Ancestors save tree snakes

JCU’s Dr John Llewelyn and colleagues studied the Common Tree Snake (Dendrelaphis punctulatus).

Some snakes from lineages originating in Asia had developed a physiological tolerance to toad toxins, having been exposed to Asian toad species (with similar toxins to cane toads) over millions of years. But that was not the case with the tree snake.

“Their lineage originated in Asia, but they are highly sensitive to toad toxins. A medium-sized toad would likely kill a tree snake that tried to eat it. Yet the tree snakes have not declined markedly, even though cane toads are common in most of their range,” said Dr Llewelyn.

Instead of developing a physiological resistance, the scientists found tree snakes had adapted their behaviour. Experiments showed tree snakes were reluctant to attack cane toads and were unlikely to keep hold of a toad if they did strike it.

“Tree snakes ate native frogs of all sizes, but they avoided toads unless they were very small toads with low toxic loads. Importantly, we looked at tree snakes from areas where there were toads and also from areas with no toads. They both showed the same behaviour.

“This means they didn’t adapt within Australia, they were pre-adapted to deal with toads, likely due to their Asian ancestors’ exposure to different species of toad,” said Dr Llewelyn.

“What this means is that when assessing the likely impact of an invasive species we not only need to identify vulnerable species, but also take into account their biogeographic origins – where they came from and what species their ancestors encountered.

“We’ve seen the tree snakes catch a lucky break with cane toads in Australia, because the snake’s ancestors have a long history with Asian toads, and evolved to co-exist.”

Link to images here.

Link to paper here.