- Two species of giant frog in the genus Mantidactylus from Madagascar have attracted researchers’ attention for their very large size, reaching body lengths of more than 10 centimeters, or 4 inches.
- A new genetic study has revealed the existence of a third species unknown until now: Mantidactylus radaka.
- The number of scientifically accepted Madagascan frog species now stands at 362 and many other species remain to be discovered.
- Scientists recommend further studies to evaluate the conservation status of giant frog habitats and species.
ANTANANARIVO, Madagascar — Traditionally called radaka, large frog species endemic to Madagascar are appreciated for their delicate taste, which is similar to chicken. Although people have hunted the frogs for ages, scientific knowledge of them remains limited, and measures to protect them are little respected.
Now, genetic sequencing has enabled scientists to identify a new member of the giant frog genus Mantidactylus.
According to a study published in the Journal of Natural History in May, the genus Mantidactylus includes 32 scientifically recognized species in Madagascar. For a long time, two of these — giant frogs endemic to the island — have held the attention of researchers for their very large size: M. guttulatus is the country’s largest frog, with a body length of 12 centimeters (4.7 inches), and M. grandidieri, with a body length of nearly 11 cm (4.2 in). Genetic analysis of these species enabled researchers to discover that they comprised not two but three species of frog. The third will be called M. radaka in reference to the common name, radaka.
“It is highly probable that other species belonging to the same group exist,” Christian Randrianantoandro, a biologist at the University of Antananarivo and co-author of the study, told Mongabay. “But the time to precisely identify them has not yet arrived. At this stage, the data about them remains largely insufficient.”
From a morphological perspective, it’s easy for even the most experienced scientists to confuse M. guttulatus and M. grandidieri, as they are so similar. The new species, M. radaka, however, presents some differences: its ear is hardly visible, and the legs of the female have tiny glands.
“They are surprisingly difficult to distinguish from each other,” said Mark D. Scherz, a biologist at the University of Munich and co-author of the article. “Yet, genetically, it is very different.”
The scientists studied samples that are more than 120 years old and preserved at the Natural History Museum in London and the National Museum of Natural History in Paris, as well as genetic material collected in natural habitats between 2000 and 2016.
The three radaka species live mainly in forests alongside waterways, and have a wide distribution: M. guttulatus occupies the southeastern regions of the island, between the district of Ivohibe and the commune of Fierenana. M. grandidieri extends over quite a large territory in the northeast, between the locality of Mangabe Moramanga and Marojejy National Park. The new species, M. radaka, inhabits the north, between Manongarivo Special Reserve and Bealanana district.
Nirhy Rabibisoa, an amphibian specialist at the University of Mahajanga in Madagascar, who was not involved in the study, said the identification of M. radaka brings the number of scientifically recorded frog species in Madagascar to 362. In reality, Madagascar could have nearly 500 species, representing 9% of the global amphibian population, according to some estimates.
In Madagascan towns, restaurants often serve frog fritters. In the countryside, hunting frogs in swamps is very easy; even children can catch them. Villagers also breed them in wells or private ponds.
“Since people consume [M. radaka] as well as engage in unchecked clearing in the north, it is probably threatened,” Scherz said. Madagascar is experiencing an increased rate of deforestation. According to specialists, the destruction of forests could precipitate the disappearance of species that are the target of uncontrolled hunting.
Scientists and conservationists say an ecological study will be necessary to determine the population status of the new species according to the IUCN. Madagascar classifies the Mantidactylus species as protected game animals. But the decree that lays out the classification of wild animals dates to 2006 and needs updating.
According to Scherz, it is crucial to protect forests growing along waterways because they shelter these giant frogs, among other creatures. “It is desirable that a survey be carried out amongst villagers to determine how frequently they consume Mantidactylus and how far they travel to hunt them, as well as to learn whether people have observed a decline in the number of specimens in the rivers where they usually catch them,” Scherz said.
Banner image: Mantidactylus radaka, a newly discovered species, presents some differences from M. guttulatus and M. grandidieri: its ear is hardly visible and the legs of the female have tiny glands. Image by Mark D. Scherz.
This story was first published here on Mongabay’s French site on June 8, 2020.
Citation:
Rancilhac, L., Bruy, T., Scherz, M.D., Pereira, E. A., Preick, M., Straube, N., … Vences, M. (2020). Target-enriched DNA sequencing from historical type material enables a partial revision of the Madagascar giant stream frogs (genus Mantidactylus). Journal of Natural History, 54(1-4), 87-118. doi:10.1080/00222933.2020.1748243
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