Traditionally, the fossil record has provided the timescale for evolutionary history. However, some evolutionary lineages are completely unrepresented in the fossil record and it is increasingly clear that the rock record in which the fossil record is entombed does not provide a uniform record of all environments at all times - it is systematically biased, but in a predictable manner. Given the frailties of the fossil record, molecular clocks have become the tool of choice in attempts to tell evolutionary time. Molecular clock methods have long been used as a basis for criticising the fossil record, since clocks have invariably yielded estimates of lineage divergence far in excess of palaeontological estimates, leading to the conclusion that the fossil record is woefully incomplete. However, there has been a sea change in perspective among molecular biologists, who are once again looking to the fossil record to better inform the assumptions on which their molecular analyses are based, with the ultimate aim of developing a reliable means of obtaining an evolutionary timescale. The aims of this project were to explore the impact of Bayesian calibration priors on the estimation of molecular divergence times. Analyses of empirical data demonstrate that molecular divergence times are extremely sensitive to the choice of parameters used to inform the calibration priors, and demonstrate that careful evaluation of available fossil evidence is required to inform constraints on node ages. However, competing approaches to calibration have never been tested, because in reality we never know the true time of divergence. The solution is to use simulated data, where the relationship between genetic divergence and fossil evidence is known. Mechanistic models of speciation, non-random fossil preservation and molecular evolution were combined to generate simulated datasets for testing the molecular clock. The results of this research demonstrate that the fossil record can provide accurate, but imprecise, constraints on divergence times, but that the accuracy of molecular divergence times is critically impacted by the way in which fossil data is modelled in the calibration of the molecular clock.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:684753 |
| Date | January 2014 |
| Creators | Warnock, Rachel Christina Margaret |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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