Susan W. Nicolson's research while affiliated with University of Pretoria and other places

Publications (160)

Article
Nectar, the main floral reward for pollinators, varies greatly in composition and concentration. The assumption that nectar quality is equivalent to its sugar (energy) concentration is too simple. Diverse non-sugar components, especially amino acids and secondary metabolites, play various roles in nutrition and health of pollinators. Many nectar co...
Article
Full-text available
Evidence from the last few decades indicates that pollinator abundance and diversity are at risk, with many species in decline. Anthropogenic impacts have been the focus of much recent work on the causes of these declines. However, natural processes, from plant chemistry, nutrition and microbial associations to landscape and habitat change, can als...
Article
Full-text available
The expression of life-history traits, such as lifespan or reproductive effort, is tightly correlated with the amount and blend of macronutrients that individuals consume. In a range of herbivorous insects, consuming high protein to carbohydrate ratios (P:C) decreases lifespan but increases female fecundity. In other words, females face a resource-...
Article
Noninvasive measurement of stress-related alterations in fecal glucocorticoid metabolite (fGCM) concentrations has considerable potential for quantifying physiological responses to very hot weather in free-ranging birds, but practical considerations related to sampling will often make this method feasible only for habituated study populations. Here...
Article
Full-text available
The major lineages of nectar feeding birds (hummingbirds, sunbirds, honeyeaters, flower-piercers, and lorikeets) are considered examples of convergent evolution. We compared sucrose digestion capacity and sucrase enzymatic activity per unit intestinal surface area among 50 avian species from the New World, Africa, and Australia, including 20 nectar...
Article
Full-text available
Optimal concentrations for nectar drinking are limited by the steep increase in the viscosity of sugar solutions with concentration. However, nectar viscosity is inversely related to temperature, which suggests advantages to foraging from flowers that are warmer than the surrounding air. The honey bee (Apis mellifera L.) dips nectar by a hairy tong...
Article
Full-text available
Optimal concentrations for nectar drinking are limited by the steep increase in the viscosity of sugar solutions with concentration. However, nectar viscosity is inversely related to temperature, which suggests advantages to foraging from flowers that are warmer than the surrounding air. The honey bee (Apis mellifera L.) dips nectar by a hairy tong...
Article
Full-text available
In herbivorous insects, the degree of host specialisation may be one ecological factor that shapes lifespan. Because host specialists can only exploit a limited number of plants, their lifecycle should be synchronised with host phenology to allow reproduction when suitable hosts are available. For species not undergoing diapause or dormancy, one st...
Article
Nutritional stress due to habitat transformation and loss is one of several factors contributing to current declines in global bee populations. Bees obtain protein from pollen, which in honeybees is consumed and digested by nurse bees. They then distribute the protein to the rest of the colony in the form of hypopharyngeal gland secretions. Little...
Article
Adult holometabolous insects may derive metabolic resources from either larval or adult feeding, but little is known of whether adult diets can compensate for deficiencies in the larval diet in terms of stress resistance. We investigated how stress resistance is affected and compensated for by diet across life stages in the marula fruit fly Ceratit...
Article
Laboratory experiments are vital to exploring the causes of pollinator loss, but for these experiments to be informative, they should attempt to replicate the hive environment and conserve social interactions. It is unclear how honeybee density and group size affect survival and behaviour in the laboratory. We manipulated cage volume (125–1312 ml)...
Article
Floral traits vary greatly between plant species, and determine which pollinators are physically capable of accessing floral rewards and carrying out effective pollination. Research on the responses of nectarivorous birds to different flower morphologies has been largely restricted to hummingbirds, while other flower specialists, the sunbirds and h...
Article
For two decades, neonicotinoid insecticides have been extensively used worldwide. Targeting neuronal receptors, they have deleterious effects on the behaviour and physiology of many of many beneficial as well as harmful insects. Bees are exposed to these insecticides in pollen and nectar while providing pollination services to agricultural crops, a...
