Evolutionary transitions between marine and freshwater habitats are rare events that can have profound impacts on aquatic biodiversity. The main goal of my thesis is determining the processes involved in transitions between marine and freshwater biomes, and the resulting patterns of diversity using phylogenetic approaches. To test hypotheses regarding the geography, timing, frequency, and mechanisms regulating biome transitions I generated multi-locus time-calibrated molecular phylogenies for groups of fishes that include both exclusively marine and freshwater species. My analysis of anchovies demonstrated that Neotropical freshwater anchovies represent a monophyletic radiation with a single origin in South American freshwaters. I used a phylogeny of herring and allies (Clupeiformes) to investigate the evolution of diadromy, a migratory behavior in which individuals move between oceans and freshwater habitats for reproduction and feeding. These analyses do not support the hypothesis that differences in productivity between marine and freshwater explain the origins of diadromous lineages. Diadromy has been considered an evolutionary pathway for permanent biome transitions, however I found that diadromy almost never produces a fully marine or freshwater clade. Marine lineages often invade continental freshwaters during episodes of marine incursion. In South America, the rich diversity of marine derived fish lineages invaded during Eocene marine incursions from either the Pacific or the Caribbean, and Oligocene marine incursions from the Caribbean. I falsified the highly cited Miocene marine incursion hypothesis, but found that the Pebas Mega-Wetland catalyzed diversification in some marine derived lineages. Using diversification analyses, I investigated the evolutionary processes that have generated disparate patterns of diversity between continents and oceans. I found that freshwater silversides have higher speciation and extinction rates than marine silversides. Lineages accumulation plots suggest ecological limits are not regulating clade growth in either marine or freshwater biomes. Overall, biome conservatism is a widespread pattern among fishes, and this pattern is largely driven by competition in clades that are physiologically capable of biome transitions. Biome transitions are facilitated by rare paleogeographic events, such as marine incursions. Finally, a difference in net diversification rate is the macroevolutionary mechanism that best explains the difference in diversity between continents and oceans.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/35169 |
| Date | 19 March 2013 |
| Creators | Bloom, Devin |
| Contributors | Lovejoy, Nathan |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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