Browsing by Author "Steenhuisen, Sandy-Lynn"

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    Open Access
    Community ecology of small-mammal pollinated proteas
    (2013) Kuhn, Nicola; Midgley, Jeremy; Steenhuisen, Sandy-Lynn
    The floral characteristics of small-mammal pollinated (SMP) Protea species have been assessed in a number of previous studies. This study aimed to determine whether the inflorescences of Protea canaliculata, Protea sulphurea and Protea humiflora possess these traits and are pollinated by small mammal species. An additional aim of this study was to determine whether there is a variation in pollinator efficiency of different animal species. Floral characteristics that may influence plantpollinator interactions were measured, including floral dimensions, nectar production and spectral reflectance. Live-trapping was conducted using Sherman traps and mean facial and faecal pollen load was determined for the different species caught. Furthermore pollinators were observed through footage from motion sensor cameras placed facing the inflorescences of SMP proteas. The results of this study confirmed that Protea canaliculata, Protea sulphurea and Protea humiflora are pollinated by small mammal pollinators. The evidence supporting this is that the afore-mentioned species have traits that correspond to those possessed by known small-mammal pollinated proteas including: bowlshaped inflorescences, high nectar concentrations (ranging between 24.1-42.9%), sucrose-rich nectar composition, a "yeasty" scent, floral colours that are visible to small mammals, and a winter flowering season. These proteas were found to have separated peak flowering times, providing a nectar source throughout winter for small mammals at this site. Fifty-eight small mammals of seven different species, were trapped in P. canaliculata and P. sulphurea stands over 98 hours. The average nighttrapping success was 22.7% and day-trapping success was 5.7%, indicating a relatively abundant nocturnal small-mammal population. A separation in pollinator efficiency was observed for different small mammal species, with Elephantulus edwardii identified as the most effective pollinator as it showed the greatest pollen removal (highest faecal pollen load) and spent the longest time foraging on inflorescences (±28 seconds per inflorescence). Another important pollinator was Aethomys namaquensis because it visited flowers 75% more frequently than any of the other pollinators. Camera trapping was shown to be a superior method than conventional trapping for assessing pollination by providing insight into pollinator behaviour, identifying new pollinators of 'trap-shy' species and also due to its more animal-friendly disposition.
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    Open Access
    The pollination and scent ecology of selected Cape milkweeds (Apocynaceae: Asclepiadoideae)
    (2017) Chirango, Yolanda Tendai; Midgley, Jeremy J; Steenhuisen, Sandy-Lynn; Shuttleworth, Adam
    Milkweeds (Asclepiadoideae, Apocynaceae) possess a complex floral morphology that has made them prime candidates for investigating the evolution of plant-pollinator relationships. In South Africa, the pollination ecology of this diverse group has largely been focused in the summer rainfall region. This study focused on Western Cape species in the winter and summer-winter rainfall transition zones. The aim was to determine the pollinators of the study species and assess, describe and quantify their floral attractants. Thus offering a basis of comparison with the previously studied summer rainfall species. The pollination systems of seven milkweed species occurring in the Western Cape were investigated by determining floral visitors and several floral traits that may act as attractants of these visitors. For each study species an attempt at pollinator observations was carried out in several sites across the Cape; floral scent samples were collected through headspace sampling and analysed using GC-MS (gas chromatography-mass spectrometry); floral colour was analysed using spectral reflectance measurements; and nectar was measured to quantify floral rewards. Some Cape milkweeds displayed a more generalized pollination system compared to their summer rainfall congeners. A diverse range of visitors were observed on two Gomphocarpus species, Gomphocarpus cancellatus and G. filiformis in the Fynbos and Succulent Karoo biomes respectively, in contrast to their summer rainfall congeners, which are exclusively wasp pollinated or much less generalized. These two Gomphocarpus species offered floral visitors nectar as a reward with a concentration of 53% in G. cancellatus and a lower 15% in G. filiformis. The species emitted very different scents, G. cancellatus produced a scent dominated by irregular terpenes while G. filiformis scent largely consisted of benzenoid compounds. Although visited by a variety of different insect families and lesser-double collared sunbirds, honeybees and Balbyter ants were found to be the most efficient at removing pollinaria from G. cancellatus and G. filiformis respectively. Eustegia minuta, a Cape endemic, is almost exclusively pollinated by bibionid flies. This is the first record of the pollinators for this monotypic genus, as well as the first for the tribe Eustegieae. Additionally, this study is the first record of a milkweed-bibionid pollination system. The flowers produced very low nectar volumes, displayed minimal visual cues but produced a strong pungent odour dominated by an unidentified compound. This strong scent is thought to play an important role in attracting bibionids while also deterring other potential visitors. The scent profiles of four other previously unstudied Cape milkweeds, namely Cynanchum obtusifolium, C. zeyheri, Fockea capensis and Secamone alpinii were also analysed and shown to be mainly dominated by monoterpenes and benzenoids. Their scent profiles differed markedly from each other as well as to their congeners. The presence of skatole in S. alpinii suggests that it may attract coprophagic flies, small Nematoceran flies were observed drinking nectar from its flowers. While F. capensis produced scent associated with moths. Further observations are needed to confirm true pollinators for both species. The two Cynanchum species produced scent that was very different to each other as well as their congeners. Cynanchum obtusifolium is known to be bee pollinated however its scent profile did not align with this. While C. zeyheri produced a benzenoid-dominated scent with compounds associated with moths. Scent appears to be the most prominent pollinator attractant in the study species compared to floral colour. The concentration and volume of nectar rewards may also be significant. The structural complexity of the flowers is suggestive of a strong floral filter in some species (e.g. Eustegia minuta). Morphologically similar species were found to employ vastly different floral chemical strategies to attract but possibly also deter and filter out floral visitors. The Cape milkweeds therefore offer many opportunities for further pollination studies.
