Female African treefrogs mate with several males simultaneously; together they whip up...

In a fascinating display of cooperation, female African treefrogs engage in simultaneous mating with multiple males, a behavior that directly contributes to building larger, more protective foam nests. This strategy offers a compelling explanation for why females in many species choose multiple partners, according to new research.

The study introduces the "nesting-assistance hypothesis," proposing that additional male partners actively help construct better nests, thereby enhancing the survival prospects of tadpoles. Researchers observed African gray foam-nest treefrogs (Chiromantis xerampelina) over a full breeding season, finding a direct correlation between male assistance and nest quality.

During the hot, rainy nights of southeastern Africa's summer, females construct nests by whipping a mixture of fluid and water into a thick foam using their hind legs. This process takes several hours and requires fertilization from male partners throughout. While some females mate with a single male, most attract several, with groups of 10 to 15 males being common. These males don't just fertilize eggs; they actively participate in whipping the foam alongside the female, increasing the nest's size and stability.

The larger nests are crucial for protecting hundreds of eggs from drying out in the intense heat for nearly a week until the tadpoles hatch. Nests built by a single pair were found to be small and often dried out before hatching. In contrast, nests constructed with the help of multiple males retained moisture longer, ensuring the tadpoles' survival. In return for their labor, these males gain a share in fathering the offspring, making this cooperative breeding strategy a winning formula.