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Paper 1: Role of inbreeding depression and purging in captive
breeding…
Paper 1: Role of inbreeding depression and purging in captive
breeding and restoration programmes (Lebirg & Firmin, 2008)
Result and Discussion
This graph tells that bottleneck event is more severe in population where it involves the purging of deleterious alleles of the population genetic makeup which makes them hard to adapt to the environment.
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The major caused of threats to these population are bottleneck event, inbreeding and fixation of alleles.
Population that experienced fixation of deleterious allele and multiple bottleneck event is said to be susceptible to extinction.
The population founded by siblings had a slower growth where the accumulation relatedness associated with bottleneck make them susceptible to extinction.
Successful reproduction occurred in only 33 of the
48 mesocosm populations. Some unsuccessful reproduction due to small population that have inbreeding.
Introduction
:lock: Major threat to the viability of many small
populations :-
:!: Inbreeding depression,
:!: the resulting reduction in mean population fitness.
:check: Inbreeding exposes deleterious, recessive alleles to selection by increasing genomic homozygosity.
:check: Purging, selection decreases the frequency of deleterious recessive alleles in a population, reducing future
inbreeding depression.
:check: Purging = possible tool in management of endangered species and for re-introduction programme.
:check: First Objectives = To briefly review several issues that could affect how small populations, resulting from captive breeding and wildlife releases.
:check: Second Objectives = To present some results from an experiment assessing whether past bottlenecks reduce the susceptibility of fish populations to additional close inbreeding.
:lock: The genetic basis of inbreeding depression
- Inbreeding depression confers reduced fitness among the offspring of genetic relatives.
:lock:Purging and recovery of fish population:
- Bottleneck effect reduce the effect of inbreeding on the population viability.
- Effect of purging in vertebrates species is unclear because their larger broods might increase the viability of the population.
- the differences in growth and reproduction can be found in small lineages.
:lock:Purging and population viability:
- Inbreeding will cause problems to occur.
- In very small population that is undergoing intensive breeding and stressful conditions, the population will become extinct.
- If the rate of inbreeding decrease, it will slightly improve the efficiency of purging. But it is not enough to prevent compromising of population viability.
- The loss of genetic variation caused by drift will reduce the potential to adapt to changes.
:lock:Environment And Purging:
- Environmental factors
- High purging, Low Relative fitness of homozygous deleterious recessives.
- Purging more success under stressful and competitive environments
- Alleles become fixed in one environment.
:lock:Response to different levels of inbreeding:
- Duration and size of bottleneck influence purging.
- Small Population = High rate of inbreeding ; High rate of drift conterferes selection, change in allele frequencies= Result in fixation of deleterious allele.
- Pop. Size low, Highly Deleterious. - Low rate of inbreeding (Large population) : Purge genetic load more their rapid inbreeding
Conclusion
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After experiencing several bottlenecks, the alleles that may notbe lethal but still affect the individual cannot be removed through selection by further inbreeding.
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Methods
Founders used for the experimental population were generally selected at random from available adults
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Six population were established with the offspring of fish that experienced no bottleneck and six populations experienced a bottleneck of a single pair of individual
A serial bottleneck treatment consisted of 12 initial population that experienced four bottlenecks before our experiment: 1 female and 2 male sibling, 1 male and 2 female (nonsib), 4 female and 1 male (nonsib), and 1 pair of sibling
In our experiment, the six populations in both the control and single bottleneck treatments were each represented by two mesocosms, one which was founded by sibling
Each of the two lineages in the serial bottleneck treatment was represented in 12 mesocosms (half founded by sibling)
We treated each lineage experiencing serial bottleneck as separate treatment, but because the mean responses of the two lineage were never significatly different (P>0.10)
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