It’s not just love that keeps these frogs together. Photo: Courtesy of Keitaro Henmi
For the common rain frog, mating begins with a big hug.
The male, a jagged brown-and-white creature, leaps at his chosen mate and latches onto his butt. His short arms, unable to encircle the much rounder, ball-shaped female, rest on his behind. As the pair burrows into the ground and begins the reproductive process, releasing eggs and sperm at the same time, the male remains attached to the female like glue.
Although common rain frogs, whose scientific name is Breviceps adspersus, have long been known to secrete an adhesive while mating, scientists had not been able to determine which sex possessed the special glue. New research from Japan has found the answer: the fixation is mutual.
Atsushi Kurabayashi, who leads the study at the Nagahama Institute of Bioscience and Technology in Japan, told VICE World News that he artificially aroused the frogs to get their skin secretion using a device called the Transcutaneous Amphibian Stimulator. The animals were first anesthetized before being pricked by the machine, which applies a weak electrical current to stimulate the glands that produce the secretion.
After testing 20 frogs, 10 of each sex, Kurabayashi found that the males secreted the glue on their chests and arms, while the females produced an adhesive on their backs, where the male latches on.
Using a tensile strength indicator, the scientists also discovered how sticky the frogs’ glue is: very sticky. Their bond becomes as strong as Velcro after staying together for about an hour, she said, and the secretion naturally loses its sticky properties only after three days. (Frogs have been known to cling to each other for sometimes months to lay eggs.)
“So if humans wanted to use this secretion, maybe the form would be like sticky notes, which you would write down for 3-day assignments,” he joked. The findings were published in February in Salamander, a German journal for herpetology, the study of amphibians and reptiles.
Aaron Bauer, a biology professor at Villanova University who has published papers on common rain frog species, said the research clarified assumptions about the frogs.
“It suggests that animals are pretty good at not wasting secretion, that they’ll only produce it where it’s really useful to them,” Bauer, who is not affiliated with the study, told VICE World News. .
There are more than 5,000 known species of frogs. The Breviceps genus, known simply as rain frogs, is found primarily in arid areas of eastern and southern Africa. All known species of this genus are subterranean, meaning that they burrow underground, where they spend most of their time, during the dry season and come out during the wet months to breed. Amphibians also often mate at night.
That means scientists only have a short window of opportunity to study their mating habits. “If you want to see the moment they mate, you have to stay up all night,” Kurabayashi said.
What researchers in Japan haven’t been able to figure out, though, is why females also secrete the sticky, given that only males are sticky enough.
Case in point: When Kurabayashi and his team were doing fieldwork in South Africa, they came across a male common rain frog attached to the back of a female frog of a different species, one that doesn’t produce adhesive.
“We didn’t aim for that to happen, but we accidentally found that the male frog was fooling his species,” he said. That’s another mystery the animal bioscientist wants to solve.
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