The stonefly is the largest animal inhabiting the glaciers of Patagonia. What the inch-long insect eats and excretes on the ice is central to the overall glacier ecosystem. Also known as the Patagonian Dragon, the stonefly occupies a near-apex position in the truncated glacier food chain. Stonefly larvae develop in glacial meltwater pools, where the larvae spends most of its life as a waterbound nymph, consuming algae, fungi, and other small inhabitants found in cryoconite sediments. The wingless adults wander the ice surface in search of food and mating opportunities. Despite their significant influence on glacier biogeochemical cycles, glacier invertebrates like the stonefly and their associated bacteria remain understudied. New research published in the journal Environmental Microbiology provided the first look at the genetics underlying the gut microbiome of stonefly nymphs.
The research team, comprised of Japanese and Chilean scientists, traveled by horseback and camped at Tyndall Glacier in Chile, collecting samples for analysis in a Tokyo laboratory. The team were surprised to find some bacteria in the stonefly gut were not present on the glacier surface. Not only was the bacteria absent from the surface of the Tyndall Glacier, but they were also distinct from bacteria catalogued in other glacier environments, indicating a symbiotic relationship between the Patagonian stonefly nymph host and its gut bacteria. The stonefly nymph provides an enriching gut environment and in turn the bacteria aids in the insect’s nutrition and material cycle of the glacier environment.
Insects and animals, including humans, host a variety of microorganisms in their digestive tracts. These microorganisms and other bacteria, called gut flora, help perform a variety of functions critical to the health of their host. For example, humans lack enzymes necessary to break down certain fibers, starches, and sugars. Our gut flora keeps us healthy and enables us to ingest a wide range of foods we would otherwise be unable to digest. Similarly, the stonefly’s gut community enables it to benefit from seemingly nutritionless cryoconite sediments.
According to Takumi Murakami, from Japan’s National Institute of Genetics and principal author of the study, glacier stonefly nymphs and their gut bacteria likely drive the decomposition of organic materials on the glacier. The gut bacteria-invertebrate symbiosis may even be a common phenomenon in glacier ecosystems beyond Patagonia. Understanding the role of high trophic level invertebrates, like the stonefly, and their bacteria in glacier ecosystems is key to understanding the big picture of glacier nutritional networks.
Japanese scientists have compiled a significant body of research on invertebrates and their gut flora, particularly those inhabiting glaciers. In 1984, Japanese researcher Shiro Kohshima documented a novel discovery on a visit to the Yala Glacier in Nepal; a cold-tolerant midge. Later he visited Patagonia to examine the glacier-indigenous insects of the region. Kohshima enlisted collaborators, who in turn brought their students, which has resulted in the present day team of glacier-insect specialists, including Murakami. Their diligence in studying glacier ecosystems has produced a prolific body of published work, helping fill knowledge gaps at the headwaters of organic decomposition.
Further underscoring the importance of the research, Murakami told GlacierHub, “Recent studies suggested that glacier ecosystems are the source of nutrition for downstream soil, river, and ocean ecosystems.” Were it not for the bacteria inhabiting the gut of the Patagonian Dragon, the organic matter would not be processed, and thus would not contribute to the glacier or downstream ecosystems.
Murakami adds, “Since glacier environments are susceptible to climate change, it is essential to accumulate the knowledge on the current glacier ecosystems for future studies, otherwise we will lose the opportunity.” Murakami’s concern is not unfounded. In the U.S., the stonefly is the poster child of understudied species that are quickly disappearing due to rapidly changing habitats. Petitions listing two species of stonefly under the Endangered Species Act are under consideration.