In biology, outbreeding depression happens when crosses between two genetically distant groups or populations result in a reduction of fitness.[1] The concept is in contrast to inbreeding depression, although the two effects can occur simultaneously.[2]Outbreeding depression is a risk that sometimes limits the potential for genetic rescue or augmentations.[1] It is considered postzygotic response because outbreeding depression is noted usually in the performance of the progeny.[3]
Outbreeding depression manifests in two ways:
Generating intermediate genotypes that are less fit than either parental form. For example, selection in one population might favor a large body size, whereas in another population small body size might be more advantageous, while individuals with intermediate body sizes are comparatively disadvantaged in both populations. As another example, in the Tatra Mountains, the introduction of ibex from the Middle East resulted in hybrids which produced calves at the coldest time of the year.[4]
Breakdown of biochemical or physiological compatibility. Within isolated breeding populations, alleles are selected in the context of the local genetic background. Because the same alleles may have rather different effects in different genetic backgrounds, this can result in different locally coadaptedgene complexes. Outcrossing between individuals with differently adapted gene complexes can result in disruption of this selective advantage, resulting in a loss of fitness.
The different mechanisms of outbreeding depression can operate at the same time. However, determining which mechanism is likely to occur in a particular population can be very difficult.
There are three main mechanisms for generating outbreeding depression:
Fixed chromosomal differences resulting in the partial or complete sterility of F1 hybrids.[1]
Some mechanisms may not appear until two or more generations later (F2 or greater),[5] when recombination has undermined vitality of positive epistasis. Hybrid vigor in the first generation can, in some circumstances, be strong enough to mask the effects of outbreeding depression. An example of this is that plant breeders will make F1 hybrids from purebred strains, which will improve the uniformity and vigor of the offspring, however the F2 generation are not used for further breeding because of unpredictable phenotypes in their offspring. Unless there is strong selective pressure, outbreeding depression can increase in further generations as coadapted gene complexes are broken apart without the forging of new coadapted gene complexes to take their place. If the outcrossing is limited and populations are large enough, selective pressure acting on each generation can restore fitness. Unless the F1 hybrid generation is sterile or very low fitness, selection will act in each generation using the increased diversity to adapt to the environment.[6] This can lead to recovery in fitness to baseline, and sometimes even greater fitness than original parental types in that environment.[7] However, as the hybrid population will likely to go through a decline in fitness for a few generations, they will need to persist long enough to allow selection to act before they can rebound.[8]
Examplesedit
The first mechanism has the greatest effects on fitness for polyploids, an intermediate effect on translocations, and a modest effect on centric fusions and inversions.[1] Generally this mechanism will be more prevalent in the first generation (F1) after the initial outcrossing when most individuals are made up of the intermediate phenotype.
Examples of the second mechanism include stickleback fish, which developed benthic and limnetic forms when separated. When crosses occurred between the two forms, there were low spawning rates. However, when the same forms mated with each other and no crossing occurred between lakes, the spawning rates were normal. This pattern has also been studied in Drosophila and leaf beetles, where the F1 progeny and later progeny resulted in intermediate fitness between the two parents. This circumstance is more likely to happen and occurs more quickly with selection than genetic drift.[1]
For the third mechanism, examples include poison dart frogs, anole lizards, and cichlid fish. Selection over genetic drift seems to be the dominant mechanism for outbreeding depression.[1]
In plantsedit
For plants, outbreeding depression represents a partial crossing barrier.[3] Outbreeding depression is not understood well in angiosperms. After observing Ipomopsis aggregata over time by crossing plants that were between 10–100 m apart, a pattern was noticed that plants that were farther away spatially had a higher likelihood of outbreeding depression.[3] Some general takeaways from this were that spatial patterns of selection on plant genotypes will vary in scale and pattern, and outbreeding depression reflects the genetic constitution of "hybrid" progeny and the environments in which the parents and progeny grow.[3] This means that although outbreeding depression cannot be predicted in angiosperms yet, the environment has a role in it.
This article incorporates public domain material from Michael Lynch. Inbreeding depression and outbreeding depression. National Park Service.
