Rotifers

Gaurav Kumar

What are Rotifers?

Rotifers are considered multicellular and microscopic organisms that dwell mostly in freshwater. Some of the species of the rotifers were also found in brackish water, saltwater, lichens, and damp mosses. They are also known as wheel animalcule that includes almost 2000 species in the phylum Rotifera. These organisms include a circular arrangement of the microscopic hair-like structure known as cilia that looks like a rotating wheel. They are miraculous organisms that can survive radiations, desiccation, boiling, and even freezing naturally or in liquid nitrogen. They could easily persist in nature without having sex for millions of years. They could adapt to any given environment and are able to clone themselves after they thaw out. Recently, 24000 years old rotifer was surprisingly unearthed that remarkably challenged the studies of several researchers and scientists in this field. This bdelloid Siberian permafrost creature was found alive even after being in deep freeze for almost 24000 years. This is considered a new surviving record for any species in history.

Other species like rotifers

This remarkable discovery isn’t the only organism on the list. Roundworms were previously unearthed from the region’s permafrost and were found that they survived for about 40000 years in deep-freeze or permafrost conditions. Along with this several ancient seeds, bacteria, viruses, and mosses have also depicted the same impressive longevity in permafrost. This makes a big legitimate concern regarding the emergence of any potentially harmful microbes from this permafrost or glaciers that may challenge the survival of humankind. Several other microscopic level organisms like bacteria, viruses, protists, rotifers, and nematodes could be found alive beneath the ice surface.

Role in the food chain

Most of the rotifers are free-living while some of them are parasitic. Some of the rotifers live as an individual while some of their lives in the colonies. Rotifers are concerned as the predators of various detritus, algae, and bacteria; therefore there is no requirement of any legitimate concern regarding this specific discovery. These rotifers exist at the bottom of the food chain and there was no sign of their existence for several millennia.

This newly re-emerged species could be found reintegrating in our modern ecosystem very soon. Rotifers generally feed upon protozoans, algae, dead bacteria, and organic detritus. They feed upon the organisms up to 10 micrometers long. They include a special feature of nutrient recycling and therefore used for cleaning the fish tank. They require planktonic sources of food like copepods and cladocera. They also fall prey to several other organisms like tardigrades, starfish, jellyfish, comb jellies, bryozoan, salmon fish, herring fish, and copepods.

Body Structure and functioning

The size of the rotifers may range from 0.1 to 0.5 nm. The structure of the body of the rotifers is generally flattened and spherical which resembles a bag or worm-like structure. A thin cuticle surrounds the body wall. Locomotion and feeding are basically done by the tufts of cilia. These cilia are responsible for extracting tiny organisms as their food from the water. They could also feed on some big organisms like other rotifers, algae, or crustaceans. A digestive tract and mouth are also present in the body structure. The mouth of the rotifers includes a mastax, also known as the muscular pharynx that consists of tiny and rough jaws that are used for eating other organisms. The total numbers of cells in each and every variant of these species are equivalent. The genome size of rotifers is about 244 Mb.

Reproduction

Several species of rotifers includes different reproduction process like some reproduce parthenogenetically, while some of them reproduce both sexually and asexually. Male rotifers are very less in number as compared to females. According to cryology scientists, these living bdelloids could be found in the permafrost sample through the process of culturing them for few days. Bdelloid is a kind of rotifers that have the ability to reproduce parthenogenetically into the females, through which the source specimen has been originated.

This process includes the cloning of the organism that may create a huge challenge for the researchers to identify the parent of the developed clone. Therefore this concerns the researchers for further investigating the behavior and characteristics of these permafrost creatures. Another challenge is the contamination present in the specimen samples may create some difficulties in the research. However, there was no match found to the discovered rotifers according to the phylogenetic analysis, but some species were found in Belgium that consist the similar properties to the rotifers found in Siberia.

Science behind their survival

The Pushchino cryology lab in Russia has been unearthing the permafrost in Siberia in order to discover some ancient organisms that may have survived in a deep freeze. Several researchers are digging the Siberian permafrost for this cause for over a decade. Radiocarbon dating can be used for estimating the age of the discovered species by testing the soil sample from the surrounding organism. However, researchers concluded that there is no chance of any vertical movement in the permafrost. Last year, a frozen zoo was demonstrated by the researchers that included almost 35 viable species that have the nucleus in the body structure but they were not fungus, plant, or animal according to their behavioral properties. The age of these organisms in the frozen zoo was estimated at about 100 to 10000 years old.

The team of Researchers at Pushchino cryology lab performed several experiments in order to understand and insight into how these organisms survive for such a long interval of time. They froze the cloned sample at about -150 degrees C for a week and observed the reaction of the specimen to the given environment. They concluded that some of the rotifers survived to the given environment while some of them didn’t. It was clear that the clones were not as capable of adapting to the frozen environment as their parent does that were brought from the Asian tropics, North America, Europe, Alaska, Iceland, and African tropics. They observed that these organisms can survive the freezing process for about 45 minutes. Researchers concern about the metabolism behind the survival of these organisms. They also planned for some additional testing regarding their survival in warmer climates.

References:

Jaturapruek, R., Fontaneto, D., & Maiphae, S. (2020). The influence of environmental variables on bdelloid rotifers of the genus Rotaria in Thailand. Journal of Tropical Ecology, 36(6), 267-274. doi:10.1017/S0266467421000018

Jaturapruek, R, Fontaneto, D, Meksuwan, P, Pholpunthin, P and Maiphae, S (2018) Planktonic and periphytic bdelloid rotifers from Thailand reveal a species assemblage with a combination of cosmopolitan and tropical species. Systematics and Biodiversity 16, 128–141.

Kaczmarek, Ł, Roszkowska, M, Fontaneto, D, Jezierska, M, Pietrzak, B, Wieczorek, R, Poprawa, I, Kosicki, JZ, Karachitos, A and Kmita, H (2019) Staying young and fit? Ontogenetic and phylogenetic consequences of animal anhydrobiosis. Journal of Zoology 309, 1–11.

Kuczyńska-Kippen, N (2018) The use of bdelloids in reference to rotifer biocoenotic indices as an indicator of the ecological state of small field water bodies: the effect of macrophytes, shading and trophic state of water. Ecological Indicators 89, 576–583.

Renault, Marion (7 June 2021). “This Tiny Creature Survived 24,000 Years Frozen in Siberian Permafrost – The microscopic animals were frozen when woolly mammoths still roamed the planet, but were restored as though no time had passed”. the New York Times.

https://www.cell.com/current-biology/fulltext/S0960-9822(21)00624-2

Song, MO and Lee, C-H (2019) Four new bdelloid rotifers from Korea. Zootaxa 4571, 201–224.

Vakhrusheva, O.A.; Mnatsakanova, E.A.; Galimov, Y.R.; et al. (18 December 2020). “Genomic signatures of recombination in a natural population of the bdelloid rotifer Adineta vaga”. Nature.

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