Nectar Diet Research Articles

Sugar assimilation underlying dietary evolution of Neotropical bats

Dietary specializations in animals lead to adaptations in morphology, anatomy and physiology. Neotropical bats, with their high taxonomic and trophic diversity, offer a unique perspective on diet-driven evolutionary adaptations. Here we assess the metabolic response to different dietary sugars among wild-caught bats. We found that insectivorous bats had a pronounced metabolic response to trehalose, whereas bats with nectar and fruit-based diets showed significantly higher blood glucose levels in response to glucose and sucrose, reaching levels over 750 mg dl−1. The genomic analysis of 22 focal species and two outgroup species identified positive selection for the digestive enzyme trehalase in insect eaters, while sucrase–isomaltase showed selection in lineages with omnivorous and nectar diets. By examining anatomical and cellular features of the small intestine, we discovered that dietary sugar proportion strongly impacted numerous digestive traits, providing valuable insight into the physiological implications of molecular adaptations. Using hybridization chain reaction (HCR) RNA fluorescence in situ hybridization, we observed unusually high expression in the glucose transporter gene Slc2a2 in nectar bats, while fruit bats increased levels of Slc5a1 and Slc2a5. Overall, this study highlights the intricate interplay between molecular, morphological and physiological aspects of diet evolution, offering new insights into the mechanisms of dietary diversification and sugar assimilation in mammals.

Flowering phenology influences butterfly nectar foraging on non-native plants in an oak savanna.

The negative impacts of non-native species have been well documented, but some non-natives can play a positive role in native ecosystems. One way that non-native plants can positively interact with native butterflies is by provisioning nectar. Relatively little is known about the role of phenology in determining native butterfly visitation to non-native plants for nectar, yet flowering time directly controls nectar availability. Here we investigate the phenological patterns of flowering by native and non-native plants and nectar foraging by native butterflies in an oak savanna on Vancouver Island, British Columbia, Canada. We also test whether native butterflies select nectar sources in proportion to their availability. We found that non-native plants were well integrated into butterfly nectar diets (83% of foraging observations) and that visitation to non-natives increased later in the season when native plants were no longer flowering. We also found that butterflies selected non-native flowers more often than expected based on their availability, suggesting that these plants represent a potentially valuable resource. Our study shows that non-native species have the potential to drive key species interactions in seasonal ecosystems. Management regimes focused on eradicating non-native species may need to reconsider their aims and evaluate resources that non-natives provide.

Effects of dietary supplementation with abscisic acid on Apis mellifera colonies confined in overwintering nucleus: studies on the adult honey bee population, nosemosis, and expression of nutrition- and immune-related genes

Due to the complex interactions between pathogens and environmental and anthropogenic stressors, in temperate climates, honey bee populations suffer depopulation and/or colony death, mainly during overwintering. Nosema spp. comprises one of the primary pathogens affecting Apis mellifera colonies, and cold ambient temperature promotes its intensity in worker bees. Additionally, the drastic reduction of plants decreases the diversity and quality of pollen and nectar diet for bees, leading to malnutrition of honey bee colonies and compromising the immunity of individuals, increasingly vulnerable to parasites and pathogens. Previous studies showed that abscisic acid (ABA) stimulates the health of honey bees at individual and colony levels against different stress conditions. This study aimed at evaluating the effect of supplementing the diet with ABA on overwintering nuclei, considering the population growth of honey bee colonies, nosemosis dynamics, and the nutrition- and immune-related gene expression of honey bees. Results in this work showed that ABA had no significant effect on any of the parameters studied. However, taking into account the results observed in the variables measured, we encourage the development of more studies focused on this topic, using more colonies per group and measuring the blooming period and the plant species involved.

