The genomes of 24 species of fish from Antarctica have been sequenced by an international team working from the Wellcome Sanger Institute in the United Kingdom, the University of Oslo in Norway, the Netherlands, Switzerland, and the United States. Their work, which was published in Nature Communications, makes it possible to learn how these fish survive in the subzero Southern Ocean and how they evolved.
Notothenioids are a distinct class of fish. They live in the frigid waters below the Antarctic ice, which are mostly cut off from the rest of the marine world by a current that goes around the continent. The Notothenioids have developed antifreeze proteins that enable them to withstand water temperatures as low as -2 degrees Celsius—a hostile environment for most species. One subgroup of notothenioids, called icefish,” has lost their oxygen-restricting hemoglobin proteins, and that spreads the word about them as the main vertebrates that do not have red platelets.
The genomes of 24 notothenioid fish species were sequenced by the researchers. The team was able to decipher the sequence of novel, complex, and repetitive DNA regions in the genome thanks to the most recent long-read technologies used to generate this new genome data. They investigate the notothenioids’ evolutionary history and the mechanisms that enable them to adapt to extreme cold using this brand-new data. They demonstrate that the cold-resistant notothenioids split off from other species about 10.7 million years earlier than was previously thought and that many new species began rapidly evolving around 5 million years earlier.
“Survival in such a harsh environment necessitates additional organismal compensations, and these fish have developed special proteins that act as antifreeze to keep them from freezing,”
Dr. Iliana Bista.
This group’s survival and establishment have been aided by a number of genomic characteristics. The species that specialize in extreme cold, such as the “icefish” family of Channichthyidae, had their genomes double in size, according to the study. A significant increase in the number of genomic elements known as transposons, which are capable of copying themselves into new positions within the genome and potentially introducing new functions, was the cause of this expansion in the size of the genome.
At the same time, the “icefish” have lost functions like making hemoglobin, which are normally thought to be necessary for survival.
According to Dr. Iliana Bista, “survival in such a harsh environment requires additional compensations of the organism,” and these fish have developed antifreeze-like proteins to prevent freezing.
“These fish are the only vertebrate known to have lost all of their hemoglobins, and their blood appears white. This is remarkable because oxygen transport is dependent on hemoglobins; Their loss in icefish is only possible due to additional genomic and physiological adaptations and the fact that oxygen dissolves more easily in very cold water.”
Notothenioid fish live on the brink of survival. The process of sequencing a large number of their genomes helps us comprehend a crucial ecosystem and sheds light on how they have managed to survive there. Professor Richard Durbin says, “This study is a great example of how advances in genomics are revolutionizing our ability to understand biodiversity around the world.”
More information: Iliana Bista et al, Genomics of cold adaptations in the Antarctic notothenioid fish radiation, Nature Communications (2023). DOI: 10.1038/s41467-023-38567-6
