The tempo of evolution and the causes of rate variation among lineages are central foci of evolutionary biology. I evaluated two hypothesized sources of variation in molecular evolutionary rate, and I applied a variable molecular clock to estimate the timescale of diversification in three families of Neotropical birds.
First, I examined the phylogenetic evidence for molecular punctuated equilibrium, the hypothesis that speciation drives accelerated molecular evolution. Recent findings that rates of DNA evolution and speciation are linked implicate molecular punctuated equilibrium as an important cause of rate variation among lineages. I used phylogenetic simulations to test this reported link, and I found that it was entirely attributable to a methodological artifact. In a review of the topic, I found no unequivocal empirical evidence for molecular punctuated equilibrium and I concluded that its predicted phylogenetic consequences are theoretically implausible.
Second, I tested the metabolic rate hypothesis, which holds that mutation rate in mtDNA is correlated with mass-specific metabolic rate. This hypothesis predicts that small-bodied lineages should evolve rapidly. Previous studies verified this prediction, but none utilized adequately large samples of independent contrasts among appropriate taxa. The use of many such contrasts from bird mtDNA sequences conspicuously failed to corroborate the link between metabolic and mtDNA rates. On the contrary, high rates of nonsynonymous substitution were associated with large body mass, implicating population size as a pervasive cause of evolutionary rate variation.
Third, I developed molecular phylogenies for puffbirds, jacamars, and motmots to test hypothesized area relationships in the Neotropics. I used penalized likelihood to estimate node times while accommodating significant rate variation under a set of biologically realistic assumptions. Phylogenetic patterns in each family were consistent with expansion following the formation of the Central American Landbridge and subsequent vicariance across the Andes. I applied a calibration based on the final uplift of the Isthmus of Panama, 3.1 Ma. Average estimated rates were close to the commonly cited 2% sequence divergence/Myr. Concordant area relationships were found among co-distributed species complexes; however, the timescale of divergence was variable, suggesting that common dispersal corridors rather than common vicariant events may be driving co-phylogenetic patterns.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-11122004-054504 |
| Date | 16 November 2004 |
| Creators | Witt, Christopher C. |
| Contributors | Mike Hellberg, Fred Sheldon, Van Remsen, Robb Brumfield, Frank Rohwer, Mark Hafner |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-11122004-054504/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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