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Marmosets trafficked as pets now threaten native species in Atlantic forest

  • Decades of illegal trafficking have led to the movement of marmosets from Brazil’s Cerrado and Caatinga biomes into the southeastern Atlantic rainforest, where they now threaten the survival of native species.
  • According to a study, the invasive marmosets crossbreed with native species, producing a hybrid population that could lead to the extinction of the endemic species.
  • One of the native Atlantic rainforest species, the buffy-tufted-ear marmoset (Callithrix aurita), is one of the world’s 25 most endangered primate species.

One of the most devastating effects of the illegal trafficking of wild animals in Brazil is the proliferation of marmosets in large urban centers. There are two species in particular that have spread: the black-tufted marmoset (Callithrix penicillata), which is native to Brazil’s Cerrado biome and known as mico-estrela in Portuguese; and the common marmoset (Callithrix jacchus), originally from the Brazilian northeast. Both were trafficked in large numbers during the 1980s and 1990s, resulting in their introduction to the Atlantic rainforest in Brazil’s southeast.

“These two species are common in the southeast today. Even though trafficking may not have led to the release of so many in nature, those that were introduced multiplied in absurd numbers,” says Fabiano Melo, a professor in the forestry engineering department at Viçosa Federal University (UFV) in Minas Gerais state.

Initially purchased as pets, the marmosets largely ended up being abandoned by people in forested areas close to large urban centers, where they multiplied.

The problem is that when the small primates were introduced to the southeast, there were already two endemic species of marmosets in the region. Today, both are considered threatened on the IUCN Red List. The buffy-tufted-ear marmoset (Callithrix aurita), native to the states of São Paulo, Minas Gerais and Rio de Janeiro, is listed as endangered and the buffy-headed marmoset (Callithrix flaviceps), found in a small area in the states of Minas Gerais and Espírito Santo, is critically endangered.

Difficult to find in nature, the buffy-tufted-ear marmoset was once widespread in the southeast, but is now listed as one of the 25 most threatened primates in the world. Another two Brazilian primates are on this list: the pied tamarin (Saguinus bicolor), a marmoset native to the Amazon rainforest, and the northern brown howler monkey (Alouatta guariba guariba), native to the Atlantic rainforest in Brazil and Argentina.

The common marmoset (Callithrix jacchus) is a species native to Brazil’s Northeast, originally from the Cerrado and Caatinga biomes, but has become common in the Atlantic rainforest of Brazil’s Southeast, where it has crossed with native marmosets. Image by Leszek Leszczynski via Wikimedia Commons (CC BY 2.0).

Genetic mixing

Invasive species have long proliferated in Brazil’s southeast, interfering with the balance of the biome and threatening the native marmosets. But a study led by biologist Joanna Malukiewicz shows that the problem may be even more serious. “One of the most important things we found in the study was that, because of cross-breeding, the genetic material from the exotic species became part of the genetics of the native species,” she says. “All these species end up crossbreeding and in the southeast, we have a mixture of exotic, native and hybrid marmoset populations.”

For five years, Malukiewicz and her team gathered and analyzed 49 animal samples and, based on their mitochondrial DNA, detected the presence of three exotic marmoset species and four hybrid species among the marmosets native to the southeast. The concerning aspect revealed by the study was that marmosets that looked exactly like the buffy-tufted-ear marmoset were not genetically pure but had DNA from the invasive species.

Fabiano Melo, coordinator of UFV’s Tufted-ear Marmoset Conservation Center, who was not involved in the study, says it shows how hard it is to find animals with pure genetics. “We have fewer native individuals in nature than we imagined,” he says. “We would need to capture the animals and analyze their DNA to separate the pure from the hybrid individuals.”

Among those marmosets analyzed in the study were buffy-tufted-ear marmosets raised in captivity at Guarulhos City Zoo in São Paulo state, whose genetic material was proven to be pure. This ensures a stock of native individuals for a future reintroduction program to the biome. “It is very important to check that the animals are in fact genetically pure and not hybrids when reintroducing rare marmoset species back into nature,” Malukiewicz says.

