The New Mini Frogs of Madagascar

Candice Gaukel Andrews February 11, 2020 0

In the highlands of eastern Madagascar is the Vohimana Reserve, a rain forest that’s one of the most amphibian-rich places in the world. ©Frank Vassen, flickr

More than 350 types of frogs live in Madagascar, the world’s fourth largest island after Greenland, New Guinea and Borneo. The nation stretches across 226,917 square miles (approximately the size of France or Texas) off the coast of East Africa. This gives Madagascar possibly the highest frog diversity per square mile of any country in the world.

Now, scientists at the Ludwig-Maximilians-Universitat and the Bavarian State Collection of Zoology—both in Munich, Germany—have named five new species of frogs found in the island’s rain forests. The largest of these amphibians could sit on your thumbnail, and the smallest is hardly longer than a grain of rice.

Three of these five Madagascar species belong to a group that is wholly new to science. They’ve been formally dubbed Mini.

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Madagascar is world-famous for its 60 types of lemurs—primates that look something like a cat crossed with a dog and a squirrel. But it has more than 350 species of frogs, 99 percent of which are endemic.

Minimum, miniscule and miniature

Because of their size, the tiny frogs were exceptionally hard to find, and that may explain why they are now just coming to light. The scientists often spent months in the forests, searching under leaf litter and within the dense bases of grass tussocks in the mountainous north. Cyclones often batter Madagascar’s east coast in the December–March rainy season, which can make searching even more challenging. But tough conditions for biologists can make great conditions for frogs. The trick, the biologists say, is to listen for the frogs’ calls, and then track them.

Successfully capturing the diminutive frogs was simply the first hurdle, however. It’s hard enough to distinguish between normal-sized species on the basis of superficial differences; but when the animals are Lilliputian-sized, identifying separate species becomes close to impossible. But the hard work paid off. With the help of genetic and molecular analysis, as well as micro-CT scanning, the scientists were able to determine that they had chanced upon five entirely new types of frogs in the Microhylidae family, commonly referred to as “narrow-mouthed frogs.”

One of the new species, dubbed Mini mum, was found in the Manombo Reserve in east Madagascar and is one of the smallest frogs in existence. Adult males and females measure just .31 and .44 inches, respectively. A Mini mum frog could sit on a paper staple. The Mini scule frog is from the Sainte Luce Reserve in southeast Madagascar. It is slightly larger than Mimi mum and has teeth in its upper jaw. Mini ature, the largest of the three at a whopping .59 inches but with a similar build, is from Andohahela National Park, also in southeast Madagascar. But even Mini ature could sit on your thumbnail with room to spare.

Ninety-eight species of frogs live in Ranomafana National Park, one the most spectacular protected areas in Madagascar. ©Richard, flickr

The other two new species, Rhombophryne proportionalis and Anodonthyla eximia, are just .43- to .47-inches long, and are much smaller than their closest relatives. Found in Tsaratanana in north Madagascar, the unique Rhombophryne proportionalis is a proportional dwarf, which means that it has the proportions of a large frog but is only about half-an-inch long. This is extremely unusual among tiny frogs, which typically have large eyes, big heads and other characteristics that are baby-like, called paedomorphisms.

Anodonthyla eximia from Ranomafana National Park in southeast Madagascar is distinctly smaller than any other of its Anodonthyla sister species and has adapted to living on land, suggesting, say scientists, that miniaturization and adapting to life on the ground may be evolutionarily linked.

Diversity in the dinky

While the five new frogs found on Madagascar are endemic to the island, narrow-mouthed frogs are found on every continent except Antarctica and Europe. Although most narrow-mouthed frogs are small to moderately large, many are tiny. It’s thought that miniaturization developed as a means to help smaller frogs access new food resources and to take advantage of ecological niches unavailable to larger creatures, such as being be better equipped to hunt down tiny ant and termite prey.

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From the forested mountains of the north to the rain forests of the east, and from the deserts of the south to the steppes of the center, Madagascar is an island with many landscape faces.

An exciting sidenote to the new frog discovery is that all of the frogs appear to have independently evolved to be much smaller in body size, indicating that evolution in Madagascar’s miniature frogs is far more dynamic than previously thought. Tiny frogs in Madagascar have evolved at least four times—often several times within a single region—and perhaps even more. That suggests something interesting is going on: why are so many different groups getting small? Is there a reproduction advantage? Are they more likely to divide into more species? Does that make individual lineages more likely to avoid extinction and diversify further?

Researchers will be looking closer at the evolution of these frogs to try to figure out what is driving and limiting the changes in their ecology, as well as to piece together the evolution of their distribution over Madagascar. They also plan to work with local conservation groups to protect the forested areas where the frogs live.

Deemed deserving

Madagascar is a treasure trove of biodiversity. In fact, in 2015 and 2016, more previously unknown species were found. In 2017, 26 new species of dwarf frogs were discovered, bringing the total number of Madagascar microfrogs to 108. On average, 10 new species are identified and described per year in the country.

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According to WildMadagascar.org, more dollars pour into conservation efforts in Madagascar than in any other part of Africa. For the sake of the nation’s wildlife, we all hope those endeavors will be successful.

Each of the three new Mini frogs exists only in one location in Madagascar. Mini mum, in particular, has an extremely limited range and known population, prompting the study authors to recommend a listing of critically endangered. Rhombophryne proportionalis has so far been seen in just two localities within Tsaratanana National Park, and the researchers suggest listing it as endangered. As for Mini ature and Anodonthyla eximia, both should be considered “data deficient” by the International Union for Conservation of Nature (IUCN), given the general lack of information on the species’ ecologies and natural histories.

Unfortunately, researchers are working in a very tight time frame. Madagascar’s forests are dwindling at an astounding rate. The country is one of the poorest; and with a growing population, the forests bear the brunt of human needs. Protecting fragments of the forest is the first line of defense against direct human encroachment, but a globally warming climate makes it hard to know what the full future will be like for these frogs. In the past, they might have shifted to higher elevations to maintain their temperatures, but connectivity has now been lost, so moving to cooler areas is no longer an option.

Luckily, conservation work in Madagascar is intensifying. Let’s hope that these tiny, newly discovered denizens will be deemed deserving of a tomorrow.

Here’s to finding your true places and natural habitats,

Candy

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