Scientists have described three new frog species that dwell exclusively in the spiky leaves of pandan trees in Madagascar’s eastern rainforests.

Lead researcher Hugh Gabriel, from the Technical University of Braunschweig in Germany, described the frogs’ sounds as “soft clicks that sound like rain falling on leaves.” And he would know. Gabriel and his team spent years braving the razor-sharp leaves to reveal not just the new frogs but entire communities dependent on the water that collects in the grooves and nooks of Pandanus trees.

“Each tree was like a treasure chest; once we got past the jagged, barbed leaves, there was a wealth of biodiversity within each plant,” Gabriel told Mongabay in an email. “I spent my research days crashing towards the center of these trees where the water collects, alongside my guide Evariste.”

While the frogs are new to science, many locals, including Gabriel’s local guide Evariste Desire were already aware of the frogs. “They’ve been seen by Malagasy people for thousands of years, known as the secretive Sahona vakoa, or ‘frogs of the Pandanus,’” Gabriel said.

Recognizing the frogs as new species, Gabriel said, was “a gradual event — a slow assembly of different observations that culminated in the declaration that it was, indeed, a new species.” While studying frogs in the Guibemantis genus, he noticed an unusual specimen that didn’t match known species descriptions. Further investigation over several years with mentor Miguel Vences, also at Braunschweig, led to the naming of three new Pandanus-dwelling frog species — Guibemantis rianasoa, G. vakoa and G. ambakoana — in the journal Zootaxa.

“The frogs were all given names in Malagasy to enable their description to be more accessible by local guides and frog-enthusiasts,” Gabriel said. “Rianasoa is named for a beautiful waterfall in Mantadia National Park, where the frogs can also be found. The clear water of the waterfall’s pool, reflecting the blue and green shadows of the forest, reminded Evariste [Desire] and I of the coloration of the beautiful new frog. Vakoa is the Malagasy word for Pandanus, and ambakoana means ‘living within Pandanus.’”

The frogs have a unique life cycle completely restricted to the trees. Up in the foliage, the frogs lay their eggs in gel masses on the leaves. When the tadpoles hatch, they drop into tiny pools of rainwater trapped by the leaves. The tadpoles grow into froglets that mature among the spiky leaves, coming out only to breed following the same unusual cycle, known only in one other genus of frogs.

This arboreal lifestyle means the frogs depend entirely on intact Pandanus trees. “If Pandanus trees are removed, all three species will suffer,” Gabriel said.

Pandanus trees are themselves a unique ecosystem. The rainwater in their leaf axils provides habitat not just for frogs and tadpoles. Crabs, spiders, day geckos, snakes, katydids, ant colonies and fungi are also regularly found within these trees.

They’re also widespread enough that logging poses less of an immediate threat than deforestation driven by mining, agriculture and development. Slashing, burning and deforestation threaten the island’s extraordinary biodiversity.

Climate change presents another conservation challenge for the rare frogs. Their life cycle depends on sufficient rainfall to fill Pandanus leaf pools, but shifting precipitation patterns and increased droughts due to climate change could quickly render their arboreal homes uninhabitable.

What’s needed to protect the frogs? “The simple answer is the preservation of rainforest habitat in Eastern Madagascar,” Gabriel said. But Madagascar’s economy is struggling, and “it’s not easy to tell struggling farmers not to clear land to make a living.”

He cited Mitsinjo, a small ecotourism initiative focused on forest restoration, frog conservation, environmental education, lemur monitoring, and improvement of the members livelihoods, as, “a good example of local-led tourism and sustainable development.”

“Mitsinjo means look into the future,” Desire said.

Banner image of Guibemantis rianasoa, a new frog species from Madagascar. Image courtesy of Hugh Gabriel

Liz Kimbrough is a staff writer for Mongabay and holds a Ph.D. in ecology and evolutionary biology from Tulane University, where she studied the microbiomes of trees. View more of her reporting here.

Photos: Top species discoveries from 2023

Citation:

Gabriel, H., Rothe, L.-D., Köhler, J., Rakotomanga, S., Edmonds, D., Galán, P., … Vences, M. (2024). Unexpected diversity and co-occurrence of phytotelmic frogs (Guibemantis) around Andasibe, one of the most intensively surveyed amphibian hotspots of Madagascar, and descriptions of three new species. Zootaxa, 5397(4), 451-485. doi:10.11646/zootaxa.5397.4.1

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