Genetic Barriers, a Warming Ocean, and the Uncertain Future for an Important Forage Fish 'It's all temperature driven, and the implications for this,
Published:18 Dec.2022    Source:ScienceDaily
In the vast oceans, one would assume their inhabitants can travel far and wide and, as a result, populations of a species would mix freely. But this doesn't appear to be the case for a vital forage fish called the sand lance.Sand lance are small schooling fish impressively rich in lipids, which makes them a fantastic and significant food source for at least 70 different species ranging from whales and sharks to seabirds.
The researchers distinguished two distinct groups, one north and one south of the divide, with parts of the genome differing quite dramatically -- namely on chromosomes 21 and 24. Without obvious physical barriers like a mountain range separating the groups,  it's logical to ask how these differences are possible. When fish from the north reproduce and drift south, they are genetically less adapted to warmer southern waters, even if it's five or six degrees warmer in the winter, they are just not surviving. These populations may be linked by the ocean currents, but the realized connectivity is basically zero. This finding is a first for the sand lance, but it has been shown in other species such as lobsters, cod, and scallops, and this research adds further evidence to an apparent temperature divide at 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 kinds of things that prevent that constant mixing. When researchers find adaptation in an environment where mixing is continuous, like in the ocean, the question is how it is possible that groups stay different, even though they are constantly encountering other genotypes.
Parts of the genome in many species have what we call a 'genetic inversion,' which means that the genes on the chromosome from one parent 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 the same area, but they're flipped. These inversions mean recombination cannot occur; therefore, the genes are passed down through the generations and play an important role in adaptation.