The world’s largest living lizard – the Komodo dragon – reproduced with a species of lizard only found in Australia, a new study into its unusual breeding habits reveals.
While fossil findings have previously shown the three-metre-long Komodo dragon, now only found on a handful of Indonesian islands, originated in Australia, researchers from the Australian National University have established a genetic link.
An evolutionary biologist and the report’s lead author, Carlos Pavón Vázquez, said when they dug deeper into the genetic data they found evidence that Komodo dragons interbred with an ancestor of the sand monitor – a type of goanna found only in Australia.
“There was a mystery,” Pavón Vázquez says. “In this case the mystery was what is causing this conflict in the evolutionary relationship between the Komodo dragon and its close relation, the sand monitor.”
“What we found out is that millions of years ago, the Komodo dragon hybridised, which means it bred with another group of lizard.”
He said it was the first clear evidence of this type of interbreeding in wild monitor lizards.
The two species may be separated by an ocean, with the sand monitor only found in Australia and southern Papua New Guinea, but Pavón Vázquez said the research helped fill in gaps about what happened before the Komodo dragon became extinct on the southern continent.
“In order for the Komodo dragon to breed with sand monitors, they would need to live together,” he said. “So they were here doing Komodo dragon things and having affairs with other species. Then they crossed the sea at a point when the ocean was low and somehow got into Indonesia but went extinct in Australia.
“It’s only because of the palaeontological research that we know the Komodo dragon was in Australia. Meanwhile, the ancestral sand monitor after many millions of years diversified into four species that are alive today.”
Pavón Vázquez said the next step was to examine whether the close relations between the two species had given the sand monitors an evolutionary advantage.
“Because we see the physical appearance was affected by this hybridisation event, that changed the way they interacted with their environment, so it’s likely that there was some positive effect of this,” he said.
Dr Kailah Thorn from the University of Western Australia, a palaeontologist who was not involved in the study but is familiar with the research, said it neatly married genetic data with evidence from the fossil record to piece together a little-understood evolutionary process.
“We know hybridisation happens between living species of monitor lizards but often our simple reconstructions of evolutionary pathways assume this didn’t happen in the past,” Thorn said.
“Fossils are our primary evidence of the occurrence of Komodo dragons living in Australia but we now have genetic evidence of them hybridising with endemic Australian lizard species before Komodos were isolated to the lesser Sunda Islands of Indonesia.
“The authors’ detailed biogeographical models demonstrate that Komodo dragons most likely had an ancestral origin in the tropical grasslands of northern Australia. A terrifying concept when you remember that this area was also home to the giant megalania at this time – two behemoth goannas topping the food chain in prehistoric Australia.”
