Thesis (PhD)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Introduced species displace native species and alter ecological communities, affect
agriculture as well as human health and are economically costly to eradicate. Long term
monitoring of introduced species including the documentation of levels of genetic variation is
therefore of the utmost importance. This study investigated the distribution of genetic variation
in two introduced species distributed across South Africa the bud gall-forming wasp
Trichilogaster acaciaelongifoliae and the Argentine ant Linepithema humile.
The bud gall-forming wasp was introduced into South Africa as a biological control
agent to curb the spread of the invasive long-leaved wattle Acacia longifolia. In addition to the
intended (target) host, the bud gall-forming wasp has also colonised A. floribunda, a noninvasive
ornamental plant. Limited genetic variation was found across South Africa based on
the mitochondrial DNA cytochrome oxidase subunit I (COI) gene. Only 3 haplotypes
characterized 53 individuals collected from 23 localities (nucleotide diversity £k = 0.002 ¡Ó
0.001, haplotype diversity h = 0.482 ¡Ó 0.045). No significant partitioning of genetic variation
was found across South Africa including between host plants (target host = A. longifolia, non
target host = A. floribunda) or between the core (sites of introduction) and edge (naturally
dispersed) sites (ĦST = 0.094, P = 0.288). The limited genetic variation and the absence of
significant genetic structure are congruent with patterns described for many other introduced
species and may suggest that propagule pressure plays only a minor role in species
establishment and spread of the gall-forming wasp across South Africa.
Mitochondrial and nuclear markers were used to describe the distribution of genetic
variation within Argentine ants across their introduced range in South Africa. For the
mitochondrial DNA, low genetic diversity was found for the COI gene with only five haplotypes, separated by single mutational changes, characterizing 101 specimens from 35
localities (nucleotide diversity π = 0.001 ± 0.001, haplotype diversity h = 0.151 ± 0.048).
Notwithstanding the low levels of genetic diversity, mitochondrial variation was significantly
structured (ST = 0.54, P < 0.001) across the landscape. In contrast, microsatellite analyses of
230 ants from 23 localities, employing six polymorphic microsatellite markers, revealed a
relatively high amount of genetic diversity (HE = 0.51 ± 0.22). Significant population structure
was similarly evident (RST = 0.14, P < 0.001) with the localities of Elim2, Porterville2 and
Bloemfontein2 clustering as a distinct population from the remainder of the localities.
Importantly, individuals from these localities also had a unique mitochondrial haplotype and,
when taken with the nuclear results, may indicate the occurrence of more than one introduction
event (and possibly more than one colony) in South Africa. This is further underscored by the
presence of unique microsatellite alleles in these three populations.
In an attempt to establish the source populations for the introduction of Argentine ants
into South Africa, mitochondrial cytochrome b sequences were generated for a subset of ants
representing the two major genetic clades across South Africa. A comparison with the
published data from across the world including the native range of the Argentine ant in South
America grouped Argentine ants from South Africa with three potential source populations
namely Ocampo and Rosario in Argentina and Passo do Lontra in Brazil.
The results of this study underscore the role of human-mediated dispersal in shaping the
levels of genetic variation in both species. Human-mediated dispersal can lead to genetic homogenization across populations. / AFRIKAANSE OPSOMMING: Indringer spesies verplaas of verander ekologiese gemeenskappe, beinvloed landbou
asook menslike gesondheid en is ekonomies duur om te verwyder. Langtermyn monitering van
indringer spesies asook die dokumentasie van genetiese variasie is dus baie belangrik. Hierdie
studie bestudeer die verspreiding van genetiese variasie in twee indringer spesies wat regoor
Suid-Afrika voorkom, naamlik die kroongal-vormende wespe Trichilogaster
acaciaelongifoliae en die Argentynse mier Linepithema humile.
