Several new populations of koalas have been introduced to islands to help conser

Question

Several new populations of koalas have been introduced to islands to help conserve the species (Seymour et al. 2001). Populations of koalas that have gone through founding bottlenecks when introduced to islands show an increased frequency of testicular aplasia (a failure of testicular development) and other indications of inbreeding depression. The two plots below show the distributions of allele frequencies present at six microsatellite loci populations of koalas from South Australia. One of these samples is from a large natural population of koalas and the other sample is from a newly founded island population. Which of these two populations is most likely to be a recently founded island population? Explain the basis for your answer.

Explanation / Answer

In naturally occurring population, due to the effect of natural selection, there is an increase in the proportion of protective alleles (positive selection) and decrease in the proportion of harmful alleles (negative selection). This process of natural selection ensures the survival of the fittest and only the positive alleles are transmitted to the future generations.

Random allele changes are seen in two conditions: founder effects and bottlenecks. The founding effect is seen when small group moves and makes an entirely new population. The bottleneck phenomenon occurs when there is rapid decrease in the population due to environmental changes and the new population will have the genetic lineage of only the few surviving population.

In the question, two charts are given representing the frequencies of alleles in two different populations: Mt Lofty ranges and Strzelecki ranges. The distribution of allele frequencies in Mt Lofty range is more uniform than the Strzelecki ranges. Further, in Strzelecki ranges, the allele frequency of 0 is present in high proportion which cannot occur in the presence of natural selection which occurs in a large natural population. Therefore, the population in Strzelecki range is most likely to be a recently founded island population.

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