Mesenchytraeus solifugus

Mesenchytraeus solifugus, commonly called an ice worm, is a species of oligochaete worm that inhabits coastal glaciers in northwestern North America. M. solifugus is dark brown and grows to about 15 mm long and 0.5 mm wide. It has a high population density and is common in suitable habitat. It can only survive at temperatures of approximately –7 °C to 5 °C. The ice worm is studied for its ability to survive in low temperatures. It has heavy pigment, absorbing most colors; however, it burrows into the glacier to avoid strong sunlight.

Mesenchytraeus solifugus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata
Order: Tubificida
Family: Enchytraeidae
Genus: Mesenchytraeus
Species:
M. solifugus
Binomial name
Mesenchytraeus solifugus
(Emery, 1898)
M. solifugus on Nisqually Glacier, Mount Rainier

History and taxonomy

This species was first reported from Muir Glacier in Alaska.[1] Carlo Emery named it solifugus in 1898, meaning "fleeing from the sun".[2] Phylogeny suggests that it evolved from an aquatic ancestor.[2]

Description

Ice worms are the only known psychrophilic annelids.[3] Adult ice worms are approximately 1.5–2.5 centimeters (0.6–1.0 inch) long.[1] They live their entire lives in snow or ice. The ice worm’s dark pigmentation helps protect it from solar ultraviolet radiation.[4] Their fluid and flexible body are able to squeeze through air holes and tiny crevasses in ice. Their lifespan is believed to be five to ten years.

Ice worms have an elongated head pore,[2] with sensing organs located on their prostomium and ventral surface.[1] These organs are responsible for chemo-, thermo, and photorecepetion.[5] However, the worms lack eyes or eyespots.[2] They have setae that curve at the tips, unlike those of related organisms.[2]

Little is known about the life cycle of the ice worm; it is thought to be unusually slow. It requires temperatures of 0 °C for a successful reproduction. Cocoons are dispersed by birds.[6] Not much is known about the ice worm's diet, but it is thought to eat snow algae, as well as some bacteria.[4]

Habitat

Ice worms inhabit glaciers and can be found in snowfields, avalanche cones, and glacier rivers and pools.[1] These environments have temperatures near the freezing point and are nutrient poor.[7] The organisms require permanent glacial environments for survival and reproduction.[8]

As well as the northwestern United States, ice worms have been found in glaciers of southern Alaska and certain parts of British Columbia.[4] They can be abundant, with typical densities of about 100 per square meter and peak recorded densities of up to 6,000 per square meter.[9] Though they are found in snowfields, rivers and pools, they are not found on dirty snow or rock.[1]

Ecology and behavior

M. solifugus have a very narrow acceptable temperature range. Their metabolisms have adapted to cold temperatures.,[7] and they are the only known worm to spend their entire life in temperatures near 0 C (32 °F), where they are most active[3] and their ability to produce adenosine triphosphate (ATP) is at its peak.[10][11][12] They freeze at around −6.8 °C (19.8 °F), and their bodies decompose after continuous exposure to temperatures above 5 °C (41 °F). This decomposition process, known as autolysis, occurs when the cells produce digestive enzymes and self-destruct. The body, figuratively, melts.

Even if other places are equally cold, ice worms never venture onto any other terrain. They eat the abundant snow algae and pollen carried by the wind.

Ice worms are most active in late spring.[8] In the summer, they follow a diurnal cycle—at the first light in the morning, they sink into the glacier. A few hours before sunset, they poke out from the snow.[1] In this respect they resemble some other oligochaetes that avoid strong radiation but are attracted to dim light.[1]

Little is known about the ice worm during the winter as the inaccessibility of glaciers prevents further study. Since in the winter the surface temperature on a glacier can reach −40 °C (−40 °F), the worms most likely remain below the surface. They may burrow as deep as several feet into the glacier in search of an area with a favorable temperature.[13] The snowfall provides insulation, and the temperatures below remains a stable 0 C (32 °F). Ice worms can still find plenty of algae in the firn layer, the layer of packed snow in transition to ice.

In glacial ponds or small streams, ice worms can be found in broad daylight. The freezing water provides the worms with a comfortable temperature, countering any heating of their dark bodies from the sun. In fast-flowing glacial streams, ice worms cling to the ice surface.[2] Researchers have observed the worms gyrating their heads in the stream, possibly catching algae and pollen carried by the water. In still ponds, ice worms gather in bundles. Researchers speculate this is reproductive behavior. Ice worms do not graze in groups on the surface, so the contact in still ponds provides the rare opportunity for breeding.

