Article: Microbial Species-Area Relationships in Antarctic Cryoconite Holes Depends on Productivity by Sommers and colleagues (2020)
Background: Glacial ecosystems offer unique opportunities to study microbial life in extreme conditions absent of larger multicellular populations (e.g., plants and animals). To better understand the geographic distribution of microbial communities (i.e., biogeography), it is important to research similar microbial communities across different geographic ranges with few differing environmental factors. As such, Sommers and colleagues analyze Antarctic cryoconite holes, which are naturally formed holes found in glaciers that are made up of microbes, partially degraded organic matter, and small rock particles. Between different cryoconite holes, they study a phenomena known as island species-area relationship (ISAR). ISAR asserts that larger islands (i.e., isolated habitats) have a greater number of species than smaller islands due to the presence of more resources. Each cryoconite hole compared represents a singular ‘island’ in this model, and factors, such as community evenness (i.e., how close in number the population of each species of a community are) and DNA concentration, will represent differences in island productivity and microbial diversity between holes.
Methods: Sommer and colleagues collected cryoconite hole samples using a corer from Taylor (less productive; n = 11) and Canada (more productive; n = 23) glaciers in Taylor Valley, Antarctica. Sediment samples from each cryoconite hole were isolated and measured for organic matter content. DNA was extracted from each sample and sequenced to determine DNA concentration and the diversity of bacteria and eukaryote species. ISAR was calculated using species number, cryoconite hole area, and other parameters. Factors such as DNA concentration and community evenness were compared to the ISAR.
Findings: Species diversity was higher in cryoconite holes with greater areas on both glaciers, but the increase was higher on the more productive Canada glacier than the Taylor glacier. This difference was significant for bacteria (p = 0.001) and eukaryote (p < 0.001) species; more bacteria than eukaryotic species were found at each hole at both glaciers. DNA concentration nor microbial community evenness contributed to the ISAR at either glaciers.
Conclusions: In Taylor Valley, Antarctica, the more productive (i.e., more photosynthetic microbial activity) Canada glacier was found to support cryoconite holes with greater bacteria and eukaryotic populations than the less productive Taylor glacier. Further, both cryoconite hole area and productivity were associated with increased species richness (i.e., diversity). Adjacent habitats, like streams and rivers, likely influenced the presence of specific species (e.g., cyanobacteria and microalgae) within the cryoconite holes. The ISAR model developed from the glacial microbial communities studied were similar to other ISAR models from non-microbial species and larger study sites, such as actual islands. Since the cryoconite holes were found to represent the ISAR similar to other studies, further ISAR research could be conducted to better understand glacial microbial biogeography and microbial ecology.
Figure: Cryoconite hole identification and extraction. (a) Dark blue circles allow for detection of cryoconite holes on glacier surface. (b) Birdseye view of collection team on glacier. (c) Coring of cryoconite hole sample. (d) Sample extracted from corer; the dark sediment was used for the analyses described. (e) Melted ice under the extracted cryoconite sediment during the summer.
Reference:
Sommers, Pacifica, et al. "Microbial Species–Area Relationships in Antarctic Cryoconite Holes Depend on Productivity." Microorganisms 8.11 (2020): 1747.
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