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Ancestors of Australia’s most poisonous snakes arrived by sea

A new study led by the University of Adelaide has found the first tangible evidence that the ancestors of two of Australia’s most venomous snakes – a tiger and a brown “elapid” (front-fanged snakes) – arrived by sea rather than by land, which is the most common dispersal route of other Australian reptiles.

“While we know all marine and semi-marine sea snakes descended from a common Australian land-based ancestor, the origin of Australian elapids has been debated for some time,” said study corresponding author David Adelson, a biologist at the University of Adelaide. “Some believe their ancestors travelled by land, whereas others hold the more contentious view that a marine or semi-marine ancestor swam here.”

By analyzing the genomes of these two elapid species and comparing them to those of marine and semi-marine elapid sea snakes and Asian elapids, Professor Adelson and his colleagues discovered that the ancestor of all Australian elapids seems to have accumulated self-replicating and self-mobilizing genes (“jumping genes”) which were not present in their land relatives but came from another source.

“In our research we found a number of genes that were present in the ancestor of all Australian elapids but could not be traced to a snake ancestor; instead they could be traced to similar transposable gene sequences found in marine life, including fish, sea squirts, sea urchins, bivalves, and turtles,” explained Adelson.

“This indicates the marine environment transferred the new genetic material into the snakes and offers new support to the argument that the first Australian elapids swam to our shores. They must have previously acquired the new genetic material during an ancestral period when they were adapted to marine life.”

The scientists identified 14 transfer events of genetic material from other marine organisms, with eight genes being present only in the marine and semi-marine sea snake genomes. Thus, the major genetic differences between land and marine/semi-marine snakes appears to be a consequence of migration into a marine environment.

“This is the first time that jumping genes have been used to confirm the evolutionary history of any animal species, and this research definitively proved that the common ancestor of all Australian elapids adapted to a marine environment. It may also have made it easier for the subsequent land to marine transition of sea snakes,” Professor Adelson concluded.

The study is published in the journal Genes.

By Andrei Ionescu, Staff Writer

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