Die kroongal-vormende wesp is na Suid Afrika gebring as biologiese beheeragent om
die verspreiding van indringer lang-blarige wattle Acacia longifolia te beveg. Die kroongalvormende
wespe het sowel die teiken spesies, asook A. floribunda, ‘n nie-indringer
ornamentele plant gekoloniseer. Beperkte genetiese variasie is gevind regoor Suid Afrika
gebasseer op die mitochondriale DNA sitokroom-oksidasie subeenheid I (COI) geen. Slegs 3
haplotipes karakteriseer 53 indiviue van 23 bevolkings (nukleotied diversiteit π = 0.002 ±
0.001, haplotiep diversiteit h = 0.482 ± 0.045). Geen beduinde groepering van genetiese variase
is gevind regoor Suid Afrika nie (ST = 0.094, P = 0.288). Hierdie bevinding geld onafhanklik
van die gasheer plant (teiken gasheer = A. longifolia, nie-teiken gasheer = A. floribunda). Ook
is geen beduidende genetiese groepering gevind tussen die sentrale (plek van inisiele
blootstelling) en perifêre (natuurlik verspreide) lokaliteite nie. Die kleinskaalse genetiese
variase en die afwesigheid van beduidende genetiese struktuur wat hier gevind is, verskil van
die patrone wat voorheen vir baie ander indringer-spesies beskryf is. Dit mag daarop dui dat
‘propagule’ druk slegs ’n klein rol speel in spesies-vestiging en verspreiding van die galvormende
wespe regoor Suid-Afrika. Mitochondriale asook kern merkers is gebruik om die verspreiding van genetiese
variasie in Argentynse miere in Suid Afrika te beskryf. Vir die mitochondriale DNA is lae
genetiese variase gevind vir die COI geen, met slegs 5 haplotipes, gedifferensieer deur enkele
mutasie veranderinge wat 101 monsters van 35 lokaliteite karakteriseer (nukleotied diversiteit
π = 0.001 ± 0.001, haplotiep diversiteit h = 0.151 ± 0.048). Desondanks die lae genetiese
variasie, is gevind dat mitochondriale variasie beduidend gestruktureerd is (ST = 0.54, P <
0.001) oor die landskap. Hierteenoor het mikrosatelliet analises van 230 miere van 23
lokaliteite, deur gebruik te maak van ses polimorfiese mikrosatelliet merkers, ’n relatiewe hoë
hoeveelheid genetiese diversiteit aangedui. Beduidende bevolkingstruktuur was ook gevind
(RST = 0.14, P < 0.001) in die areas Elim2, Porterville2 en Bloemfontein2 wat saam groepeer
as eiesoortige bevolkings vergeleke met die res van die areas. Ook van belang is dat individue
van die areas ’n unieke mitochondriale haplotipe besit, en in kombinasie met die kern resultate,
mag dit die voorkoms van meer as een blootstellingsgeleentheid (en moontlik meer as een
kolonie) in Suid Afrika aandui. Hierdie bevinding word verder beklemtoon deur die
teenwoordigheid van unieke mikrosatelliet allele in die drie bevolkings.
In ‘n poging om die oorsprong van die oorsprong-bevolking vir die blootstelling van
Argentynse miere in Suid Afrika vas te stel, is mitochondriale sitokroom b volgordes
gegenereer vir ’n substel miere wat die twee hoof genetiese klades in Suid Afrika voorstel.
Vergelyking met gepubliseerde data van regoor die wêreld, insluitende die endemiese gebied
van die Argentynse mier in Suid Amerika, het die Argentynse mier van Suid Afrika met drie
potensiele oorsprong-bevolking verbind, naamlik Ocampo en Rosario in Argentina en Passo do Lontra in Brazil.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4840 |
| Date | 12 1900 |
| Creators | Lado, Thomas Francis |
| Contributors | Jansen van Vuuren, Bettine, Chown, Steven L., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbsoch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 90 p. : ill., maps |
| Rights | Stellenbosch University |
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