Dissertation (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Historically, isopods of the suborder Phreatoicidea were thought to be represented in southern
Africa by four species belonging to the endemic genus Mesamphisopus. This taxonomy was
based on poor collections and the extent of variation among and within populations were
poorly understood. In the present study, intensive sampling was undertaken to determine the
diversity, distribution and biogeography of phreatoicidean isopods within South Africa.
Analyses of allozyme data and mitochondrial DNA sequences (from the 12S rRNA and
protein-coding COI genes) were used to examine differentiation among populations, extricate
species boundaries (in combination with morphometric and morphological data) and to
elucidate the evolutionary relationships among taxa. Additionally, conservation units were
identified among the sampled populations and conservation threats highlighted.
First, genetic and morphometric differentiation was examined among populations identified
morphologically as M. capensis. Collection localities spanned two mountainous regions in
the Western Cape and these were separated by a coastal plain remnant. Five
morphometrically and genetically distinct species were identified. These taxa are also
geographically partitioned in two regions, which were regarded as Evolutionarily Significant
Units. Differentiation among populations of the two regions, and similar patterns in other
taxa, was attributed to Cenozoic sea-level fluctuations.
Second, populations, variably assigned to M. abbreviatus or M. depressus, were examined to
determine whether they were conspecific. A large geographic area was sampled to account
for intraspecific differentiation. Limited morphometric discrepancies were observed, with
individual populations being either similar to the M. abbreviatus or the M. depressus
syntypes. Genetic support for the recognition of a cryptic species complex among the
sampled populations was equivocal. Substantial genetic differentiation and a lack of gene
flow were observed among all populations. Clear patterns of isolation by distance were not
detected, and genetic structure appeared to be unrelated to geography or drainage systems.
The mosaic pattern of relatedness among populations was best explained by stochastic
demographic processes, such as extinction-recolonization events or population bottlenecks.Thirdly, detailed taxonomic descriptions and illustrations of six new species, identified
genetically and morphometrically among the populations included in the above analyses, were
provided. These species were largely distinguished from each other, and the four original
species, using a combination of setation, mouthpart, pleopod and uropod features.
Lastly, phylogenetic relationships among all ten recognized Mesamphisopus species, and an
additional unresolved group of populations, were examined. MtDNA data partitions and a
recoded allele frequency matrix were analysed independently and in combination. Topologies
indicated unrecognized species-diversity within an unresolved group of populations.
Evolutionary relationships, the identification of six biogeographic centres, and the dating of
divergences using a relaxed Bayesian clock suggested that differentiation and speciation
within Mesamphisopus was largely allopatric or vicariant and driven by Mesozoic sea-level
and climate change. Chance long distance dispersal events would, in turn, explain spurious
phylogenetic relationships and distributions.
This study contributes significantly to the understanding of the diversity and the conservation
of the little-studied southern African freshwater invertebrates. Moreover, this study is the first
to investigate genetic and morphometric differentiation, and phylogenetic relationships, below
the generic level within the Phreatoicidea; thus establishing a methodological and theoretical
framework for species delineation and the accurate determination of biodiversity within
individual phreatoicidean genera. / AFRIKAANSE OPSOMMING: Isopoda van die suborder Phreatoicidea was histories in suidelike Afrika verteenwoordig deur
vier spesies wat almal aan die endemiese genus Mesamphisopus behoort. Hierdie taksonomie
is op ’n beperkte hoeveelheid versamelings gebaseer en die omvang van variasie tussen (en
binne) bevolkings was swak verstaan. In die huidige studie is ekstensiewe versameling
onderneem om die verspreiding, diversiteit asook biogeografie van dié Isopoda in Suid Afrika
te bepaal. Analises van allosiem data en mitokondriale DNS volgorderbepalings (van die 12S
rRNS en die proteïenkoderende COI geen) was gebruik om differensiasie tussen bevolkings te
ondersoek, om (in kombinasie met morfometriese en morfologiese data) spesiesgrense te
bepaal asook om die evolusionêre-verwantskappe tussen taksa te definieer. Benewens word
bewaringseenhede binne die studie-bevolkings geïndentifiseer en moontlike bedreigings
uitgelig.
