Critter Catalog

What do they look like?

Water bears get their name from their resemblance to bears; they are thick and round, with four sets of short legs that have claws on the end. They are 0.5 mm in length on average, and have a waxy skin that covers the body. Females are usually larger than males. On the front of their face is a round tube used for feeding. This species, Hypsibius dujardini, can be distinguished from other species by its claws, feeding tube, skin, and length. This species has two branched clawss that face opposite directions and are different in length. Their skin is also smoother than other species'. (Coulson, 2000; Guidetti, et al., 2012; Nelson and Marley, 2000; Pigon and Weglarska, 1955; Pilato, et al., 2013)

• Other Physical Features
• bilateral symmetry
• polymorphic

• Sexual Dimorphism
• female larger

• Average length

  0.50 mm

  0.02 in

Where do they live?

Hypsibius dujardini is a species of tardigrade, a tiny microscopic organism. They are also commonly called water bears. This species is found world-wide. It has been found in the Palearctic, Neotropical, Nearctic, Afrotropical, Antarctic, and Indomalaysian regions. In the Nearctic region, this water bear species is the most commonly-found water bear. In North America, it has been collected in the United States (Arkansas, California, District of Columbia, Louisiana, Maryland, North Carolina, New York, and Tennessee), Canada (New Brunswick), and Greenland. (McFatter, et al., 2007; Meyer, 2001)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• antarctica
  • native

• Other Geographic Terms
• holarctic
• cosmopolitan

What kind of habitat do they need?

This water bear species lives in freshwater, and has been collected from the sediment of lakes, rivers, and streams. It is often found in or near algae, moss, and other plants. It has even been found in holes in glaciers. In Lake Michigan and Lake Erie, this species has been collected as deep as 23 meters. (McFatter, et al., 2007)

• These animals are found in the following types of habitat
• temperate
• tropical
• polar
• freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools

• Other Habitat Features
• intertidal or littoral

• Range depth

  0 to 23 m

  0.00 to 75.46 ft

• Average depth

  0.0 - 0.01 m

  ft

How do they grow?

Females lay an average of 3 to 4 eggs at a time, and these take 4 to 4.5 days to hatch. In a laborator, this time increases to 13 to 14 days. Molting, the shedding of the skin, occurs throughout their lives, usually between 4 to 12 times. Each molt takes 5 to 10 days, as the claws, cuticle, and hindgut are all shed. This includes the feeding tube, so the water bear is unable to eat right after molting. (Bertolani, 2001; Gabriel, et al., 2007; Glime, 2013a)

How do they reproduce?

There is no information available regarding the mating habits of this water bear. Mating between males and females is not always necessary, as this species can reproduce by parthenogensis, which is the process of producing offspring without mating. (Bertolani, 2001)

When these water bears shed their skin, the shed skin is used as a place to lay the eggs. Sexual reproduction between males and females can occur, as there are usually both males and females present in populations. They also reproduce by parthenogenesis, when mating between males and females does not take place, and an unfertilized egg still develops into a fully-functioning offspring. In laboratories, hermaphrodites have been observed, where one individual has both male and female genitals. This species has multiple reproductive cycles in their lives, meaning they can reproduce multiple times. In each cycle, an average of 3 to 4 eggs are laid (range of 1 to 10), and all are independent upon hatching. (Bertolani, 2001)

• Key Reproductive Features
• iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• simultaneous hermaphrodite
• parthenogenic
• sexual
• oviparous

• Range number of offspring

  1 to 10

• Average number of offspring

  3-4

• Average gestation period

  4 days

• Average time to independence

  0 minutes

Water bears are not known to provide any care to their offspring. Once they lay their eggs, they leave them to develop and survive on their own. (Nelson and Marley, 2000)

• Parental Investment
• no parental involvement

How long do they live?

These water bears are estimated to live 4 to 12 years in the wild on average. Other related water bear species live only 1 to 2 years, but this difference in lifespan is not well understood. (Altiero and Rebecchi, 2001; Glime, 2013a; Nelson and Marley, 2000)

• Range lifespan
  Status: captivity

  13.25 (high) months

• Typical lifespan
  Status: wild

  4 to 12 years

How do they behave?

Water bears are able to survive in very extreme conditions, such as extreme temperatures, high levels of radiation, lack of water, and even the vacuum of space. They can do so by a biological response called cryptobiosis, specifically a type of cryptobiosis called anhydrobiosis. In the event of extreme conditions, these water bears become dehydrated, and stop development, activity, and metabolism. When conditions become better for survival, usually when water becomes available, the water bear can rehydrate and resume its normal behavior. They are able to stay in this inactive state for a long time, up to several years. One individual water bear has been reported becoming active again after being dormant for 120 years. (Jonsson, et al., 2008; Rebecchi, et al., 2007; Welnicz, et al., 2011)

• Key Behaviors
• natatorial
• motile

How do they communicate with each other?

There is no information available on the communication methods or sensory methods of this species. Related species of water bears have been found to have sensory organs on their front end, and other species have receptors that can detect light. (Biserova and Kuznetsova, 2012)

What do they eat?

