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Six species of invasive amphibians are identified in the country

Researchers publish in PLoS ONE first survey of toads, frogs and tree frogs that arrived in Brazilian biomes

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The invasion of Brazilian ecosystems by species from other biomes, countries or continents is a challenge for conservationists. There are several examples, such as wild boars originating in Europe and imported to farms in Uruguay, from where they escaped to Brazil in the 1990s, spreading since then throughout the South and Southeast regions.

Among the invaders there are also amphibians. A group of biologists from universities in São Paulo have just published the first survey of invasive amphibians in Brazilian biomes. They recorded the presence of no less than six different species, including toads, frogs and tree frogs, spread across much of the country.

Some invasions are recent, as is the case of the whistling tree frog (Eleutherodactylus johnstonei), accidentally introduced into the city of São Paulo less than a decade ago. Other cases are older, such as the cane toad (Rhinella Jimi), who arrived in the Fernando de Noronha archipelago 130 years ago.

Results of the work were published in PLoS ONE in article by Lucas Forti, from the Biology Institute (IB) at Unicamp, Luis Felipe Toledo, head of the Natural History Laboratory of Brazilian Amphibians at IB, Célio Haddad, professor at the Biosciences Institute at the São Paulo State University (Unesp), and others. The research received various support from FAPESP, in the form of grants and scholarships.

The idea of ​​carrying out a survey of invasive amphibians in Brazilian biomes arose in the summer of 2013-2014, when Forti observed an infestation of bromeliad tree frogs in the gardens of a condominium in Guarujá (SP).Phyllodytes luteolus). “This is a species whose original habitat is the portions of the Atlantic Forest that extend from the north of Rio de Janeiro to Paraíba,” he said.

The herpetologist suspects that bromeliad tree frogs must have been introduced to Guarujá accidentally, through the trade in ornamental plants, since the species, as its name indicates, usually lives in accumulations of water between the leaves of bromeliads.

Photo: Scarpa
Luís Felipe Toledo, head of the Natural History Laboratory of Brazilian Amphibians at IB: “The good news is that, of the six invasive species identified, four will have their distribution area reduced by 2100”

According to Forti, the invasion puts at risk the survival of native tree frogs that live in habitats similar ones in Baixada Santista, especially that of the Ischnocnema . The risk comes from the vocalization of the invaders. It turns out that males of P. luteolus, in their nocturnal songs to attract the attention of females, vocalize in the same frequency range as males of Ischnocnema.

The noise caused by the vocalization of an invasive species probably harms the acoustic communication system in native species, a fact that, specifically, may put reproduction at risk in the native species of the genus. Ischnocnema in places of sympatry – when two species occur in the same geographic area – with P. luteolus.

“This potentially disrupts the acoustic communication of the species and could perhaps have negative effects on the ability of females to locate males in the breeding environment,” Forti said.

Another invasion was identified in some streets in the Brooklin neighborhood, in the south zone of the city of São Paulo. In 2014, several families began to complain about a deafening noise that kept them up at night (check out the video at www.youtube.com/watch?v=9cV11UPneHc).

Haddad, a professor at Unesp in Rio Claro, was contacted by residents to investigate the cause of the noise and ended up identifying bioinvasion. It was the song of hundreds of whistling tree frogs.

“All the noise is made by the male of the species, as the female is mute. It is the male who has the role of croaking to attract the female. The species is native to the Antilles and we think it was accidentally brought in as ornamental plants”, said Haddad, who coordinates the Thematic Project “Diversity and conservation of Brazilian amphibians”.

The problem of whistling tree frogs in the São Paulo neighborhood is already causing economic consequences, such as the devaluation of real estate in those streets where the invasion is currently limited. The animals are breeding in the backyards of homes.

According to Haddad, the problem must be combated and eliminated while the invasion is restricted to a neighborhood. “If nothing is done, the whistling treefrog population will spread and, if it reaches a forested area, it will get out of control,” he said.

Cururu and bullfrog

There are two other cases of bioinvasion that scientists have long known about. One of them is on the island of Fernando de Noronha, where the first cane toads, native to the Northeast, were introduced by Father Francisco Adelino de Brito Dantas (1825-1893), who in 1888 became the chaplain of the penal colony that operated there.

It is estimated that the religious man took cururu as a form of biological control of the insects that infested his vegetables. Another assumption is that the cururu was introduced by the United States military during the Second World War, when they maintained a base on the island. They would have brought cururus as a way of controlling the mosquito population.

The problem with the cururu is its voracity. “In Noronha, we know that the cururu is eating animals that are threatened with extinction,” said Toledo, who studied the problem of the cane invasion in the archipelago.

The bioinvasive amphibian with the widest presence in Brazil and with the most serious consequences is the bullfrog (Lithobastes castesbeianus). Native to North America, it was imported for frog farming in the 1930s and soon escaped from frogs into the environment, and is now widespread throughout patches of the Atlantic Forest in several states in the South and Southeast. It is a large animal, up to 20 centimeters long, and eats everything, including insects, young mammals, small birds and even young members of its own species.

In addition to competing with native species for resources, the bullfrog is a natural reservoir of Batrachochytrium dendrobatidis, a fungus that threatens the global amphibian population. The fungus is the cause of a disease called chytridiomycosis, which attacks the skin of amphibians and interferes with the animals' gas exchange with the environment.

Photo: Disclosure
The bullfrog, one of the invasive species | Photo: Disclosure

In recent years, a marked extinction of amphibian species has been recorded in several regions of the planet. The bioinvasion of bullfrogs, which is spreading across several continents, may be related to such mass extinctions, as the fungus was identified by Brazilian scientists in the skin of the bullfrog, which is resistant to the disease.

“Everything indicates that the invasive proliferation of the bullfrog is spreading the fungus. If this is the case, this is a very important finding and will serve as a basis for combating the disease and protecting the various populations of threatened amphibians,” said Toledo.

The other two species of bioinvasive amphibians identified in the study are the tree frog (Scinax x-signatus), native to Venezuela and Colombia and which, like the cururu, also infests Noronha, and the pepper frog (Leptodactylus labyrinthicus), which today proliferates in the central Amazon.

The authors of the invasive amphibian survey also investigated what the future distribution of the six species might be as a result of climate change. Simulations were carried out based on climate forecasts for 2100 from the Intergovernmental Panel on Climate Change (IPCC).

“The good news is that, of the six invasive species identified, four will have their distribution areas reduced by 2100, including the infamous bullfrog. This is not the case, however, with the whistling tree frog and the cane toad, which may have their distribution expanded,” said Toledo.

The article Perspectives on invasive amphibians in Brazil, by Lucas Rodriguez Forti, C. Guilherme Becker, Leandro Tacioli, Vânia Rosa Pereira, André Cid FA Santos, Igor Oliveira, Célio FB Haddad and Luís Felipe Toledo, can be read at https://doi.org/10.1371/journal.pone.0184703.
 

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Luís Felipe Toledo, head of the Natural History Laboratory of Brazilian Amphibians at IB

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