Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Twenty five years after the last major morphological revision, phylogenetic
relationships were inferred on the basis of a new DNA dataset for the African orchid
subtribe Disinae, which includes the large genus Disa and the small genus
Schizodium. One nuclear gene region (ITS) and two plastid gene regions (trnLF and
matK) were sequenced for 136 ingroup, representing 70% of all known Disinae
species, as well as for 7 outgroup taxa. The combined data matrix contained 4094
characters and was analysed using parsimony and Bayesian inference. The generic
status of Schizodium can no longer be supported, as it is deeply embedded within the
genus Disa. Furthermore, the currently recognised subgenera do not reflect the
phylogenetic relationships. Several of the currently recognised sections are
monophyletic, others contain misplaced elements, while some are polyphyletic. These
results necessitate a re-classification of the Disinae. A monotypic subtribe Disinae and
a subdvision of Disa into eighteen sections is formally proposed. These sections are
monophyletic, well-supported, morphologically distinguishable and are delimited to
maximize the congruence with the previous classification. All currently known
species are enumerated and assigned to sections.
Likelihood optimisation onto a dated molecular phylogeny is subsequently used to
explore the historical biogeography of Disa, as well as of three other Cape lineages
(Irideae p.p., the Pentaschistis clade and Restionaceae), to find out where these
lineages originated and how they spread through the Afrotemperate region. Three
hypotheses have been proposed: (i) a tropical origin with a southward migration
towards the Cape; (ii) a Cape origin with a northward migration into tropical Africa
and (iii) vicariance. None of these hypotheses, however, has been thoroughly tested.
In all cases, tropical taxa are nested within a predominantly Cape clade and there is
unidirectional migration from the Cape into the Drakensberg and from there
northwards into tropical Africa. Dating estimates show that the migration into tropical
East Africa has occurred in the last 17 million years, consistent with the Mio-Pliocene
formation of the mountains in this area. The same technique is then utilised to reconstruct the temporal occurrence of ancestral
ecological attributes of the genus Disa. The first appearance of species in the
grassland and savanna biomes, as well as in the subalpine habitat, are in agreement
with the existing, reliable geological and paleontological information. This suggests
that phylogenies can be used to date events for which other information is lacking or
inconclusive, such as the age of the fynbos biome and the start of the winter rainfall
regime in southern Africa. The results indicate that these are much older than what is
currently accepted and date back to at least the Oligocene. / AFRIKAANSE OPSOMMING: Vyf-en-twintig jaar na die laaste groot morfologiese hersiening, is die filogenetiese
verwantskappe van die Afrika orgideë subtribus Disinae, wat die groot genus Disa en
die klein genus Schizodium insluit, in hierdie studie op grond van ‘n nuwe DNA
datastel afgelei. Daar is van 136 binnegroep, wat 70% van alle bekende Disinae
spesies verteenwoordig, sowel as sewe buitegroep taksa geenopeenvolgings van een
nukleêre geen streek (ITS) en twee plastiedgeen streke (trnLF en matK) bepaal. Die
gekombineerde data matriks het 4094 karakters bevat en is met die parsimonie en
Bayesian metodes ontleed. Die generiese status van Schizodium kan nie hieruit
ondersteun word nie, en is diep ingebed binne die genus Disa. Die huidiglik
aanvaarde subgenera word ook nie deur hierdie filogenie ondersteun nie. Verskeie van
die huidiglik herkende seksies is bevind om monofileties te wees, ander bevat
verkeerd geplaasde spesies, terwyl ander polifileties blyk te wees. ’n Monotipiese
subtribus Disinae en ’n onderverdeling van Disa in agtien seksies word formeel
voorgestel. Dié seksies is monofilities, goed ondersteun, morfologies onderskeibaar
en omskryf om maksimaal ooreen te stem met die vorige klassifikasie. Alle huidiglik
bekende spesies word gelys en toegewys aan seksies.
Waarskynlikheidsoptimalisering op ’n gedateerde molekulêre filogenie is dan gebruik
om die historiese biogeografie van Disa te ondersoek, tesame met drie ander Kaapse
groepe (Irideae p.p., die Pentaschistis klade en Restionaceae), om te bepaal waar
hierdie groepe hulle oorsprong gevind het en hoe hulle na die “Afrotemperate“ streek
versprei het. Drie hipoteses word voorgestel: (i) ’n tropiese oorsprong met ’n
suidwaartse migrasie na die Kaap; (ii) ’n Kaapse oorsprong met ’n noordwaartse
migrasie na tropiese Afrika, en (iii) vikariansie. Geen van hierdie hipoteses is egter
vantevore deeglik getoets nie. In alle gevalle is bevind dat die tropiese taksa
oorwegend binne ’n Kaapse klade gesetel is, en dat daar ’n eenrigting migrasie is van
die Kaap na die Drakensberge en van daar noordwaarts na tropiese Afrika.
Dateringsskattings toon dat die migrasie na tropiese Oos-Afrika in die laaste 17
miljoen jaar plaasgevind het, ooreenstemmend met die Mio-Plioseen vorming van die
berge in die area. Dieselfde tegniek is daarna aangewend om die temporale voorkoms van voorvaderlike
ekologiese eienskappe van die genus Disa te rekonstrueer. Die eerste voorkoms van
die spesies in die grasveld en savanna biome, sowel as die subalpiene habitat, is in
ooreenstemming met bestaande, betroubare geologiese en paleontologiese informasie.
Dit suggereer dat filogenieë gebruik kan word om gebeurtenisse te dateer waarvoor
daar informasie ontbreek of nie beslissend is nie, soos die ouderdom van die Fynbos
bioom en die begin van die winterreënval stelsel in suider-Afrika. Die resultate dui
daarop dat dit heelwat ouer is as wat tans aanvaar word en terugdateer na ten minste
die Oligoseen.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19441 |
| Date | 03 1900 |
| Creators | Bytebier, Benny (Benny Leopold Germaine) |
| Contributors | Bellstedt, Dirk U., Linder, H. Peter, Stellenbosch University. Faculty of Science. Dept. of Biochemistry. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | x, 116 leaves : ill. |
| Rights | Stellenbosch University |
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