Macrobiotus

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Macrobiotus
Stec et al 2018 Fig 1 Macrobiotus shonaicus habitus.tif
Macrobiotus shonaicus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Tardigrada
Class: Eutardigrada
Order: Parachela
Family: Macrobiotidae
Genus: Macrobiotus
C.A.S. Schultze, 1834
Type species
Macrobiotus hufelandi
C.A.S. Schultze, 1834

Macrobiotus is a genus of tardigrades consisting of about 100 species within the family Macrobiotidae. [1] Of genera within the phylum Tardigrada, Macrobiotus is one of the most species-abundant. [2] Macrobiotus hufelandi , identified by German researcher Carl August Sigismund Schultze in 1834, is recognized as the first taxonomically named tardigrade species. [3] [4] By extension, Macrobiotus was the first ever described tardigrade genus. Macrobiotus shares similarities to other tardigrade genera, particularly in moulting a non-living cuticle over multiple life stages and robust stress tolerance mechanisms. [5] However, Macrobiotus tends to be differentiated from other tardigrades by being one of few genera that freely lay ornamented eggs in reproduction. This genera has a relatively diverse distribution in both terrestrial and aquatic environments. [6]

Contents

Anatomy and Morphology

Claws

Macrobiotus species commonly exhibit uniform diploclaws on their legs. [2]

Macrobiotus rybaki, typical claw conformation. Macrobiotus rybaki (10.3897-zse.97.65280) Figure 11.jpg
Macrobiotus rybaki , typical claw conformation.

Cuticle

Macrobiotus belong to the clade Ecdysozoa, characterized for non-living cuticle layers that can be moulted over various life stages. [5] This cuticular exoskeleton layer facilitates gas and water exchange. Protective benefits of the cuticle typically outweigh the energy costs required to moult.

Nervous System

Macrobiotus neurons innervate a brain with inner and outer connectives, the latter connecting the brain to the trunk. [7] Anterior leg nerves, posterior leg nerves, and peripheral nerves branch off of trunk ganglia. Connectives bridge adjacent trunk ganglia, and interpedal commissures bridge adjacent connectives.

Other Physiological Features

Many Macrobiotus species also share a firm buccal tube containing a ventral lamina without a ventral hook, a pharynx with one microplacoid and two macroplacoids, and tend to exhibit 10 peribuccal lamellae. [2]

Habitat and Distribution

Habitat

Macrobiotus tend to inhabit limnoterrestrial habitats primarily consisting of mosses, though some Macrobiotus have also been discovered near lichens or aquatic plants. [6] [8] Some species of Macrobiotus are obligatory freshwater invertebrates. [9]

Known Global Distribution of Macrobiotus
ContinentRegion
AfricaSouth West Africa [10]
Tanzania [10]
AntarcticaSub-Antarctic Islands [8]
AsiaChina [11]
Israel [12]
Kyrgyzstan [13]
Malaysia [14]
EuropeFinland [15]
Germany [3] [4]
Portugal [16]
Sweden [17]
North AmericaCanada [2]
Greenland [12]
South AmericaBrazil [6]
French Guiana [14]

Diet

Macrobiotus sapiens is an example of a herbivorous diet consisting of algae. [18] [19]

Behaviour

Reproduction

Macrobiotus shonaicus, ornamented egg chorion morphology. Stec et al 2018 Fig 7 Macrobiotus shonaicus egg SEM.tif
Macrobiotus shonaicus , ornamented egg chorion morphology.

Macrobiotus species exhibit a unique style of ornamented egg morphology and deposition process of freely laying ornamented eggs, contrasting to the ancestral state of freely laying smooth eggs. [5] This is a synapomorphy of two families, Eohypsibioidea and Macrobiotidae, with Macrobiotoidea including the genus Macrobiotus. Ornamented eggs can limit water evaporation due to surface tension between water molecules and the egg’s ornamentation.

Free-laying of eggs also differs from other common reproductive tendencies for tardigrades, whereby the old cuticle (or the exuvia) is used as an ‘egg keeper’ to allow egg development after laying. [5] It is hypothesized that releasing eggs into the environment reduces predation of embryonic Macrobiotus species, providing an evolutionary advantage compared to laying eggs in only one place within the exuvia.

