Genetic viability

Genetic viability is the ability of the genes present to allow a cell, organism or population to survive and reproduce.[1][2] The term is generally used to mean the chance or ability of a population to avoid the problems of inbreeding.[1] Less commonly genetic viability can also be used in respect to a single cell or on an individual level.[1]

Main article: Natural selection

Inbreeding depletes heterozygosity of the genome, meaning there is a greater chance of identical alleles at a locus.[1] When these alleles are non-beneficial, homozygosity could cause problems for genetic viability.[1] These problems could include effects on the individual fitness (higher mortality, slower growth, more frequent developmental defects, reduced mating ability, lower fecundity, greater susceptibility to disease, lowered ability to withstand stress, reduced intra- and inter-specific competitive ability) or effects on the entire population fitness (depressed population growth rate, reduced regrowth ability, reduced ability to adapt to environmental change).[3] See Inbreeding depression. When a population of plants or animals loses their genetic viability, their chance of going extinct increases.[4]

Necessary conditions

To be genetically viable, a population of plants or animals requires a certain amount of genetic diversity and a certain population size.[5] For long-term genetic viability, the population size should consist of enough breeding pairs to maintain genetic diversity.[6] The precise effective population size can be calculated using a minimum viable population analysis.[7]  Higher genetic diversity and a larger population size will decrease the negative effects of genetic drift and inbreeding in a population.[3] When adequate measures have been met, the genetic viability of a population will increase.[8]

Causes for decrease
Population bottleneck can decrease genetic viability leading to possible extinction [3]

The main cause of a decrease in genetic viability is loss of habitat.[4][9][10] This loss can occur because of, for example urbanization or deforestation causing habitat fragmentation.[4] Natural events like earthquakes, floods or fires can also cause loss of habitat.[4] Eventually, loss of habitat could lead to a population bottleneck.[3] In a small population, the risk of inbreeding will increase drastically which could lead to a decrease in genetic viability.[3][4][11] If they are specific in their diets, this can also lead to habitat isolation and reproductive constraints, leading to greater population bottleneck, and decrease in genetic viability.[12] Traditional artificial propagation can also lead to decreases in genetic viability in some species.[13][14]

Population conservation

Habitat protection is associated with more allelic richness and heterozygosity than in unprotected habitats.[15] Reduced habitat fragmentation and increased landscape permeability can promote allelic richness by facilitating gene flow between populations that are isolated or smaller.[15]

The minimum viable population needed to maintain genetic viability is where the loss of genetic variation because of small population size (genetic drift) is equal to genetic variation gained through mutation.[16] When the numbers of one sex is too low, there may be a need for crossbreeding to maintain viability.[17]

Analyzing

When genetic viability seems to be decreasing within a population, a population viability analysis (PVA) can be done to assess the risk of extinction of this species.[18][19][20] The result of a PVA could determine whether further action is needed regarding the preservation of a species.[18]

Applications

Genetic viability is applied by wildlife management staff in zoos, aquariums or other such ex situ habitats.[21] They use the knowledge of the animals' genetics, usually through their pedigrees, to calculate the PVA and manage the population viability.[21]

