Mistletoe Fruit Research Articles

Comparison of Antioxidant, Antiradical and Antibacterial Activities of Mistletoe (Viscum album L.) Fruits and Leaves Growing on Different Host Tree Genus

Comparison of Antioxidant, Antiradical and Antibacterial Activities of Mistletoe (Viscum album L.) Fruits and Leaves Growing on Different Host Tree Genus

Effects of Post-Fire Mulching with Loranthus europaeus Jacq. on Surface Runoff and Rainsplash Erosion in a Semi-Arid Pine Forest

To avoid flooding and erosion hazards, post-fire management actions are essential in Mediterranean forests after severe wildfires. In this regard, mulching is the most common action but some mulch materials, such as straw, may lead to adverse impacts in burned forests. The use of yellow mistletoe fruits (Loranthus europaeus Jacq., hereafter “LE”) for the production of biodegradable mulch and its effectiveness in post-fire hydrology have never been studied. To fill this gap, this study has evaluated surface runoff and rainsplash erosion in a pine forest in Central Eastern Spain burned by a wildfire and mulched by a mixture of LE fruits and straw (with or without adding clay particles) using a portable rainfall simulator. Compared to untreated sites, runoff increased in burned and mulched soils (by 13.6% for the mixture without clay and by 17.2% when clay was added, in the latter case significantly). This increase was mainly due to the compact layer created by mulch application on the soil surface. However, the peak flow and the time to peak were lower in mulched soils (on average by 32.7% and 60.5%, significantly only for the mulch mixture without clay), thus indicating that, in these soils, peak runoff takes longer and its maximum value is lower compared to untreated sites. Soil erosion noticeably and significantly decreased (up to 97%) in mulched areas in comparison to untreated sites without significant differences between the two mixtures. Overall, this study indicates to land managers that soil mulching with a mixture of Loranthus europaeus Jacq. and straw is an effective post-fire management action to reduce the soil erosion risk after a wildfire.

Biotechnological Potential of Different Organs of Mistletoe (Viscum album L.) Collected from Various Host Tree Species in an Urban Area

From an economic and ecological standpoint, it is crucial to investigate the biologically active compounds of mistletoe plants, which are currently discarded by pruning urban mistletoe-infested trees. In the present study, the content of phenolic compounds, triterpenic and organic acids, as well as the antioxidant activity of the extracts of various mistletoe organs (leaves, stems, and fruits) collected from the most infested tree species were investigated. The mistletoe samples collected from Betula pendula, Acer platanoides, Crataegus monogyna, and Sorbus aucuparia showed the highest content of phenolic acids and flavonoids as well as antioxidant activity, as measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), and ferric reducing/antioxidant power (FRAP) assays. The leaves and stems of mistletoe from Tilia cordata were characterized by a high content of triterpenic acids (oleanolic, ursolic, and betulinic). The leaves and fruits of mistletoe plants from Populus nigra and Salix alba contained a high concentration of organic acids, particularly succinic and citric acids. Compared to stem and leaf extracts, the antioxidant activity of the mistletoe fruit extracts was 1.5–3 times higher. The obtained results indicate that mistletoe is a valuable raw material and can be used as a source of phenolic compounds and triterpenic and organic acids, as well as for producing extracts with antioxidant properties.

Evaluation of antitumoral effect of mistletoe fruit extract on Ehrlich ascites tumor cells with muse cell analyzer and argyrophilic nucleolar organizer region staining method

