Lithodytes lineatus is a tiny, unassuming, Amazonian frog. But watch the frog among colonies of leaf-cutter ants and their behaviour gives a clue to the amphibian’s secret weapon.
While leaf-cutter ants will attack other frog species — and other animals — Lithodytes lineatus is able to shelter, breed, and build its nest in the midst of their colonies, and, bizarrely, the frog is readily accepted by the ants.
The key to this acceptance lies within the frog’s skin, which is covered with chemicals that deter the ants from attacking.
You may think of it as a kind of natural ant repellent, but perhaps it’s more than that, as André Barros of the National Institute of Amazonian Research in Brazil explains: “It helps the frog blend in, because it imitates the ants' own chemical signals.”
In imitating these signals, the ants may actually accept Lithodytes lineatus as one of their own.
Such chemical-based mimicry is often seen in parasitic invertebrates, but this kind of adaption is infrequently seen in vertebrates, and even less so in frogs. In fact, this ability is only known in two other species of African frog.
As leaf-cutter ants recognise each other and communicate by using chemical odours, Barros’ team speculated that the frog’s skin must be covered with a similar chemical that results in the ants recognising them as ‘friendly’.
To test this theory, the team ran two experiments. The first involved placing the yellow-striped Lithodytes lineatus along with four similar species in a glass vessel for 10 minutes along with leaf-cutter ants. Lithodytes lineatus made no attempts at escape, while the other frogs all tried to jump or climb out and were attacked by the ants.
In a second experiment, researchers covered 10 Rhinella major frogs with skin extract taken from Lithodytes lineatus, and 10 with ultrapure water.
The results were conclusive: the team observed the ants attacking the frogs covered with the water, while the remaining frogs coated with the skin extract were left unharmed.
“Our results demonstrate that the skin of frog Lithodytes lineatus has chemicals that prevent the attack of two species of leaf-cutting ants,” says Barros.
“It therefore seems that Lithodytes lineatus has chemical skin compounds that are recognised by ants of genus Atta, which may allow for coexistence between ants and frogs.”
Source: Behavioral Ecology and Sociobiology.
Main image: Lithodytes lineatus is the only species of frog in South America known to mimic the chemical signals of another species. © Albertina Pimentel Lima