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Diversity

Mammals to the surface

Biologists find an average of eight new species of mammals a year in South America

YURI LEITE / UFESExclusive to the Atlantic Rain Forest: the gracile mouse opossum, one of the smallest marsupials in the worldYURI LEITE / UFES

A little monkey (not even 20 centimeters without the tail) with dark fur on its back and orange colored in front, with a dark triangular crown, found in the Amazon, was baptized as the black-crowned dwarf marmoset (Callibella humilis). A piebald tuco-tuco may represent a new species of the Ctenomys genus, since these underground rodents, common in Rio Grande do Sul, are usually sandy or brown in color. These are examples of mammals discovered in the north and the south of the country in the last ten years. According to Yuri Leite, a biologist from the Federal University of Espírito Santo (Ufes), the highlight of the 1st South American Congress of Mastozoology (the study of mammals), held in October in the city of Gramado, Rio Grande do Sul, was “the finding that the number of species (and genera) of South American mammals has increased absurdly”.

In Brazil, the country with the greatest biological diversity in the world, to date about 530 mammals have been described, in general small ones. Our marsupials are not the boxing kangaroos of the cartoons: they can be the size of a finger, like the Brazilian gracile mouse opossum (Gracilinanus microtarsus), one of the smallest of this group. The destruction of the forest threatens the existence of these animals, with 66 endangered species at on the Brazilian Institute for the Environment and Renewable Natural Resources (Ibama)’s red list in 2003. Despite this, more field work and new techniques of work have rapidly increased the number of known species.

Leite, Leonora Costa and other biologists from Ufes report in the Megadiversidade [Megadiversity] magazine that on average one new genus and eight new species of mammals are discovered a year. The estimate is that in the next 20 years the number of mammals cataloged in South America will more than double. Many of them are new to the scientific records, but the major part come from revisions of their classification. In the American Museum Novitates of October 19, Marcelo Weksler, a Brazilian biologist at the University of Alaska, Alexandre Percequillo, from the Federal University of Paraíba (UFPB), and Robert Voss, from the American Museum of Natural History of New York, added ten genera of rodents to South America.

For a group of animals that has been studied for centuries, it is surprising that there is still so much left to be discovered. In the last 12 years, three new orders have arisen in the world, 94 genera (the majority from reclassifications, and 29 ones new to science), and 815 species (298 new ones and 125 from South America). This assessment was made by the American, Jim Patton, from the University of California at Berkeley, who compared the second (1993) and the third editions (2005) of the book Mammal Species of the World, by Wilson & Reeder, which lists the known species of mammals.

So many new animals are emerging because more refined techniques of analysis are distinguishing details that would pass unobserved before. Animals may look different from each other and belong to the same species. A furry gray cat and another short-haired piebald one are equally cats. On the other hand, species that at first sight are the same may have differences invisible to the naked eye that make them not be able to procreate amongst themselves, which separates them from the biological point of view. According to Leonora, the proliferation of the number of species derives above all from the impact of the analysis of differences in the DNA amongst groups of animals. Furthermore, new measurement techniques, such as geometric morphometry, are beginning to be used more and should expand knowledge about biodiversity.

PEDRO PELOSO / UFESA new species of the Juliomys sylvan rodentPEDRO PELOSO / UFES

Digital ruler
Traditionally, part of the distinction between species is based on measures taken of the skull. The instrument most used is the pachimeter, a ruler with two arms, one of which slides to measure distances on curved or irregular surfaces. But modern techniques make more refined and precise analyses possible. The group of Gabriel Marroig, from the University of São Paulo (USP), uses a device that look like a pen, hanging from an articulated arm. The equipment has a point of rest, and translates any movement into three-dimensional coordinates. When it touches on specific points of the skull being studied, the pen transmits this information to a computer. A digital image is formed that can be used to take measurements or to compare the skull with the skull of other species. Marroig uses this technique to understand the evolution of the South American primates.

To attain a more precise classification, the researchers add up information of various kinds. During her doctoral studies, Leonora analyzed the DNA of Brazilian marsupials to understand their origins and their diversity. To refine her conclusions, she is now complementing the data with observations from the morphology of the animals. These results have helped to increase by 70% the number of species of South American marsupials in the last 13 years.

Besides the new techniques, something has contributed towards the advance of the knowledge about mammals is the integration of areas, promoted by professionals willing to collaborate. The systematists, who analyze the data to put order in the genealogical trees and give a name to the new animals, are often not the same who do the genetic or morphometric studies. For this reason, little would be done without joint efforts.

According to Leonora, concern with the environment became stronger after the Rio Conference in 1992, and the interest in studying biological diversity increased. Conservation initiatives like that of the World Conservation Union (IUCN) consist of gathering information to draw up global lists of threatened species, altered as the researches advance. This may be the case of the Brazilian arboreal mouse (Rhagomys rufescens), which Yuri Leite and collaborators have shown to be not so rare as used to be thought. To find it, all that was needed was to innovate in the capture method: what works is the old technique called pitfall, which is no more than a bucket buried in the ground. “Based on the most recent data”, says Leonora, “the Rhagomys ought to be removed from the list of fauna threatened with extinction”.

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