Male Thoropa taophora frogs mate with the same two females throughout the breeding season
Fábio de Sá
A species of frog native to the Brazilian Atlantic rainforest is the first amphibian found to mate exclusively with the same two females throughout its breeding season.
Fábio de Sá at São Paulo State University in Brazil and his colleagues noticed that Thorapa taophora tadpoles from the same breeding site – or seep – always had the same father and one of two mothers, suggesting a mating system with fidelity similar to that seen in mammals, birds and fish.
“It was very surprising,” says de Sá, because this type of mating behaviour hadn’t been seen before in amphibians. “Fidelity was previously known for amphibians, but usually associated with monogamy,” he says.
Instead, T. taophora shows what is known as a single-male polygyny with fidelity, where the male frog stays loyal to the same two females. “It was exciting to reveal this mating system in a frog,” says de Sá. It isn’t yet clear how widespread this mating strategy is among frogs and other amphibians.
In the Brazilian frog species, the mating strategy appears to be most beneficial when resources are limited. “A female mating with an already paired male at a superior-quality breeding site will likely have equal or higher reproductive success than a female mating with an unpaired male at a poorer-quality site,” says de Sá.
For the males, it is likely that the primary benefit is to maximise their fitness by mating with more than one female. De Sá thinks that the limit of two females per male may arise because of female choosiness, with female frogs trying to select males with the best traits and breeding location but then tending to stay put once they have found a suitable male.
Once mating occurred, the researchers observed that the male frogs didn’t always treat their two mates equally. There was a hierarchy among the females in each mating group, with one of the two females being dominant over the other.
Male frogs tended to mate more with the dominant female than the secondary female – between 56 and 97 per cent of the tadpoles from seven breeding seeps analysed by the researchers descended from dominant females.
Journal reference: Science Advances, DOI: 10.1126/sciadv.aay1539
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