Article
Full-text available
Flowers that mimic carrion or faeces exhibit unusual traits, the evolution and functional significance of which remain poorly understood. Odour is an important pollinator attractant, but visual traits and interactions between visual and scent traits have seldom been considered. We studied pollination of the “carrion flowers” of Ceropegia mixta [= O...
Article
Full-text available
Honey bees feed on floral nectar and pollen that they store in their colonies as honey and bee bread. Social division of labor enables the collection of stores of food that are consumed by within-hive bees that convert stored pollen and honey into royal jelly. Royal jelly and other glandular secretions are the primary food of growing larvae and of...
Article
Pollen, the main protein source for honey bees, is mixed with regurgitated nectar or honey during collection and then stored as 'bee bread' before its consumption, mainly by young nurse workers. It has been suggested that storage of pollen improves its nutritional value and digestibility, but there is little evidence for such changes. We fed two fr...
Article
Full-text available
In insects, lifespan and reproduction are strongly associated with nutrition. The ratio and amount of nutrients individuals consume affect their life expectancy and reproductive investment. The geometric framework (GF) enables us to explore how animals regulate their intake of multiple nutrients simultaneously and determine how these nutrients inte...
Article
Full-text available
Many dilute nectars consumed by bird pollinators contain secondary metabolites, potentially toxic chemicals produced by plants as defences against herbivores. Consequently, nectar-feeding birds are challenged not only by frequent water excess, but also by the toxin content of their diet. High water turnover, however, could be advantageous to nectar...
Article
Full-text available
The influence of pheromones on insect physiology and behavior has been thoroughly reported for numerous aspects, such as attraction, gland development, aggregation, mate and kin recognition. Brood pheromone (BP) is released by honey bee larvae to indicate their protein requirements to the colony. Although BP is known to modulate pollen and protein...
Article
Despite potential links between pesticides and bee declines, toxicology information on honey bee larvae (Apis mellifera) is scarce and detoxification mechanisms in this development stage are virtually unknown. Larvae are exposed to natural and synthetic toxins present in pollen and nectar through consumption of brood food. Due to the characteristic...
Article
Honey bees (Apis mellifera) are generalist pollinators that forage for nectar and pollen of a very large variety of plant species, exposing them to a diverse range of secondary metabolites produced as chemical defences against herbivory. Honey bees can tolerate high levels of many of these toxic compounds, including the alkaloid nicotine, in their...
Article
The ecological function of secondary metabolites in plant defence against herbivores is well established, but their role in plant-pollinator interactions is less obvious. Nectar is the major reward for pollinators, so the occurrence of defence chemicals in the nectar of many species is unexpected. However, increasing evidence supports a variety of...
Data
Cumulative consumption and details of the different amount of nutrient eaten during the Choice Experiment. Every values are in mg/bee ±s.e.m., except for the P:C ratio columns. The “Cumulative Consumption” column is the same as the last column in Table 1. Honey bees were offered the choice between two unbalanced diets, differing in their P:C ratios...
Data
Daily nutrient intake is influenced by the amount of dietary protein, but not by the THX pesticide dose. The panels show the effect of THX doses among different diets. The top panel is the choice experiment, where bees were able to regulate their nutrient intake. The four panels below the line represent the no-choice experiment with the four differ...
Article
Full-text available
Over a decade, declines in honey bee colonies have raised worldwide concerns. Several potentially contributing factors have been investigated, e.g. parasites, diseases, and pesticides. Neonicotinoid pesticides have received much attention due to their intensive use in crop protection, and their adverse effects on many levels of honey bee physiology...
Data
Statistical data. (A) Choice experiment. (B) No-Choice experiment–THX Dose effect. (C) No-Choice experiment–Dietary protein effect. (PDF)
Article
Nectarivorous birds typically consume smaller meals of more concentrated than of less concentrated sugar solutions. It is not clear, however, whether they use taste to decide how much to consume or if they base this decision on post-ingestive feedback. Taste, a cue to nectar concentration, is available to nectarivores during ingestion whereas post-...
