Browsing by Author "Cozien, Ruth Jenny."

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The importance of sunbirds as pollinators of the southern African plants Alberta magna and Streptocarpus dunnii.
(2023) Jansen, Cally Julia.; Johnson, Steven Dean.; Cozien, Ruth Jenny.
Bird pollination is important for plant reproduction and is found in about 65 flowering plant families. I studied putative bird pollination systems of two southern African plant species, Alberta magna (Rubiaceae), which grows above cliffs and Streptocarpus dunnii (Gesneriaceae), which occurs among boulders in open grassland. A special emphasis of this study was to test the utility of close-focusing motion-activated camera traps for documenting bird pollination of plant species that are rare and occur in habitats that present challenges for conventional bird pollination studies. The aims of this project were to 1) quantify floral traits for comparison with other bird-pollinated species; 2) establish the breeding systems, including reliance on pollinators for reproduction; 3) identify floral visitors and measure their contribution to reproductive success; and 4) determine if seed production is pollen limited. Floral traits of S. dunnii, including large volumes of dilute nectar and long tube lengths, also aligned with an ornithophilous pollination syndrome. In naturally-pollinated plants, overall fecundity was high, with 80% of flowers developing fruits with large numbers of seeds. Malachite sunbirds (Nectarinia famosa) were the only legitimate visitor to flowers of S. dunnii. Greater double-collared sunbirds (Cinnyris afer), which have shorter bills than malachite sunbirds, occasionally rob flowers of nectar. Streptocarpus dunnii was found to be fully self-compatible but does not self-autonomously. Selective exclusion experiments showed that the species is almost entirely reliant on birds for seed production. The species did not experience pollen limitation, indicating that sunbirds are effective pollinators. Measured floral traits of A. magna, including large volumes of dilute nectar and long tube lengths, were consistent with an ornithophilous pollination syndrome. Motion triggered cameras and observations showed that southern double-collared sunbirds (Cinnyris chalybeus) and olive sunbirds (Cyanomitra olivacea) were the most common visitors to A. magna, while amethyst sunbirds (Chalcomitra amethystina) were occasional visitors. Selective exclusion experiments showed that bird visitors are important for reproductive success which was found not to be pollen-limited. The low levels of fecundity in A. magna indicate that there may be other potential factors that limit seed production in this species and the degree of self-compatibility in this species was not firmly established. I conclude that both species are specialized for pollination by sunbirds and that close-focusing camera traps are effective for documenting bird pollination systems of rare plant species which occur in habitats that are challenging for conventional human observations.
Pollinator-driven divergence among populations of a self-fertilizing lily, Hesperantha coccinea (Iridaceae).
(2021) Cozien, Ruth Jenny.; Johnson, Steven Dene.; Harder, Lawrence David.
Two major trends in floral evolution – pollinator shifts and the evolution of autonomous selffertilisation – are generally considered alternative evolutionary responses to pollen-limitation of plant reproductive success. However, pollinator-specialised species often are also autofertile. The apparent contradiction of “opposing contrivances” for attracting pollinators and reproducing independently of them, may represent an optimal Best-of-Both-Worlds strategy whereby delayed self-fertilisation provides reproductive assurance in unpredictable pollination environments. In this thesis, I demonstrate pollinator-driven divergence among autofertile populations of Hesperantha coccinea (Iridaceae) based on evidence of local adaptation to different pollinators and experimental quantification of the contributions of pollinators and autonomous self-fertilisation to reproductive success. Floral colour, morphology, orientation and nectar characteristics differ between populations pollinated by a butterfly or a longproboscid fly. Reciprocal translocation of plants, assessment of pollinator effectiveness and preference experiments demonstrate that this intraspecific divergence involved adaptation to the morphology and preferences of the locally-dominant pollinators at low and high elevations, creating a geographic mosaic of floral variation. Despite this divergence, reproduction by both ecotypes involves a combination of pollinator-mediated outcrossing and autonomous self-fertilisation. Hand-pollinations showed self-compatibility and high autofertility in both ecotypes. Nevertheless, analysis of SSR markers revealed mixed selfing and outcrossing in populations of both colour forms. Most autonomous self-pollination occurred late during a flower’s lifespan, as expected for Best-of- Both-Worlds reproduction. Furthermore, similar performance of selfed and outcrossed progeny from three populations in a greenhouse indicated little genetic cost of selfing. Emasculation experiments showed extensive variation in the relative contributions of autonomous self-pollination and pollinators to fecundity among populations and flowering seasons. Overall, pollinator activity and autonomous self-fertilisation accounted for 75% and 25% of fecundity, respectively. The contribution of autonomous self-fertilisation varied among populations from zero to more than 90% of seed set and differed within populations between years by an average of 30%. The relative importance of pollinators and autonomous self-fertilisation did not vary geographically in relation to proximity to range edge, flower number, size, or herkogamy. This independence identifies autonomous self-fertilisation as part of a stable Best-of-Both-Worlds strategy employed by H. coccinea to contend with unpredictable pollination. Weak inbreeding depression in combination with conditions otherwise consistent with Best-of-Both-Worlds reproduction suggests that the importance of siring advantages of pollinator-mediated pollen transfer have been underestimated in these systems.
The importance of flies for pollination at high elevation: a case study of Erica caffrorum.
(2023) Thupsie, Viren.; Van der Niet, Timotheus.; Cozien, Ruth Jenny.; Jordaens, Kurt.
Pollinator communities typically vary across elevation gradients. In particular, the contribution of bee pollination typically declines at higher elevations in favour of other pollinators, such as birds, butterflies and flies. Erica caffrorum occurs at high-elevation sites in the South African Drakensberg Mountains and has floral traits suggestive of pollination by short-tongued insects. Most Erica species with similar floral traits studied to date occur in the Cape Floristic Region at low elevations and are pollinated by honey bees. I present a case study of pollination in Erica caffrorum, including characterization of the breeding and pollination system, quantification of the associated floral traits, and experimental determination of the significance of flower colour and scent for pollinator attraction. Hand-pollination experiments confirmed that similar to most Erica species, E. caffrorum is self-incompatible. At five study sites, between 1800 and 2500 meters above sea level, pollinator observations revealed that most visitors were not honey bees but Diptera, which were identified into morphospecies and identifications verified using DNA barcoding. Assessment of pollinator importance based on pollen loads and visitation frequency identified Muscidae, Rhiniidae and Scatophagidae as the most important pollinators. Analysis of floral scent using GC-MS indicated that benzaldehyde and 2-methyl butanoic acid dominated the odour bouquet across all populations. In bioassays, a significant preference for white colour in the presence of scent was found for flies across all three experimental sites and for other visitors at one of two sites, but no other consistent preferences for colour or scent alone were detected. Across three sites, a combination of acid and benzaldehyde attracted significantly more flies than the unscented control. A similar pattern was observed for acid alone but not for benzaldehyde. This study provides novel evidence for short-tongued fly pollination in an Erica species, mediated through a combination of floral scent and colour. The similarity in traits between E. caffrorum and several other distantly related plant species in the highelevation ecosystems of the Drakensberg mountains suggests that the pollination of scented, small, white flowers by short-tongued flies found here likely represents a more widespread pollination system whose importance in southern African mountain regions is currently underestimated.