Abstract Introduction Mistletoe has been used alone or as a complementary therapy in the treatment of different diseases for years. In this study, the antitumoral effect of mistletoe fruit extract on Ehrlich ascites tumor (EAT) cells was evaluated. Materials and Methods EAT cells from preformed stock mice were transferred to culture dishes containing 5-fluorouracil (5-FU) and mistletoe extracts at different doses (100, 200, 400, and 800 μg/ml). These cells were incubated at 37 °C in an environment with 95% humidity and 5% CO2. At the end of the incubations, the apoptosis status of the cells, cell cycle, mitochondrial membrane potential, and proliferation status with the argyrophilic (Ag) nucleolar organizer region staining (NORs) method were evaluated. Results As a result, it was observed that the mistletoe fruit extract and 5-FU induce apoptosis of EAT cells. It was concluded that the 5-FU substance arrests the cell cycle at the G0/G1 stage, while the mistletoe arrests the cell cycle at the S and G2/M stages. The depolarization rate of the mistletoe treated cells was higher. As a result of the evaluation made with the AgNORs method, it was seen that mistletoe and 5-FU could be effective in reducing the proliferation of EAT cells. Conclusions It was seen that mistletoe fruit extract could be effective in stimulating the apoptosis and depolarization of cancer cells. The results of other studies in the literature and our study support each other. It was concluded that the mistletoe plant may be useful in cancer treatment.

Habitat use and behavioral patterns of Cassin's Kingbird (Tyrannus vociferans) in an urban park of Mexico City

Changes in vegetation structure and species composition affect habitat use and behavior in most bird species by altering the distribution and abundance of their resources. We explore how the mating and foraging behavior of Cassin's Kingbirds (Tyrannus vociferans) varies by habitat type within a 2,450 ha urban park in Mexico City. The study site includes primarily water bodies, riparian vegetation, willow and Montezuma cypress stands, maize fields, and grasslands. We recorded kingbird behavior twice a week along 21 transects throughout 2012 and 2015. Courtship and reproductive behaviors were displayed in autumn (Sep) and early winter (Dec). Intraspecific agonistic behaviors were associated with courtship and mating events, particularly in 2015. Cassin's Kingbird generally favored open vegetation. The main foraging strategy in open habitats was flycatching but foliage gleaning became frequent when mistletoe plants produced fruits in infested willow stands. The use of mistletoe fruits, presumably a secondary diet item, coincided with the breeding season. In addition to these observations, our study is the first report of Cassin's Kingbird winter mating at low latitudes.

Habitat use and behavioral patterns of Cassin's Kingbird (Tyrannus vociferans) in an urban park of Mexico City

Changes in vegetation structure and species composition affect habitat use and behavior in most bird species by altering the distribution and abundance of their resources. We explore how the mating and foraging behavior of Cassin's Kingbirds (Tyrannus vociferans) varies by habitat type within a 2,450 ha urban park in Mexico City. The study site includes primarily water bodies, riparian vegetation, willow and Montezuma cypress stands, maize fields, and grasslands. We recorded kingbird behavior twice a week along 21 transects throughout 2012 and 2015. Courtship and reproductive behaviors were displayed in autumn (Sep) and early winter (Dec). Intraspecific agonistic behaviors were associated with courtship and mating events, particularly in 2015. Cassin's Kingbird generally favored open vegetation. The main foraging strategy in open habitats was flycatching but foliage gleaning became frequent when mistletoe plants produced fruits in infested willow stands. The use of mistletoe fruits, presumably a secondary diet item, coincided with the breeding season. In addition to these observations, our study is the first report of Cassin's Kingbird winter mating at low latitudes.

Bird species use of Tapinanthus dodoneifolius mistletoes parasitising African locust bean trees Parkia biglobosa in Amurum Forest Reserve, Nigeria

The relationship between mistletoes and their host trees constitutes one of the unique host–parasite interactions in ecosystems. Most West African studies have reported on the parasitic nature of the relationship between Tapinanthus dodoneifolius mistletoes and Parkia biglobosa trees. However, there is little on bird species’ use and subsequent dispersal of the mistletoe on P. biglobosa, and consequently, we investigated aspects of this relationship in the present study. We conducted our study in Amurum Forest Reserve, located in the central part of Nigeria, from May to September 2017. The study area consists of a mosaic of savanna, gallery forest, and rocky outcrops. Of the bird community in this area, the yellow-fronted Tinkerbird Pogoniulus chrysoconus had the highest number of visits to T. dodoneifolius fruits, while the Senegal Eremomela Eremomela pusilla spent the most time foraging on the fruits. Four sunbird species were recorded feeding on T. dodoneifolius flowers for nectar; all but the Copper Sunbird Cinnyris cupreus were observed opening the flowers of T. dodoneifolius. Other bird species were recorded foraging on insects on T. dodoneifolius, and some simply perching on twigs or pecking on mistletoe fruits. This was a mutualistic relationship between the respective bird species and the mistletoe. This indirectly benefitted the parasitised host by attracting potential pollinators, seed dispersers, and insectivores for the host, hence, improving the rate of visitation to the host. These patterns of visitation behaviours highlighted the ecological importance of T. dodoneifolius within the reserve, particularly in enhancing the survival of other taxa within the reserve. Findings from this study contribute to developing more-nuanced conservation strategies for mixed high savannah habitat types across the tropics.