Article
The paradox of secondary metabolites, toxic defence compounds produced by plants, in nectar and fruits is well known. Deterrence of feeding by nectarivorous and frugivorous birds is better understood than the effect of these chemicals on the digestive performance of birds. Digestive parameters such as transit time and sugar assimilation are importa...
Article
Full-text available
Insecticides are thought to be among the major factors contributing to current declines in bee populations. However, detoxification mechanisms in healthy, unstressed honey bees are poorly characterised. Alkaloids are naturally encountered in pollen and nectar, and we used nicotine as a model compound to identify the mechanisms involved in detoxific...
Article
Secondary compounds in nectar may play a decisive role in determining the spectrum of floral visitors on plants. Flowers of the African coral tree Erythrina caffra are visited mainly by generalist passerine nectarivores, such as weavers and bulbuls. As the nectar of this species tastes very bitter to humans, it was hypothesized that secondary compo...
Article
Full-text available
Animals strongly regulate the amount of protein that they consume. The quantity of individual essential amino acids (EAAs) obtained from dietary protein depends on the protein source, but how much EAA proportions in diet affect nutrient balancing has been rarely studied. Recent research using the Geometric Framework for nutrition has revealed that...
Article
Full-text available
Herbivory in some Nicotiana species is known to induce alkaloid production. This study examined herbivore-induced defenses in the nornicotine-rich African tobacco N. africana, the only Nicotiana species indigenous to Africa. We tested the predictions that: 1) N. africana will have high constitutive levels of leaf, flower and nectar alkaloids; 2) le...
Article
The effects of pesticides on honeybee larvae are less understood than for adult bees, even though larvae are chronically exposed to pesticide residues that accumulate in comb and food stores in the hive. We investigated how exposure to a plant alkaloid, nicotine, affects survival, growth and body composition of honeybee larvae. Larvae of Apis melli...
Article
Full-text available
Regulation of energy and water are by necessity closely linked in avian nectarivores, because the easily available sugars in nectar are accompanied by an excess of water but few electrolytes. In general, there is convergence in morphology and physiology between three main lineages of avian nectarivores that have evolved on different continents - th...
Article
Full-text available
Dietary sources of essential amino acids (EAAs) are used for growth, somatic maintenance and reproduction. Eusocial insect workers such as honeybees are sterile, and unlike other animals, their nutritional needs should be largely dictated by somatic demands that arise from their role within the colony. Here, we investigated the extent to which the...
Article
Full-text available
Nectar concentration and composition vary widely between plant species. Nectarivorous birds that associate floral characteristics with nectar quality may be able to avoid less rewarding flowers and therefore forage more efficiently. We assessed the abilities of amethyst sunbirds (Chalcomitra amethystina) to utilize color cues to discriminate betwee...
Article
Full-text available
Understanding the causes and consequences of pollinator declines is a priority in ecological research. However, across much of the globe we have a poor understanding of pollinator assemblages, population trends and the ecological and economic importance of particular pollinators, due to a marked geographic bias in research effort. Here, we show tha...
Article
Full-text available
Abstract Nectar-feeding birds generally demonstrate preference for hexose solutions at low sugar concentrations, switching to sucrose/no preference at higher concentrations. Species vary in the concentration at which the switch from hexose preference occurs; this could reflect physiological constraints that would also influence nectar selection whe...
Article
Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti‐herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator intera...
Article
Coloured nectar is a rare phenomenon best known from islands and insular habitats. Islands are also known for lizard pollination, where coloured nectar potentially acts as a visual cue to attract pollinators, advertising the sweet reward. However, nectar may also contain secondary metabolites with toxic or deterrent effects. The aim of this study w...
Article
Full-text available
Insect pollinators of crops and wild plants are under threat globally and their decline or loss could have profound economic and environmental consequences. Here, we argue that multiple anthropogenic pressures – including land-use intensification, climate change, and the spread of alien species and diseases – are primarily responsible for insect-po...
