Population genetics of Pseudobarbus phlegethon, Barbus calidus and Barbus erubescens (Teleostei: Cyprinidae) of the Olifants River System, Western Cape Province

Swartz, Ernst Roelof (2000-03)

Thesis (MSc)--University of Stellenbosch, 2000.

Thesis

ENGLISH ABSTRACT: Endemic redfin minnows of the Olifants River System are under threat of extinction, mainly because of alien predatory fish, water extraction and pollution. The taxonomic position and biogeography of redfins in relation to other barbs are uncertain. Enzyme electrophoresis was employed to assess genetic differentiation within and among certain Barbus and Pseudobarbus taxa. Fourteen enzymes were routinely recorded from muscle tissue extracts, yielding a differential number of active loci. The latter is due to different ploidy levels. Polyploid species showed fewer loci than the tetraploid or hexaploid number of loci expected just after the polyploidy event. Barbus aenus (hexaploid) expressed 6.2 % of the duplicated loci expected after the hexaploidy event. The tetraploid Pseudobarbus and serrated Barbus spp., expressed 37.5 % and 31.2 % of the duplicated loci expected after the tetraploidy event, respectively. This suggests that the ploidy event in Barbus aenus is more ancient than in the above-mentioned tetraploid barbs. The similar amount of diploidization in Pseudobarbus and tetraploid serrated Barbus spp. investigated, suggests a shared ploidy event between these two lineages. The number of active loci is apparently not a good indication of the ploidy level of African barbs, as hexaploid Barbus aenus expressed less active loci than the tetraploid barbs investigated. Initial screening of allozyme loci yielded fixed allele differences at 22 loci, but polymorphism only at seven. This suggests more potential for delineating species boundaries than for assessing gene flow and genetic diversity of populations. Genetic differentiation within and among populations of Pseudobarbus phlegethon, Barbus calidus and Barbus erubescens were investigated by screening 27 allozyme loci. A clear divergence between Pseudobarbus phlegethon populations from the Olifants and Doring Rivers was found (Nei's unbiased genetic distance = 0.355; F-statistic for subpopulation against the total = 0.877). Preference and adaptation for mountain stream habitat might explain the past isolation and subsequent divergence of Pseudobarbus phlegethon populations between these two rivers. Barbus calidus was genetically homogenous over its distribution (Nei's unbiased genetic distance = 0-0.009; F-statistic for subpopulation against the total = 0.135). It is proposed that Barbus calidus is better adapted than Pseudobarbus phlegethon to disperse through the main stream. The genetic divergence between Barbus calidus and Barbus erubescens (Nei's unbiased genetic distance = 0.063) is characteristic of conspecific populations. There seems to have been a loss of genetic diversity in redfin populations of the Doring River tributaries (heterozygosity = 0-0.01), compared to the redfin populations of the Olifants River tributaries (heterozygosity = 0.01- 0.04). From phylogenetic analysis ofallozyme characters, it seems as if the serrated tetraploid barbs from South Africa is the sister-group of Pseudobarbus, whilst Barbus anoplus was rejected as a sister-species for the latter. Barbus calidus, Barbus erubescens and Barbus serra were found to be closely related to each other. The ancestor of the redfins seems to have been present in the Cape Fold Mountains since at least the late- Tertiary. On the basis of distributional and allozyme information, conservation units reflecting historical divergence, historical gene flow and current gene flow were identified as Evolutionarily Significant Units, Historical Management Units and Current Management Units respectively. The Olifants and Doring River populations of Pseudobarbus phlegethon should be recognized as two distinct Evolutionarily Significant Units. Barbus calidus forms a separate Evolutionarily Significant Unit from Barbus erubescens. Twelve Historical Management Units and nineteen Current Management Units were recognized for redfins of the Olifants River System. The size of Current Management Units should be expanded and secured to prevent loss of genetic diversity. It is recommended that a recovery program of redfins should establish new populations of at least Barbus erubescens and Doring River Pseudobarbus phlegethon Evolutionarily Significant Unit. Centrarchids should be irradicated, as they are the main reason for the decline of red fins.

