A species of frog from the Brazilian rainforest became the first amphibian to be seen living in a harem system, with a loyal male to two loyal females.
It is believed that this mating system, the polygynyIt is the most common among animals and has been previously found among fish, reptiles, mammals, birds and even in some invertebrates, Fabio de Sa, a zoologist at the State University of Campinas, explained to the AFP news agency.
But until the publication of this study in the journal Science Advances on Wednesday, it had never been described in an amphibian.
Animal mating systems are held between polygyny, associated with an earlier stage of evolution, and monogymy, which arises when the offspring of a species require intensive parental care.
Polygyny tends to occur when males are forced to compete with each other for females and by fickle environmental resources, such as water and food.
De Sa and his colleagues decided to investigate whether Thoropa taophora, a species of frog found in the Atlantic rainforest of Brazil and known to be polygamous in areas of abundance, might exhibit polygyny in other circumstances.
Thumb war
These frogs prefer rocks and have a reddish-brown coloration that helps them blend in with the environment.
Males have long spines attached to their thumbs that they use in combat.
The team recorded the frogs at rocky sites on the edge of the rainforest where there are relatively few freshwater irrigated sites or “seeps” available to them and they are more exposed to the sun. Effectively, the resource-poor environment had an impact.
Males patrolled their breeding grounds and made aggressive calls to ward off intruders, and stayed close to their eggs and tadpoles to protect them.
When other male invaders ignored their warnings, they pounced on them with leaps, kicks, and used the spines of their thumbs to attack.
Long term relationship
The researchers found that males are related to only two females, mostly with a dominant but also with a secondary. Dominant females attempt to induce mating by responding to courtship calls from males with their own vocalizations.
While this happens, the secondary females remain immobile to one side.
Among other findings, the team confirmed with the presence of older tadpoles from the same parents that the mating relationships were long-term.
The arrangement appears to have advantages for both sexes. Males must prevent others from using their hard-to-get breeding grounds, and it is advantageous to diversify genetics with multiple partners.
“The advantage for the female is that it is better to have a male and a good quality breeding site to share with another female, rather than being exposed and not finding another male or a lower quality one,” added De Sa.
The scenario also sparked competition between females, which is rare: Dominant females actually responded to male calls and appeared to drive out secondary females during courtship.
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