The reproductive biology of four geoflorous Protea species (Proteaceae)

Master Thesis


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University of Cape Town

Pollination systems of previously unstudied plant species are often inferred from floral traits that are shared among unrelated plant taxa. However, these ‘pollination syndromes’ are often not reliable predictors of the primary pollinator of a plant species, and may in fact represent adaptations to multiple pollinator groups or even minor pollinators. As such, conducting comprehensive field-based research into the pollination and breeding system of unstudied plant species is important for furthering our understanding of evolutionary processes underlying shifts in pollination systems within plant lineages. Protea cordata, P. decurrens, P. scabra and P. subulifolia are cryptic, geoflorous shrubs that are predicted to be pollinated by non-flying mammals based on their floral traits, although there has been no experimental evidence in support of this. The aims of this study were to quantify key functional traits that mediate interactions between these four Protea species and their pollinators, as well as to experimentally determine their pollination and breeding systems. We further aim to establish the main vertebrate pollinators of the study species, their relative rates of visitation and their temporal patterns of activity using remote camera footage. Rodents were found to be the most frequent visitors to the flower heads of the study species. Floral morphology, nectar volume and sugar concentration of the study species conform to the general syndrome of non-flying mammal pollination system in this genus. In particular, the short (14-20 mm) distance between pollen and nectar ensures pollen deposition on the body of rodent foragers. Excluding small mammals from flower heads did not significantly reduced seed set, suggesting that insects can play an important role in cross-pollination in the study species. Breeding system experiments revealed that Protea cordata and P. scabra are self- incompatible, and are reliant on animal vectors for successful seed set. Supplemental hand pollination on P. cordata and P. scabra indicated that resource limitation is prevalent among these plant species. This study adds to the growing knowledge of the reproductive biology of Protea and will improve our ability to reconstruct the history of pollinator shifts in the genus.

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