Biochemical analysis of European mistletoe (Viscum album L.) foliage and fruit settled on Persian ironwood (Parrotia persica C. A. Mey.) and hornbeam (Carpinus betulus L.)

Abstract Mistletoe (Viscum album L.) from Santalaceae family is a hemiparasitic plant containing triterpene acids which widely was used as complementary remedy in cancer therapy for decades. Mistletoe is growing on various tree species as well as some endemic and native species of Hyrcanian forests of Iran such as Parrotia persica (Persian ironwood) and Carpinus betulus (Hornbeam). The aim of this work was to compare the amount of triterpene acids including oleanolic acid (OA), betulinic acid (BA) and ursolic acid (UA) in foliage (leaves and stems) and fruit of mistletoes settled on P. persica and C. betulus as hosts in autumn. In this study, mistletoe plant parts were collected from three bases of each host species in Daeiz forest of Hyrcanian forests of Iran. The samples were extracted with ethyl acetate and analyzed by HPLC. The results indicated that the host species had no significant effect on the amount of triterpene acids in the mistletoes. But the organ type (foliage and fruit), had significant effect on the BA content meanwhile it didn't show any significant effect on the OA. The highest level of BA was significantly detected in foliage of mistletoes on P. persica and C. betulus (1.23 and 0.97 mg/g dry weight) respectively. Independence of statistical analysis, the highest content of OA (8.52 mg/g dry weight) was observed in the foliage of V. album on P. persica. On the other hand, BA was not detected in mistletoe fruits on both host species. UA was not detected in any samples.

Infrapopulation size and mate availability influence reproductive success of a parasitic plant

Abstract Aggregated distributions of parasite individuals across host individuals are nearly ubiquitous among parasitic taxa. The size and sex ratio of the population of one parasite species infecting a single host (hereafter “infrapopulation”) can influence parasite fitness through intraspecific competition, mate availability and the ability to attract vectors for transmission of parasite propagules. Competition for resources and for pollen and seed vector services may limit reproductive success (pollen receipt, fruit production and seed dispersal) in large infrapopulations of parasitic plants, while mate limitation or reduced ability to attract vectors may limit this success in small infrapopulations. Using a dioecious parasitic plant, desert mistletoe Phoradendron californicum, we experimentally removed reproductive tissue from male parasites in whole infrapopulations to test for independent effects of infrapopulation size and within‐host mate availability on female fitness. As desert mistletoe requires both pollen and seed vectors for successful reproduction, the species provides the opportunity to test how infrapopulation characteristics affect multiple components of parasite fitness. We found that insect‐mediated pollen receipt decreased for parasites on treated hosts, consistent with within‐host mate limitation. Additionally, the relationship between mate availability and fruit production per flower ranged from neutral to positive depending on year of the experiment. As expected if competition for host resources limits reproductive success more than mate availability in larger infrapopulations, the greater pollen receipt to females in large infrapopulations did not generally translate into increased mistletoe fruit production. Relationships between mistletoe fruit production per flower and infrapopulation size ranged from negative to neutral. Both pollen receipt and pollinator visitation increased with infrapopulation size, indicating that larger populations can be more attractive to pollen vectors independent of mate availability. However, we found no relationship between infrapopulation size and fruit removal by dispersers and, thus, no evidence that attraction of seed dispersal vectors increases with infrapopulation size. Synthesis. These results highlight the interactive roles of within‐host processes (resource competition, mate availability and vector attraction) in determining the fitness of biotically transmitted parasite individuals.