Approximate distribution of marmoset species from the genus Callithrix in Brazil and geographic origins of the samples used in the study. Image by Malukiewicz et al. (2020).

Aside from the threats of forest fragmentation, trafficking and hybridization, the primates were also recently affected by outbreaks of yellow fever and Zika virus. The brown howlers were the species most affected by yellow fever, but marmosets also died during the outbreak. Many of the reported deaths were among hybrid marmosets, which may be due to the fact that hybrids would be more susceptible to yellow fever. However, the hybrid species are also more widespread than the pure species in the urban areas hit by the outbreak. “We don’t have enough information on how susceptible Brazilian primates are to yellow fever, Zika and other viruses, but biomedical studies have shown that marmosets suffer from symptoms of these viruses in a manner similar to humans,” says Malukiewicz, who is developing a study to understand these primates’ genetic vulnerability to the diseases.

There are six marmoset species from the genus Callithrix in Brazil, each with distinct visual characteristics and vocalizations. These aspects are part of a natural prezygotic reproductive isolation mechanism. This mechanism is fragile, however, and since they live in the same region, the species end up crossbreeding and over time to produce only hybrid individuals. “This is why we have seen genetic deterioration of the species,” Melo says.

Aside from threatening the native marmosets, the introduction of invasive animals causes other imbalances. For example, feeding habits can change the flora because of a preference for certain fruits and the resulting distribution of different seeds. Other wildlife is also affected. “The invasive marmosets are expert predators and eat many bird eggs and hatchlings. The native species are having quite a difficult time,” Melo says.

The buffy-tufted-ear marmoset (Callithrix aurita) is a primate endemic to the Atlantic rainforest of Brazil’s southeast. As its habitat disappears and marmosets from the Cerrado grasslands invade its territory, the species has become one of the 25 most threated primates on the planet. Image by Orlando Vital/UFV.

38 million wild animals trafficked every year

Brazilian legislation has prohibited the trafficking of animals since 1967, and the Environmental Crimes Law of 1988 classifies wildlife trafficking as a minor criminal offense. Because of the activity’s clandestine nature, it’s difficult to determine the number of animals actually sold on the black market. It’s estimated that 38 million animals are taken from the wild in Brazil every year, 90% of which die before reaching their final destinations. Birds are among the most captured animals in Brazil. A study published on animal trafficking in the Amazon rainforest between 2012 and 2019 shows that the most captured animals there were fish and turtles. Primates continue to be popular because of their appeal as pets and are hunted for their meat.

According to the National Network to Combat the Trafficking of Wild Animals, an NGO known by its Portuguese acronym RENCTAS, most of the wild specimens sold illegally come from Brazil’s north, northeast and central-west. They’re shipped along interstate highways to the south and southeast, mostly to Rio de Janeiro and São Paulo. There, they are sold or exported via the region’s main ports and airports.

The marmosets native to the southeast are still limited to their region of origin. “No one has taken southeastern marmosets to the other biomes; in fact, it would be difficult for them to survive there. They are adapted to the coastal Atlantic rainforest, which is more humid and offers more food,” Melo says. “The invasive marmosets do well in the southeast because they are from the Cerrado and Caatinga, which are more hostile environments.”

Because marmosets look cute when they’re young, many people want to keep them as pets. But after some time, the owners realize the animals have undesirable habits for pets, or decide they are too much work, releasing them into nearby forests without much thought. Over the decades, this repeated behavior has led to the imbalance seen today. Marmosets thrive in urban neighborhoods, in backyards and running along power lines. People constantly offer them food, which is strongly discouraged by experts.

Feeding the animals can cause intestinal damage or hormonal and protein imbalance, harming their health. “Direct contact should be avoided because we can transmit human illnesses and viruses like herpes simplex type 1, which can kill them,” Malukiewicz says. “On the other hand, there is a risk that marmosets can transmit rabies to humans.”

Melo adds, “If an animal is fed, it can reproduce even more quickly and occupy even more of the space that belongs to the native species.”

Banner image of a buffy-headed marmoset (Callithrix flaviceps), a critically endangered species native to the Brazilian southeast, by Sarisha Trindade/UFV.

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