either.

Naylor said, it was all Mary, but it paid off. If they had used the original gene capture idea, “we would have completely missed it.”

Just as it was, they almost missed it. Pierre Lesturgie, the first author of the study, was tasked with analyzing the genome (2.5 billion pairs of 2.5 billion pairs). Something strange caught his eye as he looked through the data.

“There was a big area in Chromosome 2 that I thought was strange. They were behaving in a way that I couldn’t understand, so I considered removing it from the analysis,” says Lesturgie. He thought it could be an abnormality or potentially an error introduced during the sequencing process, and worried about reducing the accuracy of the results. When Naylor said that something that comes from inversion of genes seemed like a natural process in which DNA sequences were inverted in the wrong direction, he was about to throw it in the trash.

Most organisms, including humans, have at least some inversions in the genome, so while they are not uncommon, they rarely make observable differences between individuals. However, since it had to be continued by all researchers, they checked whether inverse sequences existed in both large and small spiny skates. That wasn’t the case. Only the large thorny skates had a stretch of DNA with a mirror. They need to do more work to confirm it, but they found their answer. A pop bottle of champagne and a celebratory cheer.

Understanding what caused the size difference is just the first step, Kneebone said. Researchers can now proceed to formulating conservation plans. The next step involves good old observations. Before gene inversion was discovered, distinguishing between large and small was difficult and in some cases impossible.

“It’s bigger than anything else, so we were able to identify big men and women,” Naylor said. Upon maturation, men of large and small develop long, subsequent claspers on either side of the tail, giving the overall appearance of kites with streamers. “So when we have little guys with big classpers, we know it’s an adult. But we don’t know if they’re just babies to get bigger, so we can’t do anything with little women.”

This limitation has hindered research into species, Kneebone said: Currently, they are not distinguished by stock ratings, so thorny skates are thorny skates.

The final step is to understand why sawny skates continue to decline in some of their range. Luckily, scientists already have some good leads. Current evidence suggests that it is difficult to confuse where the two sizes are reduced more than the other sizes. This natural, partial breeding barrier can be exacerbated by climate change.

Spiny skates are the most problematic in the Bay of Maine. Here, sea surface temperatures have increased faster than 99% of the world’s oceans over the past few years. This has had all sorts of unpleasant effects, like the collapse of the cod fisheries in the area.

It is yet to be seen whether climate change is partially responsible for the light-shape of spiny skates, and if so, why it has an undue negative effect on this single species compared to other skates living in the same area. To decide that, Kneebone said more data would be needed.

“We are trying to make decisions about how to best manage and maintain our populations using the best available science.”