Randomly amplified polymorphic DNA variation in populations of eastern Australian koalas, Phascolarctos cinereus
Fowler, EV, Hoeben, P & Timms, P 1998, Biochemical Genetics, vol. 36, nos. 11/12, pp. 381-393.
An analysis of molecular variation in eight eastern Australian koala populations showed greater genetic diversity in northern koala populations from New South Wales and Queensland than in southern populations from Victoria and South Australia. Population differentiation was evident based on the presence of polymorphisms in fragments of DNA amplified using randomly amplified polymorphic DNA (RAPD) as molecular markers. The genetic variation between individuals was twice as variable for northern populations than southern populations.
Utilising RAPD markers is an affordable and simple method of detecting population differentiation based on genetic differences between individuals and is suitable for use without prior knowledge of individual DNA sequences. DNA fragments of differing lengths are amplified in individuals depending on the presence and absence of polymorphisms in sequences across the genome via polymerase chain reaction (PCR). Visualised as varying band sizes in gel electrophoresis, a number of RAPD profiles can be determined to differentiate individuals. In this study population differentiation was evident and the level of polymorphism, as measured by the number of RAPD markers present in the population, was greater in all northern populations (New South Wales and Queensland) than in southern populations (Victoria and South Australia). Despite the overall low level of genetic diversity, the genetic differentiation detected between individuals by utilising RAPD indicated this method was appropriate for exploring genetic relationships in this species.
Previous studies utilising molecular markers suggested low genetic diversity in southern populations compared to northern regions; however, these methods required prior knowledge of genetic sequences to be utilised. RAPD markers proved useful in identifying the level of genetic variation between individuals and showed a significant difference in diversity between regions. The lack of genetic diversity observed in southern populations may be explained by rapid population declines at the end of the 1800s, ascribed to threats including hunting, habitat loss, natural disaster and disease. The genetic bottleneck that occurred, and subsequent population growth from only a few individuals, reduced the genetic variation present. Of the four populations in the southern region studied, both French Island and Kangaroo Island showed the lowest level of genetic diversity, and were populated by only two to three and 18 individuals respectively. In comparison, greater genetic diversity in northern populations may be due to an initially more populous region leading to a faster rate of recovery from decline, or later human settlement reducing the impact of these threats.
Similar results gleaned from studies using molecular markers such as microsatellites consolidate the utility of RAPD markers to identify genetic variation in individuals and populations. High levels of genetic variation detected within individuals by RAPD in this study and across many other species in previous studies highlights the usefulness of this method for identifying variation in populations.
Summarised by Meredith Kraina
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