Morphology and stomatal density of developing Arceuthobium americanum (lodgepole pine dwarf mistletoe) fruit: a qualitative and quantitative analysis using environmental scanning electron microscopy

Arceuthobium americanum Nutt. ex Engelm., the lodgepole pine dwarf mistletoe, is a dioecious parasitic flowering plant infecting lodgepole pine (Pinus contorta subsp. latifolia (Engelm.) Critchfield) in the Pacific Northwest, compromising timber value by stunting the host’s growth. The plant disperses its seeds by explosive discharge, and thus understanding its reproduction is an integral step toward managing its spread. The life cycle of Arceuthobium americanum occurs over five to six years, and the fruit matures over two consecutive growing seasons, dispersing in the second. Using low-vacuum environmental scanning electron microscopy (eSEM), we examined branching architecture as well as the morphology and anatomy of fruits during their second year of development up to explosive discharge. We found that branching patterns shifted from opposite-decussate to verticillate after several years’ growth. In addition, the perianth parts (sepals), style, and stigma persisted through the season, and the fruit’s abscission zone developed slightly distal to the end of the pedicel. Stomata, found only on the sepals, were located in crypts surrounded by two subsidiary cells, and stomatal density significantly decreased during development. The decline in stomatal density along with the thick pericarp cuticle may function in retaining water inside the fruit to facilitate discharge and (or) provide a heating mechanism through reduced transpiration.

Asymmetrical Dependence Between a Neotropical Mistletoe and its Avian Seed Disperser

AbstractThe degree of interdependence among interacting species has major implications for our understanding of the coevolutionary process and biodiversity maintenance. However, the mutualism strength among fruiting plants and their seed dispersers remains poorly understood in tropical ecosystems. We evaluated simultaneously the effectiveness of the avian seed dispersers of the mistletoe Struthanthus flexicaulis (Loranthaceae) and the contribution of its fruits to their diets in a highland rocky savanna in southeastern Brazil. The mistletoe fruits are small lipid‐rich pseudoberries available throughout the year. Four passerine birds fed on fruits, but Elaenia cristata (Tyrannidae) was the most effective disperser, responsible for more than 96 percent of the dispersed seeds. This bird swallowed fruits whole, expelling and depositing undamaged seeds by regurgitation and bill wiping on perches. From 646 dispersed seeds, 56 percent were deposited on safe sites, thin live twigs of 38 susceptible host species. Elaenia cristata were predominantly frugivorous, feeding on typically ornithocoric fruits of at least 12 species, but also on arthropods. Although fruits represented 75 percent of the feeding bouts along the year, S. flexicaulis fruits represented only 34 percent of the E. cristata diet. Our results highlight the asymmetrical nature of this mutualistic interaction, with the mistletoe life cycle locally linked to one highly effective seed disperser that is more weakly dependent on mistletoes fruits as a food source. We suggest that merging the seed dispersal effectiveness framework with diet assessment of seed dispersers is needed to clarify the asymmetries in mutualistic pairwise interactions involving plants and their animal partners.

Mistletoe (Cladocolea loniceroides) Fruit Extract on Viability of Breast Cancer Cell Cultures (LB366)

Mistletoe is a tree parasitic plant; its impact is rather negative causing great tree mortality and economic losses around the world. Cladocolea (C.) loniceroides, Mexican mistletoe represents a serious pest and it has not been studied until today. It was considered useless because of the pruning problem, however the authors found that aqueous fruit extract of C. loniceroides presents antioxidant activity. The aim of this research was to identify if the antioxidant aqueous extract of mistletoe fruit provokes cell death in various breast cancer cell cultures.Doses‐response curves were built to ZR75‐1, MCF7, MDA‐MB‐231 and MCF10A as negative control. LC50 were 91, 42, 45.6 and 198.6 µg gallic acid eq./mL, respectively after 48 h treatment. Mistletoe fruit extract induces cell death to breast cancer cultures; which are most sensitive (two times por ZR75‐1 and four times for MCF7, respectively) than noncancerous cell line and this effect may be possible by the presence of some phytochemicals with antioxidant activity.

