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      Low genetic variability of the koalaPhascolarctos cinereusin south-eastern Australia following a severe population bottleneck

      , , , ,
      Molecular Ecology
      Wiley

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          Abstract

          Genotyping of koalas at CA-repeat microsatellite loci has revealed significant differences in the levels of allelic diversity (A) and expected heterozygosity (H(E)) between populations from north-eastern and south-eastern Australia. In the 10 populations studied, allelic diversity ranged from 8.0 in the Nowendoc population to 1.7 in the Kangaroo Is. population, and values of H(E) ranged from 0.831 in the Nowendoc population to 0.331 in the Kangaroo Is. population. Data from pooled populations revealed koalas from the north-eastern region had significantly higher levels of allelic diversity (A = 11.5 +/- 1.4) than those from south-eastern Australia (A = 5.3 +/- 1.0). Furthermore significantly higher heterozygosity levels were found in the north-eastern (H(E) = 0.851) vs. the south-eastern (H(E) = 0.436) regions of Australia. Following a near-extinction bottleneck in the 1920s, mainland Victorian and Kangaroo Is. koalas have been involved in an extensive program of relocations. The source populations of the relocated animals were islands in Westernport Bay, which were founded by very few individuals in the late 1800s and early 1900s. The significantly lower levels of variation between south-eastern Australian populations suggests that human intervention has had a severe effect on levels of genetic diversity in this region, and this may have long-term genetic consequences.

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          Most cited references28

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          BIOSYS-1: a FORTRAN program for the comprehensive analysis of electrophoretic data in population genetics and systematics

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            Genetic basis for species vulnerability in the cheetah.

            A population genetic survey of over 200 structural loci previously revealed that the South African cheetah (Acinonyx jubatus jubatus) has an extreme paucity of genetic variability, probably as a consequence of a severe population bottleneck in its recent past. The genetic monomorphism of the species is here extended to the major histocompatibility complex, since 14 reciprocal skin grafts between unrelated cheetahs were accepted. The apparent consequences of such genetic uniformity to the species include (i) great difficulty in captive breeding, (ii) a high degree of juvenile mortality in captivity and in the wild, and (iii) a high frequency of spermatozoal abnormalities in ejaculates. The species vulnerability of the cheetah was demonstrated by an epizootic of coronavirus-associated feline infectious peritonitis in an Oregon breeding colony in 1983. Exposure and spread of the coronavirus, which has a very low morbidity in domestic cats (approximately 1 percent), has decimated a heretofore productive and healthy captive population. The extreme genetic monomorphism, especially at the major histocompatibility complex, and the apparent hypersensitivity of the cheetah to a viral pathogen may be related, and provide a biological basis for understanding the adaptive significance of abundant genetic variation in outbred mammalian species.
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              Inferences about linkage disequilibrium.

              B Weir (1979)
              Existing theory for inferences about linkage disequilibrium is restricted to a measure defined on gametic frequencies. Unless gametic frequencies are directly observable, they are inferred from genotypic frequencies under the assumption of random union of gametes. Primary emphasis in this paper is given to genotypic data, and disequilibrium coefficients are defined for all subsets of two or more of the four genes, two at each of two loci, carried by an individual. Linkage disequilibrium coefficients are defined for genes within and between gametes, and methods of estimating and testing these coefficients are given for gametic data. For genotypic data, when coupling and repulsion double heterozygotes cannot be distinguished. Burrows' composite measure of linkage disequilibrium is discussed. In particular, the estimate for this measure and hypothesis tests based on it are compared to the usual maximum likelihood estimate of gametic linkage disequilibrium, and corresponding likelihood ratio or contingency chi-square tests. General use of the composite measure, whether or not random union of gametes is an appropriate assumption, is recommended. Attention is given to small samples, where the non-normality of gene frequencies will have greatest effect on methods of inference based on normal theory. Even tools such as Fisher's z-transformation for the correlation of gene frequencies are found to perform quite satisfactorily.
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                Author and article information

                Journal
                MEC
                Molecular Ecology
                Wiley
                09621083
                1365294X
                April 1996
                April 1996
                : 5
                : 2
                : 269-281
                Article
                10.1046/j.1365-294X.1996.00089.x
                8673272
                116b0cb8-5ae4-4686-b721-30697594ec4f
                © 1996

                http://doi.wiley.com/10.1002/tdm_license_1.1

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