^ abcdefFrankham, Richard; Ballou, Jonathan D.; Eldridge, Mark D. B.; Lacy, Robert C.; Ralls, Katherine; Dudash, Michele R.; Fenster, Charles B. (2011-04-12). "Predicting the Probability of Outbreeding Depression". Conservation Biology. 25 (3): 465–475. doi:10.1111/j.1523-1739.2011.01662.x. ISSN 0888-8892. PMID 21486369. S2CID 14824257.
^Frankham, R.; Ballou, J.D.; Briscoe, D.A. (2002). Introduction to Conservation Genetics. Cambridge. pp. 382. ISBN0521702712.
^ abcdWaser, Nickolas M.; Price, Mary V.; Shaw, Ruth G. (2000). "Outbreeding Depression Varies Among Cohorts of Ipomopsis Aggregata Planted in Nature". Evolution. 54 (2): 485–91. doi:10.1554/0014-3820(2000)054[0485:odvaco]2.0.co;2. ISSN 0014-3820. PMID 10937225.
^Turcek, FJ (1951). "Effect of introductions on two game populations in Czechoslovakia". Journal of Wildlife Management. 15 (1): 113–114. doi:10.2307/3796784. JSTOR 3796784.
^Fenster, Charles (2000). "Inbreeding and Outbreeding Depression in Natural Populations of Chamaecrista fasciculata (Fabaceae)". Conservation Biology. 14 (5): 1406–1412. doi:10.1046/j.1523-1739.2000.99234.x. S2CID 16051555.
^Erickson and Fenster (2006). "Intraspecific hybridization and the recovery of fitness in the native legume Chamaecrista fasciculata". Evolution. 60 (2): 225–33. doi:10.1554/05-020.1. JSTOR 4095211. PMID 16610315. S2CID 6822055.
^Lewontin & Birch, R.C. & L.C. (February 3, 1966). "Hybridization as a source of variation for adaptation to new environments". Evolution. 20 (3): 315–336. doi:10.2307/2406633. JSTOR 2406633. PMID 28562982.
^Frankham, Ballou, & Briscoe, R., J.D. & D.A. (2002). Introduction to Conservation Genetics. Cambridge. p. 388 ISBN0521702712
April 10, 2024
outbreeding, depression, biology, outbreeding, depression, happens, when, crosses, between, genetically, distant, groups, populations, result, reduction, fitness, concept, contrast, inbreeding, depression, although, effects, occur, simultaneously, risk, that, . In biology outbreeding depression happens when crosses between two genetically distant groups or populations result in a reduction of fitness 1 The concept is in contrast to inbreeding depression although the two effects can occur simultaneously 2 Outbreeding depression is a risk that sometimes limits the potential for genetic rescue or augmentations 1 It is considered postzygotic response because outbreeding depression is noted usually in the performance of the progeny 3 Outbreeding depression manifests in two ways Generating intermediate genotypes that are less fit than either parental form For example selection in one population might favor a large body size whereas in another population small body size might be more advantageous while individuals with intermediate body sizes are comparatively disadvantaged in both populations As another example in the Tatra Mountains the introduction of ibex from the Middle East resulted in hybrids which produced calves at the coldest time of the year 4 Breakdown of biochemical or physiological compatibility Within isolated breeding populations alleles are selected in the context of the local genetic background Because the same alleles may have rather different effects in different genetic backgrounds this can result in different locally coadapted gene complexes Outcrossing between individuals with differently adapted gene complexes can result in disruption of this selective advantage resulting in a loss of fitness Contents 1 Mechanisms 2 Examples 3 In plants 4 See also 5 ReferencesMechanisms editThe different mechanisms of outbreeding depression can operate at the same time However determining which mechanism is likely to occur in a particular population can be very difficult There are three main mechanisms for generating outbreeding depression Fixed chromosomal differences resulting in the partial or complete sterility of F1 hybrids 1 Adaptive differentiation among populations Population bottlenecks and genetic driftSome mechanisms may not appear until two or more generations later F2 or greater 5 when recombination has undermined vitality of positive epistasis Hybrid vigor in the first generation can in some circumstances be strong enough to mask the effects of outbreeding depression An example of this is that plant breeders will make F1 hybrids from purebred strains which will improve the uniformity and vigor of the offspring however the F2 generation are not used for further breeding because of unpredictable phenotypes in their offspring Unless there is strong selective pressure outbreeding depression can increase