Mistletoebirds and xylose: Australian frugivores differ in their handling of dietary sugars.

Carbohydrate-rich mistletoe fruits are consumed by a wide range of avian species. Small birds absorb a large portion of water-soluble nutrients, such as glucose, via the paracellular pathway. d-xylose, a pentose monosaccharide, is abundant in some nectars and mistletoe fruits consumed by birds, and it has been suggested that it is most likely absorbed via the paracellular pathway in birds. We measured apparent assimilation efficiency ([Formula: see text]) and bioavailability (f) for d-xylose and d- and l-glucose in three frugivorous Australian bird species. Mistletoebirds, silvereyes, and singing honeyeaters showed significantly lower [Formula: see text] for d-xylose than for d-glucose. Across two diet sugar concentrations, silvereyes and singing honeyeaters significantly increased f of both l-glucose (a metabolically inert isomer of d-glucose commonly used to quantify paracellular uptake) and d-xylose on the more concentrated diet, probably because of increased gut processing time. By contrast, mistletoebirds (mistletoe fruit specialists) did not vary f of either sugar with diet concentration. Mistletoebirds also showed higher f for d-xylose than l-glucose and eliminated d-xylose more slowly than silvereyes and singing honeyeaters, demonstrating differences in the handling of dietary xylose between these species. Our results suggest that d-xylose may be absorbed by both mediated and nonmediated mechanisms in mistletoebirds.

Do bird species richness and community structure vary with mistletoe flowering and fruiting in Western Australia?

Worldwide, mistletoes act as a keystone resource, providing food (nectar, fruit and foliage) and structural (nesting sites) resources to hundreds of fauna species. In Australia, loranthaceous mistletoes depend on birds for pollination and dispersal, and provide important nectar and fruit resources to a large number of nectarivorous and frugivorous species of bird. We investigated whether avian species richness and community structure varies with flowering and fruiting of two common mistletoe species (Loranthaceae: Wireleaf Mistletoe, Amyema preissii; and Box Mistletoe, A. miquelii), conducting monthly surveys of both birds and mistletoes over 1 year at five sites in south-western Western Australia (WA). Flowering and fruiting periods were distinct and differed both among sites and between mistletoe species. Nectar and ripe fruit were available for up to 5 months (Box Mistletoe) or 6–7 months (Wireleaf Mistletoe) at individual sites, but were available every month of the year across all sites. The presence of fruiting, but not flowering, mistletoe was associated with changes in bird community structure. Mistletoebirds (Dicaeum hirundinaceum) were significantly more likely to be recorded during months when ripe mistletoe fruit was present and the overall bird species richness was higher for these survey months. Mistletoes provide important resources, but further investigation is required to assess whether they act as a keystone resource in south-western WA.

The Relative Contribution of Specialists and Generalists to Mistletoe Dispersal: Insights from a Neotropical Rain Forest

AbstractMistletoes rely on birds for seed dispersal, but the presumed importance of mistletoe‐specialist frugivores has not been critically examined nor compared with generalist frugivores and opportunistic foragers. The contribution of these three groups was compared directly by quantifying bird visitation to fruiting mistletoe plants ( Oryctanthus occidentalis: Loranthaceae) at Barro Colorado Island, Panama, and by comparing these results with proportions calculated from other empirical studies of mistletoe visitation conducted elsewhere. After more than 100 h of timed watches, 23 bird species were recorded visiting eight heavily infected host trees ( Luehea seemannii: Tiliaceae). Eight of these species visited mistletoe, of which five (all tyrannids) consumed mistletoe fruit. Although two mistletoe specialist frugivores ( Tyrannulus elatus and Zimmerius vilissimus) removed most fruit (73%), more than a quarter was consumed by one generalist frugivore ( Mionectes oleagineus) and two opportunists ( Myiozetetes cayanensis and Myiozetetes similis). Post consumption behaviour varied: the specialists flew from mistletoe to mistletoe, the generalist rested in the subcanopy and understory, and the opportunists spent most time hawking insects and resting high in the canopy. Integrating these data with previous work, the dietary specialization, short gut passage rate and strict habitat preferences of mistletoe specialists suggests that their services relate primarily to intensification and contagious dispersal, while species with broader diets are more likely to visit uninfected trees and establish new infections. The presumed importance of mistletoe‐specialist frugivores was not supported and mistletoes are considered to be comparable to many other bird‐dispersed plants, relying on both specialist and generalist frugivores, while opportunists may be disproportionately important in long‐distance dispersal.

