Cane toads the meat in the ant’s sandwich

Not much can kill a cane toad, and predators learn quickly not to eat them, but a Sydney research team has discovered that a species of native ant has a taste for baby Bufo marinus.

In what is properly termed a maladaptive trait, cane toad metamorphs seem to be a bit stupid when it comes to the large, predatory meat ant species, Iridomyrmex reburrus.

This ant is common in tropical parts of Australia and often hangs around waterholes. Cane toads and native frogs do this also, but the frogs seemed to have learned to avoid the ants, while cane toads, an invasive species, haven’t worked it out yet.

A team led by the University of Sydney’s Professor Rick Shine, and including honours student Georgia Ward-Fear, have found that cane toads have yet to learn of the danger the ants present.

While the seven species of baby native frog studied are nocturnal and avoid encountering meat ants, which are active during the day, cane toads are decidedly diurnal. Frogs nestle safely in vegetation during the day, while ants and toads are open-habitat specialists.

In a series of experiments, the Sydney team also found that toads failed to detect and hop away from approaching ants, they weren’t too quick about it when they did hop away, and they had a tendency to freeze when seized by an ant, rather than kicking and croaking.

The research, published today in Functional Ecology, has some interesting ramifications. One is that invasive species are often maladapted – native frogs have evolved with native ants and have developed an appropriate protective response, while the cane toads, an American species, have yet to evolve defences.

Such mismatches between a translocated species and its new environment, the researchers write, could offer potential for control of invasive species.

Another is the possibility of controlling cane toad populations naturally, by manipulating ant populations in cane toad-dense areas.

“Further research to explore this option is warranted,” they say.