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Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals
Thesis (MSc)--Stellenbosch University, 2022.
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| Format: | Thesis |
| Language: | af_ZA |
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Stellenbosch : Stellenbosch University
2022
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| _version_ | 1867613846932291584 |
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| access_status_str | Open Access |
| author | Malan, Amore |
| author2 | Matthee, Conrad A. |
| author_browse | Malan, Amore Matthee, Conrad A. |
| author_facet | Matthee, Conrad A. Malan, Amore |
| author_sort | Malan, Amore |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2022. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/125100 |
| institution | Stellenbosch University (South Africa) |
| language | af_ZA |
| last_indexed | 2026-06-10T12:42:38.497Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2022 |
| publishDateRange | 2022 |
| publishDateSort | 2022 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/125100 Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals Malan, Amore Matthee, Conrad A. Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. Phylogeography Marine mammals -- Geographical distribution -- Climatic factors South African fur seal -- Ecology Climatic changes -- Southern Ocean Population genetics Seals (Animals) -- Genetics Seals (Animals) -- Environmental aspects UCTD 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 the local scale, brown fur seals are not influenced by geographical barriers, and site philopatry is not strong enough to result in subpopulation structuring. Demographic models suggest that the divergence time between the two subspecies coincides with the Last Glacial Maximum (LGM). Arctocephalus p. pusillus founded A. p. doriferus through a colonisation event out of Africa and ceased to show meaningful gene exchange after ~12 Kya. At the height of the LGM, lower sea levels likely facilitated migrations from Southern Africa to Australia when more landmasses of mid-oceanic islands were exposed and the subsequent increase in sea-level disrupted gene flow, resulting in a potential speciation event. With the data at hand, it seems reasonable to conclude that early stages of speciation in this Arctocephalus species are the direct result of a LGM paleoclimatic event, altering the marine habitat to such an extent that long-distance dispersal was possible from Southern Africa to Australia - ultimately giving rise to the two brown fur seal subspecies. AFRIKAANSE OPSOMMING: Die uitdagings wat die groote van oseaan bied, verduister ons begrip van spesiasiemeganismes in mariene omgewings. Gevolglik bestaan meeste van ons hedendaagse begrip van wat spesiasie in mariene omgewings dryf slegs uit 'n paar taksonomiese groepe. In die geval van kus seesoogdiere, word die meganismes wat vir spesiasie verantwoordelik is veral deur groot oseaniese afstande en waargenome swak verspreidingshindernisse verduister. Slegs 'n paar studies ondersoek spesiasiemeganismes wat by seesoogdiere betrokke is. Dus het hierdie tesis gemik om uit te brei op ons evolusionêre begrip van seesoogdiere deur te fokus op 'n gevallestudie van die Suidelike Oseane bruin pelsrob, Arctocephalus pusillus, wat uit twee subspesies bestaan: Arctocephalus p. pusillus in Suider-Afrika en A. p. doriferus in Australië. Die volgende twee hoofhipoteses word gestel: i) die subspesie is geneties gedifferensieer omdat kruis-oseaniese verspreidings skaars is, en ii) oseaniese afstand tesame met paleoklimaat het 'n belangrike rol gespeel in die beginnende spesievorming van hierdie takson. Om hierdie hipoteses aan te spreek, het ek die bevolkingsgenetiese struktuur, migrasietempo's en demografiese geskiedenisse beraam deur diversiteit- en variansiemetrieke, Bayesiaanse groeperingsanalises, Diskriminerende Analise van Hoofkomponente (DAPC) en benaderde Bayesiaanse berekening (ABC) te gebruik. Hiervoor is dertien mikrosatelliete van 268 robbe gegenotipeer en by 'n reeds bestaande mitochondriale beheergebied (mtCR) datastel bygevoeg. Resultate het bevestig dat die subspesies in twee genetiese groepe verdeel het, wat daarop dui dat die Indiese Oseaan tans as 'n geografiese versperring vir geenvloei optree, soos waargeneem in die aansienlike differensiasie tussen subspesies (nuDNA: FST = 0,101, p ≤ 0,0001; mtCR: ΦST = 0.269, p ≤ 0.0001), die sterk ondersteuning vir twee kontinentale genetiese groepte in ‘Structure’ (ΔK = 1813.1), en 'n gebrek aan immigrante na divergensie (minder as een immigrant per generasie). Op plaaslike skaal word bruin pelsrobbe nie deur geografiese hindernisse beïnvloed nie, en terreinfilopatie is nie sterk genoeg om subpopulasiestrukturering te veroorsaak nie. Demografiese modelle dui daarop dat die divergensietyd tussen die twee subspesies ooreentem met die Laaste Gletser Maksimum (LGM). Arctocephalus p. pusillus vestig A. p. doriferus deur 'n kolonisasiegebeurtenis uit Afrika en het opgehou om betekenisvolle geenuitruiling te toon na ~12 Kya. Op die hoogtepunt van die LGM het laer seevlakke migrasies van suidelike Afrika na Australië vergemaklik toe meer landmassas van middel-oseaniese eilande blootgestel is en die daaropvolgende toename in seevlak genevloei ontwrig het, wat gelei het tot 'n moontlike spesiasiegebeurtenis. Met die data byderhand, lyk dit redelik om tot die gevolgtrekking te kom dat die vroeër stadiums van spesiasie in hierdie Arctocephalus- spesie die direkte gevolg is van 'n LGM paleoklimatiese gebeurtenis wat die mariene habitat so verander het dat langafstandverspreiding van Suider-Afrika na Australië moontlik was - wat uiteindelik gelei het tot die twee bruin pelsrob subspesies. Masters 2022-02-10T10:40:53Z 2022-04-29T12:53:58Z 2022-08-14T03:00:10Z 2022-04 Thesis http://hdl.handle.net/10019.1/125100 af_ZA Stellenbosch University xv, 87 pages : illustrations(some color), maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Phylogeography Marine mammals -- Geographical distribution -- Climatic factors South African fur seal -- Ecology Climatic changes -- Southern Ocean Population genetics Seals (Animals) -- Genetics Seals (Animals) -- Environmental aspects UCTD Malan, Amore Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| title | Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| title_full | Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| title_fullStr | Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| title_full_unstemmed | Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| title_short | Marine mammal speciation: the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| title_sort | marine mammal speciation the role of oceanic distance and historical climatic change on the evolutionary divergence of brown fur seals |
| topic | Phylogeography Marine mammals -- Geographical distribution -- Climatic factors South African fur seal -- Ecology Climatic changes -- Southern Ocean Population genetics Seals (Animals) -- Genetics Seals (Animals) -- Environmental aspects UCTD |
| url | http://hdl.handle.net/10019.1/125100 |
| work_keys_str_mv | AT malanamore marinemammalspeciationtheroleofoceanicdistanceandhistoricalclimaticchangeontheevolutionarydivergenceofbrownfurseals |