References
  1. Hartl DL (2020-06-25). A Primer of Population Genetics and Genomics (4th ed.). Oxford University Press. doi:10.1093/oso/9780198862291.001.0001. ISBN 978-0-19-886229-1.
  2. Luo L, Zhang YM, Xu S (March 2005). "A quantitative genetics model for viability selection". Heredity. 94 (3): 347–55. doi:10.1038/sj.hdy.6800615. PMID 15536483.
  3. Lacy RC (1997-05-21). "Importance of Genetic Variation to the Viability of Mammalian Populations". Journal of Mammalogy. 78 (2): 320–335. doi:10.2307/1382885. JSTOR 1382885.
  4. Robert A (September 2011). "Find the weakest link. A comparison between demographic, genetic and demo-genetic metapopulation extinction times". BMC Evolutionary Biology. 11 (1): 260. doi:10.1186/1471-2148-11-260. PMC 3185286. PMID 21929788.
  5. Tensen L, van Vuuren BJ, Du Plessis C, Marneweck DG (2019-06-01). "African wild dogs: Genetic viability of translocated populations across South Africa". Biological Conservation. 234: 131–139. doi:10.1016/j.biocon.2019.03.033.
  6. Cegelski CC, Waits LP, Anderson NJ, Flagstad O, Strobeck C, Kyle CJ (2006-04-01). "Genetic diversity and population structure of wolverine (Gulo gulo) populations at the southern edge of their current distribution in North Americawith implications for genetic viability". Conservation Genetics. 7 (2): 197–211. doi:10.1007/s10592-006-9126-9. S2CID 44217068.
  7. Nunney L, Campbell KA (July 1993). "Assessing minimum viable population size: Demography meets population genetics". Trends in Ecology & Evolution. 8 (7): 234–9. doi:10.1016/0169-5347(93)90197-W. PMID 21236157.
  8. Zhang B, Li M, Zhang Z, Goossens B, Zhu L, Zhang S, et al. (August 2007). "Genetic viability and population history of the giant panda, putting an end to the "evolutionary dead end"?". Molecular Biology and Evolution. 24 (8): 1801–10. doi:10.1093/molbev/msm099. PMID 17513881.
  9. Vonholdt BM, Stahler DR, Smith DW, Earl DA, Pollinger JP, Wayne RK (January 2008). "The genealogy and genetic viability of reintroduced Yellowstone grey wolves". Molecular Ecology. 17 (1): 252–74. doi:10.1111/j.1365-294X.2007.03468.x. PMID 17877715. S2CID 9222840.
  10. Agroforestry and biodiversity conservation in tropical landscapes. Schroth, G. (Goetz). Washington: Island Press. 2004. pp. 290–314. ISBN 1-4237-6551-6. OCLC 65287651.CS1 maint: others (link)
  11. Young AG, Clarke GM, Clarke GM, Cowlishaw G (2000-10-12). Genetics, Demography and Viability of Fragmented Populations. Cambridge University Press. ISBN 978-0-521-79421-3.
  12. Zhang B, Li M, Zhang Z, Goossens B, Zhu L, Zhang S, et al. (August 2007). "Genetic viability and population history of the giant panda, putting an end to the "evolutionary dead end"?". Molecular Biology and Evolution. 24 (8): 1801–10. doi:10.1093/molbev/msm099. PMID 17513881.
  13. Reisenbichler RB, Rubin SP (August 1, 1999). "Genetic changes from artificial propagation of Pacific salmon affect the productivity and viability of supplemented populations". ICES Journal of Marine Science. 56 (4): 459–466. doi:10.1006/jmsc.1999.0455.
  14. McClure MM, Utter FM, Baldwin C, Carmichael RW, Hassemer PF, Howell PJ, et al. (May 2008). "Evolutionary effects of alternative artificial propagation programs: implications for viability of endangered anadromous salmonids". Evolutionary Applications. 1 (2): 356–75. doi:10.1111/j.1752-4571.2008.00034.x. PMC 3352443. PMID 25567637.
  15. Dellinger JA, Gustafson KD, Gammons DJ, Ernest HB, Torres SG (October 2020). "Minimum habitat thresholds required for conserving mountain lion genetic diversity". Ecology and Evolution. 10 (19): 10687–10696. doi:10.1002/ece3.6723. PMC 7548186. PMID 33072289.
  16. Traill LW, Brook BW, Frankham RR, Bradshaw CJ (January 2010). "Pragmatic population viability targets in a rapidly changing world". Biological Conservation. 143 (1): 28-34. doi:10.1016/j.biocon.2009.09.001.
  17. Piyasatian N, Kinghorn BP (2003). "Balancing genetic diversity, genetic merit and population viability in conservation programmes". Journal of Animal Breeding and Genetics. 120 (3): 137–149. doi:10.1046/j.1439-0388.2003.00383.x.
  18. Menges ES (1990). "Population Viability Analysis for an Endangered Plant". Conservation Biology. 4 (1): 52–62. doi:10.1111/j.1523-1739.1990.tb00267.x. ISSN 0888-8892.
  19. Beissinger SR, McCullough DR (2002). Population viability analysis. Chicago: University of Chicago Press. ISBN 0-226-04177-8. OCLC 48100035.
  20. Boyce MS (1992-11-01). "Population Viability Analysis". Annual Review of Ecology and Systematics. 23 (1): 481–497. doi:10.1146/annurev.es.23.110192.002405. ISSN 0066-4162.
  21. Lacy RC (January 2019). "Lessons from 30 years of population viability analysis of wildlife populations". Zoo Biology. 38 (1): 67–77. doi:10.1002/zoo.21468. PMID 30585658.
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