Please enable JavaScript.

Coggle requires JavaScript to display documents.

G2-Roles of inbreeding depression & purging (Lebirg & Firmin,2008)…

- - - - the increasing probability of relatedness among mating individuals (panmictic inbreeding or nonrandom mating)
    - - reduced fitness of offsprings of related individuals.
    - - the ability of an organism to survive and reproduce.
    - - the probability that a population will persist in the face of extinction threats.
    - - the relative difference between the average fitness of a population’s members and the fitness of the fittest genotype.
    - - reduces a population’s genetic load by reducing the frequencies of deleterious alleles.
    - - only have an influence on phenotypes when present as homozygotes.
    - - strong influence on phenotype and mask the presence of recessive alleles
    - - effects of a recessive allele on the phenotype are only partially masked by the effects of the dominant allele.
    - - heterozygous genotypes have higher fitness than homozygous genotypes.
    - - a population of a finite size in which matings between related individuals are likely to occur.
    - - the temporary reductions of populations to a very small number of individuals.
  - - - Inbreeding exposes deleterious, recessive alleles to selection by increasing genomic homozygosity.
    - - Reduction in mean population fitness as a result of the increase in mating between relatives in a small population.
    - - Purging will decrease the frequency of deleterious recessive alleles in a population making them less susceptible to future reductions in population size (great for re-introduction programmes).
- - - - Highly deleterious alleles are successfully purged but slightly
        deleterious alleles become fixed through drift.
    - - Expected in cases where inbreeding depression was due
        to overdominance or many slightly deleterious recessives.
    - - Expected with highly deleterious alleles,
        results in a recovery of fitness after a period of reduced fitness.
- - - - Environmental variation can play another role in assessing the efficiency of purging by giving the appearance of purging when little loss of deleterious recessives may have happened.
    - - Alleles that become fixed in one environment during purging might have deleterious effects in other environments.
      - Stressful or competitive conditions makes purging to be effective.
- - - - Purging in the management of small populations is not recommended due to many unknowns concerning
        
        Genetic basis
        of inbreeding depression in most species
        
        Stochastic
        effects associated with bottlenecks
        
        Variation in efficiency of purging in different environments
      - Factors affecting the effectiveness of purging:
        
        High component of mildly
        deleterious alleles
        
        Overdominance
        
        Insufficient stressful selective
        environment
        
        Drift overwhelming selection
      - Avoid negative effects of inbreeding depression via traditional approaches:
        
        Minimize the severity and duration of population bottlenecks
        
        Use captive breeding designs that avoid
        matings between close relatives
- - - - However, purging does affect the population viability.
      - Population may go extinct during purging especially when under intensive inbreeding depression.
      - Reducing inbreeding might improve the effect of purging but not enough to overcome loss of population viability
      - Risk of non-lethal deleterious alleles being fixed into the population after purging.
      - Evidence suggest that purged population may experience reduced ability to adapt to a new environment.
  - - - Studies using insect models shows that bottleneck might reduce the effects of inbreeding on population viability. :
      - However, this is unclear for cases of vertebrates because insects have large brood sizes which might increase the viability of population during purging.
      - Therefore, population of western mosquitofish is used to investigate response to reductions of population size and environmental stress.
      - This fish has median brood size which is closer to other vertebrates compared to insects.