New Amazon frog species discovered by its slow 'lazy' song
Scientists have identified a new species of cryptic frog in the Amazon floodplains, distinguished primarily by its unusually slow and infrequent mating
A new species of frog has been discovered in the Amazonian floodplain forests of Ecuador and northwestern Brazil. The tiny brown frog, named Adenomera varcena, is distinguished not by its appearance but by its remarkably slow and infrequent mating call.
Lead author Marianna Borburema, a researcher at the University of São Paulo, told Mongabay she finds the frog beautiful despite its unassuming looks. She spent three weeks analyzing its sounds. "Because of natural selection, the pressure isn’t on the frog’s appearance, it’s on the call," Borburema said. She explained that evolution happens faster in their call because the song is what interests the female.
A Cryptic Species
The frog is considered a cryptic species, meaning its external traits are very similar to those of related species. It is roughly 22 to 24 millimeters long with brown skin and dark blotchy patterns. Scientists identified A. Varcena as one of nine genetically distinct groups within the Adenomera simonstuarti species complex.
The species was first flagged by co-author Thiago Carvalho, a herpetologist at the Federal University of Minas Gerais. Carvalho and colleagues outlined potential lineages using DNA analysis in 2020. They collected more samples in the seasonally flooded forests near the upper Juruá River in Brazil in 2021.
The 'Lazy' Call
The frog's call is its most defining characteristic. Related species in the genus typically call frequently, some producing up to 70 notes per minute. In stark contrast, the songs of A. Varcena include just one to five notes per minute. This is the slowest rate documented in the genus.
Each note lasts less than a tenth of a second and lacks the pulsing rhythm found in most of its relatives. "It’s as if the frog is feeling lazy," Borburema remarked. The following table compares the call rates:
| Species Group | Typical Call Rate (notes per minute) |
|---|---|
| Related Adenomera species | Up to 70 |
| Adenomera varcena | 1 to 5 |
A Unique Habitat
A. Varcena is the only species in its genetic lineage to live in floodplains. All of its closest relatives inhabit dry land forests. This ecological separation in the Amazon basin likely contributed to its distinct evolutionary path.
The discovery shows the hidden biodiversity within the Amazon. Borburema emphasized the importance of studying such species. "Even though it’s a small, brown frog that doesn’t call much, it is worthy of being studied, it is worthy of being known, and more than that, it is worthy of being protected," she said. She added that a species can only be protected if it is known.
The research team's work, including genetic analysis and acoustic studies, was essential in distinguishing this new frog from its look-alike cousins. The finding adds another piece to the complex puzzle of Amazonian ecology.