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    Open Access
    Population genetics of South African Protea L. (Proteaceae) species associated with various pollinator guilds
    (2019) Smith, Megan; Midgley, Jeremy; Steenhuisen, Sandy-Lynn; Prunier, Rachel
    South Africa hosts plant species with a large variety of floral traits associated with different pollinator guilds. Suites of specialised floral traits associated with particular pollinators are known as pollination systems or syndromes. However, it is often uncertain how these pollination systems affect gene flow between plant populations, mating system outcome, and subsequent genetic health of plant species. Genetic variability is an important aspect in understanding the long-term survival of a species because excessive homozygosity, as a result of high amounts of inbreeding, may restrict a species’ long-term local adaptive potential. The African genus, Protea, is an ideal study system for exploring the evolution and maintenance of mating systems, because the pollination system for many species have been confirmed by pollinator exclusion experiments. The genus has several pollination systems including birds, insects and non-flying mammals. Comparative estimates of pollinators’ outcrossing abilities are rare and confined to bird and insect guilds. Furthermore, 10 microsatellite markers have been developed for the genus, but have not been used to assess the outcrossing abilities of various pollinators. This study thus had two aims: Firstly, to use microsattelite markers to estimate the outcrossing rates and subsequent genetic diversity of Protea species primarily pollinated by either birds (P. laurifolia and P. roupelliae), insects (P. caffra and P. simplex) or non-flying mammals (P. amplexicaulis and P. humiflora). Secondly, I aimed to understand how birds and non-flying mammal pollinators affect population connectivity and gene dispersal. This was done by comparing indirect estimates of gene flow in the therophilous, P. amplexicaulis, and ornithophilous, P. laurifolia. These estimates included population differentiation (G”st) between subpopulations and spatial genetic structuring within metapopulations of each species. I expected that less vagile pollinators, such NMP’s (non-flying mammal pollinators), would contribute the least to gene flow and cause high selfing rates and low genetic diversity within therophilous populations. Contrastingly, flying pollinators would be able to travel longer distances resulting in more genetic connectivity between plant populations. The high energetic demands and interplant movements of flying animals were predicted to result in high outcrossing rates in ornithophilous and entomophilous species. Non-flying mammal-pollinated (NMP) Protea species had high (> 0.8) and non-significantly different (p > 0.05) outcrossing rates relative to species pollinated by flying animals. Similarly, hand pollen supplementation experiments also revealed that small mammals were effective pollen vectors since P. amplexicualis individuals were not pollen limited. High multilocus outcrossing rates (> 0.80) may have resulted in all sampled Protea species exhibiting high levels of heterozygosity (> 0.7) and low levels of inbreeding. However, some of the outcrossing events were between kin (approximately 14 %), giving evidence for biparental inbreeding. Furthermore, the relationship between geographic distance and genetic distance was significant for sampled P. amplexicaulis individuals. In contrast, sampled P. laurifolia individuals were genetically similar across the landscape. This pattern was reflected in fine-scale (> 500 m) spatial genetic structuring in a sampled metapopulaton of P. amplexicaulis and a homogeneous distribution of P. laurifolia genotypes. Restricted gene dispersal recorded for P. amplexicaulis in this study may have been a result of the high levels of biparental inbreeding. It was not clear whether poor gene flow was primarily a result of restricted pollen dispersal created by NMP’s or restricted seed dispersal. Nevertheless, continuous limited gene dispersal between NMP populations may result in allopatric speciation over time. This provides a hypothesized reason as to why many of the therophilous Protea species are located in small and isolated populations. Additionally, there is a concern that restricted population size in combination with poor gene flow may lead to increased levels of inbreeding over time. This study provided the first evidence for localised gene dispersal, but high outcrossing rates, in NMP proteas.
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    The reproductive biology of four geoflorous Protea species (Proteaceae)
    (2014) Zoeller, Kim Christie; Midgley, Jeremy J; Steenhuisen, Sandy-Lynn; Johnson, Steven D
    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.