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A Phylogenetic Synthesis for Oceanic Dolphins: Total Evidence, Cytonuclear Discordance, and Possible Introgressive Hybridization


Introgressive hybridization is increasingly being detected in vertebrate taxa but was thought to be rare in mammals. Recent evidence suggests that this view might not correct and cetaceans may be pre-disposed for the capacity to hybridize. Numerous instances of cetacean (dolphins, whales, and porpoises) hybridization have been reported both in captivity and in the wild, many of which occurred in oceanic dolphins: family Delphinidae. The rapid radiation of Delphinidae commenced during the Miocene, and is a prime example of an explosive radiation. Coinciding with reports of delphinid hybridization, many relationships within this cetacean family have been difficult to resolve. Conflicting phylogenetic hypotheses have resulted for some taxa from the use of nuclear versus mitochondrial sequence. In this thesis, I examine conflicting phylogenetic hypotheses for family Delphinidae by compiling the largest dataset for phylogenetic analyses yet assembled. This dataset consists of entire mitochondrial genomes, over 40 nuclear loci, and 282 morphological characters scored for extant and extinct taxa. I execute a combination of analyses, including parsimony, maximum likelihood, phylogenetic supernetworks, and gene-tree based coalescent reconstruction methods. I construct phylogenetic hypotheses from combined and individual datasets and explore conflict/support for alternative hypotheses arising from mitochondrial data, nuclear data, and morphology. In addition, I report on all known instances of cetacean hybridization from the literature. The resultant phylogenetic hypotheses provide evidence of alternative patterns of descent for some taxa. The sum totals of evidence suggest that mitochondrial introgression might be the source of phylogenetic discordance for some delphinids.

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