Frog Fathers Provide Transport, Piggyback Style

Bijal P. Trivedi
National Geographic Today
August 7, 2002

Absentee dads are common in the animal kingdom—most sow their seed and leave without further ado. But in remote tropical rain forests of Papua New Guinea—where biodiversity literally drips from the branches and new species abound—a researcher has discovered some frog fathers that not only guard the eggs but also provide transport, piggyback style, for up to 24 froglets after they emerge from the shell.

The two species who practice piggyback paternal care—Liophryne schlaginhaufeni and Sphenophryne cornuta—belong to a family of frogs called microhylids.

"The microhylid frogs of New Guinea are the only known large group of terrestrial vertebrates in which male care predominates," wrote David Bickford, an evolutionary biologist at the University of Miami in Coral Gables, Florida, in a report published in the August 8th issue of the journal Nature.

Microhylid frogs of Papua New Guinea, of which there are at least 150 species, all undergo "direct development." That is, they bypass the tadpole stage and develop from larvae to miniature versions of the adult inside the egg. Direct development is a key adaptation that allows the frog to reproduce in regions without bodies of water nearby.

Parental Duties

After the mother lays the eggs in the leaf litter on the forest floor, she is long gone. The father dutifully fertilizes the eggs. Then, like a mother hen, he shelters the clutch, warding off predators and hydrating the eggs for about a month until they're ready to hatch. As the tiny froglets emerge from their shells, usually a brood of up to 25, each climbs onto the father's back. He waits patiently until every last froglet is aboard.

Then the father departs with his brood on his back, like an overloaded school bus, for an odyssey that lasts up to nine days.

Traveling only after dark, he hops as far as 50 feet or so per night. Along the way, one by one, the froglets leap off to begin their own independent lives.

"This is really fascinating because, though males are known to guard eggs, they have never been known to transport the froglets," said Janalee P. Caldwell, specialist in amphibian biology at the University of Oklahoma. "What makes this particularly interesting is that the fathers are transporting froglets that are fully developed and completely independent at this point."

"One explanation for the father's behavior may be that he wants to be sure that the progeny are his, and guards the clutch to prevent other males from fertilizing the eggs," Bickford hypothesized. The advantage of this system is that froglets are dispersed over a broad area, reducing the chance of future inbreeding and competition for food, said Bickford.

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