Water bears use their feeding tube to eat algae. They also may feed on lichens and moss. Other water bear species have been known to eat nematodes and rotifers, though this has not been seen in this species. (Glime, 2013a; Nelson and Marley, 2000; Pilato, et al., 2013; Schill, et al., 2011)

• Primary Diet
• herbivore
  • algivore

• Plant Foods
• bryophytes
• lichens
• algae

What eats them and how do they avoid being eaten?

No research has been conducted on known predators of this species.

What roles do they have in the ecosystem?

Ballocephala pedicellata is a parasitic fungus that uses this water bear species as a host. Both the fungus and water bear live and eat in the moss, so it is easy for the fungus to infect water bears and to use their body to reproduce within. (Glime, 2013b; Glime, 2013a; Pohlad and Bernard, 1978)

• Ecosystem Impact
• biodegradation

Do they cause problems?

There are no known negative effects of Hypsibius dujardini on humans.

How do they interact with us?

There are no known positive effects of this water bear species on humans.

Are they endangered?

This water bear is not an endangered species.

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Contributors

Fionna Surette (author), Radford University, Karen Powers (editor), Radford University, Angela Miner (editor), Animal Diversity Web Staff.

References

Altiero, T., L. Rebecchi. 2001. Rearing tardigrades: results and problems. Zoologischer Anzeiger, 240: 217-221.

Bertolani, F. 2001. Evolution of the reproductive mechanisms in tardigrades - a review. Zoologischer Anseiger, 240: 247-252.

Bertolani, R., R. Guidetti, K. Jonsson, D. Boschini, L. Rebechhi. 2004. Experiences with dormancy in tardigrades. Journal of Limnology, 63: 16-25.

Biserova, N., K. Kuznetsova. 2012. Head sensory organs of Halobiotus stenostomus (Eutardigrada, Hypsibiidae). Biology Bulletin, 39/7: 579-589.

Coulson, S. 2000. A review of the terrestrial and freshwater invertebrate fauna of the High Arctic archipelago of Svalbard. Norwegian Journal of Entomology, 47: 41-63.

Gabriel, W., R. McNuff, S. Patel, T. Gregory, W. Jeck, C. Jones, B. Goldstein. 2007. The tardigrade Hypsibius dujardini, a new model for studying the evolution of development. Developmental Biology, 312: 545-559.

Glime, J. 2013. Chapter 5-2: Tardigrade Reproduction and Food. Pp. 521-5216 in Bryophyte Ecology, Vol. 2. Not listed: Michigan Technological University.

Glime, J. 2013. Chapter 5-6: Tardigrade Ecology. Pp. 1-24 in Bryophyte Ecology, Vol. 2. Not listed: Michigan Technological University. Accessed December 05, 2013 at http://www.bryoecol.mtu.edu/chapters_VOL2/5-6Tardigrade_Ecology.pdf.

Guidetti, R., T. Altiero, T. Marchioro, L. Amade, A. Avdonina, R. Bertolani, L. Rebecchi. 2012. Form and function of the feeding apparatus in Eutardigrada (Tardigrada). Zoomorphology, 131: 127-148.

Jonsson, K., E. Rabbow, R. Schill, M. Harms-Ringdahl, P. Rettberg. 2008. Tardigrades survive exposure to space in low Earth orbit. Current Biology, 18/17: R729-R731.

McFatter, M., H. Meyer, J. Hinton. 2007. Nearctic freshwater tardigrades: a review. Proceedings of the Tenth International Symposium on Tardigradia, 66: 84-89. Accessed December 08, 2013 at http://ncate.mcneese.edu/bitcache/a2cec65785d444996580b794b01c2182228f9403?vid=544&disposition=inline&op=view.

Meyer, H. 2001. Tardigrades of Louisiana and Arkansas, United States of America. Zoologischer Anzeiger, 240: 471-474.

Nelson, D., N. Marley. 2000. The biology and ecology of Iotic Tardigrada. Freshwater Biology, 44: 93-108.

Pigon, A., B. Weglarska. 1955. Rate of metabolism in tardigrades during active life and anabiosis. Nature, 176/4472: 121-122.

Pilato, G., M. Binda, R. Catanzaro. 2013. Remarks on some tardigrades of the African fauna with the description of three new species of Macrobiotus Schultze. Tropical Zoology, 4/2: 167-178.

Pilato, G., M. Binda. 2001. Biogeography and limno-terrestrial tardigrades: are they truly incompatible binomials?. Zoologischer Anzeiger, 240: 511 - 516.

Pohlad, B., E. Bernard. 1978. A new species of entomophthorales parasitizing tardigrades. Mycological Society of America, 70/1: 130-139.

Rebecchi, L., T. Altiero, R. Guidetti. 2007. Anhydrobiosis: the extreme limi of desiccation tolerance. ISJ, 4: 65-81.

Schill, R., K. Jonsson, M. Pfannkuchen, F. Brummer. 2011. Food of tardigrades: a case study to understand food choice, intake and digestion. Journal of Zoological Systematics and Evolutionary Research, 49: 66-70.

Welnicz, W., M. Grohme, L. Kaczmarek, R. Schill, M. Frohme. 2011. Anhydrobiosis in tardigrades - the last decade. Journal of Insect Physiology, 57: 577 - 583.