James_Worth_Honours_thesis.pdf (614.53 kB)
Cryptic Glacial Refugia
thesisposted on 2023-05-26, 07:58 authored by Worth, JRP
Nothofagus cunninghamii (Hook.) Oerst. is the dominant component of most cool temperate rainforest in southeastern Australia. N. cunninghamii has a long history in the region and has endured through a period of great climatic changes, including the glacial-interglacial cycles. Currently the possible roles of glacial refugia, postglacial migration and long distance dispersal of seed are not well understood to explain the patchy distribution of the species, especially for regions such as northeastern Tasmania where no fossil record of the species is available. The PCR-RFLP technique was employed to determine the pattern of variability of chloroplast DNA using 134 samples across the species range. Four mutations were detected defining five haplotypes, displaying strong geographic structure. A relatively high level of variation detected in a sample size of 72 individuals compared to an initial small sample size of eight demonstrates the importance of using large sample sizes in PCR-RFLP studies for the purpose of finding polymorphic enzyme/fragment combinations. The occurrence of a common and ancestral haplotype across much of the species range makes it impossible to determine the possible roles of migration and fragmentation in regions where this haplotype is the only one present. However, derived haplotypes restricted to the central highlands of Victoria suggest glacial survival, supporting fossil evidence. A haplotype almost restricted to the northeast of Tasmania also suggests glacial survival, but this assertion is not yet definitive since the haplotype was also found in western Tasmania. In addition, two haplotypes restricted to western Tasmania suggest another possible separate refugia in this region. The presence of two haplotypes in southern Victoria may be indicative of a post-glacial migration event across Bass Strait. Further sampling and the detection of greater variation in the chloroplast genome of N. cunninghamii are required to make stronger biogeographical conclusions.
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