Not one but at least seven species of silky anteater identified

Ever since the tenth edition of Linnaeus’s Systema Naturae (1758), it was thought there was only one species, but new research describes six more.

By Peter Moon  |  Agência FAPESP – This is a story that begins in 1758 with the publication of the tenth edition of Systema Naturae, the magnum opus of Swedish naturalist Linnaeus (Carl Nilsson Linnaeus, 1707-78), the father of taxonomy.

Among the 4,200-odd species of animals described by Linnaeus in his book (as well as over 9,000 plant species) was the silky anteater Cyclopes didactylus. Known in Brazil as tamanduaí, or pygmy anteater, it is a cute, shy, small animal with two toes, a short snout, nocturnal habits and a preference for inhabiting tree crowns, where it feeds solely on ants.

It is found in tropical forests in South and Central America, as well as in the few remaining fragments of Atlantic rainforest in Northeast Brazil. All populations of this animal are practically identical, and for 259 years, they were believed to constitute a single species. Now, we know there are at least seven.

The descriptions of six new species of anteater derive from research conducted by Flávia Miranda, a veterinarian affiliated with the Federal University of Minas Gerais’s Biodiversity & Molecular Evolution Laboratory (LBEM-UFMG) in Brazil. Miranda was part of the team of taxonomists, zoologists and geneticists from UFMG and the University of São Paulo who studied the biology and ecology of the new species. They also sequenced the nuclear and mitochondrial DNA of 287 specimens.

The results are in the article “Taxonomic review of the genus Cyclopes Gray, 1821 (Xenarthra: Pilosa), with the revalidation and description of new species”, published in Zoological Journal of the Linnean Society. The research was supported by FAPESP via a scholarship for a research internship abroad and a PhD scholarship, as well as by Fundação Boticário, the Wildlife Conservation Society, FAPEMIG, CAPES and CNPq.

Six populations of C. didactylus were discovered in the nineteenth and early twentieth centuries, with habitats ranging from southern Mexico to northern Bolivia, and eastwards in the Brazilian Amazon (Pará and Maranhão States) and Northeast (Alagoas State).

All the collected specimens appeared to be practically identical. Any morphological differences were too slight to justify the creation of a new species, so all were considered subspecies of C. didactylus, the only species in the family Cyclopedidae.

This was the state of knowledge until 2005, when Miranda, the vet, entered the picture. She has worked with the order Xenarthra for over 20 years and leads Project Anteater, whose mission is the conservation of sloths, anteaters and armadillos.

In 2005 Miranda took part as an expert on xenarthrans in a meeting of the International Union for Conservation of Nature (IUCN) to verify the status of C. didactylus with a view to its conservation.

One of the points raised was whether a population of silky anteaters still existed in Northeast Brazil. No sightings had been reported for years. “I said I’d received a specimen in the conservation breeding facility where I was working in Recife in 2000,” Miranda told Agência FAPESP. This justified a trip to check out the area where it had been found.

Miranda decided to survey populations of anteaters in the Northeast and Amazon regions. In the ensuing two years, she carried out fieldwork in Pará and Maranhão. She also reconnoitered the banks of the São Francisco River in Alagoas. She reported sightings and collected specimens, steadily becoming more convinced that distinct species were indeed involved.

“I realized there were differences in coloring,” she said. “The animals I saw in Maranhão were entirely different from those I saw in the Xingu area. Were they the same species? Did the apparent morphological similarity of individuals in the various populations mask profound differences at the molecular level?”

The advent of molecular biology has shown taxonomists that not everything is identical, however much it may appear so. Miranda spent the last ten years organizing and undertaking expeditions to all parts of Brazil where sightings of silky anteaters had been reported. There have been ten expeditions, to Santa Isabel do Rio Negro (Amazonas State), Oriximiná (Pará), the Parnaíba River Delta (Piauí State), Maranhão, Amapá, and Surinam, among other places.

She sometimes trekked through the forest for as long as 60 days. “Without the help of local people, I would never have been able to find all the specimens I located,” she said.

“It was always very hard to spot the animals in the forest. Imagine a little creature that weighs only 250 g, lives in the crowns of tall trees beside creeks or in mangroves and flooded areas, never comes down to the ground, never vocalizes, and is active only at night. I’d been in the field for two years before I made my first sighting.” 

