The genus Erica has undergone an extreme radiation in the Cape and exhibits a diversity of pollination syndromes and floral traits. This makes Erica well-suited to study the evolution of floral traits and how they impact speciation. The first chapter explored the role of ultraviolet colouration by recording its prevalence across Erica pollination syndromes. Ultraviolet was rare in wind-, rodent and small insect-pollinated species, but it was common in bird-pollinated species and ubiquitous in long-proboscid fly (LPF)-pollinated species. Testing their preference revealed that sunbirds can see ultraviolet, but they have no innate preference. LPFs on the other hand were not attracted to flowers where ultraviolet reflectance was removed, thus displaying a strong preference. Chapter 2 focused on the role of stickiness for nectar robbers. I experimentally added stickiness to Erica flowers of one species and further compared stickiness to nectar robbing across several communities. Stickiness appears to reduce damage due to nectar robbing within and between species. Further, I found that stickiness is strongly correlated with pollination by birds and LPFs which might be due to their large nectar rewards. Chapter 3 investigated how the sister species Erica shannonea and Erica ampullacea co-occur despite sharing a pollination syndrome. Pollination experiments and observations showed that they are pollinated by LPFs from two families. The horizontal flowers of E. shannonea are pollinated by a tabanid which has a fixed forward-pointing proboscis, while the vertical flowers of E. ampullacea are pollinated by a nemestrinid which can swivel its proboscis downwards. The nemestrinid in turn has a shorter proboscis which prevents it from accessing nectar in the long-tubed E. shannonea. Due to their different biomechanics, each fly can only access the flower it pollinates resulting in effective reproductive isolation between these species. Chapter 4 compared flower orientation in relation to the two LPF families across all LPF-pollinated species. Using a phylogenetically corrected analysis, I found that flowers pollinated by Tabanidae tend to be horizontal, while nemestrinid flowers are more variable in orientation and more often vertical. This confirms the importance of pollinator biomechanics for the evolution of floral traits. The last chapter investigated how pollen transfer efficiency differs between Erica pollination syndromes. I found that LPF- and bird-pollinated species have higher pollen transfer efficiency in comparison to bee-pollinated species which might have facilitated the shifts from ancestral bee pollination.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/38513 |
| Date | 11 September 2023 |
| Creators | McCarren, Sam |
| Contributors | Midgley, Jeremy |
| Publisher | Faculty of Science, Department of Biological Sciences |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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