Frogs Gamble on Their Young's Survival by Rearing Them in Pools of Cannibals

When male dyeing poison frogs are charged with choosing a location to grow newborn tadpoles, they often forgo an empty pool for a spot full of larger, but conspecific, tadpoles, despite the chance of their young being cannibalized by the larger members of the group.

Bibiana Rojas of the University of Jyväskylä in Finland, found this to be the case with dyeing poison frogs she observed in the forests of French Guiana.

Writing in the journal Behavioral Ecology and Sociobiology, Rojas reports that father frogs only choose to place their young in unoccupied pools when others are already occupied by tadpoles of similar size to their own.

Rojas suggests that the frogs place their developing young in the water with larger conspecific tadpoles in spite of the risk of cannibalism, because the frogs view the larger tadpoles as a testament to the quality of the location of the pool and therefore a spot where their own young may thrive.

She also noted that suitable options may be limited, which suggests that even though a healthy pool teeming with cannibals might not be the ideal location for a group of young tadpoles to develop, it may be the best option in a crowd of poor choices.

Rojas called the decision a gamble for the father frogs.

"Chances are that its tadpole gets eaten by a large resident in an occupied pool, but an unoccupied pool might mean, for example, that other requirements for development, such as the stable presence of water, are not met," she said. "If the father is lucky and its tadpole is not eaten, it may ultimately be safer in a stable pool than in one that could easily dry out."

Female dyeing poison frogs (Dendrobates tinctorius) lay clutches of four to five eggs. When hatched, father frogs carry the tadpoles to water-filled cavities in trees or on the forest floor. Once the tadpoles are released, they are stuck in the pool until they undergo metamorphosis into frogs, a process that takes about two months.

Therefore, choosing a good spot for the tadpoles to develop is essential, not only for the tadpoles' survival, but for the continuation of the parents' genetic line, because the conditions the larvae experience will affect their overall development.

"The presence and the size of conspecifics influence parental decision-making in the context of choosing a rearing-site for their offspring," Rojas said. "Apparently strange parental decisions, such as depositing offspring with large cannibals, may ultimately not be that strange."