Molecular clock

Miranda undertook 17 expeditions to collect specimens in Brazil and Surinam, measuring and photographing them, and taking blood samples for molecular analysis. Sex and geographic location were recorded. Age was determined on the basis of body mass, fur density, and fur length. Morphological and morphometric information was also sought from 20 natural history collections in several countries.

Analysis of the animals’ nuclear and mitochondrial DNA removed all doubt about the existence of several species in the genus Cyclopes, supported by morphological and morphometric differences, as well as geographic location.

The most surprising discoveries came from analysis using the molecular clock technique, which estimates when two species diverged on the basis of the number of molecular differences in their DNA.

The molecular clock showed that the separation of several species is not at all recent. On the contrary, it is very ancient. The authors estimate that the Cyclopedidae diverged from other anteaters in the early Oligocene, 30 million years ago (giving rise to the giant anteater, Myrmecophaga tridactyla, and the collared anteater, Tamandua tetradactyla).

Molecular evidence suggests the first divergence in the genus Cyclopes occurred 10.3 million years ago, during the late Miocene. This was when the ancestors of the lineages found west of Amazonas State, Acre and Rondônia States and also in the Peruvian Amazon separated.

This diversification is probably associated with a change in the course of the Amazon River, which once ran from east to west but reversed direction approximately 10 million years ago, when the Andes rose. An immense floodplain formed at that time in western Amazonia.

The wetlands disappeared approximately 7 million years ago, isolating there the ancestors of two new species now described, C. rufus and C. thomasi. These may have separated 3.4 million years ago owing to the formation of the Purus and Madeira Basins, which functioned as biogeographic barriers that isolated the two populations. The Bolivian species C. catellus may also have emerged as a result of the same events.

The researchers estimate that C. ida diverged approximately 5.8 million years ago in the western Amazon and Ecuador, while C. xinguensis probably separated 4.6 million years ago in the area of the Xingu River, to which it has remained confined.

The Mesoamerican lineage C. dorsalis would have separated from its South American kin approximately 3 million years ago, with the continuing rise of the Andean barrier.

The species originally described by Linnaeus, C. didactylus, which lives on the left bank of the Amazon (and in the Negro River basin), in the Brazilian states of Amapá and Pará and also in Northeast Brazil from Maranhão to Alagoas (as well as in Venezuela and Surinam), is thought to have diverged some 2.3 million years ago, with the advent of the first glaciations of the Pleistocene. 

The researchers plan to assess conservation of the population of silky anteaters in Northeast Brazil, which is threatened above all by deforestation. “The idea is to classify the population in the Northeast as an evolutionarily significant unit, or ESU,” Miranda said.

So many millions of years of separation between species would be more than sufficient for these anteaters to have accumulated various modifications. However, this is not what has happened. The genus Cyclopes has proved extremely conservative throughout its evolutionary history, changing very little or not all in morphological terms.

“The reason for this may be the life habits of these animals. All species occupy a similar and highly specialized ecological niche with no competition,” Miranda said.

Geometric morphometrics

While molecular evidence is definitive for the naming of new species, the analysis of morphological and ecological data is important to corroborate the descriptions.

“Historically this genus has always been considered monospecific,” explained zoologist Fabio de Andrade Machado, former holder of a scholarship from FAPESP and currently at the Bernardo Rivadavia Natural Science Museum in Buenos Aires, Argentina.

Machado specializes in analyzing morphometric traits that differentiate species. In this project he helped diagnose morphometric differences in search of evidence to confirm the descriptions of new species.

“I used a technique called geometric morphometrics,” he said. “It’s based on multivariate analysis of point sets, or anatomical marks, which are used to map the shapes of biological structures. This technique can be used to investigate overall skull structure and identify general differences between species in terms of form.”

According to Machado, this analysis showed that the main difference in the species studied referred to the Mesoamerican taxon (C. dorsalis), which has a smaller rostrum (snout) than the other South American groups. 

Another conclusion was that the animals from the Northeast of Brazil, French Guiana (C. didactylus) and Xingu (C. xinguensis) have a slimmer, less robust skull than the rest. “Despite the lack of a precise diagnosis, as in the case of C. dorsalis, this suggests there are more than one or two species in the genus,” Machado said.

The article “Taxonomic review of the genus Cyclopes Gray, 1821 (Xenarthra: Pilosa), with the revalidation and description of new species” (doi: 10.1093/zoolinnean/zlx079) by Flávia R. Miranda, Daniel M. Casali, Fernando A. Perini, Fabio A. Machado and Fabrício R. Santos can be read at: doi.org/10.1093/zoolinnean/zlx079.