Eerstens is genetiese en morfometriese differensiasie tussen bevolkings, wat as M. capensis
geïdentifiseer is, ondersoek. Versamelingslokaliteite was versprei oor twee bergagtige streke
in die Weskaap wat geskei word deur ’n voormalige kusvlakte. Vyf morfometries- en
geneties-afsonderlike spesies is geïdentifiseer. Dié taksa was geografies geskei tot die twee
streke, wat elk as ’n Evolusionêre Beduidende Eenheid (ESU) gesien kan word.
Differensiasie tussen populasies van die twee streke en vergelykbare patrone binne ander
taksa word aan Cenosoïese seevlak veranderings toegeskryf.
Tweedens is bevolkings wat as M. abbreviatus óf as M. depressus geïdentifiseer kan word
ondersoek om te bepaal of hulle konspesifiek is. Bevolkings is oor ’n groot geografiese
gebied versamel om intraspesifieke variasie in aanmerking te neem. Beperkte morfometriese
verskille is waargeneem – enkel bevolkings was morfometries identies aan of die M.
abbreviatus of die M. depressus sintipes. Genetiese getuienis vir die herkenning van ’n
kriptiese spesieskompleks was dubbelsinnig. Bevolkings is gekenmerk deur merkbare
genetiese differensiasie en die afwesigheid van geenvloei. Duidelike bewys van isolasie-metafstand
was nie waargeneem nie en genetiese struktuur was nie verwant aan geografiese
ligging of riviersisteme nie. Die mosaïese patroon van verwantskappe is moontlik teweeg
gebring deur stogastiese demografiese prosesse soos uitsterwing en hervestiging of deur
afnames in bevolkingsgrootte.Derdens is omvattende taksnomiese beskrywings en illustrasies van ses nuwe spesies wat deur
bogenoemde analises geneties en morfometries uitgelig was, verskaf. Dié spesies is van
mekaar, asook die ander vier spesies onderskeibaar deur ’n kombinasie van setasie-,
monddeel-, pleiopoot- en uropooteienskappe.
Laastens is die filogenetiese verwantskappe tussen al tien herkende Mesamphisopus-spesies
en ’n groep bevolkings waarvan verhoudings onseker was, ondersoek. MtDNS datastelle en
’n hergekodeerde alleelfrekwensie matriks is afsonderlike en in kombinasie geanaliseer.
Topologië het onherkende spesies-vlak diversiteit binne die bogenoemde groep bevolkings
aangedui. Evolusionêre verwantskappe, die herkenning van ses biogeografiese gebiede, en
die bepaling van tye van divergensie (d.m.v. ’n ontspanne Bayesiaanse molekulêre klok) het
aangetoon dat spesiasie binne Mesamphisopus grootliks allopatries was en deur Mesosoïese
seevlak- en klimaatsveranderings teweeg gebring is. Toevallige lang-aftstand verspreiding
kon dan eienaardige filogenetiese verhoudings en verspreidings verklaar.
Dié studie lewer ’n wesenlike bydrae tot die kennis van die diversiteit en tot die bewaring van
die onbestudeerde Suid Afrikaanse varswater ongewerweldes. Daarenbowe, is hierdie studie
die eerste om genetiese en morfometriese differensiasie benede die genusvlak binne die
Phreatoicidea te ondersoek; sodoende word die metodologiese en teoretiese raamwerk vir die
herkenning van spesies en die akkurate beskrywing van diversiteit binne afsonderlike genera
van die Phreatoicidea geskep.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16052 |
| Date | 12 1900 |
| Creators | Gouws, Gavin |
| Contributors | Cook, B.A., Matthee, C.A., University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxiv, 343 leaves : ill. |
| Rights | University of Stellenbosch |
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