Inside the Gut of the Patagonian Dragon

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.

The Tyndall Glacier is one of the largest glaciers in the Southern Patagonian Ice Field (Source: Takumi Murakami).

 

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.

Stonefly nymphs and cryoconite sediment in a meltwater pool (Source: Takumi Murakami).

 

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.

(Source: Nicolas Ferrier/Instagram)

 

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.

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Glacier Retreat Threatens Insect with Extinction

As glaciers retreat, a species of glacier-dependent stonefly faces extinction.

In 2010, the Center for Biological Diversity petitioned for Zapada glacier, a western glacier stonefly only found in alpine streams of Glacier National Park, Montana, to be listed as endangered species under the U.S. Endangered Species Act. This species – one of more than 3500 species of stonefly –  is highly restricted to cold, glacial meltwater with limited dispersal ability.

stonefly
Zapada glacier adult female from the Grinnell Glacier Basin in Glacier National Park (approximate length is 12 mm) (Source: Giersch et al./Freshwater Science).

Now, in an effort to save this endangered stonefly, the Center for Biological Diversity filed a lawsuit against the U.S. Fish and Wildlife Service to address the urgency of protecting this stonefly. The insect could potentially be taken to other clean cold streams outside its established range, perhaps further north or at higher elevation where it might survive – but time is running out.

Species evolve to survive in specific temperature ranges; however, when the environmental conditions have exceeded the range, species are unable to adapt to new conditions immediately. Climate change has put many species in danger, but this is the first time that an insect species has been threatened with extinction by glacier retreat.

“Protection can’t come soon enough for this stonefly,” said Tierra Curry, a senior scientist at the Center for Biological Diversity. “Glacier National Park will have no glaciers in 15 years if we don’t take action to curb climate change.”

Stoneflies are a particularly ancient order of insects that spend most of their lives in water. They are considered the most sensitive indicators of water quality in streams as they require fresh, clean water and don’t tolerate pollution. The insects have a one to two-year life cycle starting in the nymph stage in fresh meltwater. They usually emerge from the water in late spring when the stream is uncovered by melting snow. Z. glacier has a narrow temperature preference around 3.3 degrees Celsius. It is this narrow temperature preference that makes this insect especially susceptible to climate change.

Between 1960 to 2012, the average summer temperature in Glacier National Park has risen by approximately 1 degree Celsius. Additionally, since 1850, 125 of the 150 glaciers in Glacier National Park have melted away while the remaining 25 are predicted to disappear by 2030. The loss of glaciers as well as restricted suitable environmental conditions and limited dispersal ability of the stonefly threaten the species’ ability to survive.

Many Glacier in GNP (Source: Esther Lee/Flickr).
Glaciers in Glacier National Park (Source: Esther Lee/Flickr).

Few studies have investigated the impacts of climate change on alpine species distributions. To compensate for this knowledge gap, J. Joseph Giersch from US Geological Survey and other researchers looked at the current status and distribution of Z. glacier. Their results were published in Freshwater Science.

Giersch et al. sampled 6 alpine streams, where Z. glacier was historically known to live, to examine the relationship between species occurrence and environmental variations of temperature and glacial extent. In order to identify the current geographic distribution and distinguish Z. glacier from the other 6 Zapada species in Glacier National Park, the researchers used morphological characteristics, the outward appearance of adults and the DNA of nymphs.

Giersch et al. identified 28 suitable alpine locations in Glacier National Park as potential habitats for Z. glacier. From this study, Z. glacier was only found in 1 of the 6 historically occupied streams – the outlet of Upper Grinnell Lake. The results suggest increased temperature and glacier retreat have already caused local extinction of Z. glacier from several historical locations.

Upper Grinnell Lake in Glacier National Park, where Zapada glacier can be found (Source: GlacierNPS/Flickr).
Upper Grinnell Lake in Glacier National Park, where Zapada glacier can be found (Source: GlacierNPS/Flickr).

The stonefly was also detected in 2 new high-elevation locations in Glacier National Park. Therefore, only 3 out of the 28 potential habitats have Z. glacier. The results indicate that the historical distribution of this stonefly in Glacier National Park was already restricted and its distribution will be further reduced in the future due to increased stream temperatures and habitat loss.

“The plight of the glacier stonefly is a wakeup call that unless the United States takes major action to reduce our greenhouse gas emissions, this special insect and more than one-third of all plants and animals on Earth could go extinct by 2050,” said Curry.

For more stories on invertebrates near glaciers, read here and here.

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