Partner finding behaviour occurs for freely-ovipositing Macrobiotus shonaicus species, where the male touches a female tardigrade’s cloaca with their mouth several times, finishing their courtship ritual once the female tardigrade stops moving. [20] Freely-ovipositing species are thought to identify partners using pheromones to accommodate only having simple light detection abilities.

Some free-laying egg species like M. shonaicus utilize chemotaxis for spermatozoa released during ejaculation to identify and swim towards the female’s cloaca. [20] Eggs are typically laid shortly after reproduction by the female, ranging from 16 minutes to 2 days after mating.

Macrobiotus exhibits bisexual achiasmy, whereby the process of crossing-over of genetic information between homologous chromosomes in meiosis is absent in both the male and female sex. [21]

Stress Response

Anhydrobiosis

Macrobiotus can withstand desiccation conditions by entering a state of anhydrobiosis. [22] [23] Compared to other tardigrades, Macrobiotus displays a moderate degree of desiccation tolerance. Some species have been observed to accumulate trehalose during anhydrobiotic states. Trehalose can induce the anhydrobiotic state, serving as a potential energy source while also protecting cellular membranes and proteins in freezing and desiccation conditions. [24] Survival during anhydrobiosis depends on body size, particularly the size of energy-storing storage cells, though the reproductive state of oocyte maturation has no effect. [22] It is predicted that the exoskeletal cuticle likely facilitates anhydrobiosis. [5]

Some Macrobiotus may also demonstrate an encysted state primarily during periods of rest, but also metabolic depression. [23]

Starvation

One example species, M. sapiens , forms storage cells within their internal cavity in response to reduced food availability. [18] This strategy helps Macrobiotus species survive for several weeks without food, during which storage cell sizes significantly decrease.

Moulting

Macrobiotus, like other tardigrades, requires periodic moutling of their cuticle exoskeleton to grow in size. [5] Cuticle lining the foregut independently moults first and is expelled through the mouth, followed by moutling the cuticles lining the exterior body and hindgut. Moulting may occur in response to poor environmental conditions or starvation as overall body size decreases.

Both male and female partners of M. shonaicus , a freely-ovipositing species, moult immediately before reproduction, moulting during the process of developing mature oocytes. [20]

Species

The genus includes the following species: [1]

