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This Frog Mates With Two Females in an Unusual Love Triangle

Relationships like these are rare among amphibians, scientists say

A male Thoropa taophora, pictured near Sununga beach in Brazil. (Fábio de Sá)
smithsonianmag.com

You know when your girlfriend is trying to cannibalize your other girlfriend’s offspring, so you wrap her in a tight platonic hug to distract her? No? Must just be a Thoropa taophora thing then.

In a study published this week in Science Advances, lead author Fábio de Sá with the São Paulo State University in Brazil describes the unusual mating dynamics of T. taophora, a frog that lives in Brazil’s Atlantic rainforest. In mating season, males of this species tend to pair up with just two females, an unusual dynamic that sometimes produces tension among competing females when resources are scarce, reports Katherine J. Wu for the New York Times.

Many animals such as lemurs, elephant seals or many types of fish, mate in polygynous mating systems. Typically, multiple females will mate with a single male in what’s known as a “harem” polygyny. However, scientists had never before witnessed polygynous behavior in amphibians, Issam Ahmed reports for AFP.

De Sá and his team of researchers collected data on larval development, captured video footage of frogs and conducted genetic analyses of eggs to determine the relationships among the frogs, they write in the study. “It was very surprising,” de Sá tells New Scientist’s Layal Liverpool. “Fidelity was previously known for amphibians, but usually associated with monogamy,” he says.

Scientists hypothesize that this mating structure is advantageous for males, because it allows them to mate with more than one female. Conversely, “[t]he advantage for the female is it’s better to have a good quality male and a good quality breeding site sharing it with another female—rather than being exposed and not finding another frog or finding a lower quality frog,” de Sá tells New Scientist.

Most frog species tend to fall on the extremes of the spectrum, either totally monogamous or “philanderers,” reports Wu for the Times. In contrast to their peers, T. taophora frogs will form long-lasting bonds with just two, and sometimes three, females, although one “dominant” female usually does most of the mating.

Male frogs will battle to claim the best seeps—wet, rocky spots where they wait for females to arrive, mate and deposit eggs. Long spines attached to the males’ thumbs aid in combat, per AFP.

Sometimes, females would arrive at a male’s seep and try to eat the eggs that other females had laid in the spot. As Nina Pullano reports for Inverse, males would sometimes react to this behavior by chasing the female away or beginning to mate with them.

Other times, they’d use their strong forearms to briefly embrace the female until she stopped trying to eat his progeny. Lauren O’Connell, a biologist at Stanford University not involved in the study, describes this behavior to the Times as a kind of “distraction hug.”

O’Connell tells the Times that scientists had long expected that these kinds of polygynous mating behaviors existed in amphibians. “But this was really a test of that idea,” O’Connell says. The study is “a really heroic effort of explaining the mating system of a species in the wild,” she adds.

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