Newswise – In vast oceans, one would assume that their inhabitants can travel very far and therefore populations of a species would mix freely. But that doesn’t seem to be the case for a vital forage fish called the sandeel.
Sandeel is a small school of fish incredibly high in lipids, making it a fantastic and important food source for at least 70 different species ranging from whales and sharks to seabirds, says UConn Associate Professor of Marine Science Hannes Baumann.
The northern sandeel can be found from the waters off New Jersey to northern Greenland. Researchers including Baumann and Ph.D. student Lucas Jones have been interested in whether the sandeel constitutes a massive, homogeneous population, or whether there are genetically distinct groups. Their findings are published in the ICES Marine Science Journal.
Baumann says these are important questions that need to be answered when considering the conservation and sustainable management of the species, especially since the areas where the sandeel live are warming faster than many parts of the planet. due to climate change.
Sampling fish from such a wide range is no small task, but two years ago Baumann and Jones began contacting other researchers to see if they had any tissue samples to spare. Baumann credits the work to the international group of colleagues who provided samples, including co-authors from Canada and Greenland, and who helped sequence and analyze the data, including co-authors from Cornell University. .
In total, Baumann, Jones and the team were able to sequence and analyze nearly 300 samples from various locations across the sandeel’s range using a technique called low-coverage whole genome sequencing. They also sequenced the first sandeel reference genome.
In a nutshell, Baumann says they’ve found an area on the Scotian Shelf, off Nova Scotia, where a genetic break is occurring. The researchers distinguished two distinct groups, one north and one south of the divide, with very different parts of the genome, namely on chromosomes 21 and 24. Without obvious physical barriers like a chain of mountains separating the groups, Baumann says it makes sense to ask how these differences are possible.
“That’s the scientific riddle,” says Baumann, and the answer, it seems, lies in the currents.
“When northern fish spawn and drift south, they are genetically less suited to the warmer southern waters, even if it is five or six degrees warmer in winter, they just don’t survive,” says Baumann. . “These populations may be linked by ocean currents, but the connectivity achieved is basically zero.”
This discovery is a first for sand lance, but has been demonstrated in other species such as lobsters, cod and scallops, and this research adds further evidence of an apparent temperature differential on the Scotian Shelf. and helps demonstrate that temperature is an important factor in survival.
“Example after example shows that the ocean is not as homogeneous a place as expected, and there are all sorts of things that prevent this constant mixing,” Baumann says. “We found another striking example of this.”
When researchers find adaptation in an environment where mixing is continuous, such as in the ocean, Baumann says, the question is how it is possible for groups to remain different, even though they constantly encounter other genotypes. This is where powerful genomic methods, like the ones used in this article, come in handy.
“Parts of the genome of many species have what we call ‘genetic inversion’, which means that the genes on one parent’s chromosome have a certain order and the genes on the same chromosome that come from the other parent that code for the same thing, and they’re in the same area, but they’re reversed,” says Baumann.
These inversions mean that recombination cannot occur; therefore, genes are passed down from generation to generation and play an important role in adaptation.
“We found on chromosomes 21 and 24 that there are whole regions that are completely different and it’s like the signature of what we call an inversion because there’s no recombination going on. “
Baumann says it’s important to know that there are genetic and ecological barriers on the Scotian Shelf because with climate change that barrier may shift north and while that may be good news for southern fish, this is bad news for the fish that are there right now.
The researchers were also somewhat relieved to find two clusters, because if there had been many smaller clusters, it could make management and conservation more difficult, especially given scenarios such as the construction of wind farms. offshore. Potentially well-situated areas for wind turbines may also be sandeel habitats, and construction disturbs the habitats. If there were many small population groups, a single construction project could run the risk of completely wiping out a group, whereas with more dispersed populations, although the local population may be temporarily disturbed, they do not soon to be able to restore once construction is complete.
Baumann plans to focus his research on investigating the genetic basis of thermal fracture.
“We want to make sure that these fish are productive and resilient, despite climate change, so we need to make sure those areas where they happen are protected,” Bauman said. “These decisions should include experts to ensure that if there is an area that is very critical for sand lance, that any disturbance is temporary.”
It’s not an insoluble conflict, but it’s something we need to do, says Baumann, who also notes that it’s possible the sandeel north of the thermal divide is already suffering more from warming because the region is heats up faster.
“It could be that these two clusters have different vulnerabilities to climate change,” he says. “We don’t know yet, but it’s something that should be pursued.”
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