A Cline in Genetic Diversity in River She-Oak Casuarina cunninghamiana

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Abstract
Twenty populations of Casuarina cunninghamiana Miq. covering its large geographic range were used in a study of genetic diversity. Genetic variation was measured by analysing 19 allozyme loci using 50 seedlings from each of the populations. The overall genetic diversity (HT = 0.287) in C. cunninghamiana is high compared to many other plant species. A significant fraction (26.4%) of the total genetic diversity could be apportioned among populations. This genetic differentiation between populations was not random. Populations in the eastern part of the range had high correlation (r = 0.91) of genetic diversity with latitude and this involved changes in allelic frequencies at several loci. At the population level, there was a significant positive correlation between genetic diversity and 1 year height growth. The western population from King River in the Northern Territory was very distinct genetically from all the other populations and this supported previous suggestions that the northwest part of the range is occupied by a different race of the species.