Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: It is thought that a large proportion of the great variety of floral structures in flowering plants
reflect adaptations to different biotic pollen vectors. Divergence in flower traits and pollinators
is linked to speciation. Pollinator-driven speciation is thought to have played a large role in the
spectacular floral diversity found in South African Iridaceae and the genus Tritoniopsis is a
particularly good example of this. This study focuses on Tritoniopsis revoluta, a pink irid
occurring in the Swartberg and Langeberg Mountains, as well as Potberg Mountain. I tested the
hypothesis that variation in flower tube-lengths of Tritoniopsis revoluta are related to the
geographic distribution of pollinators and the variation of their tongue lengths. It was
determined that this species is highly variable in respect to corolla tube-length and is pollinated
by different fly species across its range. Also, the tongue-lengths of the fly pollinators
corresponded almost exactly with the tube-length of the flowers they were pollinating in each
population. In some populations, where long-proboscid flies were absent, bees were observed
visiting T. revoluta flowers. This presents evidence for pollinator-driven floral variation within a
single plant species, and most of this vast diversification in floral morphology has probably
been driven by morphological variation found within a single fly family. In one population I
found variable tube-lengths which appeared to exhibit a bimodal distribution of corolla tubelengths.
I hypothesized that the two Tritoniopsis revoluta ecotypes at this population are
pollinated by two different pollinators, leading to assortative mating, and ultimately strong
inter-ecotype incompatibility. Tritoniopsis revoluta is self-incompatible and exists as two discrete entities (morphotypes) at the Gysmanshoek Pass site, and these entities differ in tubelength,
color, nectar volume and sugar content. These morphotypes were not pollinated by
long-proboscid flies, but seems to represent a recent shift to pollination by Amegilla bees.
However, ecotypes are not reproductively isolated as short and long flowers can produce
offspring, rather tube-length differences are possibly maintained through spatial separation. To
compliment the correlatory data between flower tube-lengths and pollinator tongue-lengths, I
used molecular tools (chloroplast markers and AFLPs) to elucidate the patterns of tube-length
evolution in Tritoniopsis revoluta. I aimed to determine the directionality and frequency of
transitions between tube-length categories. Tube-length transitions would be suggestive of
flower morphology being labile, and together with the tube-tongue length correlation it suggests
pollinator shifts may drive the changes in tube length. Character state reconstructions using
tube-length as character determined that four evolutionary transitions to shorter tube-length
categories and two transitions to longer categories occurred. I also tested whether
morphological divergence between populations corresponds to patterns of divergence from neutral genetic markers. Population genetic structure in this system showed that the different
populations of T. revoluta are vicariant and tube-length differences between them could have evolved through selection. / AFRIKAANSE OPSOMMING: Dit is ‘n algemene gedagte dat die groot verskeidenheid blom strukture in die angiosperme dui
op aanpassings tot verskillende biotiese stuifmeel draers. Die diverse blom strukture in baie
van die groot Kaapse genera kan verduidelik word deur aanpassings tot veranderinge in
bestuiwings-sisteme. ‘n Aantal studies hieroor stel voor dat bestuiwers nie net die
veranderinge in blom morfologie bewerkstellig nie, maar ook ‘n rol speel in die aanpassende
uiteenlopendheid van blomplant kenmerke. Spesiasie bewerkstellig deur bestuiwers het
moontlik ‘n groot rol gespeel in die blom-diversiteit wat gevind word in die Suid-Afrikaanse
Iridaceae familie, en die genus Tritoniopsis is ‘n baie goeie voorbeeld hiervan. Hierdie studie
fokus spesifiek op Tritoniopsis revoluta, ‘n pienk iris wat voorkom in die Swart- en Langeberge,
asook by Potberg. Die hipotese dat die variasie in buis-lengtes van T. revoluta verwant is aan
die geografiese verspreiding van bestuiwers en die variasie in hul tong-lengtes is hier getoets.
Dit is bepaal dat hierdie spesie groot variasie toon in terme van buis-lengtes en bestuif word
deur verskillende vlieg spesies regoor sy verspreiding. Die tong-lengtes van hierdie vlieë
korrespondeer ook met die buis-lengtes van die blomme wat hul bestuif in elkeen van die T.
revoluta populasies. In sommige van die populasies, waar lang-tong vlieë afwesig was, is bye
wat die T. revoluta blomme besoek, opgemerk. Hierdie resultate lewer bewyse vir die hipotese
dat bestuiwers blom morfologie kan beïnvloed; die interessante hiervan is dat die variasie in
buis-lengtes in hierdie spesie heel moontlik te danke is aan die morfologies variasie wat gevind
word in ‘n enkele lang-tong vlieg familie. In een van die populasies het ek ‘n bimodale
verspreiding van buis-lengtes gevind. ‘n Logiese afleiding is dat hierdie twee verskillende buislengtes
– ekotipes – deur twee verskillende bestuiwers besoek word, en dat dit lei tot sterk
onversoenbaarheid tussen ekotipes. Tritoniopsis revoluta is nie instaat tot self-bestuiwing nie en die twee ekotipes verskil in terme van buis-lengtes, kleur, nektar volume en suiker inhoud.
Kort- en lang-buis blomme word nie eksklusief bestuif deur lang-tong vlieë in die Gysmanshoek
Pas nie, maar word in die algemeen ook bestuif deur bye van die genus Amegilla. Die twee
ekotipes is in staat om te reproduseer met mekaar, so die buis-lengte verskille word moontlik
in stand gehou deur hul geografiese skeiding. Om die korrelasie analise tussen blom buislengtes
en vlieg tong-lengtes te komplimenteer, het ek molekulêre tegnieke (chloroplast
merkers en AFLPs) gebruik om die patrone van buis-lengte evolusie in Tritoniopsis revoluta
duidelik te maak. Ten eerste het ek bepaal of verkortings en verlengings van buis-lengtes een
keer in die verlede gebeur het, of as meermalige gebeurtenisse. Meermalige veranderinge in
buis-lengtes kan moontlik dui op verskuiwings tussen verskillende bestuiwers, asook
taksonomiese verdelings wat korrespondeer met bestuiwer veranderinge. Ek het ook bepaal of die buis-lengte verskille in die verskillende populasies toegeskryf kan word aan seleksie
prosesse. Deur buis-lengte as karakter te gebruik, het ek karakter-status rekonstruksies
gedoen en bepaal dat vier ewolutionêre transisies na korter buis-lengte kategorieë, en twee
transisies na langer kategorieë plaasgevind het. Populasie genetiese struktuur in die sisteem
dui daarop dat T. revoluta populasies geïsoleer is deur afstand. Die konklusie wat ek trek
gebasseer op hierdie resultate is dat verskille in buis-lengtes in hierdie sisteem moontlik
ontstaan het as gevolg van die verskillende bestuiwers wat aktief is in die verskillende T.
revoluta populasies, en dat natuurlike prosesse nie die hoofrol spelers in hierdie sisteem is ten opsigte van buis-lengte evolusie nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4198 |
| Date | 03 1900 |
| Creators | Ros, Petra |
| Contributors | Anderson, Bruce, Ellis, Allan, University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 87 p. : ill. |
| Rights | University of Stellenbosch |
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