Finding and describing new species is a tricky business. Scientists often look for unique characteristics that distinguish one species from another. However, variation is a continuum and is not always easy to quantify. At one extreme, multiple species that appear similar despite being different species are known as cryptic species.

The new species of Irrawaddy viper discovered by Dr. Chen Jianan in Myanmar illustrates the complexity of viper species differentiation. The species, which has characteristics of both red-tailed bamboo and mangrove bamboo, was initially thought to be a hybrid, but genome analysis confirmed it was distinct. Image source: Wolfgang Wüster

At the other extreme, individual species can be so variable that they give the illusion of separate species. But what happens if you encounter these two extremes at the same time?

A study led by herpetologist Dr. Chan Kin Onn (formerly of the Lee Kong Chian Museum of Natural History in Singapore and now at the Institute for Biodiversity and the Museum of Natural History at the University of Kansas in the US) describes a new species of pit viper in Myanmar that is both similar and distinct from its sister species. The findings were published in the open-access journal ZooKeys.

Challenges in distinguishing Asian pit vipers

"Asian pit vipers of the genus Bamboo are notoriously difficult to distinguish because of their variable morphology. Some groups contain multiple similar-looking species, while other groups contain species that look very different but are actually the same species," they said.

Trimeresuruserythrurus is distributed in the northern coastal areas of Myanmar. It is completely green and does not have any markings on its body. There is also a mangrove species in southern Myanmar called Trimeresurus purpureomaculatus. This viper usually has distinct spots on its back, and its back can vary in color, including gray, yellow, brown and black, but never green. Interestingly, in central Myanmar, sandwiched between the distribution areas of red-tailed Bamboo-leaf and mangrove Bamboo-leaf-green, there exists a unique population, which is green with varying degrees of spots and appears to be a mixture of red-tailed Bamboo-leaf and mangrove Bamboo-leaf.

A specimen of Trimeresurusayeyarwadyensis at Meinmahla Kyun Wildlife Sanctuary, Pyapon District, Ayeyarwady Region, Myanmar. Image source: Hlatun

The researchers said: "This mysterious population in central Myanmar puzzled us, and we initially thought it might be a hybrid population. In another paper, Dr. Chan used modern genomic technology to determine that the population in central Myanmar was actually a unique species rather than a hybrid population."

But that's not the end of the story. The researchers discovered another surprise while studying the snake's morphological characteristics: They found that the new species was also highly variable. Some species are dark green with noticeable spots, easily distinguishable from their close relative, the red-tailed sagebrush, which is bright green with no spots. However, some populations of the new species are bright green, without spots, and look almost identical to the red-tailed bamboo leaf green.

Dr. Chen said: "It is an interesting phenomenon that a species is both similar and different from its close relative (Red-tailed Bamboo Leaf Green). We believe that at some time in the past, the new species may have exchanged genes with the Northern Red-tailed Bamboo Leaf Green and the southern mangrove Bamboo Leaf Green."

The new species is called Trimeresurusayeyarwadyensis, a reference to the Ayeyarwady River, one of Myanmar's largest and most important rivers. The Ayeyarwady River forms a vast delta, bounded by the Badlin River to the west and the Yangon River to the east. These rivers and their associated watersheds are also the westernmost and easternmost areas of Ayeyarwady's Ayeyarwady distribution.

Compiled from //scitechdaily