Genome sequencing of antarctic fish reveals how they survive in extreme cold

A team of international researchers, based at esteemed institutions including the University of Cambridge, the Wellcome Sanger Institute, the University of Oslo, as well as institutes in the Netherlands, Switzerland, and the United States, has successfully sequenced the genomes of 24 Antarctic fish species. Their groundbreaking work, which has been published in the prestigious journal Nature Communications, provides valuable insights into the survival strategies of these fish in the subzero waters of the Southern Ocean and sheds light on the evolutionary history of these remarkable creatures.

The fish species in question, known as notothenioids, possess unique adaptations that enable them to thrive in the frigid waters beneath the Antarctic ice. Isolated from the rest of the marine world by a circular current surrounding the continent, notothenioids have developed antifreeze proteins that allow them to withstand water temperatures that can plummet to as low as -2°C. Among the notothenioids, a subgroup called “icefish” has undergone a fascinating evolutionary change—they have lost their oxygen-binding hemoglobin proteins, making them the only known vertebrates without red blood cells.

To achieve their research goals, the team successfully sequenced the genomes of 24 notothenioid fish species. This was made possible by utilizing cutting-edge long-read technologies, which facilitated the deciphering of complex, repetitive sections of DNA within the genome—a task that had previously proven challenging. Armed with this newly acquired genomic data, the researchers delved into the evolutionary history of notothenioids and investigated the mechanisms that enable their adaptation to extreme cold. Their findings indicate that the notothenioids capable of surviving in harsh cold conditions diverged from other species approximately 10.7 million years ago—a more recent split than previously believed. Furthermore, they discovered that numerous new species began evolving rapidly around 5 million years ago.

Several genomic features have played vital roles in the survival and proliferation of this fish group. Notably, the researchers observed that the species specializing in extreme cold, such as the Channichthyidae family or “icefish,” displayed a doubling of their genome size. This expansion was primarily attributed to a significant increase in the number of transposons—genomic elements with the ability to copy themselves into different positions within the genome, potentially introducing new functions.

Conversely, certain functions typically deemed essential for survival, such as hemoglobin production, have been lost in the icefish. Dr. Iliana Bista explains that the extreme environment necessitates additional compensatory mechanisms in these organisms. Icefish have developed unique proteins that serve as antifreeze agents, preventing them from freezing. Dr. Bista elaborates on this remarkable adaptation, stating that icefish are the sole vertebrates known to have completely lost their hemoglobins, resulting in their blood appearing white. This extraordinary characteristic is made possible due to the fact that oxygen dissolves more efficiently in water at extremely low temperatures, in addition to other genomic and physiological adaptations.

Professor Richard Durbin highlights the significance of the study, stating that notothenioid fish inhabit the threshold of viability. By sequencing a diverse range of their genomes, scientists gain invaluable insights into the evolutionary strategies these fish have developed to survive in their extreme environment. This comprehensive study serves as a prime example of how advancements in genomics are revolutionizing our understanding of biodiversity worldwide.

Source: Wellcome Trust Sanger Institute

Genome sequencing of antarctic fish reveals how they survive in extreme cold

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