Steven D. Johnson
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View article: Generalization for both diurnal and nocturnal pollination in the mass‐flowering desert geophyte <i>Nerine laticoma</i> (Amaryllidaceae)
Generalization for both diurnal and nocturnal pollination in the mass‐flowering desert geophyte <i>Nerine laticoma</i> (Amaryllidaceae) Open
The evolutionary limits to generalization in plant pollination systems are often determined by trade‐offs in which adaptations to one set of flower visitors reduces the effectiveness of another set of visitors. A key question is whether fl…
View article: Floral specialization for beetle pollination and its implications for pollen dispersal in an African orchid
Floral specialization for beetle pollination and its implications for pollen dispersal in an African orchid Open
Premise Pollination by beetles is relatively rare in orchids, and this has been attributed to the clumsy behavior of beetles being unsuitable for the precise pollen transfer mechanisms that characterize the orchid family. We investigated f…
View article: Pollinators are critical to the achievement of Sustainable Development Goals.
Pollinators are critical to the achievement of Sustainable Development Goals. Open
The Sustainable Development Goals (SDGs) are a major focus for policy globally. Pollinators provide an informative nexus between natural ecosystems and human society, upon which both are highly dependent. Many SDGs are thought to have intr…
View article: Regional flower visitor assemblages and divergence of floral traits of the baobab <i>Adansonia digitata</i> (Malvaceae) across Africa
Regional flower visitor assemblages and divergence of floral traits of the baobab <i>Adansonia digitata</i> (Malvaceae) across Africa Open
Regional differences in flower visitor assemblages can lead to divergence of floral traits in plants. We investigated variation in floral traits and flower visitors across the distribution range of the African baobab, Adansonia digitata, f…
View article: Functions of heteranthery and enantiostyly for wing pollination by pollen-collecting bees in <i>Dilatris ixioides</i> (Haemodoraceae)
Functions of heteranthery and enantiostyly for wing pollination by pollen-collecting bees in <i>Dilatris ixioides</i> (Haemodoraceae) Open
Background and Aims Evolutionary floral modifications that enable plants to exploit particular body parts of animals for pollen transfer are considered a key contributor to the angiosperm radiation. Species of Dilatris (Haemodoraceae) have…
View article: Anther mimicry in an African orchid pollinated by pollen‐feeding beetles
Anther mimicry in an African orchid pollinated by pollen‐feeding beetles Open
Flowers of many species have yellow markings that appear to mimic anthers or pollen and attract the attention of pollen‐seeking insects (usually female bees). We investigated a putative case of anther mimicry in Disa similis, an orchid wit…
View article: Resolving taxa in a challenging orchid species complex using evidence from phylogenetics, morphometrics and floral scent chemistry
Resolving taxa in a challenging orchid species complex using evidence from phylogenetics, morphometrics and floral scent chemistry Open
Species can be difficult to circumscribe using morphology alone, and additional data can thus be useful for resolving challenging species complexes. Here we provide a case study of a South African orchid species complex which we resolved b…
View article: Antbears and underground melons: A highly specialized seed dispersal mutualism mediated by scent
Antbears and underground melons: A highly specialized seed dispersal mutualism mediated by scent Open
Societal Impact Statement Seed dispersal is critical for the establishment and persistence of populations of most plant species. We investigated the seed dispersal biology of an African melon, Cucumis humifructus , which is closely related…
View article: Pollination efficiency and the evolution of sex allocation – diminishing returns matter
Pollination efficiency and the evolution of sex allocation – diminishing returns matter Open
Summary Immobility of flowering plants requires them to engage pollen vectors to outcross, introducing considerable inefficiency in the conversion of pollen production into sired seeds. Whether inefficiencies influence the evolution of the…
View article: Pollination ecotypes and the origin of plant species
Pollination ecotypes and the origin of plant species Open
Ecological niche shifts are a key driver of phenotypic divergence and contribute to isolating barriers among lineages. For many groups of organisms, the history of these shifts and associated trait–environment correlations are well-documen…
View article: Rocksitter Flies (Lauxaniidae: <i>Cestrotus</i>) are Key‐Pollinators of <scp><i>Ceropegia pulchellior</i></scp>—A Threatened and Localised South African Endemic With Foetid‐Scented Flowers
Rocksitter Flies (Lauxaniidae: <i>Cestrotus</i>) are Key‐Pollinators of <span><i>Ceropegia pulchellior</i></span>—A Threatened and Localised South African Endemic With Foetid‐Scented Flowers Open
Short‐tongued saprophilous flies are a diverse but under‐appreciated group of pollinators, which are particularly important for flowers in the subtribe Stapeliinae (Apocynaceae‐Asclepiadoideae‐Ceropegieae). This clade of plants is characte…
View article: Pollinator-mediated isolation promotes coexistence of closely related food-deceptive orchids
Pollinator-mediated isolation promotes coexistence of closely related food-deceptive orchids Open
Identifying the factors that contribute to reproductive isolation among closely related species is key for understanding the diversification of lineages. In this study, we investigate the strength of premating and postmating reproductive i…
View article: Scent‐mediated bee pollination and myrmecochory in an enigmatic geophyte with pyrogenic flowering and subterranean development of fleshy fruits
Scent‐mediated bee pollination and myrmecochory in an enigmatic geophyte with pyrogenic flowering and subterranean development of fleshy fruits Open
