Flowers with style : the role of pollinators in the origin and maintenance of Proteaceae diversity with a focus on the genus Leucospermum

Johnson, Christopher Michael (2015-03)

Thesis (PhD)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: It is believed that angiosperm diversification can regularly be explained by adaptation to pollinators. This may result from a shift to a new pollinator, recruitment of a supplemental pollinator, employing the traditional pollinator in a new way, or relying less on pollinators altogether and instead placing a stronger emphasis on self-pollination. Diversification can transpire when a population finds itself in a new habitat lacking the traditional pollinator or when taxa overlap in the utilization of a shared pollinator resource. Competition between taxa that utilize the same pollinator ceases once pollinator partitioning is sufficiently achieved if taxa do not compete for pollinator visits. Therefore, pollinators can also be a determinant of angiosperm community composition in addition to drivers of speciation. Throughout this thesis I examine how angiosperms adapt to pollinators as a resource, how pollinators drive speciation, and how pollinators maintain communities by focusing on the southern African genus Leucospermum (Proteaceae). Adaptation to fluctuations in the pollinator mosaic can drive diversification of floral morphology and denotes the onset of speciation. In Chapter 2 we examine pollinator driven adaptive divergence between two closely related Leucospermum taxa that have distinct floral morphologies and employ different pollinators. We suggest that these two varieties are ecotypes that originated through adaptation to different pollinators. Angiosperms in the Cape Floristic Region often evolve elaborate features that allow them to utilize atypical pollinators. In Chapter 3 we explore remarkable adaptations for non-flying mammal pollination in an endangered Leucospermum species. We show that unique nectar characteristics accommodate gerbil and mice pollinators, that proximity to the ground does not influence seed production, and that frequent grooming by non-flying mammals quickly diminishes the pollen available for outcrossing. In Chapters 2 and 3 we show that pollinators can select for floral traits as well as drive speciation. But how often do pollinator shifts occur? What traits must evolve to utilize specific functional groups of pollinators? What morphological features and/or pollination modes encourage autonomous self-pollination? To answer such questions one must incorporate phylogenetics into analyses to account for relatedness among taxa. In Chapter 4 we construct the first Leucospermum phylogeny and use it to test for correlated evolution between floral morphology, pollination mode, and autonomous selfing using 7 floral measures and 10 functional groups of pollinators. We show that floral traits are highly correlated with pollination modes and that the evolution of autonomous selfing is coupled with the bird pollination syndrome. Along with being drivers of floral diversity, pollinators can also act to shape and maintain floral communities. Since pollinators are a limited resource, pollinators act as ecological filters by restricting certain species from a community while permitting others. When species coexist and utilize the same pollinators there is potential for competition for pollinator visits as well as through interspecific pollen transfer. In Chapter 5 we provide evidence that co-flowering Leucospermum and Mimetes trees utilize discrete pollen attachment sites on a shared pollinator and density dependent interactions promote a mutualistic interaction between the two species.

AFRIKAANS OPSOMMING: Daar word geglo dat die diversiteit van blomplante verklaar kan word as aanpassing by bestuiwers. Hierdie aanpassings kan die gevolg wees van 'n verskuiwing na 'n nuwe bestuiwer, werwing van 'n aanvullendebestuiwer, die gebruik van die voormalige bestuiwer op 'n nuwe manier, of verskuiwing na self-bestuiwing. Diversifikasie kan plaasvind wanner 'n populasie homself bevind in die afwesigheid van die voormalige bestuiwer, of as gevolg van kompetisie wanneer taxa oorvleuel in die benutting van 'n gedeelde bestuiwings hulpbron. Dus speel bestuiwers ook 'n rol in die samestelling van plant gemeenskappe. In hierdie tesis ondersoek ek hoe blomplante aanpas by bestuiwers as 'n hulpbron, hoe bestuiwers spesiasie aandryf, en hoe bestuiwers gemeenskaps komposisie beïnvloed deur te fokus op die Suider-Afrikaanse genus Leucospermum (Proteaceae). Aanpassing by variasie in die bestuiwer mosaïek kan diversifisering van blom-morfologie aandryf. In Hoofstuk 2 ondersoek ons bestuiwer-aangedrewe divergensie tussen twee nouverwante Leucospermum taksa wat duidelik verskil in blom-morfologie. Ons stel voor dat die takse twee ekologiese rasse is wat ontstaan het deur aanpassing by verskillende bestuiwers. Angiosperme in die Kaapse Floristiese Streek ontwikkel dikwels ingewikkelde strukture wat hulle toelaat om van ongewone bestuiwers gebruik te maak. In Hoofstuk 3 ondersoek ons merkwaardige aanpassings vir nie-vlieënde soogdier-bestuiwing in 'n bedreigde Leucospermum spesie. Ons wys dat unieke nektar eienskappe haarpootnagmuise en streepveldmuise as bestuiwers akkommodeer, dat die nabyheid van blomme aan die grond nie saad produksie beïnvloed nie, en dat die deeglike skoonmaak gewoontes van hierdie knaagdiere vinnig die hoeveelheid stuifmeelkorrels beskikbaar vir kruisbestuiwing verminder. In hoofstukke 2 en 3 wys ons dat bestuiwers natuurlike seleksie uitoefen op blom eienskappe en dus spesiasie aandryf. Maar hoe dikwels vind dit plaas? Watter plant eienskappe word geassosieer met spesifieke funksionele groepe van bestuiwers? Watter morfologiese kenmerke en / of metodes van bestuiwing word met self-bestuiwing geassosieer? Om sulke vrae te beantwoord moet 'n mens filogenetiese informasie in die analise inkorporeer om verwantskap tussen taksa in ag te neem. In Hoofstuk 4 bou ons die eerste Leucospermum filogenie en gebruik dit om te toets vir gekorreleerde evolusie tussen blom-morfologie en bestuiwing. Die analise sluit 7 blom-eienskappe en 10 funksionele groepe van bestuiwers. Ons wys dat blom eienskappe hoogs gekorreleed is met bestuiwings-metodes en dat die evolusie van outonome self-bestuiwing geassosieer is met die voël bestuiwing sindroom. Buiten hulle rol in die oorsprong van plant diversiteit speel bestuiwers ook „n rol in die ekologiese strukturering van plant gemeenskappe. Wanneer spesies saamleef en dieselfde bestuiwers gebruik is daar potensiaal vir kompetisie vir bestuiwer besoeke, sowel as kompetisie deur interspesifieke stuifmeel oordrag. In Hoofstuk 5 wys ons dat mede-blommende Leucospermum en Mimetes bome kompetisie vermy deur afsonderlike stuifmeel aanhegtingsplekke op suikervoëls te gebruik, en dat hierdie gedeelde bestuiwer dus 'n mutualistiese interaksie tussen hierdie twee plantspesies bewerkstellig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96722
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