| Summary: | Thesis (MSc)--Stellenbosch University, 2022. ENGLISH ABSTRACT: The challenges presented by the vast ocean confounds our understanding of speciation mechanisms in marine environments. As a result, most of our contemporary understanding of what drives speciation in marine environments is limited to a few taxonomic groups. In the case of coastal marine mammals, investigating the mechanisms responsible for speciation is especially confounded by disjunct distributions and perceived weak dispersal barriers. Only a few studies exist that investigates speciation mechanisms involved in marine mammals. This thesis thus aims to expand on our evolutionary understanding of marine mammals by presenting a case study from the Southern Oceans brown fur seal, Arctocephalus pusillus, which comprises two subspecies: Arctocephalus p. pusillus in Southern African and A. p. doriferus in Australia. The following two main hypotheses are posed i) the subspecies are genetically differentiated because cross-oceanic dispersals are rare, and ii) oceanic distance coupled with paleoclimate played an influential role in the incipient speciation of this taxon. To address these hypotheses, I estimated the population genetic structure, migration rates, and demographic histories using diversity- and variance metrics, Bayesian cluster analyses, Discriminant Analysis of Principal Components (DAPC), and approximate Bayesian computation (ABC). For this, thirteen microsatellites from 268 seals were genotyped and added to a previously sequenced mitochondrial control region (mtCR) dataset. Results confirmed that the subspecies have significantly diverged into two genetic groups, suggesting that the Indian Ocean currently acts as a geographical barrier to gene flow, as evident in the significant differentiation between subspecies (nuDNA: FST = 0.101, p ≤ 0.0001; mtCR: ΦST = 0.269, p ≤ 0.0001), the strong support for two continental clusters in Structure (ΔK = 1813.1), and a lack of immigrants after divergence (less than one immigrant per generation). At ...
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