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Title: The molecular evolution of planktic foraminifera and its implications for the fossil record
Author: Stewart, Iain A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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The marine microfossils of planktic foraminifers are widely used for investigating palaeoceanographic and palaeoclimatic conditions. The objective of this project was to investigate genotypic variation within planktic foraminiferal morphospecies and the spatial distribution of genotypes in the subpolar, transitional and subtropical North Atlantic. Foraminiferal genomic DNA was extracted and the ~1000 base pair 3' terminal region of the small subunit ribosomal RNA gene was amplified using the polymerase chain reaction. Using distance-based molecular phylogenetic analysis, a neighbour-joining phylogeny was reconstructed based on 31 planktic and15 benthic previously sequenced foraminifera and extended to include 15 genotype sequences obtained from the North Atlantic during this study. Bulk plankton samples were collected for preliminary examination of genotype/morphotype relationships. The molecular phylogeny is largely consistent with the foraminiferal fossil record. It supports the suggestion that the origins of planktic foraminifers are polyphyletic, as the spinose planktic foraminifers cluster separately from the non-spinose planktic foraminifers within the phylogeny. Brachn length variation within the planktic cluster reflects large differences in evolution rate between morphospecies. Within the North Atlantic, genotypic variation has been identified within the morphospecies, Globigerina bulloides, Turborotalita quinqueloba, Globigerinella siphonifera, Globigerinella calida, Globigerinoides ruber and Neogloboquadrina pachyderma. The distribution of genotypes is complex, and it has been found that genotypes, representing a single morphospecies, often co-exist within the water column. This could be indicative of cryptic speciation, suggesting that North Atlantic planktic foraminiferal diversity is much higher than fossil record interpretations have indicated. The genotypes within G. bulloides, G. siphonifera, G. calida and T. quinqueloba have different geographic distributions within the North Atlantic. It is apparent that G. bulloides Types IIa and IIb and G. siphonifera Types IIa and IIb have extensive distributions suggesting that they are more generalist in adaptation, and tolerant to a wide range of oceanic conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available