Discovery of a new snake species in Myanmar

 New Species of Snake Discovered in Myanmar, looks like multiple species at once       

Finding and describing new species can be a tricky endeavor. Scientists typically look for distinctive characters which can differentiate one species from another. However, variation is a continuum that is not always easy to quantify. At one extreme, multiple species can look alike even though they are different species, these are known as cryptic species. At the other extreme, a single species can be highly variable, creating an illusion of being different species. But what happens when you encounter both extremes simultaneously? Scientists have uncovered a fascinating new species of pit viper in Myanmar which seems to blur the very definition of what a species is. This snake, now named the Ayeyarwady pit viper, puzzled researchers because it looks like a mix between two known species, sometimes resembling one, sometimes the other, and occasionally something in between. Initially suspected to be a hybrid, genetic analysis revealed it is actually its own distinct species.

Identifying a new species is not always straightforward. Scientists usually rely on physical traits that separate one species from another, but in nature those differences do not always fall into neat categories. Sometimes two different species look almost identical. These are called cryptic species. In other cases, a single species can vary so much in appearance that it seems like several different species instead. The challenge becomes even greater when both patterns show up at the same time. The Ayeyarwady pit viper, a new species discovered in Myanmar by Dr. Chan Kin Onn, illustrates the complexities of species differentiation in pit vipers. This species, which displays traits of both the redtail and mangrove pit vipers, was initially thought to be a hybrid but was confirmed as distinct through genomic analysis. Herpetologist Dr. Chan Kin Onn (previously at the Lee Kong Chian Natural History Museum, Singapore, now with the University of Kansas Biodiversity Institute and Natural History Museum, USA) led research on a pit viper from Myanmar which seemed to be both similar to and distinct from its closest relatives. The work was published in the open access journal ZooKeys, building on an earlier genomic study in Systematic Biology which had already indicated the snakes represented a separate evolutionary lineage.

"Asian pit vipers of the genus Trimeresurus are notoriously difficult to tell apart, because they run the gamut of morphological variation. Some groups contain multiple species that look alike, while others may look very different but are actually the same species," they say. The redtail pit viper (Trimeresurus erythrurus) occurs along the northern coast of Myanmar and is invariably green with no markings on its body. A different species called the mangrove pit viper (Trimeresurus purpureomaculatus) occurs in southern Myanmar. This species typically has distinct dorsal blotches, and incredibly variable dorsal coloration including gray, yellow, brown and black, but never green. Interestingly, in central Myanmar, sandwiched between the distribution of the redtail pit viper and the mangrove pit viper, a unique population exists which is green with varying degrees of blotchiness, which appears to be a blend between the redtail pit viper and the mangrove pit viper. The story became even more interesting when the team examined the snakes' physical features in more detail. They found that this newly recognized species is also highly variable in appearance. Some populations are dark green with obvious blotches, making them fairly easy to distinguish from the redtail pit viper, which is bright green and unmarked. But other populations are bright green and lack blotches, making them look almost identical to the redtail pit viper.

"This is an interesting phenomenon, where one species is simultaneously similar and different from its closest relative (the redtail pit viper). We think that at some point in the past, the new species may have exchanged genes with the redtail pit viper from the north and the mangrove pit viper from the south," says Dr. Chan. That interpretation is consistent with the previous genomic study, which focused on species delimitation in this pit viper group while accounting for gene flow. One close relative, the redtail pit viper (Trimeresurus erythrurus), lives along the northern coast of Myanmar and is consistently bright green with no body markings. Another, the mangrove pit viper (Trimeresurus purpureomaculatus), is found in southern Myanmar and usually has dark blotches along its back. Between those two ranges, in central Myanmar, researchers found an unusual population of green snakes with different amounts of blotching. At first glance, they looked like a blend of the two known species. 

"This mysterious population in central Myanmar baffled us and we initially thought that it could be a hybrid population," the researchers said. But the earlier genomic analysis showed something more surprising. The snakes were not hybrids. They represented a distinct species of their own. The new snake was named the Ayeyarwady pit viper (Trimeresurus ayeyarwadyensis), after the Ayeyarwady River, the largest and one of the most important rivers in Myanmar. Its broad delta lies between the Pathein River to the west and the Yangon River to the east. Those river systems and their surrounding basins also mark the westernmost and easternmost known distribution limits of the species described in the study. In a separate paper, Dr Chan used modern genomic techniques and determined that the population in central Myanmar was actually a distinct species. But this was not the end of the story. The researchers discovered another surprise when they examined the snake’s morphological features: they found that the new species was also highly variable. Certain populations are dark green with distinct blotches, easily distinguishable from its closest relative, the redtail pit viper, which is bright green with no blotches. However, some populations of the new species are bright green with no blotches and look virtually identical to the redtail pit viper.