Ice worms move on the surface of ice at about 3 m/h (meters per hour) and move through snow by squeezing between the grains.[2] Lateral movement is usually along the surface of the glacier and they penetrate the glacier vertically.[1]

Research studies and medical uses

Researchers are investigating what prevents the worm from freezing at temperatures below 0 °C (32 °F) and are looking at the evolutionary steps by which the ice worm diverged from related species. Understanding the ice worm's physiology could suggest means by which to preserve organs for transplantation[4] and could aid in the understanding of potential extraterrestrial life on cold planets, as well as species on Earth which survive in climates colder than previously thought possible.[14]

References
  1. Hartzell, Paula L.; Nghiem, Jefferson V.; Richio, Kristina J.; Shain, Daniel H. (2011-02-15). "Distribution and phylogeny of glacier ice worms (Mesenchytraeus solifugus and Mesenchytraeus solifugus rainierensis)". Canadian Journal of Zoology. 83 (9): 1206–1213. doi:10.1139/z05-116.
  2. Shain, Daniel H.; Carter, Melissa R.; Murray, Kurt P.; Maleski, Karen A.; Smith, Nancy R.; McBride, Taresha R.; Michalewicz, Lisa A.; Saidel, William M. (2000). "Morphologic characterization of the ice worm Mesenchytraeus solifugus". Journal of Morphology. 246 (3): 192–197. doi:10.1002/1097-4687(200012)246:3<192::AID-JMOR3>3.0.CO;2-B. ISSN 1097-4687. PMID 11077431.
  3. Napolitano, Michael J.; Nagele, Robert G.; Shain, Daniel H. (2004-01-01). "The ice worm, Mesenchytraeus solifugus, elevates adenylate levels at low physiological temperature". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 137 (1): 227–235. doi:10.1016/j.cbpb.2003.10.005. ISSN 1095-6433. PMID 14720608.
  4. "Ice Worms – North Cascade Glacier Climate Project". Retrieved 2021-04-06.
  5. Farrell, Angela H.; Hohenstein, Kristi A.; Shain, Daniel H. (2004). "Molecular Adaptation in the Ice Worm, Mesenchytraeus solifugus: Divergence of Energetic-Associated Genes". Journal of Molecular Evolution. 59 (5): 666–673. Bibcode:2004JMolE..59..666F. doi:10.1007/s00239-004-2658-z. ISSN 0022-2844. PMID 15693622. S2CID 22139929.
  6. Hotaling, Scott; Shain, Daniel H.; Lang, Shirley A.; Bagley, Robin K.; Tronstad, Lusha M.; Weisrock, David W.; Kelley, Joanna L. (2019-06-26). "Long-distance dispersal, ice sheet dynamics and mountaintop isolation underlie the genetic structure of glacier ice worms". Proceedings of the Royal Society B: Biological Sciences. 286 (1905): 20190983. doi:10.1098/rspb.2019.0983. PMC 6599980. PMID 31213183.
  7. Murakami, Takumi; Segawa, Takahiro; Bodington, Dylan; Dial, Roman; Takeuchi, Nozomu; Kohshima, Shiro; Hongoh, Yuichi (2015-03-01). "Census of bacterial microbiota associated with the glacier ice worm Mesenchytraeus solifugus". FEMS Microbiology Ecology. 91 (3). doi:10.1093/femsec/fiv003. ISSN 1574-6941. PMID 25764456.
  8. Dial, Roman J.; Becker, Melissa; Hope, Andrew G.; Dial, Cody R.; Thomas, Joseph; Slobodenko, Katarina A.; Golden, Trevor S.; Shain, Daniel H. (2016). "The Role of Temperature in the Distribution of the Glacier Ice Worm, Mesenchytraeus solifugus (Annelida: Oligochaeta: Enchytraeidae)". Arctic, Antarctic, and Alpine Research. 48 (1): 199–211. doi:10.1657/AAAR0015-042. ISSN 1523-0430. S2CID 130333586.
  9. Doughton, Sandi. "Ice worms' survival secrets could help humans". chicagotribune.com. Retrieved 2021-04-06.
  10. Lang, Shirley A.; McIlroy, Patrick; Shain, Daniel H. (2020-02-28). "Structural Evolution of the Glacier Ice Worm Fo ATP Synthase Complex". The Protein Journal. 39 (2): 152–159. doi:10.1007/s10930-020-09889-x. ISSN 1572-3887. PMID 32112190. S2CID 211554768.
  11. Napolitano, M. J.; Shain, D. H. (2004-08-07). "Four kingdoms on glacier ice: convergent energetic processes boost energy levels as temperatures fall". Proceedings of the Royal Society of London. Series B: Biological Sciences. 271 (suppl_5): S273-6. doi:10.1098/rsbl.2004.0180. ISSN 0962-8452. PMC 1810069. PMID 15503992.
  12. Lang, Shirley A.; Saglam, Naim; Kawash, Joseph; Shain, Daniel H. (2017). "Punctuated invasion of water, ice, snow and terrestrial ecozones by segmented worms (Oligochaeta: Enchytraeidae: Mesenchytraeus)". Proceedings: Biological Sciences. 284 (1864): 1–10. doi:10.1098/rspb.2017.1081. ISSN 0962-8452. JSTOR 44685478. PMC 5647291. PMID 29021169.
  13. Napolitano, Michael J.; Nagele, Robert G.; Shain, Daniel H. (2004-01-01). "The ice worm, Mesenchytraeus solifugus, elevates adenylate levels at low physiological temperature". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 137 (1): 227–235. doi:10.1016/j.cbpb.2003.10.005. ISSN 1095-6433. PMID 14720608.
  14. Mauri, Pelto. "North Cascade Glacier Climate Project". Nichols College. Archived from the original on 9 February 2009. Retrieved 17 November 2016.

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