The Eastern indigo snake, Drymarchon couperi, is not only magnificently beautiful but also non-venomous, non-aggressive towards humans, and federally listed as a threatened species. Despite this protection status, the numbers of Eastern indigos are decreasing. In 2015, I had the extraordinary opportunity to volunteer with the Orianne Society https://www.oriannesociety.org/,  a non-profit dedicated the amphibian and reptile conservation, in their annual Indigo Days surveillance count.

Most people present had been on several of these indigo days counts, but I was a newbie. We broke into groups and were given transect assignments with the instructions that if we saw an indigo, jump on it, gently hold it still, and shout out for help. Um, OK. These snakes are up to nine feet long and thicker around than my arm, but um, OK. Of course, the first indigo I saw I froze, but someone else gleefully jumped and pinned him down. Over the course of the day, we captured several indigos who all gently submitted to measurements, "wanding" to detect prior tagging, and if no tag, the insertion of a radio-tag. I was impressed by how gentle and calm these creatures were, and happily posed with one that displayed incredible structural color in the sunlight

Once released, the indigo sped back to his underground burrow, which is often shared with gopher tortoise, though we did not verify roommate status with this particular one. Another snake was faster than we and was halfway down his burrow before someone grabbed him by the latter 1/2 of his body. We were cautioned that trying to extricate the snake from the burrow could injure him, so reluctantly we let him go. But, never fear, gone from our hands but not from our observations! The Orianne Society trip leaders had brought a long scope with a video monitor so we could see him curled up deep inside his lair. If you are interested in seeing an indigo yourself, and maybe holding, measuring, and tagging one, log onto https://www.oriannesociety.org/ join the Orianne Society (only $30, a contribution to a good conservation cause), and watch for announcements of the next Indigo Days!

Don't Hold Your Breath! Article Review: Berman et al. (2019)

            A recently released article in Scientific Reports details an extreme amphibian adaptation. In a study entitled “The Siberian wood frog survives for months underwater without oxygen,” Berman and colleagues explore hypoxic resistance in the Siberian wood frog, Rana amurensis. Contrary to popular belief, Berman et al. (2019) demonstrates that the distribution of R. amurensis in northern Asia is not necessarily limited by oxygen depletion in waterbodies that do not freeze. Like other cold-tolerant ranid species, R. amurensis can survive in cold climates like Siberia’s by spending the winter months (overwintering) underwater where it does not freeze. Since R. amurensis can also overwinter on land, many scientists believed that this species was more cold tolerant that others, allowing it to occupy a large geographical range in northern Asia. However, other studies have shown that R. amurensis does not tolerate cold temperatures better than other ranid species. Perhaps the secret to its large distribution then, as this study investigates, is its ability to survive in severely hypoxic, if not anoxic, conditions. Berman et al. (2019) demonstrates that waterbodies in this species’ habitat range are indeed extremely hypoxic, reporting oxygen levels of 0.2-2.1 mg/L. Further, the research team exposed R. amurensis individuals to highly reduced oxygen levels of 0.1-0.2 mg/L in sealed containers. Frogs in these containers were able to survive up to 97 days, with reduction in activity only occurring toward the end of the experiment. Two individuals were also transferred from one of these containers to another with the same reduced oxygen level, but also with a highly reduced volume of water on day 54. These individuals survived for an additional 24-25 days. These results suggest individuals of R. amurensis can highly reduce their oxygen consumption while still remaining active and can potentially switch to anaerobic respiration.

Many aquatic turtles also demonstrate hypoxic resistance, but such a characteristic in Amphibia is little explored. This paper reports the first known case of extreme hypoxic resistance in amphibians that overwinter underwater. Such research lends itself to a number of subsequent questions. Do any other amphibian species exhibit extreme hypoxic resistance? What physiological mechanism allows R. amurensis to survive in these conditions? Certainly these questions and more merit further research into the extreme adaptations of amphibians. Nonetheless, this study sheds light on the many amphibian anomalies scientists have yet to discover and explore.

Berman, D. I., Bulakhova, N. A., & Meshcheryakova, E. N. (2019). The Siberian wood frog survives for months underwater without oxygen. Scientific Reports, 9, https://doi.org/10.1038/s41598-018-31974-6

https://www.nature.com/articles/s41598-018-31974-6