CARBOHYDRATE, LIPID AND PROTEIN PROFILE IN CATOPSILIA PYRANTHE TREATED WITH VARIOUS CONCENTRATIONS OF SUGARS AND NECTARS

In order of Lepidoptera, butterflies are the most aesthetic insects which adds beauty to our ecosystem as well as they are the pollinators. Anthropogenic activities are hindering their survival and thus it is the time to conserve them to maintain biodiversity. Nectars are the rewards for such pollinators and their good variety can be able to maintain their coexistence. Sugar concentration in nectars varies and directly affects its mortality, fecundity and physiological, behavioral changes. The present study focuses on the physiological changes of butterflies after treating them with four different concentrations of sucrose (10 %, 20 %, 30 % and 40 %) and four different nectars on which (Catopsilia pyranthe) mottled emigrants generally feed on the field. Also the wild butterflies were collected and were compared with the control, sucrose concentrations and four varieties of nectar diets. Sucrose is selected for the treatment as it is available in nectar at higher amounts. The best results of total carbohydrates in males (0.581 ± 0.059 mg/ml) as well as females (0.509 ± 0.137 mg/ml) were recorded in Vinca rosea treated individuals, glycogen in 40 % sucrose treatments in both male (0.580 ± 0.075 mg/ml) and female (0.614 ± 0.0304 mg/ml), total lipids again in 40 % sucrose treatments in both male (0.850 ± 0.431 mg/ml) and female (0.726 ± 0.1106 mg/ml) and total proteins in wild (1.985 ± 1.782 mg/ml) in male and in 40 % sucrose (1.681 ± 0.111 mg/ml) in female individuals. In SDS PAGE, the highest number of bands of different molecular weights observed in males are Lantana camara, Vinca rosea, Stachytarpheta cayennensis treated and Wild butterflies while in female individuals, it is in Vinca rosea treated and Wild butterflies. The study also presents the 3D structures with the help of peptide search by Uniprot and homology modeling with the help of Swissprot. It is an attempt to represent the variety of physiological changes that occur due to the different concentration of sugars so it can help for further maintenance of nectar plants and ultimately to maintain our ecosystem by conserving pollinators.

Lerp-feeding behaviour of the flower-visiting Musk Lorikeet Glossopsitta concinna

Besides the primary diet of nectar, pollen, and fruits, the flower-visiting Musk Lorikeet Glossopsitta concinna feeds on lerps. However, a description of its behaviour while foraging on this latter source seems to be lacking. We describe and illustrate the feeding behaviour of the Musk Lorikeet on Spondylaspidinae psylloid lerps. The lerps were within young deformed eucalypt leaves, and the Lorikeet had to open a deformed leaf and remove the starchy lerps to feed on them. The Lorikeet took c. 1 minute to process each leaf, which suggests that these lerps are an important or satisfying food.

The Birth-and-Death Evolution of Cytochrome P450 Genes in Bees.

The birth-and-death model of multigene family evolution describes how gene families evolve and diversify through duplication and deletion. The cytochrome P450s are one of the most diverse and well-studied multigene families, involved in both physiological and xenobiotic functions. Extensive studies of insect P450 genes have demonstrated their role in insecticide resistance. Bees are thought to experience toxin exposure through their diet of nectar and pollen, as well as the resin-collecting behavior exhibited by some species. Here, we describe the repertoire of P450 genes in the orchid bee Euglossa dilemma. Male orchid bees form perfume bouquets used in courtship displays by collecting volatile compounds, resulting in exposure to compounds known to be toxic. In addition, we conducted phylogenetic and selection analyses across ten bee species encompassing three bee families. We find that social behavior and resin collection are not correlated with the repertoire of P450 present in a bee species. However, our analyses revealed that P450 clades can be classified as stable and unstable, and that genes involved in xenobiotic metabolism are more likely to belong to unstable clades. Furthermore, we find that unstable clades are under more dynamic evolutionary pressures and exhibit signals of adaptive evolution. This work highlights the complexity of multigene family evolution, revealing that multiple factors contribute to the diversification, stability, and dynamics of this gene family. Furthermore, we provide a resource for future detailed studies investigating the function of different P450s in economically important bee species.

Naturalising diet to reduce stereotypic behaviours in slow lorises rescued from wildlife trade

Providing a natural diet is a key component to improving animal welfare and potentially reducing stereotypic behaviours in captivity. Wild slow lorises (Nycticebus spp.) are threatened by illegal wildlife trade, and in Thailand, confiscations from trade have led to a large number of Bengal (Nycticebus bengalensis) and greater slow lorises (N. coucang) in rescue centers such as Bang Phra Wildlife Domestic Research Station (Bang Phra). Due to limited enclosure space and availability of natural food items, welfare may be compromised for these confiscated animals. Slow lorises in most rescue centres including Bang Phra are mainly fed with fruit and vegetables rather than their natural diet of exudates, nectar and insects. Our project aimed to increase wild-type activities and reduce stereotypic behaviours in captive slow lorises at Bang Phra by modifying the diet (especially adding exudates of gum Arabic) using environmental enrichment devices. From May to August 2019, we implemented four diet conditions on 30 individuals: baseline, gum presented in two feeding devices and insects presented in a box. Diet conditions changed individual behaviours, with more time spent feeding and foraging, less time spent resting, and less stereotypic behaviours. Fixed gum was the most successful device to encourage increased feeding (40.4 % vs ∼ 3.5 % during baseline conditions) and foraging (16.3 % vs ∼2.5 % during baseline conditions), whilst significantly decreasing stereotypic behaviours (3.2 % vs ∼16.5 % during baseline conditions). Animals with small body sizes are often placed in small cages in rescue centres despite their needs in the wild. At the same time, species with specialist diets may not thrive in rescue centres that lack the funds or infrastructure to procure food items perceived to be specialised. With wild numbers declining rapidly, rescue centres must provide adequate space and wild type diets to ensure the health and well-being of these globally threatened primates.

