19

Chance, Myth, and the Mountains of Western China

In principle, biologists regard the world’s varied biota with equanimity, recognizing the equivalent intrinsic value of each species. In reality, however, biologists are like other people—we play favorites, and some species simply capture our interest and imagination more than others. Often these are the same iconic species that nonbiologists find engaging, like the giant panda, the platypus, and even the coelacanth, a fish heralded as a living fossil when it was captured by a commercial trawler along the South African coast in 1938. More often, however, biologists bestow their favoritism upon species that have some unusual characteristic of their anatomy, behavior, ecology, or physiology or that occupy a unique position on the evolutionary tree of life. If a species is also rare—or at least rarely encountered by scientists—so much the better. Among reptiles we can see these elements of subconscious favoritism play out in two species nested in the family tree of lizards. At 3 m in length, the Komodo Dragon (Varanus komodoensis) is the largest living lizard, and biologists are as enamored of it as are other people. However, a diminutive relative of that species, the Bornean Earless Monitor (Lanthanotus borneensis), is even more intriguing to many herpetologists, not only because of its extraordinary rarity but because, in the 1950s, two biologists described its anatomy and suggested it was the closest living relative of snakes. Although additional specimens have come to light in the intervening years, and it is no longer considered a missing link between lizards and snakes, the Bornean Earless Monitor has lost little of its fascination for herpetologists, a testament to the lasting impact of a compelling evolutionary story.

In a similar way, a strange viper from the mountains of Southeast Asia occupies a position on the boundary between science and myth, at least among snake biologists. In 1888, Belgian herpetologist George Albert Boulenger, then working at the British Museum (Natural History), was studying amphibians and reptiles collected in Burma by the Italian naturalist Leonardo Fea when he encountered a single specimen that he immediately recognized as unique. Boulenger assigned it to a new species and genus, Azemiops feae, now sometimes called Fea’s Viper. However, Boulenger initially seemed a bit uncertain as to its evolutionary affinities. He included the description of his new species in the section of his paper dealing with the Elapidae (cobras and their relatives), yet he noted its similarity to the most basal group of vipers, the night adders (Causus) of Africa. Complicating Boulenger’s interpretation was his belief that the new species’ closest relative was in fact a genus and species only recently described from Venezuela, known from a single specimen that had reached the German herpetologist Wilhelm Peters after arriving in Hamburg with a shipment of lumber. Within a few years, however, Boulenger realized that the purported South American locality for Peters’ specimen had been incorrect and that Peters’ specimen, in fact, belonged to a previously described species of African night adder. In 1890 Boulenger unequivocally included Azemiops feae as a basal member of the Viperidae, unusual among vipers in having smooth, rather than keeled, dorsal scales. He also described its un-viperlike appearance, with a narrow head and a color pattern of dark gray with narrow light crossbands that were often broken and offset at the middle of the back.

Despite its uniqueness, Fea’s Viper resided in biological obscurity until 1971. Herpetologists George Rabb and Hymen Marx had been studying the evolution of vipers, especially the Old World subfamily Viperinae. The other subfamily, the Crotalinae, is believed to have arisen in eastern Asia and expanded into the New World, where it radiated explosively into such iconic groups as rattlesnakes and bushmasters. Known as pit vipers, the Crotalinae are named for the prominent pit organs in front of the eyes, which are exquisitely sensitive to infrared radiation, the wavelengths of radiant heat that emanate from their largely mammalian prey.

In those pre-genomic days, Marx and Rabb had gathered a large anatomical data set and were exploring new methods to infer evolutionary relationships from the quantitative analysis of morphology. They had identified the most basal members of both subfamilies of vipers, but Fea’s Viper was in a class by itself. Known from only a few specimens and limited to the mountainous border region of China and adjacent countries, its external characters were less viper-like than any other member of the family, and its skull was mystifying. Fea’s Viper was clearly not a pit viper, since it had no pit organs, but its skull had characteristics of the Crotalinae, not the Viperinae. It was, in some sense, a pitless pit viper. Marx and Rabb enlisted ichthyologist Karel Liem, a gifted morphologist who had trained under herpetologist Hobart Smith, to study the anatomy and phylogenetic position of Boulenger’s distinctive viper. They placed it in a new subfamily all its own, the Azemiopinae, the first new subfamily of vipers in over a century. Fea’s Viper had emerged from obscurity to attain celebrity status among snake biologists. I was about to begin my graduate studies on the morphological systematics of snakes, and the 1971 publication by Liem, Marx, and Rabb was seared into my brain.