Article
Full-text available
Honey bees are the subject of research around the world due to their great economic importance and current population declines (vanEngelsdorp and Meixner, 2010). Many studies cannot be conducted at the colony level. Controlled cage experiments provide insight into behavioural interactions (Elzen et al., 2001), diseases (Martín-Hernández et al., 200...
Article
Nectarivores face a constant challenge in terms of water balance, experiencing water loading or dehydration when switching between food plants or between feeding and fasting. To understand how whitebellied sunbirds and New Holland honeyeaters meet the challenges of varying preformed water load, we used the elimination of Intramuscular-injected [(14...
Article
Coloured nectar is a rare phenomenon best known from islands and insular habitats. Islands are also known for lizard pollination, where coloured nectar potentially acts as a visual cue to attract pollinators, advertising the sweet reward. However, nectar may also contain secondary metabolites with toxic or deterrent effects. The aim of this study w...
Article
Avian nectarivores face the dilemma of having to conserve salts while consuming large volumes of a dilute, electrolyte-deficient diet. This study evaluates the responses to salt solutions and the regulation of salt intake in white-bellied sunbirds (Cinnyris talatala) and New Holland honeyeaters (Phylidonyris novaehollandiae). Birds were first offer...
Article
Recent large-scale mortality of honeybee colonies is believed to be caused by multiple interactions between diseases, parasites, pesticide exposure, and other stress factors. To test whether a dual challenge has an additive effect in reducing survival, we experimentally stimulated the immune system of caged Apis mellifera scutellata workers from si...
Article
The nutritional needs of bees are receiving renewed attention in the context of declining bee populations and changes in land use that threaten floral resources. We present a comprehensive analysis of the nutritional composition of sunflower (Helianthus annuus L.) pollen, comparing hand-collected, bee-collected and stored pollen. As found in previo...
Article
A nectar diet is simple in nutritional composition and easily digested, but may vary greatly in its proportions of sugar and water. Here, we apply the geometric framework, a modelling approach for investigating how animals balance nutrient needs in multidimensional and dynamic nutritional environments, to captive whitebellied sunbirds (Cinnyris tal...
Article
Secondary metabolites produced by plants for herbivore defence are often found in floral nectar, but their effect on the foraging behaviour and physiological performance of pollinators is largely unknown. Nicotine is highly toxic to most herbivores, and nicotine-based insecticides may contribute to current pollinator declines. We examined the effec...
Article
Bees are herbivorous insects, consuming nectar and pollen throughout their life cycles. This paper is a brief review of the chemistry of these two floral resources and the implications for bee nutrition. Nectar is primarily an energy source, but in addition to sugars contains various minor constituents that may, directly or indirectly, have nutriti...
Article
Bees are herbivorous insects, consuming nectar and pollen throughout their life cycles. This paper is a brief review of the chemistry of these two floral resources and the implications for bee nutrition. Nectar is primarily an energy source, but in addition to sugars contains various minor constituents that may, directly or indirectly, have nutriti...
Article
Full-text available
Limited food availability disrupts the energy balance of animals, and nectarivorous birds with high metabolic requirements that necessitate frequent feeding may be particularly affected. We kept White-bellied Sunbirds (Cinnyris talatala) and Brown Honeyeaters (Lichmera indistincta) at 10�C, fed them a 0.63-M sucrose solution, and exposed them to a...
Article
Ecology Letters (2011) 14: 251–259 Ongoing expansion of large-scale agriculture critically threatens natural habitats and the pollination services they offer. Creating patches with high plant diversity within farmland is commonly suggested as a measure to benefit pollinators. However, farmers rarely adopt such practice, instead removing naturally o...
Article
Full-text available
The winter-flowering succulent Aloe marlothii provides nectar for many opportunistic avian nectarivores in southern African savannas. We assessed the importance of A. marlothii nectar sugar for opportunistic nectarivores by analysing temporal changes in stable carbon isotope ratios (δ13C) in the tissues of birds in Suikerbosrand Nature Reserve, Sou...