References

  1. 1 2 Degma, Peter; Bertolani, Roberto; Guidetti, Roberto (19 July 2021). "Actual checklist of Tardigrada species" (PDF) (40 ed.). Università di Modena e Reggio Emilia. doi:10.25431/11380_1178608 . Retrieved 21 March 2022.
  2. 1 2 3 4 5 Kayastha, Pushpalata; Roszkowska, Milena; Mioduchowska, Monika; Gawlak, Magdalena; Kaczmarek, Łukasz (2021-08-22). "Integrative Descriptions of Two New Tardigrade Species along with the New Record of Mesobiotus skorackii Kaczmarek et al., 2018 from Canada". Diversity. 13 (8): 394. Bibcode:2021Diver..13..394K. doi: 10.3390/d13080394 . ISSN   1424-2818.
  3. 1 2 Schultze, Karl August Sigismund (1834). Macrobiotus Hufelandii, animal e crustaceorum classe novum, reviviscendi post diuturnam asphyxiam et ariditatem potens (in Latin). Curths.
  4. 1 2 Schuster, Rolf; Schill, Ralph O. (2025-02-04). "Checklist of tardigrades in Germany as a contribution to biodiversity research". Organisms Diversity & Evolution. 25 (1): 167–187. Bibcode:2025ODivE..25..167S. doi: 10.1007/s13127-024-00668-5 . ISSN   1618-1077.
  5. 1 2 3 4 5 6 Guidetti, Roberto (2024-04-27). "Evolution of egg deposition strategies, exaptations of exuvia, and thanatochresis in tardigrades". Organisms Diversity & Evolution. 25 (1): 3–12. Bibcode:2025ODivE..25....3G. doi:10.1007/s13127-024-00642-1. hdl: 11380/1337209 . ISSN   1618-1077.
  6. 1 2 3 Barros, Rodolfo Corrêa de (2020-06-05). "Tardigrades Research in Brazil: an overview and updated checklist". Arquivos de Zoologia. 51 (1): 1–11. doi: 10.11606/2176-7793/2020.51.01 . ISSN   2176-7793.
  7. ↑ Martin, Christine; Gross, Vladimir; Hering, Lars; Tepper, Benjamin; Jahn, Henry; de Sena Oliveira, Ivo; Stevenson, Paul Anthony; Mayer, Georg (2017-08-01). "The nervous and visual systems of onychophorans and tardigrades: learning about arthropod evolution from their closest relatives". Journal of Comparative Physiology A. 203 (8): 565–590. doi:10.1007/s00359-017-1186-4. ISSN   1432-1351. PMID   28600600.
  8. 1 2 Degma, Peter; Gábrišová, Nina (2023-10-25). "Limno-Terrestrial Tardigrada of Sub-Antarctic Islands—An Annotated Review". Diversity. 15 (11): 1109. Bibcode:2023Diver..15.1109D. doi: 10.3390/d15111109 . ISSN   1424-2818.
  9. ↑ Greven, Hartmut (2018), Schill, Ralph O. (ed.), "From Johann August Ephraim Goeze to Ernst Marcus: A Ramble Through the History of Early Tardigrade Research (1773 Until 1929)" , Water Bears: The Biology of Tardigrades, Zoological Monographs, vol. 2, Cham: Springer International Publishing, pp. 1–55, doi:10.1007/978-3-319-95702-9_1, ISBN   978-3-319-95702-9 , retrieved 2025-03-25
  10. 1 2 3 4 5 6 Pilato, G.; Binda, M. G.; Catanzaro, R. (1991-12-01). "Remarks on some tardigrades of the African fauna with the description of three new species of Macrobiotus Schultze 1834". Tropical Zoology. 4 (2): 167–178. Bibcode:1991TrZoo...4..167P. doi:10.1080/03946975.1991.10539487. ISSN   0394-6975.
  11. 1 2 Yuan, Zhimin; Wang, Yan; Liu, Qiuju; Liu, Lijie; Li, Xiaochen (2022). "Macrobiotus hupingensis, a New Tardigrade Species in the Macrobiotus pallarii Complex from China". Zoological Studies. 61: 86.
  12. 1 2 3 4 Stec, Daniel (2024-03-29). "Integrative taxonomy supports two new species of Macrobiotus (Tardigrada: Eutardigrada: Macrobiotidae) allowing further discussion on the genus phylogeny". European Journal of Taxonomy (930): 79–123. Bibcode:2024EJTax.930...79S. doi:10.5852/ejt.2024.930.2481. ISSN   2118-9773.
  13. 1 2 Stec, Daniel (2022-10-23). "Macrobiotus rebecchii sp. nov.: A New Limno-Terrestrial and Hermaphroditic Tardigrade from Kyrgyzstan". Animals. 12 (21): 2906. doi: 10.3390/ani12212906 . ISSN   2076-2615. PMC   9653662 . PMID   36359030.
  14. 1 2 Stec, Daniel; Dudziak, Magdalena; Michalczyk, Łukasz (2020). "Integrative Descriptions of Two New Macrobiotidae Species (Tardigrada: Eutardigrada: Macrobiotoidea) from French Guiana and Malaysian Borneo". Zoological Studies. 59 (59): e23. doi:10.6620/ZS.2020.59-23. ISSN   1810-522X. PMC   7689055 . PMID   33262846.