in further generations as coadapted gene complexes are broken apart without the forging of new coadapted gene complexes to take their place If the outcrossing is limited and populations are large enough selective pressure acting on each generation can restore fitness Unless the F1 hybrid generation is sterile or very low fitness selection will act in each generation using the increased diversity to adapt to the environment 6 This can lead to recovery in fitness to baseline and sometimes even greater fitness than original parental types in that environment 7 However as the hybrid population will likely to go through a decline in fitness for a few generations they will need to persist long enough to allow selection to act before they can rebound 8 Examples editThe first mechanism has the greatest effects on fitness for polyploids an intermediate effect on translocations and a modest effect on centric fusions and inversions 1 Generally this mechanism will be more prevalent in the first generation F1 after the initial outcrossing when most individuals are made up of the intermediate phenotype Examples of the second mechanism include stickleback fish which developed benthic and limnetic forms when separated When crosses occurred between the two forms there were low spawning rates However when the same forms mated with each other and no crossing occurred between lakes the spawning rates were normal This pattern has also been studied in Drosophila and leaf beetles where the F1 progeny and later progeny resulted in intermediate fitness between the two parents This circumstance is more likely to happen and occurs more quickly with selection than genetic drift 1 For the third mechanism examples include poison dart frogs anole lizards and cichlid fish Selection over genetic drift seems to be the dominant mechanism for outbreeding depression 1 In plants editFor plants outbreeding depression represents a partial crossing barrier 3 Outbreeding depression is not understood well in angiosperms After observing Ipomopsis aggregata over time by crossing plants that were between 10 100 m apart a pattern was noticed that plants that were farther away spatially had a higher likelihood of outbreeding depression 3 Some general takeaways from this were that spatial patterns of selection on plant genotypes will vary in scale and pattern and outbreeding depression reflects the genetic constitution of hybrid progeny and the environments in which the parents and progeny grow 3 This means that although outbreeding depression cannot be predicted in angiosperms yet the environment has a role in it See also editDominance versus overdominance Haldane s rule Heterozygote advantage Inbreeding depressionReferences edit nbsp This article incorporates public domain material from Michael Lynch Inbreeding depression and outbreeding depression National Park Service a b c d e f Frankham Richard Ballou Jonathan D Eldridge Mark D B Lacy Robert C Ralls Katherine Dudash Michele R Fenster Charles B 2011 04 12 Predicting the Probability of Outbreeding Depression Conservation Biology 25 3 465 475 doi 10 1111 j 1523 1739 2011 01662 x ISSN 0888 8892 PMID 21486369 S2CID 14824257 Frankham R Ballou J D Briscoe D A 2002 Introduction to Conservation Genetics Cambridge pp 382 ISBN 0521702712 a b c d Waser Nickolas M Price Mary V Shaw Ruth G 2000 Outbreeding Depression Varies Among Cohorts of Ipomopsis Aggregata Planted in Nature Evolution 54 2 485 91 doi 10 1554 0014 3820 2000 054 0485 odvaco 2 0 co 2 ISSN 0014 3820 PMID 10937225 Turcek FJ 1951 Effect of introductions on two game populations in Czechoslovakia Journal of Wildlife Management 15 1 113 114 doi 10 2307 3796784 JSTOR 3796784 Fenster Charles 2000 Inbreeding and Outbreeding Depression in Natural Populations of Chamaecrista fasciculata Fabaceae Conservation Biology 14 5 1406 1412 doi 10 1046 j 1523 1739 2000 99234 x S2CID 16051555 Erickson and Fenster 2006 Intraspecific hybridization and the recovery of fitness in the native legume Chamaecrista fasciculata Evolution 60 2 225 33 doi 10 1554 05 020 1 JSTOR 4095211 PMID 16610315 S2CID 6822055 Lewontin amp Birch R C amp L C February 3 1966 Hybridization as a source of variation for adaptation to new environments Evolution 20 3 315 336 doi 10 2307 2406633 JSTOR 2406633 PMID 28562982 Frankham Ballou amp Briscoe R J D amp D A 2002 Introduction to Conservation Genetics Cambridge p 388 ISBN 0521702712 Retrieved from https en wikipedia org w index php title Outbreeding depression amp oldid 1192944852, wikipedia, wiki, book, books, library,
