Browsing by Author "De Kock, Celeste"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Spatial reproductive separation in a handed flower: variation across space and time
    (Stellenbosch : Stellenbosch University, 2021-12) De Kock, Celeste; Anderson, Bruce; Minnaar, Corneile; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: In many angiosperms, pollinator-driven selection has led to adaptive radiation, spe- cialisation and phenotypic variation over space and time. Most specialised floral adaptations function by improving the efficiency of cross-pollination, while also lim- iting or delaying the chances of self-pollination. This study focuses on the variation of the distances between reproductive parts in Wachendorfia paniculata, an enan- tiostylous geophyte that occurs predominantly in the Western Cape, South Africa. Wachendorfia paniculata displays geographic variation in reproductive separation between populations, as well as temporal variation facilitated by floral movement over time within populations. In Chapter 2, I investigated whether geographic vari- ation in the separation between reproductive parts corresponded with shifts in pol- linator environments between populations, and whether floral movement has any functional significance during pollination. I expected that upper anther-stigma dis- tance would decrease in populations where large pollinators were scarce or absent, whilst lower anther distances were expected to remain relatively similar. Within each population, I recorded reproductive separation distances, pollinator visitation rates, abundances and wingspans, which varied significantly between study sites. Surpris- ingly, large pollinators appeared unimportant in the present pollinator landscape. Even though the mean weighted wingspan of pollinators in a population did not pre- dict the degree of reproductive separation, honeybee visitation rate was negatively correlated with the distance between the lower anthers, suggesting that frequent vis- its by small pollinators might select for narrower distances. I also found that floral movement contributed to the observed variation by reducing the distance between reproductive parts throughout the day. These findings prompted me to investigate whether floral movement could be beneficial in populations that are dominated by small pollinators in Chapter 3. Here, I explored the functional significance of floral movement by recording floral narrowing for the duration of anthesis in a single pop- ulation. I hypothesised that floral narrowing acts as a mechanism of reproductive assurance by increasing the likelihood of pollinators making contact with the stigma and/or anthers later in the day. I measured the lateral and vertical reproductive separation distances hourly and presented virgin donor and recipient inflorescences to honey bees to record how pollen deposition and receipt rates changed with flo- ral narrowing. Floral movement was substantial and highly variable, especially for anther-stigma narrowing. The likelihood of stigmatic pollen receipt did not change with time or floral narrowing, and was dependent on the density of pollen on bee wings. I propose that floral movement might act as a reproductive assurance strat- egy when large pollinators are absent or when pollinator visitation rates are low. I argue that stigmatic movement is the result of a trade-off between receiving high quality pollen and getting pollinated: stigmas are positioned to receive high qual- ity pollen in the morning, but they shift to positions that maximize the chances of pollen receipt later in the day. While lower anther movement was not as noticeable as stigmatic movement, lower anthers were more likely to deposit pollen on pollina- tors at smaller separation distances. I conclude that the variation in reproductive separation at spatial and temporal scales is likely to be influenced by multiple biotic and abiotic factors, but that pollinator availability could still play an important part in shaping the floral morphology of W. paniculata. Key words: Geographic variation; Floral movement; Herkogamy; Enantiostyly; Pollinator adap- tation