A team of researchers led by the University of Constanza, Germany, in which the National Museum of Natural Sciences (MNCN-CSIC) participates, has achieved Sequencing the Queensland Lungfish Genome, the largest that has been deciphered to date.
Thanks to the analysis of this genome, the work, published in the journal 'Nature', confirms that these lungfish are the closest relatives of tetrapods, a group that includes amphibians, reptiles, birds and mammals, and allows a greater understanding of the innovations that allowed the conquest of the terrestrial environment and the origin of tetrapods.
"Our study confirms that the Australian lungfish, 'Neoceratodus forsteri', and not the coelacanth, as previously thought, is the aquatic relative most closely related to humans," he explains. Iker Irisarri, postdoctoral researcher at the MNCN-csic during the study and currently a researcher at the University of Göttingen (Germany).
As he points out, this species is considered a 'living fossil', since it is very similar to the fossils of the first lungfish. This group of fish has several characteristics that reveal its evolutionary closeness to tetrapods with respect to the rest of fish, among which the presence of lungs, the fleshy fins more similar to the extremities of terrestrial vertebrates, including humans, as well as their way of moving, reminiscent of salamanders. "These characteristics are, with great probability, similar to those of the common ancestor of tetrapods and lungfish, which conquered the terrestrial environment 420 million years ago," he adds.
"In addition to confirming our hypothesis about the key evolutionary position of the Australian lungfish, the analysis of its genome has given us important clues about how it was the conquest of the terrestrial environment. This was possible thanks to various adaptations in breathing, smell, movement and reproduction, "continues Irisarri.
In this regard, the study's findings include the characterization of developmental genes that reveal similar processes in the fins and hands of lungfish and humans, respectively, and in the lungs of both species, indicating a common evolutionary origin.
In addition, Irisarri explains that they identified that, during the transition between the aquatic and terrestrial environment, the species had a greater number of genes involved in smell and fewer odor receptors that are transmitted through water.
"Finally, we observed that, despite having been greatly expanded by the proliferation of repetitive elements that represent 90% of DNA, the lungfish genome has largely maintained the order of genes considered ancestral for all vertebrates and, therefore, has been preserved for 500 million years ", concludes the researcher.
Reaching these conclusions, however, was not easy, given the complexity of sequencing one of the largest genomes in the animal kingdom. Some of the lungfish chromosomes are as large as the entire genome of a human. But thanks to the latest DNA sequencing technologies and collaboration between different institutions, the researchers were able to decipher for the first time the more than 43 billion nucleotides, molecules that make up DNA, of the genome of this species, the largest sequenced to date. the date.