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Molecular clocks and rates of evolution in marine invertebrates

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Title: Molecular clocks and rates of evolution in marine invertebrates
Author: Loeza Quintana, Tzitziki del Rosario
Department: Department of Integrative Biology
Program: Integrative Biology
Advisor: Adamowicz, Sarah J.
Abstract: The molecular clock is an important tool in evolutionary biology for dating the tree of life, particularly for lineages with a poor fossil record such as many marine invertebrates. Historically, biogeographic calibrations assumed simultaneous divergence of allopatric pairs of sister lineages, which is problematic for long and complex vicariance events. This thesis presents a new methodology for calibrating the molecular clock using complex biogeographic events, the iterative calibration approach. This approach calibrates the rate of molecular evolution by finding the rate that achieves concordance between multiple lines of evidence: geographic distributions, genetic divergences, geological history, and the fossil record. Using the novel and successful method, this study explores two biogeographic events for clock dating, the opening/re-closure of the Bering Strait and the formation of the Isthmus of Panama, and investigates rates and patterns of molecular evolution in four major groups of marine invertebrates (echinoderms, molluscs, arthropods, and polychaetes) and between Arctic vs. tropical taxa. When investigating the divergence rate in 157 sister pairs of marine invertebrates based on publicly available sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene, the results show that, generally, echinoderms have slower rates of molecular evolution than molluscs and polychaetes. Interestingly, tropical arthropods have the slowest rate, while Arctic arthropods have the highest rate among the four groups. Absolute rates of molecular evolution were observed to be higher in Arctic lineages than in their tropical counterparts, which may be attributed, for example, to smaller effective population size in Arctic populations. Overall, the novel iterative calibration approach, the large geographic and taxonomic scales, and the unprecedented sample size of sister pairs used in this study provide significant advances in clock calibration research. Moreover, the rates of molecular evolution resulting from this study suggest rate heterogeneity across phyla and a difference in rates between tropical vs. Arctic lineages. This study represents a novel and valuable contribution to research in marine organisms, which are commonly understudied. Lastly, this thesis will contribute to studying the tree of life and understanding the impact of prior climate change events upon the diversification of life.
URI: http://hdl.handle.net/10214/11485
Date: 2017-08
Rights: Attribution-NonCommercial-ShareAlike 2.5 Canada
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Attribution-NonCommercial-ShareAlike 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-ShareAlike 2.5 Canada