It’s not easy being green, golden and male, according to a researcher’s observation of attempted frog cannibalism in Australia.
It was nighttime on Kooragang Island north of Sydney, Australia, when the high-pitched shrieking started.
John Gould, an ecologist at the University of Newcastle conducting postdoctoral research on the declining population of green and golden bell frogs, raced toward the chilling sounds. There, in a pond he had been surveying, he spotted a scene that might have fit in an amphibian reboot of a Hannibal Lecter movie: A large female frog was chomping down on the hind leg of a male while slowly pulling him into a hole.
“The male frog was trying really hard to prevent this from happening,” Dr. Gould said.
The act of apparent cannibalism was the first between adults recorded in this species, and it gave Dr. Gould an appetite to learn more about the topic. Ultimately, he believes that when a female green and golden bell frog isn’t pleased by the song of a male, she might opt to turn him into a meal.
The females “are almost the ultimate predators for males,” Dr. Gould said, because their ears are perfectly in tune to the calling of their would-be beaus.
Cannibalism is well known among amphibians. But usually it is the youngest frogs, toads or salamanders that end up as dinner. The tadpoles of various species eat smaller tadpoles, for example, to get ahead in life. In some cases, this happens regularly between siblings. In others, adults sometimes cannibalize eggs or larvae — researchers recently discovered that hellbender fathers may eat their young when faced with suboptimal water conditions.
But adult-on-adult cannibalism has seldom been witnessed. For a study published last month in the journal Ecology and Evolution, Dr. Gould scoured the literature and found only a couple of examples, many in the lab, of adult frogs’ cannibalizing other adults. Almost all of these occurred in cases where the females were bigger than the males. In green and golden bell frogs, for example, females can grow to about 2.75 inches in length while males usually max out at less than 2 inches.
Dr. Gould believes that a female may be able to tell whether a male is better for mating or eating based on the strength of his calls. This means males take a huge risk when trying to attract mates.
“You’ve really got to give props to the male frogs out there, that they are putting their lives on the line to reproduce,” Dr. Gould said. “Maybe there’s a reason why, males and females, you don’t often find them next to each other in ponds.”
David Pfennig, a biology professor at the University of North Carolina at Chapel Hill who was not involved in Dr. Gould’s research, called the study “a cool idea.” He has studied cannibalism among spadefoot toads — he has even seen tadpoles eat a toad that had already grown its legs.
But he would like to see more evidence of adult females cannibalizing males before agreeing that the phenomenon is more than occasional. While females may gain a clear benefit from cannibalizing males, there are also costs. Males might fight back, for example, or females could choke by biting off more than they could chew. Cannibalism can also spread disease in infected populations, Dr. Pfennig said.
Dr. Gould would also like to explore this idea more. And while tales of cannibalism don’t often have a happy ending, the male frog in Dr. Gould’s study lived to croak another day. After a struggle in which she pulled him deeper into the hole, he shrieked one more time and then managed to shake his leg free from the female’s mouth, hopping away to freedom.
