The Animal with the Largest Genome on Earth
Scientists have successfully sequenced the genome of the South American lungfish, which is 30 times larger than the human genome. Lungfish are sometimes called “living fossils” because they have existed for hundreds of millions of years. They are believed to be the closest relatives to the first four-limbed vertebrates (tetrapods), which are the ancestors of all vertebrates. Tetrapods likely developed limbs and moved onto land around 370 million years ago during the Devonian period (419 – 359 million years ago).
Previously, scientists sequenced the genomes of several lungfish species, including the Australian lungfish (Neoceratodus forsteri) and the African lungfish (Protopterus annectens). In a new study published in Nature, researchers have sequenced the genome of the South American lungfish (Lepidosiren paradoxa) and found that it has the largest genome of any animal, according to a report by Live Science on August 16th.
The South American lungfish has up to 91 billion base pairs of DNA. If stretched out, the DNA in each cell would be nearly 60 meters long, compared to about 2 meters in humans.
The research team also investigated why the South American lungfish’s genome has expanded so rapidly over the past 100 million years. Over 90% of its genetic material consists of highly repetitive transposable elements (TEs) that have copied themselves throughout the genome. This suggests that the lungfish may lack mechanisms to suppress these jumping genes.
Having an excessively large genome can present challenges. “This represents a significant cost for the South American lungfish. Eighteen of its nineteen chromosomes are each about the size of the entire human genome, requiring a tremendous amount of energy to replicate that DNA. The nucleus and surrounding cells also need to be larger,” explained Axel Meyer, a member of the research team and an evolutionary biologist at the University of Konstanz.
However, Meyer noted that abundant DNA might be advantageous for adapting to changing environments. TEs can increase or decrease gene expression, potentially facilitating faster adaptation.
While the South American lungfish holds the record for the largest genome ever recorded in the animal kingdom, it is not the largest in the biological world. That title belongs to the New Caledonian fern (Tmesipteris oblanceolata), which has about 50 times more DNA in its nucleus than humans, with a staggering 160 billion base pairs.