Premise Volatile emissions from flowers and fruits play a key role in signalling to animals responsible for pollination and seed dispersal. Here, we investigated the pollination biology and chemical ecology of reproduction in Apodolirion b…
View article: FlowerMate: Multidimensional reciprocity and inaccuracy indices for style‐polymorphic plant populations
FlowerMate: Multidimensional reciprocity and inaccuracy indices for style‐polymorphic plant populations Open
Premise Heterostyly in plants promotes pollen transfer between floral morphs, because female and male sex organs are located at roughly reciprocal heights within the flowers of each morph. Reciprocity indices, which assess the one‐dimensio…
View article: Evidence for diurnal bee pollination in the ancestrally hawkmoth-pollinated genus <i>Crinum</i> (Amaryllidaceae)
Evidence for diurnal bee pollination in the ancestrally hawkmoth-pollinated genus <i>Crinum</i> (Amaryllidaceae) Open
Shifts between diurnal and nocturnal pollination systems have been important in the radiation of the angiosperms. Here we examined the pollination ecology of Crinum campanulatum (Amaryllidaceae), an aquatic geophyte. Although visits by noc…
View article: Settling moth pollination of a rare orchid in the <i>Habenaria</i> clade revealed with close‐focusing camera traps
Settling moth pollination of a rare orchid in the <i>Habenaria</i> clade revealed with close‐focusing camera traps Open
It is challenging to make nocturnal observations of the natural behaviour of flower‐visiting moths as they are highly sensitive to visible artificial light sources. One solution, implemented here, is to use specially‐adapted close‐focusing…
View article: Long‐proboscid horseflies (<i>Philoliche</i>: Tabanidae) as pollinators of co‐adapted plants in Africa and Asia
Long‐proboscid horseflies (<i>Philoliche</i>: Tabanidae) as pollinators of co‐adapted plants in Africa and Asia Open
Elongated nectar‐feeding mouthparts have evolved in several fly families, most notably Nemestrinidae, Bombyliidae and Tabanidae. Plants pollinated by these “long‐proboscid flies” tend to have relatively specialized pollination systems. In …
View article: Pollen transfer efficiency in Erica depends on type of pollinator
Pollen transfer efficiency in Erica depends on type of pollinator Open
Pollen transfer efficiency (PTE; the proportion of pollen removed from flowers that reaches conspecific stigmas) is expected to vary with the type of pollinator and flower morphology, and to influence male siring success. Many species in t…
View article: Butterfly pollination in Platycoryne (Orchidaceae): evidence for a key pollinator shift in the large Habenaria clade
Butterfly pollination in Platycoryne (Orchidaceae): evidence for a key pollinator shift in the large Habenaria clade Open
Shifts between pollinator functional groups can explain major changes in floral phenotype. I document a novel case of butterfly pollination in Platycoryne, an African genus that is phylogenetically embedded in the very large Habenaria clad…
View article: A novel feeding mechanism: Sunbirds drink nectar via intralingual suction
A novel feeding mechanism: Sunbirds drink nectar via intralingual suction Open
Nectarivory has independently evolved many times among birds, yet little is known about the diversity of feeding mechanisms that enable specialized taxa to efficiently collect this energyrich resource. Multiple avian groups have converged …
View article: Pollination of Disa engleriana (Orchidaceae): Floral modifications for deposition of pollinaria on the abdomen of large bees and wasps
Pollination of Disa engleriana (Orchidaceae): Floral modifications for deposition of pollinaria on the abdomen of large bees and wasps Open
The evolution of complex floral morphology in orchids can be attributed largely to mechanisms that ensure precise placement of pollinaria on the bodies of animal flower visitors. Floral advertisements and rewards also play a key role in se…
View article: Complex floral morphology and scent chemistry mediate hawkmoth pollination of an African orchid in the diverse <i>Habenaria</i> clade
Complex floral morphology and scent chemistry mediate hawkmoth pollination of an African orchid in the diverse <i>Habenaria</i> clade Open
One explanation for the evolution of complex floral morphology in orchids is that it can function as a component of ‘lock-and-key’ mechanisms that ensure pollen transfer by specific flower visitors. We investigated the roles of floral morp…
View article: Nectar cardenolides and floral volatiles mediate a specialized wasp pollination system
Nectar cardenolides and floral volatiles mediate a specialized wasp pollination system Open
Specialization in plant pollination systems can arise from traits that function as filters of flower visitors. This may involve chemical traits such as floral volatiles that selectively attract favoured visitors and non-volatile nectar con…
View article: Pollination of <i>Chamaepentas nobilis</i> (Rubiaceae) by long‐proboscid hawkmoths in south‐central Africa: Trait mismatching and floral scent chemistry
Pollination of <i>Chamaepentas nobilis</i> (Rubiaceae) by long‐proboscid hawkmoths in south‐central Africa: Trait mismatching and floral scent chemistry Open
The evolution of extremely long (>10 cm) floral tubes in angiosperms is closely linked with adaptation for pollination by long‐proboscid hawkmoths. In most cases, pollen is placed on the head or body of these moths, selecting for floral tu…
View article: Incomplete resupination during floral development leads to pollination failure in a slipper orchid
Incomplete resupination during floral development leads to pollination failure in a slipper orchid Open
In many families, plants undergo floral resupination by twisting through approximately 180° during floral development so that the flower is effectively positioned upside down. In most orchids, resupination results in the median petal ( i.e…
View article: The economy of pollen dispersal in flowering plants
The economy of pollen dispersal in flowering plants Open
Mating success of flowering plants depends strongly on the efficiencies of pollen removal from flowers and its subsequent dispersal to conspecific stigmas. We characterized the economy of pollen dispersal in flowering plants by analysing p…