By Rodrigo de Oliveira Andrade
[SÃO PAULO] The siren-like call of a species of toad introduced into Brazil from the Antilles islands may result in a “sharp drop” in house prices in a São Paulo neighbourhood, according to a study on invasive species.
The tiny toad — about 3 centimetres long and known to scientists as Eleutherodactylus johnstonei — reached Brazil through the international trade in plants, according to the study, published in PLoS One. It can reproduce in shallow water, which gives it a great invasive potential, and produces a deafening sound similar to that of a siren.
“Property value is expected to depreciate in areas surrounded by calling sites,” write the authors.
The study documents six invasive species of toads and frogs spotted across different ecosystems in Brazil, and the concerned local researchers have called attention to the environmental impact of these species.
“The number of invading amphibians is exponentially increasing in Brazil, which highlights the need to monitor and control these populations and mitigate their impacts on wildlife,” says Luís Felipe Toledo, from the State University of Campinas’s Institute of Biology (IB-Unicamp) and one of the study’s authors, in an interview with SciDev.Net.
The experts point out that some of these species are reservoirs of harmful fungi, others are becoming predators of native fauna, and one is even interfering in local amphibians’ reproductive habits.
“Invasive species can negatively impact native populations, competing for food or disseminating diseases,” says biologist Cynthia Prado, from the Department of Morphology and Animal Physiology at the Faculty of Agricultural and Veterinary Sciences, São Paulo State University (FCAV-Unesp).
“It is necessary to invest in the control of these animals in these regions,” adds Prado, who did not participate in the study. Control measures vary from capturing them manually or using traps to poisoning by spraying chemicals.
Among these invasive species are some which are native in other areas of Brazil, while others come from abroad. One example is the bullfrog (Lithobates catesbeianus), which is originally from North America and was introduced into Brazil for commercial breeding.
This frog, which can grow to a length of 20 centimetres and weight of 1 kilogram, can adapt to almost any environment and has affected various parts of the Atlantic forest south and southeast of the country. This species is known for its voracity — it can eat other frogs and even small lizards — and for being a reservoir of the fungus Batrachochytrium dendrobatidis, which causes an infectious disease called chytridiomycosis.
“This fungus attacks the skin of amphibians, interfering with gas exchange through the epithelial tissue,” biologist Lucas Forti, from the IB-Unicamp and main author of the study, tells SciDev.Net. “It is considered a threat to the population of these vertebrates.”
Another invasive species has been registered in Fernando de Noronha, an archipelago in the Atlantic Ocean 360 kilometres from the city of Natal. In spite of government regulations that have prevented the archipelago from becoming a tourist resort, researchers found the Cururú toad (Rhinella marina) in these islands.
This is a species native to northeastern Brazil that is believed to have been introduced into the archipelago in the 19th century as a method of biological control of local insects. According to Toledo, Cururú toads feed on threatened insect species.
The Noronha archipelago is also affected by a species called the X frog (Scinax x-signatus), which is native to Venezuela and Colombia.
Another species, Leptodactylus labyrinthicus is colonising parts of the Amazon forest, and the impacts of this are still unknown.
Meanwhile, in the municipality of Guarujá, on Sao Paulo’s coast, the problem is the Phyllodytes luteolus, a species that usually lives among the leaves of the bromelia plant and is believed to have been introduced to the region with the trade of ornamental plants.
According to Forti, the invasion of this species can compromise the sexual reproduction of native amphibian species, such as those of the genus Ischnocnema.
These amphibians are nocturnal and use acoustic communication in their reproductive interactions to search for the best mates. “The sound of the vocalization of P. luteolus is emitted in the same frequency [as that] of the males of Ischnocnema,” he says, and this means it can affect communication with females.
The study also highlights a piece of good news: based on projections by the Intergovernmental Panel on Climate Change (IPCC) on the impacts of climate change, by 2100, four of these six species should have their distribution area reduced due to changes in climate, in particular drops in temperature and rainfall.
The study published in PLoS One is the result of projects funded by FAPESP, one of the donors of SciDev.Net.