Negligible senescence

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Some tortoises show negligible senescence.

Negligible senescence is a term coined by biogerontologist Caleb Finch to denote organisms that do not exhibit evidence of biological aging (senescence), such as measurable reductions in their reproductive capability, measurable functional decline, or rising death rates with age.[1] There are many species where scientists have seen no increase in mortality after maturity.[1] This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age.[2]

Study of negligibly senescent animals may provide clues that lead to better understanding of the aging process and influence theories of aging.[1][3] The phenomenon of negligible senescence in some animals is a traditional argument for attempting to achieve similar negligible senescence in humans by technological means.

There are also organisms[which?] that exhibit negative senescence, whereby mortality chronologically decreases as the organism ages, for all or part of the life cycle, in disagreement with the Gompertz–Makeham law of mortality[4] (see also Late-life mortality deceleration). Furthermore, there are species that have been observed to regress to a larval state and regrow into adults multiple times, such as Turritopsis dohrnii.[5]

Studies have indicated a connection between phenomena related to negligible senescence and the dynamic stability of an organism's underlying regulatory network over its lifetime. Depending on the parameters of metabolism and the connectivity of the network, on one hand, and the genetic and expressome error elimination rates (repair efficiency), on the other, organisms may function in such a way that damage is either effectively eliminated and kept under control at all times, or the amount of damage is getting exponentially amplified. The two limiting cases may correspond to the distinct regimes of non-aging and "normal" aging, respectively. [6] The boundary between the aging regimes corresponds to the phase transition line, whereas most regulatory networks of living species operate at the stability-instability boundary.[7] If the relation between aging and criticality in genetic regulatory networks and the corresponding explanation behind the negligible senescence is confirmed by further research, it may explain how weak genetic perturbation can produce switching between normal (Gompertzian) aging and negligibly senescent regimes on evolutional time scales.

In vertebrates[edit]

Some fish, such as some varieties of sturgeon and rougheye rockfish, and some tortoises and turtles[8] are thought to be negligibly senescent, although recent research on turtles has uncovered evidence of senescence in the wild.[2] The age of a captured fish specimen can be measured by examining growth patterns similar to tree rings on the otoliths (parts of motion-sensing organs).[9]

In 2018, naked mole-rats were identified as the first mammal to defy the Gompertz–Makeham law of mortality, and achieve negligible senescence. It has been speculated, however, that this may be simply a "time-stretching" effect primarily due to their very slow (and cold-blooded and hypoxic) metabolism.[10][11][12]

In plants[edit]

In plants, aspen trees are one example of biological immortality. Each individual tree can live for 40–150 years above ground, but the root system of the clonal colony is long-lived. In some cases, this is for thousands of years, sending up new trunks as the older trunks die off above ground. One such colony in Utah, given the nickname of "Pando", is estimated to be 80,000 years old, making it possibly the oldest living colony of aspens.[13]

The world's oldest known living non-clonal organism was the Methuselah tree of the species Pinus longaeva, the bristlecone pine, growing high in the White Mountains of Inyo County in eastern California, aged 4854–4855 years.[14] This record was superseded in 2012 by another Great Basin bristlecone pine located in the same region as Methuselah, and was estimated to be 5,062 years old. The tree was sampled by Edmund Schulman and dated by Tom Harlan.[15]

Ginkgo trees in China resist aging by extensive gene expression associated with adaptable defense mechanisms that collectively contribute to longevity.[16]

In bacteria[edit]

Among bacteria, individual organisms are vulnerable and can easily die, but on the level of the colony, bacteria can live indefinitely. The two daughter bacteria resulting from cell division of a parent bacterium can be regarded as unique individuals or as members of a biologically "immortal" colony.[17] The two daughter cells can be regarded as "rejuvenated" copies of the parent cell because damaged macromolecules have been split between the two cells and diluted.[18] See asexual reproduction.

Maximum life span[edit]

Some examples of maximum observed life span of animals thought to be negligibly senescent are:

Rougheye rockfish 205 years[19][20]
Aldabra giant tortoise 255 years
Lobsters 100+ years (presumed)[21]
Hydras Observed to be biologically immortal[22]
Planaria Observed to be biologically immortal[23]
Sea anemones 60–80 years (generally)[24]
Red sea urchin 200 years[25]
Freshwater pearl mussel 210–250 years[26][27]
Ocean quahog clam 507 years[28]
Greenland shark 400 years[29]

Cryptobiosis[edit]

Some rare organisms, such as tardigrades, usually have short lifespans, but are able to survive for thousands of years—and, perhaps, indefinitely—if they enter into the state of cryptobiosis, whereby their metabolism is reversibly suspended.

