Very Rare Mouse Found in the Mighty Tepuis of the ‘Lost World’

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Roraima mouse (Podoxymys roraimae)
28/01/2015
Very Rare Mouse Found in the Mighty Tepuis of the ‘Lost World’
post by
Reinout Verbeke

A team of scientists from Brazil and Belgium rediscovered one of the rarest mammals on earth, the Roraima mouse (a.k.a. Podoxymys roraimae in scientific language) from the tepuis of northern South America. Its DNA suggests ancient connections with other mice species distributed mainly on the distant Brazilian Plateau, instead of the Andes or the adjacent Amazon lowlands.

The tepuis are huge sandstone tabletop mountains in the Guiana Highlands, that form one the most remarkable landscapes on Earth. They rise abruptly above the savannas and tropical forests of southern Venezuela, west-central Guyana, and northern Brazil. This dramatic landscape has inspired writers and filmmakers for more than a century, from Sir Arthur Conan Doyle’s 1912 novel ‘The Lost World’ to Disney-Pixar’s 2009 film ‘Up’, to always depict relict creatures, like dinosaurs or giant birds, on remote and inaccessible tepui summits.

Accidental discovery

Philippe Kok, a post-doctoral researcher at the Amphibian Evolution Lab of the Vrije Universiteit Brussel in Belgium, and a research associate at the Royal Belgian Institute of Natural Sciences, found the mouse in November 2009 on the summit of Wei-Assipu-tepui (2,216 m of elevation), in the Cuyuni-Mazaruni Region, Guyana, near the Brazilian border. Kok was actually on an expedition looking for frogs and lizards, but came across this mouse sneaking around his campsite. “I’ve been exploring this region for over a decade, cataloguing hundreds of vertebrate species, but this was the first and only time I saw this mouse”, says Kok. Yuri Leite, an associate professor at the Universidade Federal do Espírito Santo in southeastern Brazil, heard this story from Kok’s field assistant and realized that this was a major finding based on the description of a small, short-tailed, short-eared, and long-clawed mouse. 

Seventh specimen

The Roraima mouse is not only one of the rarest, but also one of the most restricted mammals in terms of geographical distribution: it was previously known from only six animals collected in 1927 and 1989, all from the summit of the same tepui, Mount Roraima, on the border of Guyana, Venezuela and Brazil. Kok not only found the seventh specimen of Podoxymys roraimae and took the first picture of this little critter, but also recorded the second known locality, Wei-Assipu-tepui, at the border between Guyana and Brazil.

Leite got in touch with Kok, and called his attention to the importance of this discovery and the biogeographical implications of finding its evolutionary roots. Podoxymys roraimae has no siblings, and scientists did not know its place in the tree of life. “It is like an only child stranded on the tepuis without knowing who its closest relatives are and where they live” says Leite.

DNA analysis

To assess the evolutionary affinities of this rare animal, Leite and Kok teamed up with Marcelo Weksler, professor in zoology at the Universidade Federal do Rio de Janeiro. They obtained the first DNA sequences from the Roraima mouse and compared them with other native South American rats and mice. The results show that its closest relatives are Thalpomys and Necromys, two taxa found in open-vegetation biomes, especially the Cerrado vegetation on the Brazilian Plateau. ‘It is very surprising to discover that the closest living relative of a small mouse restricted to the summit of two very isolated tepuis, lives in a region located several thousands of kilometres from there’, says Philippe Kok.

These findings do not conform to the current predictions of how the tepui fauna evolved: for small mammals, scientists believe that this fauna is either the result of long distance dispersal of ancestral populations from the Andes, or invasions from the surrounding uplands and lowlands close to the tepuis.

The connection between the Guiana and the Brazilian shields – the new scenario Kok and colleagues suggest – is at least 2.47 million years old, as the genetic analyses show. "How the Brazilian Plateau and the tepuis of the Guiana Shield were connected in the late Pliocene still needs to be explained. Maybe there were some ecological corridors between them, and/or the ancestor’s distribution was suddenly “split” by some geological or climatological event," Kok suggests.

 

Click the image above for more pictures.

 

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