Population genetics of bush-encroaching acacia mellifera at Pniel, Northern Cape Province, South Africa

Nxele, Beka Jeremia (2010-12)

Thesis (MScConEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: Two populations of Acacia mellifera were noted in Pniel, which is a semi-arid savanna, near Kimberley in the Northern Cape province of South Africa. One population appeared on a rocky, andesitic laval ridges (soil pHKCL 6.5-7.0) along the Vaal river. The other appeared in a sandveld area (soil pHKCL 4). Bush encroachment by A. mellifera was found to be more extensive on the rocky areas than in the sandveld and the two habitats differed extensively on soil pH, clay and silt contents and also on water holding capacities. The rocky habitat was thus deduced to have a higher CEC. Seeds were sampled on a logarithmic scale for allozyme analysis and also randomly in each of the two habitats for local adaptation tests, in which case lime (CaCO3) and organic matter (cow-dung) were used in a completely-crossed design. Detected interaction effects (between population source and pH; population source and organic matter and between pH and organic matter) and significant differences could not separate the two populations as the differences occurred across populations. Random genetic differences leading to phenotypic plasticity in the two observed populations, might be responsible for the observed phenotypic differences. Allozymic data showed no significant differences between the two populations and the genetic distance between and within the populations also confirmed that the two populations had not genetically differentiated. The Mantel Test on the two populations, showed nonsignificant results. Nei‟s UPGMA dendrogram revealed that the game farm subpopulations were more primitive and genetically related to each other. Despite differences in allozyme frequencies, between the sampled sites, genetic differentiation was found to be low (FST = 0.337). Nei‟s (1972) original measures of genetic distance ranged between 0.871 and 1.000 with a mean of 0.949 ± 0.053. The study concluded that the two observed populations had not genetically differentiated and no local adaptation could be established rather phenotypic plasticity was evident and resulted in the observed divergent growth forms. Nonetheless, the overall direction of spread of encroachment appeared to be the eastward.

AFRIKAANSE OPSOMMING: Twee bevolkings van Acacia mellifera is gevind in Pniel, wat „n semi-ariede savanna is naby Kimberley in die Noord-Kaap provinsie van Suid-Afrika. Een bevolking het voorgekom op klipperige andesitiese lava riwwe (grond pHKCL 6.5-7.0) al langs die Vaalrivier. Die ander het voorgekom in „n sandveld area (soil pHKCL 4). Bos-oorskryding deur A. mellifera was meer uitgebreid op die klipperige areas as in die sandveld en die twee habitats het noemenswaardig verskil ten opsigte van grond pH, klei en silt inhoud asook waterhoukapasiteit. Dit kan was dus afgelei word dat die klipperige habitat „n hoër CEC het. Die sade was versamel op „n logaritmiese skaal vir allosiem-analise en ook ewekansig in die twee habitats vir lokale aanpassings toetse. In dié gevalle was kalk (CaCO3) en organiese material (koeimis) gebruik in „n totaal-gekruisde ontwerp. Bespeurde interaksie effekte (tussen bevolkings bron en pH; bevolkings bron en organiese material en tussen pH en organiese material) en noemenswaardige verskille kon nie die twee bevolkings skei nie, aangesien die verskille voorgekom het regdeur die twee bevolkings. Ewekansige genetiese verskille wat lei tot fenotipiese plastisiteit tussen die twee waargeneemde bevolkings mag dalk verantwoordelik wees vir die waargeneemde fenotipiese verskille. Allosiem-data het geen beduidende verskille gelewer tussen die twee bevolkings nie en genetiese afstand binne en tussen die bevolkings het ook bevestig dat die twee bevolkings nie geneties gedifferensiëer is nie. Die Mantel toets op die twee bevolkings het geen beduidende resultate gelewer nie. Nei se UPGMA dendogram get gewys dat die wildsplaas bevolkings was meer primitief en geneties verwant aan mekaar. Ten spyte van die allosiem frekwensies tussen die gemonsterde gebiede, was die genetiese differensiasie laag (FST = 0.337). Nei (1972) se oorspronlike meeting van genetiese afstand het tussen 0.871 en 1.000 beloop met „n gemiddeld van 0.949 ± 0.053. Die studie het bepaal dat die twee waargeneemde bevolkings nie geneties gedifferensiëer het nie en dat geen lokale aanpassing teenwoordig was nie. Fenotipiese plastisiteit was duidelik waarneembaar en het gelei tot die divergerende groeivorme. Nieteenstaande, was die algehele rigting van oorskryding ooswaarts.

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