Named Adenomera varcena, the frog was found during field expeditions in the Upper Juruá River region of western Acre, Brazil. Researchers surveyed forest fragments near the Moa and Crôa rivers, close to the city of Cruzeiro do Sul.
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At first glance, A. varcena looks similar to closely related frogs, but a combination of DNA analysis, recordings of its distinctive call, physical characteristics and habitat information revealed that it represents a previously unknown species.
The study, published in Ichthyology & Herpetology, involved scientists from institutions including Federal University of Minas Gerais (UFMG), São Paulo State University (UNESP), the University of São Paulo, the Federal University of Uberlândia and the Pontifical Catholic University of Ecuador.
The frog belongs to the genus Adenomera, a group generally associated with dryland forests. Its presence in seasonally flooded forest therefore reveals a previously unknown habitat association for the genus. Its scientific name refers to the Amazonian floodplain forests where it was found – ecosystems that are submerged during parts of the year.
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Several features help distinguish A. varcena from its close relatives, including the absence of a dark spot on the underside of its forearm and a distinctive mating call.
The frog produces a short call at a relatively slow rhythm, along with other acoustic characteristics that allowed scientists to separate it from species that are almost indistinguishable by appearance alone.
This phenomenon, known as cryptic diversity, occurs when organisms that look very similar are actually genetically distinct species. It means biodiversity surveys based solely on physical appearance can miss species hiding in plain sight.
Researchers do not yet know enough about A. varcena’s ecology or reproductive behaviour to predict how it will respond to climate change. However, because it appears to be associated with seasonally flooded forest, changes to the timing or extent of flooding could potentially affect its reproduction.
“Species may become locally extinct even before they're formally recognised as species through their naming and description,” said Thiago R. Carvalho, a professor at the UFMG and one of the researchers involved.
The team of scientists also identified evidence of several Adenomera lineages that have yet to be recognised as separate species.
Top image: Adenomera varcena. Credit: CBioClima