Bird pollination syndrome is the plant's adaptation to ornithophily, but nectarivorous birds are not so selective

Many tropical plants are pollinated by birds and several bird phylogenetical lineages have specialised to a nectar diet. The long‐assumed, intimate ecological and evolutionary relationship between ornithophilous plants and phenotypically specialised nectarivorous birds has nevertheless been questioned in recent decades, where such plant–pollinator interactions have been shown to be highly generalised.In our study, we analysed two extensive interaction datasets: bird–flower and insect–flower interactions, both collected on Mt Cameroon, west‐central Africa. We tested if: 1) insects and birds interact with distinct groups of plants; 2) plants with a typical set of ornithophilous floral traits (i.e. bird pollination syndrome) interact mainly with birds; 3) birds favour plants with bird pollination syndrome and; 4) if and how the individual floral traits and plant level nectar production predict bird visitation.Bird‐visited plants were typically also visited by insects, while approximately half of the plants were visited by insects only. We confirmed the validity of the bird pollination syndrome hypothesis, as plants with bird‐pollination syndrome traits were visited by birds at a higher rate and mostly hosted a lower frequency of visiting insects. However, these ornithophilous plants were not more attractive than the other plants for nectar‐feeding birds. Nectar production per plant individual was a better predictor of bird visitation than any other floral trait traditionally related to the bird pollination syndrome. Our study thus demonstrated the highly asymmetrical relationship between ornithophilous plants and nectarivorous birds.

The Disguise of the Hummingbird: On the Natural History of Huitzilopochtli in the Florentine Codex

Abstract This essay explores the avian nature of Huitzilopochtli (“Hummingbird on the Left”), the tutelary god of the Mexica, by centering the deity’s association with the hummingbird. Arguing that there is a “natural history of Huitzilopochtli” deployed in book 11 of the Florentine Codex, devoted to “earthly things,” this analysis re-entangles hummingbird ethology with Huitzilopochtli’s cult, a bond that was severed in the early days of colonization. A close reading of the Nahuatl, Spanish, and visual texts in this book reveals that seasonal cycles and hummingbird behavior—energy budgeting, flower nectar diet, swift flight, and long-haul migration—can be interpreted as inspiring the three main feasts of Huitzilopochtli in the Mexica ritual year. Furthermore, reading the natural history entries in book 11 as related to the avian god illuminates how central hummingbirds were as markers of the dry and rainy seasons and their effects in Nahua social and ritual life.

Transcriptome analysis reveals nutrition- and age-related patterns of gene expression in the fat body of pre-overwintering bumble bee queens.

Many diapausing insects undergo a nutrient storage period prior to their entry into diapause. Bumble bee queens diapause as adults in the winter preceding their spring nest initiation period. Before diapause, they sequester glycogen and lipids, which they metabolize during the overwintering period. We used RNA sequencing to examine how age and nectar diet (specifically, the concentration of sucrose in nectar) impact gene expression in the pre-overwintering bumble bee queen fat body, the "liver-like" organ in insects with broad functions related to nutrient storage and metabolism. We found that diet on its own, and in combination with age, impacts the expression of genes involved in detoxification. Age was also a strong driver of gene expression, especially at earlier ages (up to 3days). In addition to these molecular correlates of diet and age, we also found a putative molecular signature of diapause entry or preparation in adult queens in the oldest age group (12days) fed the most sucrose-rich diet, based on comparisons between our data set and another transcriptome data set from bumble bee queens. This transcriptomic pattern suggests that preparation for (or entry into) diapause might be in part mediated by nutritional state in bumble bee queens. Collectively, these findings show that there are molecular processes in the fat body that are responsive to sucrose levels in the diet and/or associated with age-related maturational changes. A better understanding of these processes may shed light on important aspects of bumble bee biology, such as queen responses to nutritional and other forms of stress, and the factors that regulate their entrance into diapause.