So the stage was set: a rare species from a remote region, with an unusual anatomy and a unique position on the snake tree of life. Unlike the Bornean Earless Monitor, which proved not to be especially close to the origin of snakes, Fea’s Viper has maintained its position as the so-called sister group to the pit vipers and still resides in its own subfamily. Over the years additional specimens came to light, and a few live individuals even made their way to researchers and zoos in the United States. Still more surprisingly, a second species was described in 2013, based on specimens from northern Vietnam. Even so, few Western biologists had encountered Fea’s Viper in the wild. I had seen one at the Dallas Zoo years ago, among the first live specimens to reach the United States—fascinating but somehow diminished in its captive circumstances. Still, like a platypus to a mammologist or a condor to an ornithologist, it occupied a prominent and, it turned out, a readily accessible shelf in my deep memory.

Many years had passed since I thought about Fea’s Viper, aside from mentioning it occasionally in passing when discussing snake diversity in my herpetology class. My research interests had also evolved, from anatomy to conservation and eventually to chemical ecology. I had been working for about 20 years with my colleague and friend, Akira Mori of Kyoto University, on the chemical defenses of a group of Asian snakes, members of the same subfamily that includes the gartersnakes of North America. Nestled within that subfamily, the Natricinae, is Rhabdophis, a genus of so-called keelbacks that has evolved specialized structures in the skin that rupture when the snake is attacked, spewing a distasteful, irritating, and toxic fluid that deters the predator. The active ingredients in the fluid are bufadienolides, a class of toxins known primarily from toads, which manufacture them in the warty glands of their skin. The only other animals known to make bufadienolides are fireflies. Akira was very familiar with the sole Japanese member of the genus, the Yamakagashi (Rhabdophis tigrinus), which feeds primarily on frogs and toads. He had suggested in the 1980s that perhaps the snakes are capable of storing—or sequestering—bufadienolides from toads they consume as prey. After about a decade of work involving many students and collaborators, we had demonstrated that Akira was right about the source of the Yamakagashi’s toxins.

Subsequently, Akira had received grant support to study other species of Rhabdophis, and he had assembled a large team of colleagues working across Asia. An early goal was to clarify the evolutionary relationships of the natricines with skin glands, which proved to belong to a single lineage. That study also revealed that a group of species in western China had shifted their primary diet from frogs to earthworms. Surprisingly, the snakes are still toxic, but the worms they consume are not. Something else must be serving as the source of their defensive toxins, and we had traveled to China a few times to try to solve that puzzle. One clue was the odd chemical structure of the worm-eaters’ toxins, which included some compounds different from those of toads. Our studies ultimately revealed that the source of the distinctive toxins were firefly larvae, unusual prey for a snake.

Our Chinese collaborators were located in Chengdu, the capital city of Szechuan Province. The Chengdu Institute of Biology is renowned as a center of herpetological research, and from that base we traveled to neighboring regions, searching for species of worm-eating Rhabdophis. In September 2018 we were headed southwest to neighboring Yunnan Province for three intensive days of fieldwork in the mountains along China’s border with Myanmar. Our goal was to collect Leonard’s Keelback (Rhabdophis leonardi), a member of the worm-eating group that we had not yet seen. The species had been described in 1927 from a specimen collected a few kilometers across the border in what was then Burma. Our Chinese colleague Li Ding and two of his students had driven ahead with most of our gear, while we awaited a final permit required for international researchers. Akira, his former postdoc Teppei Jono, and I took an evening flight from Chengdu to Tengchong, a city known for pitched battles over control of the border region during World War II. We were met at the airport by a driver and one of the graduate students, Yige Piao, who had asked to be called Spoon, an English translation of a homophone for his name. We stayed that night at an odd little hotel where the stairway, floors, and bathroom were decorated in laminate proclaiming The Motorcycle Diaries, the 2004 film based on Ché Guevara’s memoir of his youthful journey across South America.

The next morning we drove west, past endless paddy fields, to Yingjiang, even closer to the Myanmar border. At midday we checked into the upscale and aptly named Xinhua Grand Hotel, from which we could drive to field sites in the mountains above the city. That afternoon we drove up Gongshan Mountain, a forested upland that stretches toward the nearby international border. After scoping out the terrain, still largely populated by Indigenous peoples, we stopped for a dinner of stir-fried dishes cooked behind an immense open-air counter heated from below by six wood-fired ovens. We road-cruised for several hours, finding only a large White-Banded Wolf Snake (Dinodon septentrionalis), which looked eerily like one of the species of venomous banded kraits (Bungarus). Aside from a few fireflies, which we needed for our chemical studies, we saw little of interest and returned to the hotel, exhausted, well after midnight.

