Bullfrogs are considered the world’s first invasive amphibian. The American bull frog (Aquarana catesbeiana) is native to North America and was first introduced to Rio de Janeiro, Brazil in 1935 to produce meat. Now it is cultivated throughout southern and southeastern Brazil, but has also spread into the wild, negatively impacting local ecosystems by competing with native species for food and other resources, feeding on other frogs, as well as snakes, birds and even some mammals and spreading fungal and viral diseases to which local species have little or no immunity.
Recently, a team of researchers from the University of São Paulo (USP) and the State University of Campinas (UNICAMP) conducted the most comprehensive genetic analysis of the American bullfrog and discovered that there are two populations of this species in Brazil, living in frog farms or invading local ecosystems.
“We have confirmed the existence of at least two different populations of bullfrogs. One is probably descended from the first bullfrogs introduced to Brazil. This population is present in practically all of the South and Southeast. The other is mostly confined to the state of Minas Gerais, but occurs in small numbers in other states,” said study lead author Gabriel Jorgewich-Cohen, a former master’s student in biology at USP and currently a doctoral student at the University of Zürich.
“Our results show that captive and invasive bullfrogs are genetically indistinguishable, reinforcing the importance of preventing escape from farmed frogs,” added study lead author Taran Grant, professor of ecology and of evolutionary biology at the same university.
By analyzing specific genes in 324 tissue samples from 38 sites where captive and wild bullfrogs are found, scientists found that the vast majority belonged to the same population descended from animals brought from North America in 1935. another population descended from a batch of bullfrogs brought in the 1970s to Minas Gerais.
“The results of genetic analyzes are consistent with these two more documented introductions, although there is anecdotal evidence from others in the 1980s and 2000s, and isolated initiatives by some growers. If there were other introductions, the animals involved could have had the same origin or interbred and merged with the existing population. Alternatively, we just didn’t take samples from those people,” Jorgewich-Cohen explained.
Since these bullfrogs can transmit pathogens, such as amphibian chytrid fungi or ranoviruses – which often end up decimating immunologically naive local populations – it is very important to prevent farmed bullfrogs from escaping from farms and to enforce high sanitary standards by producers and consumers.
The study is published in the journal Nature Science Reports.
By Andrei Ionescu, Terre.com Personal editor