Potency of Brown Sugar as a Nectar Substitute for Trichoglossus haematodus in Captivity

Trichoglossus haematodus (Linnaeus, 1771) is nectarivorous bird that feed on nectar as a source of carbohydrate. In captivity, it is not practical to provide a continued diet of nectar from the flowers. Therefore, this study aimed to find other carbohydrate sources such as brown sugar as substitute nectar for T. haematodus. Twelve wild T. haematodus in four cages offered five types different brown sugar solution with different concentrations. Since brown sugar has low protein content, therefore the birds also offered commercial baby biscuit to meet the protein requirement. The results showed that the birds like to consume all types of brown sugar solution with sugar concentration up to 40% . However, the siwalan brown sugar solution was the most favored by the bird. over the other type of brown sugar solutions (aren, coconut, sugar cane and regular commercial “palm” brown sugar). Furthermore, the result showed that the birds prefer commercial baby biscuit was soaked in the brown sugar solution with concentration 20%. This study provides the information that the brown sugar solution based diet has potency as an alternative carbohydrate source to substitute nectar for T. haematodus in captivity which is more practical and can increase the survival rate in birds.

Maternal mouth-to-mouth feeding behaviour in flower-visiting bats, but no experimental evidence for transmitted dietary preferences

In addition to breast milk, several mammals feed their offspring with primary food items. This provisioning can offer both energetic and informational benefits: young might use parentally provided food as a source of nutrients, but also as a valuable option to socially learn about adults’ food. For bats, there are only very few and partially anecdotal reports of adults feeding their pups with primary food, and there is also a lack of information about social learning processes during ontogeny. In the present study, we provide experimental evidence that lactating flower-visiting bats (Glossophaga soricina) provide regurgitated nectar via mouth-to-mouth feeding behaviour to their pups. After licking at their mothers’ slightly opened mouth, pups defecated a marker substance that was exclusively available in the mothers’ nectar diet. We additionally investigated associated informational benefits by testing for a social transmission of dietary preferences. We experimentally induced a dietary preference for specifically flavoured nectars to mothers with non-volant pups. Subsequently, after pups became volant, we tested their dietary preferences in a choice experiment. However, we found no experimental evidence that pups adopted the preferences of their mothers.

Low energy reserves are associated with fasting susceptibility in Neotropical nectar bats Glossophaga soricina

Neotropical nectar-feeding bats consume large amounts of sugar and use most of their energy-rich diet directly from the bloodstream, suggesting an adaptation towards lower body energy reserves. Here we tested the hypothesis that bats Glossophaga soricina spare the energy costs of storing energy reserves, even if this would represent a risky susceptibility during fasting. Blood glucose concentrations in 18 h fasted bats showed a 40% decrease. Breast muscle and adipose tissue lipids, as well as carcass fatty acids and liver glycogen, were also decreased following fasting. The inability to keep normoglycemia following a short-term fasting (i.e. 28 h) confirm that nectar bats invest little on storing energy reserves and show a severe fasting susceptibility associated to this pattern. Our study also support the general hypothesis that evolutionary specializations towards nectar diets involve adaptations to allow a decreased body mass, which reduces the energy costs of flight while increases foraging time.

Metabolic partitioning of sucrose and seasonal changes in fat turnover rate in ruby-throated hummingbirds (Archilochus colubris).

Hummingbirds fuel their high energy needs with the fructose and glucose in their nectar diets. These sugars are used both to fuel immediate energy needs and to build fat stores to fuel future fasting periods. Fasting hummingbirds can deplete energy stores in only hours and need to be continuously replacing these stores while feeding and foraging. Whether and how hummingbirds partition dietary fructose and glucose towards immediate oxidation versus fat storage is unknown. Using a chronic stable isotope tracer methodology, we examined whether glucose or fructose is preferentially used for de novo lipogenesis in ruby-throated hummingbirds (Archilochus colubris). Potential seasonal changes were correlated with variation in the overall daily energy expenditure. We fed ruby-throated hummingbirds sucrose-based diets enriched with 13C on either the glucose or the fructose portion of the disaccharide for 5 days. Isotopic incorporation into fat stores was measured via the breath 13C signature while fasting (oxidizing fat) during the winter and summer seasons. We found greater isotopic enrichment of fat stores when glucose was labelled compared with fructose, suggesting preference for glucose as a substrate for fatty acid synthesis. We also found a seasonal effect on fat turnover rate. Faster turnover rates occurred during the summer months, when birds maintained lower body mass, fat stores and exhibited higher daily nectar intake compared with winter. This demonstrates that fat turnover rate can substantially vary with changing energy expenditure and body composition; however, the partitioning of sucrose towards de novo fatty acid synthesis remains constant.