An antibody against a conserved C-terminal consensus motif from plant alternative oxidase (AOX) isoforms 1 and 2 label plastids in the explosive dwarf mistletoe (Arceuthobium americanum, Santalaceae) fruit exocarp

Dwarf mistletoes, genus Arceuthobium (Santalaceae), are parasitic angiosperms that spread their seeds by an explosive process. As gentle heating triggers discharge in the lab, we wondered if thermogenesis (endogenous heat production) is associated with dispersal. Thermogenesis occurs in many plants and is enabled by mitochondrial alternative oxidase (AOX) activity. The purpose of this study was to probe Arceuthobium americanum fruit (including seed tissues) collected over a 10-week period with an anti-AOX antibody/gold-labeled secondary antibody to determine if AOX could be localized in situ, and if so, quantitatively assess whether label distribution changed during development; immunochemical results were evaluated with Western blotting. No label could be detected in the mitochondria of any fruit or seed tissue, but was observed in fruit exocarp plastids of samples collected in the last 2 weeks of study; plastids collected in week 10 had significantly more label than week 9 (p = 0.002). Western blotting of whole fruit and mitochondrial proteins revealed a signal at 30-36 kD, suggestive of AOX, while blots of whole fruit (but not mitochondrial fraction) proteins showed a second band at 40-45 kD, in agreement with plastid terminal oxidases (PTOXs). AOX enzymes are likely present in the A. americanum fruit, even though they were not labeled in mitochondria. The results strongly indicate that the anti-AOX antibody was labeling PTOX in plastids, probably at a C-terminal region conserved in both enzymes. PTOX in plastids may be involved in fruit ripening, although a role for PTOX in thermogenesis cannot be eliminated.

The restricted seed rain of a mistletoe specialist

Specialist frugivores are the dominant consumers of mistletoe fruit in many regions and have been shown to intensify infections of host plants as a result of their rapid gut passage rates and dependence on existing infections. The role of specialist frugivores in long distance dispersal of mistletoe and establishment of new infections is unclear, and has not been explicitly evaluated previously. Here we critically examine the premise that specialists are the dominant dispersers by examining the role of an Australian mistletoe specialist (mistletoebird Dicaeum hirundinaceum Dicaeidae) in dispersing mistletoe (Amyema preissii Santalales: Loranthaceae) seeds beyond infected host stands. We use two primary lines of evidence – presence of birds using remote call recorders, and presence of dispersed seeds via surveys for defecated seeds on host branches. The observed and inferred movements of the mistletoebird were wholly restricted to habitat patches containing mistletoe, and this bird was not observed to transport seeds to nearby uninfected host stands within the study system. While mistletoe specialists may provide much of the within‐stand dispersal service for mistletoes, this serves only to aggregate and intensify existing infections. We suggest that long distance dispersal of mistletoe seeds beyond existing hosts and infection centres is not performed by these dietary specialists, these services more likely to be provided by generalist frugivores and other occasional mistletoe fruit consumers.

