It’s in the genes how seals and fish adapt to Antarctic cold | Polarjournal
Temperatures in Antarctica vary considerably on land, but in the ocean they usually remain just above or at freezing point. For fish, this means a stable environment. Seals, on the other hand, alternate between land and water and are thus exposed to higher temperature fluctuations. (Photo: Dr Michael Wenger)

When you think of Antarctica, you also inevitably think of icy cold, where survival is almost impossible for animals and plants. And yet there are a large number of different animal species that not only live in Antarctica, but even spend a large part of their lives in the icy waters of the Southern Ocean. These include seals and fish, and the question arises as to how animals manage to not only survive but thrive in this environment. The answer lies in the genes.

In two studies, scientists from the USA, Sweden and Australia were able to discover genetic mechanisms in Weddell seals and the Antarctic fish Ophthalmolycus amberensis that allow the animals to spend their lives in the Southern Ocean at temperatures around freezing point. What is special about the two studies is that the two species achieved the same goal in different ways. “This tells us that the course of evolution is largely unpredictable,” explains Joanna Kelley, a biologist at Washington State University and leader of the fish study.

One study looked at how Weddell seals manage to build up their blubber without suffering the negative consequences of obesity at the same time. For the seal, which can weigh up to 450 kilograms, the layer of blubber not only provides perfect insulation against heat loss, but also a reserve of nutrients that can be consumed when the animals are changing their coats or rearing pups. Especially in the latter, the mothers invest an enormous amount of energy in the fat-rich milk so that the young grow quickly and also form a layer of fat. The team, led by study leader Allyson Hindle of the University of Nevada, discovered that Weddell seals have a special protein that transports cholesterol in the bloodstream and delivers it to various sites in the body, but without blocking vessel walls or compromising blood flow. This protein is unique to Weddell seals and allow cholesterol levels up to 10 times higher than humans and other mammals. Humans and many other mammals possess two types of protein, but one of them (the low-density lipoprotein LDL), if too high, attacks the vascular systems and causes a much higher risk of heart attacks and other vascular diseases. The significance of this seal protein will now be investigated in more detail.

The Antarctic fish Ophthalmolycus amberensis has no English name. The species belongs to the eelpouts, which are found worldwide. But this Antarctic species is special because it is not one of the dominant icefishes in Antarctica. Therefore, their adaptations are particularly interesting. The animals live at depths of up to 1,500 meters, but mostly in the range of 500 meters. Little is known about their way of life. Image: Hotaling et al (2022) Mol Ecol

The Antarctic representative of the eelpout fish group, Ophthalmolycus amberensis, has taken a completely different approach to dealing with the icy conditions. The research team, led by Scott Hotaling and Joanna Kelley of Washington State University, found that this fish, which grows to 35 centimeters and has been studied little, stores antifreeze proteins in its blood. A similar adaptation is known in Antarctic icefish. In addition, Hotaling and his colleagues discovered that the vision, thermal tolerance and membrane structures of the cells are also similar in both Ophthalmolycus amberensis and icefish. But one key difference, the team said, is that the eelpout representative still has hemoglobin in its blood, whereas icefish barely make this oxygen-carrying protein. Because in the cold and thus oxygen-rich waters of Antarctica, this is no longer so important. However, for Ophthalmolycus amberensis, it appears that it is either still important, or the species is on its way to losing this ability as well. “If you don’t need something, it’s often removed by selection or changed by chance,” Hotaling says. “There is nothing to sustain it for survival.” But the studies show that in the end, all roads do indeed lead to Rome, or in this case, to life in Antarctica.

Dr Michael Wenger, PolarJournal

Study links: Noh et al (2022) Commun Biol 5, 140 The Antarctic Weddell seal genome reveals evidence of selection on cardiovascular phenotype and lipid handling;
Hotaling et al (2022) Mol Ecol 1-17 Pathways to polar adaptation in fishes revealed by long-read sequencing;

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