Floral community predicts pollinators’ color preference: implications for Batesian floral mimicry

African long tongue fly pollinators strongly prefer colors most often associated with their nectar diet. Most flowers offer a nectar reward in exchange for pollination by animals. However, some orchids cheat pollinators, mimicking the color signals of nectar-bearing flowers but offering no reward. Using artificial flowers, we show that the color composition of a flowering community determines the success of this mimicry because of its tight link to a pollinator’s color preference.

Thiamethoxam seed treatments reduce foliar predator and pollinator populations in sunflowers (Helianthus annuus), and extra-floral nectaries as a route of exposure for seed treatments to affect the predator, Coleomegilla maculata (Coleoptera: Coccinellidae)

Neonicotinoid seed-treatments are used frequently in sunflower production to prevent early-season herbivory, and have been implicated in declines in non-target species. Over three site-years, both insecticide treated (Cruiser®, rate: 0.25 mg a.i. (thiamethoxam)/seed) and untreated sunflower (Helianthus annuus [Family: Asteraceae]) fields were planted in Eastern and Central South Dakota. Foliar and subterranean predatory arthropod communities and pollinator populations were compared among the two treatments. A greenhouse study was performed to collect and quantify toxins in extra-floral nectar from treated and untreated sunflowers. A laboratory assay was performed to examine the effect of an artificial nectar diet laced with thiamethoxam or clothianidin on survival, fecundity and mobility of Coleomegilla maculata (De Geer [Coleoptera: Coccinellidae]). Seed-treated fields had significantly fewer above-ground natural enemies and pollinators than untreated fields, while subterranean predators were unaffected. Beetle flip-over times increased as concentration of thiamethoxam in diet increased, but clothianidin showed no effect. Neither toxin affected number of eggs oviposited by beetles, or size of developing oocytes. However, there was a negative correlation between increasing thiamethoxam concentration and number of developing eggs. Extra-floral nectar (EFN) collected from treated greenhouse-grown plants contained thiamethoxam (range: 1.23 ± 0.09 ppb to 4.83 ± 0.63 ppb), but no clothianidin. Toxin-laden EFN was identified as a potential route of exposure between beneficial arthropods and seed-applied neonicotinoids. Risks of neonicotinoid seed treatment use are discussed in the light of additional exposure pathways being confirmed.

Impact of floral nectar limitation on life-history traits in a grassland butterfly relative to nectar supply in different agricultural landscapes

Wild flower diversity and abundance are strongly reduced in intensive agricultural landscapes. Flower-visiting insects may, therefore, experience limited nectar quantities and qualities. Adult insects that rely on energy-rich nectar income for flight, survival and reproduction are expected to be much more affected than insects that rely on their larval reserves. We dealt with this issue at the intraspecific level by comparing the responses of several life-history traits to different nectar diets between meadow brown butterflies (Maniola jurtina) originating from relative intensively managed and extensively managed agricultural landscapes. We used outdoor flight cages in which we simulated factorial treatments of low/high nectar quality and low/high quantity. Survival was highest in the high nectar quantity and quality treatment. Individuals from intensive landscapes were heavier, which is in line with predictions on increased capital breeding, and they survived better than those from extensive landscapes, of which the females lost body mass in all treatments. Females from intensive landscapes were able to buffer, or even increase, their body mass in the high nectar quantity treatments, but the differences with females from extensive landscapes disappeared under low nectar quantities (independent of nectar quality). In males, body mass losses were always larger for individuals from extensive landscapes compared to individuals from intensive landscapes. Forty percent of the females showed complete reproductive failure in the low quantity/low quality treatment compared to c. 7% in the other treatments. In the low quantity/low quality treatment, realized fecundity decreased strongly in females from intensive, but not extensive landscapes. Egg size was not affected by landscape of origin in the high-quality nectar treatments, but showed very different responses relative to landscape of origin in the treatments with low-quality nectar. Our results showed strong effects of reduced nectar supply on fitness-related traits, and responses were different between butterflies originating from landscapes with contrasted nectar diet. Hence, different levels of agricultural intensification changing the quantity and quality of the local nectar supply could pave the way for ecological differentiation of the organism’s behaviour, physiology and life history.