Avian consumption and seed germination of the hemiparasitic mistletoe Agelanthus natalitius (Loranthaceae)

We documented avian consumers of the mistletoe Agelanthus natalitius in the field and quantified their effects on seed germination in captive studies. Seven bird species were frequently observed to feed on mistletoe fruits in the field, namely Cape Batis (Batis capensis), Cape White-eye (Zosterops virens), Red-fronted Tinkerbird (Pogoniulus pusillus), Red-winged Starling (Onychognathus morio), Dark-capped Bulbul (Pycnonotus tricolor), Speckled Mousebird (Colius striatus) and Village Weaver (Ploceus cucullatus). Of the four bird species used in captive feeding trials (Red-winged Starling, Speckled Mousebird, Village Weaver and Cape White-eye), most of the birds removed the pulp-cover of the mistletoe fruits and left the exposed seeds in potentially germinable condition. Red-winged Starlings ingested but then regurgitated the seeds and wiped their bills on a twig to dislodge the sticky viscin-covered seeds individually. Mistletoe seeds obtained from cages of Red-winged Starlings had the highest germination success of all the seeds obtained from the captive bird study. The handling of mistletoe fruits applied by all species of birds both in the field and in captivity showed that mistletoe dispersal is likely to occur over short distances, although the seeds are likely to be dispersed to safe sites due to directed dispersal on parental host trees. Such autoinfection and local aggregation increase the interaction with already parasitised hosts, which through time may enhance local specialisation on the most frequently parasitised host species.

Vesicular cells of the lodgepole pine dwarf mistletoe (Arceuthobium americanum) fruit: development, cytochemistry, and lipid analysis

The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a parasitic angiosperm that infects conifers in western Canadian forests. A striking feature of the Arceuthobium life cycle is explosive seed dispersal, triggered by hydrostatic build-up within the fruit, localized in a tissue called “viscin.” Viscin is composed of two cell types: “viscin cells” that accrue pressure in their hydrated mucilage, and “vesicular cells” with a previously undetermined function. The objective of this work was to investigate the development and composition of vesicular cells using microscopy, cytochemistry, and gas chromatography – mass spectroscopy. We found that vesicular cells are initiated from mesocarp cells lining the viscin cells. As development of the seed progresses, vesicular cells form a single layer, enlarge, and become isodiametric. Later, the cells make up all of the remaining 3–4 outer mesocarp layers. Concomitant with enlargement, intracellular triacylglycerides (TAGs) largely composed of 16-carbon and 18-carbon fatty acids, accumulate. Immediately prior to discharge, vesicular cell boundaries become indistinct, and the cell contents become confluent, creating a lipid mass between the viscin cells and the exocarp. Vesicular cells and their resulting lipid mass likely function in discharge by acting as a hydrophobic barrier to water loss and (or) as a repellant, resistant layer.

Sources of protein in two semi‐arid zone mistletoe specialists: Insights from stable isotopes

AbstractObtaining adequate levels of dietary protein is essential for the physiology of consumers. This presents potential problems for frugivorous birds because fruit is generally low in protein rendering it nutritionally inadequate and potentially explaining the rarity of exclusive frugivory in birds. We addressed this issue by determining the isotope composition (15N/14N) in the whole blood of two mistletoe consumers, that is, painted honeyeater (Grantiella picta, Meliphagidae) and mistletoebird (Dicaeum hirundinaceum, Dicaeidae) during the grey mistletoe (Amyema quandang, Loranthaceae) fruiting peak in a semi‐arid woodland, NSW, Australia. Grey mistletoe fruit pulp and arthropods were isotopically distinct (mean δ15N fruit 4.4‰vs. arthropods 7.1‰), thus readily discriminated using the stable isotope approach. Painted honeyeaters and mistletoebirds formed a single group based on their mean δ15N values and, on average, assimilated approximately half of their nitrogen from mistletoe fruit although individual variation was high. The importance of nitrogen derived from mistletoe fruit did not track its abundance in the environment, suggesting that at least during peak fruiting, this resource is not limiting at this site. Researchers should account for intraspecific variation and take a cautious approach when reconstructing diets using stable isotopes by incorporating individual‐based analyses rather than presenting mean values alone. This is the first study to use the isotope approach to investigate the dietary relationship of mistletoe frugivores and mistletoe fruit and has implications for our understanding of the nutritional ecology of frugivores and its functional relationship to ecosystem processes such as seed dispersal.