The next morning we headed back up the mountain with Spoon and Cheng, the other student, while Ding stayed behind (the vehicle seated only five, so our three Chinese hosts rotated). It was cool and gloomy, with mist settling on the higher elevations as we visited a small sand quarry and, more interestingly, a Buddhist cemetery. Many of the ancient stone crypts appeared to emerge from the hillside like dormers on a pitched roof, their ancient stones supporting lichens, mosses, and ferns. Still, after finding no snakes we returned to town to recharge over a lunch of potstickers, boiled peanuts, and stir-fry.

Later that afternoon we again drove the switchbacks up Gongshan Mountain, revisiting the cemetery, with no luck. We returned to the quarry about 2000 hours, as the light was fading. It was decided that Ding would road-cruise on his own, while Akira, Teppei, Spoon, and I walked along the road to see what we could find at the edge of the dense forest. We spread out along both sides of the road, far enough apart to catch a glimpse from the nearest headlamp. I was walking downhill along the road, mainly staying on the more densely vegetated side from which the slope extended upward, occasionally stepping over the concrete drainage ditch that ran alongside the pavement. Such ditches are ubiquitous on montane roads that cut through the wet forests of eastern Asia. For all the walking, I saw no vertebrates whatever. Those adjacent to me on the road also saw little, although Teppei collected several genera of firefly larvae.

Eventually the person below me turned and trod back up the road, and the ones above me descended until we had all gathered. Akira had been the farthest upslope and, unlike the rest of us, had made two excellent captures, a slug snake, belonging to the complex and bewildering genus Pareas, and a Mountain Pitviper (Ovophis monticola). We crowded together to examine Akira’s catch, admiring both of his snakes when, for no particular reason, I happened to glance to the side. In that moment, the beam of my headlamp landed on a slender, gray body with narrow, widely spaced light crossbands, moving slowly uphill in the drainage ditch. Its head was already under a mat of accumulated vegetation, but I didn’t need to see it. It had not occurred to me until that moment that we were within the range of Fea’s Viper, but the mental image seared in my memory in college came immediately to my consciousness. With all the alacrity a 68-year-old could muster, I jumped into the ditch and shouted to Spoon to pass me his tongs. With shockingly little effort, I grabbed the snake with the tongs as it continued pushing under the vegetation, then lifted it onto the road, where it was quickly bagged. In the space of a minute, the evening had been transformed from an uneventful roadside stroll to an encounter with a mythical serpent.

We walked back uphill as a group, continuing to scan the roadsides, as I replayed the short mental tape of the snake’s capture over and over. Soon after we had returned to the quarry Ding arrived at the rendezvous point, having found two leaf-green snakes, a Green Cat Snake (Boiga cyanea) and a spectacular red-eyed Yingjiang Green Pitviper (Trimeresurus yingjiangensis), a species that would not be described until the next year from other specimens collected in the region. We spent over an hour photographing our catch, of which I was naturally most intrigued by the Fea’s Viper. Its blue-gray dorsal color and narrow reddish-orange bands made it unmistakable, and its spectacular facial coloration, with bold orange stripes against a gray field and shockingly white eyes, seemed in that moment to be the most beautiful I had seen on any reptile.

We still had not seen a single Leonard’s Keelback, but the trip was suddenly a complete success from my perspective. The following evening, our last night on Gongshan Mountain, our luck changed, and we found two subadult Leonard’s Keelbacks on the road, the first one alive and the second freshly killed but still in good condition. We were able to get samples of their defensive chemicals from both and stomach contents from the live one, which contained both an earthworm and a firefly larva. We flew back to Chengdu the following afternoon and two days later left China for Japan.

So much of our lives is governed by chance, and I think of the confluence of unlikely events that put me at that precise point along the road up Gongshan Mountain, admiring Akira’s catch, just as the Fea’s Viper was passing by. I think of its unhurried movement and the fact that it was constrained within the cement drainage ditch, limiting its options for escape. Most of all, I think of my sidelong glance, for no reason I can recall, and the instant recognition of a color pattern I’d scarcely thought about in years. Snakes of all sorts are fascinating, and many are beautiful, but having the privilege to find one that is also rarely encountered—an object of myth and legend, not to mention desire—alongside the road in the misty borderlands of China was a special gift.