Sugar Metabolism in Hummingbirds and Nectar Bats.

Hummingbirds and nectar bats coevolved with the plants they visit to feed on floral nectars rich in sugars. The extremely high metabolic costs imposed by small size and hovering flight in combination with reliance upon sugars as their main source of dietary calories resulted in convergent evolution of a suite of structural and functional traits. These allow high rates of aerobic energy metabolism in the flight muscles, fueled almost entirely by the oxidation of dietary sugars, during flight. High intestinal sucrase activities enable high rates of sucrose hydrolysis. Intestinal absorption of glucose and fructose occurs mainly through a paracellular pathway. In the fasted state, energy metabolism during flight relies on the oxidation of fat synthesized from previously-ingested sugar. During repeated bouts of hover-feeding, the enhanced digestive capacities, in combination with high capacities for sugar transport and oxidation in the flight muscles, allow the operation of the “sugar oxidation cascade”, the pathway by which dietary sugars are directly oxidized by flight muscles during exercise. It is suggested that the potentially harmful effects of nectar diets are prevented by locomotory exercise, just as in human hunter-gatherers who consume large quantities of honey.

The plant pathogen Phytophthora cinnamomi influences habitat use by the obligate nectarivore honey possum (Tarsipes rostratus)

Introduced plant pathogens can devastate susceptible plant communities, and consequently impact on animal communities reliant on plants for food and habitat. Specifically, plant pathogens change the floristic diversity of vegetation communities, thereby reducing availability of food sources for fauna (e.g. pollen and nectar) and result in major changes to habitat structure when canopy and understorey plant species succumb to disease. Phytophthora cinnamomi poses a threat to flowering plant species (e.g. Banksia species) which are important food sources for nectarivorous fauna. The honey possum (Tarsipes rostratus) is the only obligate nectarivorous non-flying mammal living on a restrictive diet of nectar and pollen; consequently, these tiny mammals are likely to be particularly vulnerable to the landscape-wide devastation caused by P. cinnamomi. We investigated habitat selection by honey possums in a vegetation community infested with P. cinnamomi to determine how these mammals respond to habitat affected by this pathogen. Over four seasons, 18 honey possums were fitted with radio-transmitters and tracked to identify habitat preferences. Vegetation surveys were compared for locations selected by honey possums (as determined from tracking) and randomly selected sites. Radio-tracking revealed that sites selected by honey possums were significantly taller, denser, and more floristically diverse than their paired random locations. The presence of P. cinnamomi influences habitat use by honey possums, but animals show resilience in terms of using the best of what is available in both P. cinnamomi–affected and unaffected locations. Habitat patches comprising less susceptible species, or plants that have yet to succumb to infection, provide refuge and food resources for honey possums. Management to reduce the spread of existing P. cinnamomi infestations and prevent contamination of new locations will benefit vegetation communities and associated faunal communities, while identifying honey possum food plant species that are resilient to the pathogen may support revegetation attempts.

Drinking problems on a ‘simple’ diet: physiological convergence in nectar-feeding birds

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 - the hummingbirds, sunbirds and honeyeaters. These birds show similar dependence of sugar preferences on nectar concentration, high intestinal sucrase activity and rapid absorption of hexoses via mediated and paracellular routes. There are differences, however, in how these lineages deal with energy challenges, as well as processing the large volumes of preformed water ingested in nectar. While hummingbirds rely on varying renal water reabsorption, the passerine nectarivores modulate intestinal water absorption during water loading, thus reducing the impact on the kidneys. Hummingbirds do not generally cope with salt loading, and have renal morphology consistent with their ability to produce copious dilute urine; by contrast, as well as being able to deal with dilute diets, honeyeaters and sunbirds are more than capable of dealing with moderately high levels of added electrolytes. And finally, in response to energy challenge, hummingbirds readily resort to torpor, while the passerines show renal and digestive responses that allow them to deal with short-term fasts and rapidly restore energy balance without using torpor. In conclusion, sunbirds and honeyeaters demonstrate a degree of physiological plasticity in dealing with digestive and renal challenges of their nectar diet, while hummingbirds appear to be more constrained by this diet.