See also[edit]

References[edit]

  1. ^ a b c Finch C (1994). "Negligible Senescence". Longevity, Senescence and the Genome. Chicago, IL: . University of Chicago Press. pp. 206–247.
  2. ^ a b Warner DA, Miller DA, Bronikowski AM, Janzen FJ (June 2016). "Decades of field data reveal that turtles senesce in the wild". Proceedings of the National Academy of Sciences of the United States of America. 113 (23): 6502–6507. Bibcode:2016PNAS..113.6502W. doi:10.1073/pnas.1600035113. PMC 4988574. PMID 27140634.
  3. ^ Guerin JC (June 2004). "Emerging area of aging research: long-lived animals with "negligible senescence"". Annals of the New York Academy of Sciences. 1019 (1): 518–520. Bibcode:2004NYASA1019..518G. doi:10.1196/annals.1297.096. PMID 15247078. S2CID 6418634.
  4. ^ Ainsworth C, Lepage M (2007). "Evolution's greatest mistakes". New Scientist. 195 (2616): 36–39. doi:10.1016/S0262-4079(07)62033-8.
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  7. ^ Balleza E, Alvarez-Buylla ER, Chaos A, Kauffman S, Shmulevich I, Aldana M (June 2008). "Critical dynamics in genetic regulatory networks: examples from four kingdoms". PLOS ONE. 3 (6): e2456. Bibcode:2008PLoSO...3.2456B. doi:10.1371/journal.pone.0002456. PMC 2423472. PMID 18560561.
  8. ^ Miller JK (April 2001). "Escaping senescence: demographic data from the three-toed box turtle (Terrapene carolina triunguis)". Experimental Gerontology. 36 (4–6): 829–832. doi:10.1016/s0531-5565(00)00243-6. PMID 11295516. S2CID 43802703.
  9. ^ Bennett J (1882). "Confirmation on longevity in Sebastes diploproa (pisces Scorpaenidae) from 210Pb/226Ra measurements in otoliths". Maritime Biology. 71 (2): 209–215. doi:10.1007/bf00394632. S2CID 83655808.
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  13. ^ Quaking Aspen by the Bryce Canyon National Park Service.
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  16. ^ Wang L, Cui J, Jin B, Zhao J, Xu H, Lu Z, et al. (January 2020). "Multifeature analyses of vascular cambial cells reveal longevity mechanisms in old Ginkgo biloba trees". Proceedings of the National Academy of Sciences of the United States of America. 117 (4): 2201–2210. Bibcode:2020PNAS..117.2201W. doi:10.1073/pnas.1916548117. PMC 6995005. PMID 31932448.
  17. ^ Chao L (August 2010). "A model for damage load and its implications for the evolution of bacterial aging". PLOS Genetics. 6 (8): e1001076. doi:10.1371/journal.pgen.1001076. PMC 2928801. PMID 20865171.
  18. ^ Rang CU, Peng AY, Chao L (November 2011). "Temporal dynamics of bacterial aging and rejuvenation". Current Biology. 21 (21): 1813–1816. doi:10.1016/j.cub.2011.09.018. PMID 22036179. S2CID 13860012.
  19. ^ Munk K (2001). "Maximum Ages of Groundfishes in Waters off Alaska and British Columbia and Considerations of Age Determination". Alaska Fishery Research Bulletin. 8: 1.
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  21. ^ "140-year-old lobster's tale has a happy ending". Associated Press. January 10, 2009.
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  23. ^ Sahu S, Dattani A, Aboobaker AA (October 2017). "Secrets from immortal worms: What can we learn about biological ageing from the planarian model system?". Seminars in Cell & Developmental Biology. 70: 108–121. doi:10.1016/j.semcdb.2017.08.028. PMID 28818620.
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  26. ^ Ziuganov V, San Miguel E, Neves RJ, Longa A, Fernández C, Amaro R, Beletsky V, Popkovitch E, Kaliuzhin S, Johnson T (2000). "Life span variation of the freshwater pearlshell: a model species for testing longevity mechanisms in animals". Ambio. XXIX (2): 102–105. doi:10.1579/0044-7447-29.2.102. S2CID 86366534.
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  29. ^ Pennisi E (11 August 2016). "Greenland Shark May Live 400 Years, Smashing Longevity Record". Science Magazine.