Jumping genes point to origin of iconic Australian snakes

A new study has shown that some of Australia’s most venomous snakes arrived by sea rather than by land – the route taken by most of Australia’s other reptiles.

Researchers from the University of Adelaide in South Australia analysed the genomes of two Australian terrestrial elapids (front-fanged venomous snakes) – the tiger snake (Notechis scutatus) and brown (Pseudonaja textilis) snake – and compared them to both marine and semi-marine elapids (sea snakes) and Asian elapids.

They found that the ancestor of all Australian elapids (including both terrestrial and marine elapids) had accumulated jumping genes – sequences that are able to move or copy themselves within a genome. These jumping genes are absent in non-elapid terrestrial relatives and were found to instead come from another source altogether: marine life.

This suggests that the common ancestor of Australian elapids – both sea snakes and terrestrial snakes alike – was likely a semi-marine or marine snake that arrived from Asia by sea instead of land.

“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,” says corresponding author Professor David Adelson, from the University of Adelaide’s School of Biological Sciences, Australia.

“Some believe their ancestors travelled by land, whereas others hold the more contentious view that a marine or semi-marine ancestor swam here,”

“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,” he explains.

“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.”

The researchers identified that this new genetic material from other marine organisms was transferred into Australian elapid ancestors in 14 distinct events, and that eight of these genes were unique to marine and semi-marine sea snake genomes. The acquired genes from the semi-marine snake genomes even accounted for as much as 8-12% of the total genome sequence identified. The research was published in Genes.

“This meant that we could unambiguously determine the major genetic differences between land and marine/semi-marine snakes were a consequence of migration into a marine environment,” says Adelson.

“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,” he adds. “It may also have made it easier for the subsequent land to marine transition of sea snakes.”

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