| Summary: | The sperm whale (Physeter macrocephalus) shows some of the most derived characteristics of any mammal: a large body size, large brain, complex social organization and a capacity for deep foraging dives that few other marine mammals can match. Despite a history of exploitation that removed hundreds of thousands of individuals, the sperm whale population remains relatively abundant in comparison with other large whale species. Given this abundance, and the sperm whale's matrifocal social organization, it is surprising that previous research found that mitochondrial DNA control region (mtDNA CR) diversity in sperm whales is extremely low and population structure is relatively limited within oceans. This dissertation addresses several questions spanning evolutionary and ecological time scales, including whether the low levels of mtDNA CR diversity and differentiation seen in the sperm whale have been limited by sample size and geographic scope in previous studies; how sperm whale genetic diversity is partitioned at several hierarchical levels; and hypotheses explaining the low mtDNA CR diversity. To achieve this, I generated DNA profiles representing 557 individuals from circum-equatorial regions, strandings around the coasts of New Zealand, Samoa and Oregon, and biopsy samples from the Gulf of Mexico. DNA genotypes constructed from these samples (mtDNA CR, sex, 13 microsatellite loci), and mtDNA information from 1,167 previously published samples, indicated a high degree of mtDNA CR differentiation within the previously un-sampled Indian Ocean (FST 0.314, p < 0.001). The level of differentiation seen was similar to that found with the marginal seas of the Atlantic i.e. the Gulf of Mexico and the Mediterranean (FST 0.469, p < 0.001). In contrast, levels of mtDNA differentiation seen in the Pacific were much lower (FST 0.061, p < 0.001). Microsatellite differentiation was much less marked for all three oceans, consistent with tests indicating male-biased dispersal and gene flow. In addition to regional ...
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