  15. 1 2 Vecchi, Matteo; Stec, Daniel; Vuori, Tommi; Ryndov, Serge; Chartrain, Justine; Calhim, Sara (2022). "Macrobiotus naginae sp. nov., a New Xerophilous Tardigrade Species from Rokua Sand Dunes (Finland)" (PDF). Zoological Studies. 61: 22.
  16. 1 2 Kayastha, P.; et al. (2023). "Integrative description of Macrobiotus kosmali sp. nov. (hufelandi group) from the Island of Madeira (Portugal)". The European Zoological Journal. 90 (1): 126–138. doi: 10.1080/24750263.2022.2163312 .
  17. ↑ Massa, Edoardo; Guidetti, Roberto; Cesari, Michele; Rebecchi, Lorena; Jönsson, K. Ingemar (2021-03-01). "Tardigrades of Kristianstads Vattenrike Biosphere Reserve with description of four new species from Sweden". Scientific Reports. 11 (1): 4861. Bibcode:2021NatSR..11.4861M. doi:10.1038/s41598-021-83627-w. ISSN   2045-2322. PMC   7921132 . PMID   33649358.
  18. 1 2 Wang, Yixuan (2022-12-06). "A review of recent progress on stress tolerance in tardigrades". In El-Hashash, Ahmed (ed.). International Conference on Biomedical and Intelligent Systems (IC-BIS 2022). SPIE. p. 179. doi:10.1117/12.2662611. ISBN   978-1-5106-6021-2.
  19. ↑ Reuner, Andy; Hengherr, Steffen; Brümmer, Franz; Schill, Ralph O. (2010-04-01). "Comparative studies on storage cells in tardigrades during starvation and anhydrobiosis" . Current Zoology. 56 (2): 259–263. doi: 10.1093/czoolo/56.2.259 . ISSN   1674-5507.
  20. 1 2 3 Sugiura, Kenta; and Matsumoto, Midori (2021-10-02). "Sexual reproductive behaviours of tardigrades: a review". Invertebrate Reproduction & Development. 65 (4): 279–287. Bibcode:2021InvRD..65..279S. doi: 10.1080/07924259.2021.1990142 . ISSN   0792-4259.
  21. ↑ Satomura, Kazuhiro; Osada, Naoki; Endo, Toshinori (2019-12-01). "Achiasmy and sex chromosome evolution" . Ecological Genetics and Genomics. 13: 100046. Bibcode:2019EcoGG..1300046S. doi:10.1016/j.egg.2019.100046. ISSN   2405-9854.
  22. 1 2 Wełnicz, Weronika; Grohme, Markus A.; Kaczmarek, Łukasz; Schill, Ralph O.; Frohme, Marcus (2011-05-01). "Anhydrobiosis in tardigrades—The last decade" . Journal of Insect Physiology. Dormancy and Developmental Arrest in Invertebrates. 57 (5): 577–583. Bibcode:2011JInsP..57..577W. doi:10.1016/j.jinsphys.2011.03.019. ISSN   0022-1910. PMID   21440551.
  23. 1 2 Guppy, Michael; Withers, Philip (1999). "Metabolic depression in animals: physiological perspectives and biochemical generalizations" . Biological Reviews. 74 (1): 1–40. doi:10.1111/j.1469-185X.1999.tb00180.x. ISSN   1469-185X. PMID   10396183.
  24. ↑ Murray, Alex; Kilbride, Peter; Gibson, Matthew I. (2024-09-19). "Trehalose in cryopreservation. Applications, mechanisms and intracellular delivery opportunities". RSC Medicinal Chemistry. 15 (9): 2980–2995. doi:10.1039/D4MD00174E. ISSN   2632-8682. PMC   11411628 . PMID   39309363.
  25. 1 2 3 4 Bertolani, R.; et al. (2023). "The Macrobiotus persimilis-polonicus complex (Eutardigrada, Macrobiotidae), another example of problematic species identification, with the description of four new species". Organisms Diversity & Evolution. 23 (2): 329–368. Bibcode:2023ODivE..23..329B. doi:10.1007/s13127-022-00599-z. hdl: 11380/1303147 .
  26. ↑ Massa, E.; et al. (2021). "Tardigrades of Kristianstads Vattenrike Biosphere Reserve with description of four new species from Sweden". Scientific Reports. 11 (1): 4861. Bibcode:2021NatSR..11.4861M. doi: 10.1038/s41598-021-83627-w . PMC   7921132 . PMID   33649358.
  27. ↑ Stec, D.; Vecchi, M.; Calhim, S.; Michalczyk, Ł. (2021). "New multilocus phylogeny reorganises the family Macrobiotidae (Eutardigrada) and unveils complex morphological evolution of the Macrobiotus hufelandi group". Molecular Phylogenetics and Evolution. 160: 106987. Bibcode:2021MolPE.16006987S. doi:10.1016/j.ympev.2020.106987. PMID   33059070.
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