In 2016, scientists discovered a new species of tree frog with sepia-colored skin on an expedition in the rainforests of New Guinea. The frog—dubbed the "chocolate frog," or Litoria mira, by researchers—was found in an unusual swampy area. After extensive DNA analysis, they found that the new species is actually related to the Australian green tree frog (Litoria caerulea), reports Amy Woodyatt for CNN.
Researchers suspect the previously unidentified cocoa-colored species may be widespread across New Guinea and possibly diverged from frogs in Australia. The study was published last month in the Australian Journal of Zoology.
"What's a little surprising about this discovery is that the well-known and common green tree frog of Australia has a long-overlooked relative living in the lowland rainforests of New Guinea. Because of this, we named the new frog Litoria mira because the word Mira means surprised or strange in Latin," the study's first author Paul Oliver, a phylogeneticist at Griffith University, says in a statement.
The researchers were interested in revealing the green tree frog's lineage. They searched for amphibians within both savannah-like and swampy ecosystems of New Guinea. In each ecosystem, the team collected frogs and recorded their mating calls. When analyzing the data, they found that in the southern savannah-like ecosystem, L. caerulea frogs were most common, reports Jacinta Bowler for Science Alert.
But in the boggy terrain of northern New Guinea, the researchers stumbled upon the chocolate frog. They noticed that while it appeared similar to L. caerulea and had an almost identical mating call, it was smaller and a uniform brown color, Brandon Specktor reports for Live Science. When they took a closer look at the brown frogs genese, the scientists found that L. mira is closely related to its greener cousin, L. caerulea, which is found throughout northern and eastern Australia and in southern New Guinea, Live Science reports.
Northern Australia is located 80 nautical miles from New Guinea. Around 10,000 years ago, both of the islands were connected by a land bridge called the Sahul Shelf, so it is no surprise that there are various lineages of closely related animals in Australia and New Guinea, per Live Science. The find suggests that the two frog species diverged 2.6 to 5.3 million years ago during the Pliocene Epoch—before Australia and New Guinea were separated by water—causing the two species to become distinct from one another, reports Hannah Seo for Popular Science. During the expedition, the team also found and cataloged 29 related species of green tree frogs in New Guinea, Live Science reports.
"While New Guinea is not a place most Australians know well, many animal groups are shared. So understanding biodiversity in New Guinea helps us to understand the history and origins of Australia's unique fauna," study co-author Steve Richards of the South Australian Museum says in a statement.