DNA fingerprint analysis of a free-range koala population
Timms, P, Kato, J, Maugeri, M & White, N 1993, Biochemical Genetics, vol. 31, no. 9/10, pp. 363-374.
This paper presents the first detailed genetic study of a large group of wild koalas in Queensland using the DNA fingerprinting technique.
DNA fingerprinting is an analysis technique in which short fragments of DNA derived from plant or animal samples are examined to detect genetic variations between individuals. In this study, DNA fingerprints for 36 koalas from a wild population of 60 in Mutdapilly, south-east Queensland were produced using blood samples from each. Fingerprints were determined by firstly treating DNA samples with the restriction enzyme MspI to separate samples into fragments for analysis, and secondly adding the DNA probe M13. Using gel electrophoresis, the DNA fragments were sorted into 43 bands representing unique alleles within the population being studied. Of these 43 bands, which ranged between 2300 and 7600 base pairs in length, two were common to all of the 36 koalas sampled (100% allele frequency), and 24 bands had a frequency of 50% or greater. Conversely, ten bands had a frequency of 20% or less with three of these detected in only one koala each. Allele frequency ranged from 3 - 100%, with a mean of 50%. The mean level of band sharing in the population was 74.9%. The maximum number of bands in one fingerprint was 30 and the minimum 19, while the average number was 24.7. The authors consider the technique to be highly repeatable with very low levels of within-gel (0.1 - 1.6%) and between-gel (0.1 - 2.5%) error.
Using the technique described here, all 36 koalas could be successfully identified using their unique DNA fingerprint. The level of band sharing in the sampled population (74.9%) indicates an unusually high level of genetic relatedness, or in other words, low genetic variation. This level of band sharing is far higher then previously recorded levels for humans, birds, cats, dogs and cattle, but is not as high as that of a previously reported sample of Victorian koalas which suggested band sharing was as high as 75 – 100%. The precise reason for the low genetic variability observed in the study population is not known, but could be a result of inbreeding or inherent to the koala genome.
DNA fingerprinting offers several benefits to the study of koala population genetics. Using the technique, DNA databases can be created to facilitate comparison of genetic variability between populations. It also presents a viable alternative to the physical tagging of studied animals as it allows the koala to be identifiable for life even if its tag is lost and can be conducted using a variety of bodily tissue types. The lack of genetic variability observed within the present study population warrants investigation as any further reduction in population genetic diversity may make koalas more vulnerable to the effects of stress-related conditions such as chlamydial infection. The suitability of the M13/MspI database system for this purpose has been established here.
Summarised by Joanna Horsfall
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