Four new species of see-through frogs, three of which reveal green bones, have been discovered by researchers in northern Peru.
Showing their beating hearts and other body organs in x-ray detail, the newfound amphibians belong to the aptly named glass frog family (Centrolenidae).
Uncovered during extensive surveys in the Peruvian Andes, the “four remarkable species” were described August 12 in the journal Zootaxa.
The tiny frogs, which live alongside streams, include Centrolene charapita—named for a chili pepper that the yellow splotches on the back of this species resemble. Curiously, the two specimens that were collected had hind legs lined with fleshy, zigzag protuberances.
“We have no clue” why that is, acknowledged study co-author Santiago Castroviejo-Fisher, a herpetologist at Pontifícia Universidade Católica do Rio Grande do Sul in Brazil. Of the 150 known species of glass frogs, “less than ten have such ornamentation,” he said.
Fellow discoverer Evan Twomey, a frog researcher at East Carolina University in North Carolina, speculated that the leg frills could help to break up the frog’s outline and mask it from predators. “That’s a possibility, but it’s hard to know,” he said.
Cochranella guayasamini, which like many glass frogs is mostly green where it isn’t see-through, has distinctive yellow circles around the eyes. However, its tadpoles—which emerge from spawn laid on leaves overhanging mountain streams—are a vivid reddish pink before later turning green, according to the study.
The team said this gaudy coloring could be explained by a ramped-up system of blood vessels in the transparent tadpoles’ skin, which enable them to live in oxygen-poor sediments in the streambed.
But again, that’s only a guess: Glass frog tadpoles have barely been studied, and their natural history remains largely unknown, Twomey said.
A third new species, Chimerella corleone, owes its mafia clan title to one team member’s obsession with The Godfather novel and film trilogy.
Detected only in the spray zone of waterfalls, the frog hardly looks menacing considering it’s just two centimeters (0.79 inches) in length. However, it does happen to conceal a spike-like bone in its upper arm, Twomey said.
“I guess it’s used for fighting between males,” he added. “So, for a frog that size at least, I’d say it’s fairly ruthless.”
C. corleone, along with the two species so far mentioned, were found to have green bones—a bizarre trait that’s actually widespread among glass frogs. The research team suspects the strange bone coloration is caused by an accumulation of a metabolic byproduct called biliverdin, a green bile pigment.
Green Bones Puzzle
Whether having green bones might in some way be advantageous to the frogs hasn’t been studied, Castroviejo-Fisher said, but “I have noticed that most frogs with green bones are arboreal [dwell in trees].”
The fourth newly described species, Hyalinobatrachium anachoretus, was recorded in cloud forest at an altitude of 6,725 feet (2,050 meters). Other known species in this genus are found up to a maximum elevation of 3,280 feet (1,000 meters), so the find was “very unexpected,” Castroviejo-Fisher said.
The team discovered this frog in large numbers, but only on one particular night. Other nighttime surveys of the same area failed to turn up a single specimen.
The bigger mystery scientists are struggling to solve is why these and other glass frogs allow us to see straight though them. “Without a doubt, the adaptive, developmental, and genomic basis for the transparency of glass frogs is a long-standing question in zoology,” Castroviejo-Fisher said.
In the meantime, the backlog of undescribed glass frogs in South America is mounting. “We have a bunch of new species awaiting description in our offices,” Castroviejo-Fisher said.
The see-through frogs clearly have a lot more to reveal.