AFRIKAANSE OPSOMMING: Die endemiese rooivlerkies van die Olifantsriviersisteem word bedreig deur uitsterwing, hoofsaaklik as gevolg van uitheemse roofvisse, water onttrekking en besoedeling. Die taksonomiese posisie en biogeografie van rooivlerkies in verhouding met ander barbusse is onseker. Ensiemelektroferese is gebruik om genetiese differensiasie binne en tussen sekere Barbus en Pseudobarbus taksa te bepaal. Veertien ensieme, wat verskillende hoeveelhede aktiewe lokusse gelewer het, is op roetine basis waargeneem uit spierweefselekstrakte. Die verskillende hoeveelhede aktiewe lokusse wat waargeneem is, is as gevolg van verskillende ploied vlakke. Poliploïede spesies het minder lokusse getoon as wat verwag sou word net na die tetraploïede ofheksaploïede gebeurtenisse. Barbus aenus (heksaploïed) het 6.2% van die gedupliseerde lokusse, wat verwag sou word na die heksaploiede gebeurtenis, uitgedruk. Die tetraploïede Pseudobarbus en saagagtige Barbus spp. het 37.5% en 3l.2% respektiewelik van die gedupliseerde lokusse, wat verwag sou word na die tetraploïede gebeurtenis, uitgedruk. Dit dui daarop dat die ploïede gebeurtenis in Barbus aenus meer histories as in die bogenoemde tetraploïede barbusse. Die soortgelyke hoeveelheid diploïedisasie in Pseudobarbus en tetraploïede saagagtige Barbus spp. wat ondersoek is, dui op 'n moontlike gesamentlike ploïede gebeurtenis tussen hierdie twee evolusionêre lyne. Die aantal aktiewe lokusse blyk nie 'n goeie aanduiding van die ploïed vlakke van Afrika barbusse te wees nie, aangesien die heksaploïede Barbus aenus minder lokusse as die tetraploïede barbusse wat ondersoek is, getoon het. Aanvanklike analisering van allosiem lokusse het vaste alleel verskille in 22 lokusse opgelewer, maar slegs sewe het polimorfisme getoon. Dit dui op moontlike beter potensiaalom spesie-grense vas te stel, eerder as die bepaling van genevloei of genetiese diversiteit van populasies. Genetiese differensiasie binne en tussen populasies van Pseudobarbus phlegethon, Barbus calidus en Barbus erubescens is ondersoek deur 27 allosiem lokusse te analiseer. 'n Duidelike divergensie tussen Pseudobarbus phlegethon populasies van die Olifants- en Doring- riviere is gevind (Nei se onbevooroordeelde genetiese afstand = 0.355; F-statistiek vir subpopulasie teen die totaal = 0.877). Voorkeur en aanpassing vir bergstroom habitat, mag moontlik die historiese isolasie en daaropvolgende divergensie van Pseudobarbus phlegethon populasies tussen hierdie twee riviere verduidelik. Barbus calidus was geneties homogeen oor sy verspreiding (Nei se onbevooroordeelde genetiese afstand = 0-0.009; F-statistiek vir subpopulasie teen die totaal = 0.135). Dit word voorgestel dat Barbus calidus beter aangepas is as Pseudobarbus phlegethon om deur die hoofstroom te versprei. Die genetiese divergensie tussen Barbus calidus en Barbus erubescens (Nei se onbevooroordeelde genetiese afstand = 0.063) is kenmerkend van spesiespesifieke populasies. Dit lyk of daar 'n verlies aan genetiese diversiteit in rooivlerkie populasies vanafdie Doringrivier sytakke was (heterosigositeit = 0-0.01), in vergelyking met rooivlerkie populasies vanafdie Olifantsrivier sytakke (heterosigositeit = 0.01- 0.04). Uit die filogenetiese analise van allosiem kenmerke, blyk dit dat die saagagtige tetraploiede barbusse van Suid-Afrika die sistergroep van Pseudobarbus is, terwyl Barbus anoplus verwerp word as sisterspesie vir laasgenoemde. Dit is gevind dat Barbus calidus, Barbus erubescens en Barbus serra baie naverwant aan mekaar is. Dit lyk asof die voorvader van die rooivlerkies sedert ten minste die laat-Tersiêr in die Kaapse Plooiberge aanwesig was. Bewaringseenhede wat historiese divergensie, historiese genevloei en huidige genevloei voorstel, is geidentifiseer respektiewelik as Evolusionêre Beduidende Eenhede, Historiese Bestuurseenhede en Huidige Bestuurseenhede. Dit is gedoen op grond van verspreidings- en allosieminformasie. Die Olifants en Doring populasies van Pseudobarbus phlegethon moet as twee unieke Evolusionêre Beduidende Eenhede erken word. Barbus calidus en Barbus erubescens vorm aparte Evolusionêre Beduidende Eenhede. TwaalfHistoriese Bestuurseenhede en negentien Huidige Bestuurseenhede is geidentifiseer vir rooivlerkies van die Oifantsriviersisteem. Die grootte van Huidige Bestuurseenhede moet vergroot en beveilig word om verlies van genetiese diversiteit te vermy. Dit word voorgestel dat 'n herstelprogram van rooivlerkies moet poog om nuwe populasies, van ten minste Barbus erubescens en Doringrivier Pseudobarbus phlegethon Evolusionêre Beduidende Eenhede, te vestig. Baars en blouwang sonvis moet uitgeroei word, aangesien hulle die hoofoorsaak is vir die afname van rooivlerkies.

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