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Jan. 17, 2012

The Tiny Frogs of Papua New Guinea

by Kara Rogers

Click to enlarge images

Paedophryne amanuensis on U.S. dime (diameter 17.91 mm). Photo credit: Rittmeyer EN, Allison A, Gründler MC, Thompson DK, Austin CC

Lilliputian life is all around us -- in trees and water, or as a team of U.S. scientists recently reported, in leaf litter on the forest floor. Indeed, it was beneath the leaves in the lowland rainforests of eastern Papua New Guinea where they discovered two new species of tiny frogs. The most diminutive of the two, at 7 to 8 mm in length, claims the title of world’s smallest vertebrate, and its discovery raises intriguing questions about the limits of extreme body size.

The new record-setting species is known as Paedophryne amauensis, and before it came along, the world’s largest and smallest vertebrates, the blue whale and the fish Paedocypris progenetica, respectively, were both aquatic. This relationship suggested that perhaps there was something about the buoyancy of water that supported the survival of animals with extreme body size. And while there still might be something to that hypothesis, the new frog is terrestrial, indicating that for tiny creatures at least, there is more to survival than a buoyant buffer of water.

The team’s report, published in the journal PLoS ONE, also describes the discovery of a second new species, Paedophryne swiftorum, which is a microhylid (small frog) that measures about 8 to 9 mm in length. The researchers determined that the two frogs were in fact separate species, and were different from the other two members of Paedophryne (P. kathismaphlox and P. oyatabu), using morphological, ecological, and genomic analyses. (P. kathismaphlox and P. oyatabu were reported in 2010 and are also found in eastern Papua New Guinea.)

Through genetic comparisons with other species in the family Microhylidae, to which the genus Paedophryne belongs, the scientists also were able to establish the new species’ evolutionary relationship with other small frogs. A major finding of the comparisons was the evolutionary divergence of Paedophryne, which indicated that the extremely small frogs had appeared early on in the evolution of New Guinea microhylids. Hence, the tiny creatures have been hiding in the rainforests there for a very long time. While their small size certainly made it easy for them to hide, they likely also managed to escape human notice for so long because the high-pitched calls that they make sound remarkably similar to those of stridulatory insects (such as katydids and crickets).

Based on the amount of calling by P. swiftorum, the researchers estimate that the frogs may occur relatively close to one another within the leaf litter, and thus they may be fairly common in the East Papuan Aggregate Terrain of the Papuan Peninsula (eastern Papua New Guinea). Their density and ecological position, as predator of small invertebrates and prey of larger animals, indicates that they fulfill an important role within the Papuan rainforest ecosystem.

The rich biodiversity of the Papua New Guinea rainforests suggests that there may even be other species of frogs awaiting discovery. For now, however, given that approximately 32 percent of amphibians worldwide have gone extinct or at high risk of doing so soon, simply knowing of the existence of the Paedophryne species and that they may be abundant within their habitat is encouraging.
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Kara Rogers is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is a member of the National Association of Science Writers and author of Science Up Front on the Britannica Blog. She holds a Ph.D. in Pharmacology/Toxicology, but enjoys reading and writing about all things science. You can follow her on Twitter at @karaerogers.

About Kara Rogers

Kara is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is the author of Out of Nature: Why Drugs From Plants Matter to the Future of Humanity (University of Arizona Press, 2012).

The views expressed are those of the author and are not necessarily those of Science Friday.

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