Researchers at the University of São Paulo (USP) and the State University of Campinas (UNICAMP) have conducted the most comprehensive genetic analysis ever of the American frog (Aquarana catsipiana) in Brazil, and concluded that two groups of species here live in frog farms or invade local ecosystems.
American frogs are among the world’s major invasive amphibians. An article about the study was published in Scientific Reports.
We have confirmed the existence of at least two different groups of American frogs. One probably descends from the first American toads to enter Brazil. This group is present in practically all of the south and southeast. “The other is mainly confined to Minas Gerais, but occurs in small numbers in other states,” said Gabriel Georgiewicz Cohen, first author of the article.
The study was part of his master’s research at the Institute of Biological Sciences (IB-USP) with a grant from the Brazilian National Council for Scientific and Technological Development (CNPq). A. catesbeiana is native to North America and was brought to Rio de Janeiro in 1935 for meat production. It is now farmed throughout the South and Southeast and has also spread into the wild, with negative impacts on local ecosystems, such as diseases for which there are no defenses against native species in Brazil. “Our results show that the captive and invasive American frog is genetically indistinguishable, reinforcing the importance of preventing escape from frog farms,” said Taran Grant, professor at FAPESP-supported IB-USP and principal investigator of the study. If the groups are genetically different, it will be possible to find out the origin of each animal. In theory, an analysis of a captured frog could refer to an area or farm of frogs from which he or a relative escaped, so that surveillance and law enforcement is possible. Compared with introduced populations of species studied in other countries, the Brazilian populations have the least diversity.
The researchers analyzed specific genes in 324 tissue samples. The samples came from 38 sites in seven of the nine Brazilian states where captive and feral American frogs were found. They concluded that the vast majority belonged to the same population, which is descended from animals that were first brought from North America to Rio de Janeiro in 1935, after which the American frogs spread across the country in response to incentives presented as a matter of state policy. The other inhabitants are descended from a group of animals that were brought in the 1970s to Minas Gerais under a public policy that was subsequently implemented in the state. These breeding pairs are likely imported from the United States. This species is native to the eastern United States, as well as northern Mexico and southern Canada. “The results of genetic analyzes match these two well-documented introductions, although there is anecdotal evidence for others in the 1980s and 2000s, and isolated initiatives by some producers. If there are other introductions, the animals in question may or may not have had the same origin. Instead, we simply did not collect samples from these individuals,” said Georgwich Cohen, a doctoral student at the University of Zurich in Switzerland.
Bullfrog farming reached its peak in the 1980s in Brazil. About 2,000 farms were producing at that time. Activity declined in the following decades due to a number of factors, such as a lack of private investment and public incentives. Many farms were abandoned, and the animals escaped into the wild. The species reproduces easily, lays a lot of eggs and grows quickly until individuals reach 15 cm. In addition, it is highly resistant to diseases and can coexist with fungi and viruses that have led to a global decline in the numbers of other amphibians, without necessarily seeing that their development is poor.” Toledo Professor at the Institute of Biology of the State University of Campinas (IB-UNICAMP) is supported by FAPESP.
These characteristics are desirable in any breeder species but become a major environmental problem when the animals involved invade wild areas. In the case of A. catesbeiana, adverse effects include competition with native species for food and other resources. The North American species is also a voracious predator, feeding on other frogs as well as snakes, birds and even mammals, and its loud squawking interferes with the breeding of native amphibians. “These modifications could have a significant impact on reproduction since most of the anurans [frogs and toads] It relies on voice communication to locate, assess and select mates.” The most serious environmental problem, or at least the most documented to date, is disease transmission.” After spreading through the Atlantic rainforest biome from Rio de Janeiro to Rio Grande do Sul [Brazil’s southernmost state]American toadstools affect local wildlife in different ways. The main problem is that they are carriers of the amphibian chytrid fungus [Batrachochytrium dendrobatidis] and raneros. The native amphibians lacked resistance to these two pathogens, Toledo said, which led to the species’ extinction.
Chytrid fungus causes onychomycosis, an infectious disease that penetrates the skin of adult amphibians, which become unable to breathe and die of cardiac arrest. It has wiped out the populations of at least 501 amphibian species worldwide. Rana virus is also associated with declining numbers of these animals and has been detected in the rainforests of the Atlantic Ocean.
Brazilian law requires anyone who detects a chytrid fungus or rana virus in farmed animals to notify the Ministry of Agriculture, Livestock and Food Supply (MAPA) and to carry out “sanitary slaughter” (or population removal), destroying all animals and disinfecting the facility before starting a new breeding cycle, but This is not what happens. “We detected chytrid fungus on almost all of the frog farms we visited. There is a significant amount of toadstool movement across the country. Producers are working with the Department of Agriculture, Livestock and Fisheries and state agricultural departments to try to improve legislation and control over the breeding and marketing of frogs,” said producers. exchanging animals based on the mistaken idea that this increases their genetic diversity.” The study showed that frog farms only fostered the same low genetic diversity populations by exchanging animals. This practice does not necessarily have economic or financial disadvantages. Brazil currently produces 400 metric tons of meat Frogs annually, all sold in the domestic market.
“Interest in preventing diseases caused by chytrid and ranavirus is emerging. Not many producers can sell all the meat they produce. Control and inspection must be greatly improved. An alternative strategy is to develop the industry if major meat manufacturers are interested in the product. In this case High sanitary standards must be applied by producers and consumers alike.
Reference: Jorgewich-Cohen G, Toledo LF, Grant T. Genetic composition of American frog populations in Brazil. science delegates. 2022; 12 (1): 9927. doi: 10.1038 / s41598-022-13870-2.
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