Washington: A species of frog from the Brazilian rainforest has become the first amphibian shown to live in a harem, where one male mates with two females who remain loyal to him. So-called polygyny is thought to be the most common mating system among animals and has previously been found in bony fishes, reptiles, mammals, birds, and even some invertebrates, Fabio de Sa, a zoologist at Universidade Estadual de Campinas. De Sa was the first author of a new paper that appeared in Science Advances on Wednesday which now shows that polgyny is present in all tetrapods, or four-legged animals.
Animal mating systems exist on a continuum between polygamy — which is associated with an earlier stage in evolution — and monogamy, which arises when the young of a species require intense parental investment. Polygyny tends to occur when males are forced to compete with one another for females and for patchy environmental resources such as water and food. De Sa and colleagues decided to investigate whether Thoropa taophora, a species of frog found in Brazil’s Atlantic rainforest, might exhibit polygny under the right circumstances.
These frogs favour rocks and have a reddish-brown colouration that helps them blend in with their surroundings. The males have long spines that are attached to their thumbs which they use in combat. The team recorded the frogs at rocky outcrops on the edge of the rainforest where there are relatively few freshwater breeding sites or “seeps” available to them.
The team found that the males bred with only two females — mostly with one dominant but also with a secondary. The dominant females would try to induce mating by responding to male courtships calls with their own vocalizations. They would also approach males and position themselves under them, simulating amplexus or the mating position of frogs where the male grasps the female from behind. While this was going on, secondary females stood aside motionless. The team confirmed what they saw in the video by studying the genetic material from the seeps.