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1. A reference genome for the nectar-robbing Black-throated Flowerpiercer ( Diglossa brunneiventris )

   https://doi.org/10.1093/g3journal/jkab271  

   Hiller, Anna E ; Brumfield, Robb T ; Faircloth, Brant C ( September 2021 , G3 Genes|Genomes|Genetics)

   Sethuraman, A (Ed.)

   Abstract Black-throated Flowerpiercers (Diglossa brunneiventris) are one species representing a phenotypically specialized group of tanagers (Thraupidae) that have hooked bills which allow them to feed by stealing nectar from the base of flowers. Members of the genus are widely distributed in montane regions from Mexico to northern Argentina, and previous studies of Diglossa have focused on their systematics, phylogenetics, and interesting natural history. Despite numerous studies of species within the genus, no genome assembly exists to represent these nectivorous tanagers. We described the assembly of a genome sequence representing a museum-vouchered, wild, female D. brunneiventris collected in Peru. By combining Pacific Biosciences Sequel long-read technology with 10× linked-read and reference-based scaffolding, we produced a 1.08 Gbp pseudochromosomal assembly including 600 scaffolds with a scaffold N50 of 67.3 Mbp, a scaffold L50 of 6, and a BUSCO completeness score of 95%. This new assembly improves representation of the diverse species that comprise the tanagers, improves on scaffold lengths and contiguity when compared to existing genomic resources for tanagers, and provides another avenue of research into the genetic basis of adaptations common to a nectivorous lifestyle among vertebrates. 

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2. A multifunctional role for riboflavin in the yellow nectar of Capsicum baccatum and Capsicum pubescens

   https://doi.org/10.1111/nph.19886  

   Magner, Evin_T ; Freund_Saxhaug, Katrina ; Zambre, Amod ; Bruns, Kaitlyn ; Carroll, Patrick ; Snell‐Rood, Emilie_C ; Hegeman, Adrian_D ; Carter, Clay_J ( June 2024 , New Phytologist)

   A fewCapsicum(pepper) species produce yellow‐colored floral nectar, but the chemical identity and biological function of the yellow pigment are unknown.

   A combination of analytical biochemistry techniques was used to identify the pigment that givesCapsicum baccatumandCapsicum pubescensnectars their yellow color. Microbial growth assays, visual modeling, and honey bee preference tests for artificial nectars containing riboflavin were used to assess potential biological roles for the nectar pigment.

   High concentrations of riboflavin (vitamin B₂) give the nectars their intense yellow color. Nectars containing riboflavin generate reactive oxygen species when exposed to light and reduce microbial growth. Visual modeling also indicates that the yellow color is highly conspicuous to bees within the context of the flower. Lastly, field experiments demonstrate that honey bees prefer artificial nectars containing riboflavin.

   SomeCapsicumnectars contain a yellow‐colored vitamin that appears to play roles in (1) limiting microbial growth, (2) the visual attraction of bees, and (3) as a reward to nectar‐feeding flower visitors (potential pollinators), which is especially interesting since riboflavin is an essential nutrient for brood rearing in insects. These results cumulatively suggest that the riboflavin found in someCapsicumnectars has several functions.

    

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3. Abundance and diversity of the culturable nectar mycobiome in Rhododendron catawbiense varies with elevation

   https://doi.org/10.1093/jpe/rtae079  

   Barker, Daniel_A ; Khan, Ayesha ; Kaverina, Ekaterina ; Martel, Carlos ; Arceo-Gómez, Gerardo ; Wagg, ed., Cameron ( August 2024 , Journal of Plant Ecology)

   The nectar microbiome can influence pollinator choice and plant fitness. Previous research has shown that changes in environmental conditions at large spatial scales can influence nectar microbiome composition. However, little is known about how changes in climate with increasing elevation affect nectar microbiome abundance and composition. Here, we describe the culturable nectar mycobiome (CNMB) of Rhododendron catawbiense (Ericaceae) by quantifying colony abundance, identity and richness of fungal genera. We further evaluate how the CNMB abundance, diversity and composition (i.e. the fungal species within the nectar microbiome) varies at two different elevations. Nectar samples were collected from R. catawbiense individuals at a high and low elevation and were cultured on yeast agar with 0.01% chloramphenicol media. Fungal colonies were categorized morphologically, quantified and then identified using DNA barcoding. In total, 2822 fungal colonies were recorded belonging to six genera across both elevations. Elevation did not influence CNMB diversity (Simpson’s diversity index) or genera richness per flower, however only three genera were found at the high elevation while six were found at the low elevation. Elevation had a significant effect on colony abundance with a 95% increase in the number of colonies in nectar samples at low compared with the high elevation. Variation in abundance and the overall genera composition of fungal colonies across elevations may have the potential to affect nectar quantity and quality and ultimately pollination success. This study adds to our understanding of the drivers of CNMB composition across spatial scales and its potential implications for plant–pollinator interactions.

    

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4. Elevated Temperature May Affect Nectar Microbes, Nectar Sugars, and Bumble Bee Foraging Preference

   https://doi.org/10.1007/s00248-021-01881-x  

   Russell, Kaleigh A. ; McFrederick, Quinn S. ( October 2021 , Microbial Ecology)

   Abstract Floral nectar, an important resource for pollinators, is inhabited by microbes such as yeasts and bacteria, which have been shown to influence pollinator preference. Dynamic and complex plant-pollinator-microbe interactions are likely to be affected by a rapidly changing climate, as each player has their own optimal growth temperatures and phenological responses to environmental triggers, such as temperature. To understand how warming due to climate change is influencing nectar microbial communities, we incubated a natural nectar microbial community at different temperatures and assessed the subsequent nectar chemistry and preference of the common eastern bumble bee, Bombus impatiens . The microbial community in floral nectar is often species-poor, and the cultured Brassica rapa nectar community was dominated by the bacterium Fructobacillus . Temperature increased the abundance of bacteria in the warmer treatment. Bumble bees preferred nectar inoculated with microbes, but only at the lower, ambient temperature. Warming therefore induced an increase in bacterial abundance which altered nectar sugars and led to significant differences in pollinator preference. 

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5. Nectar robbers and simulated robbing differ in their effects on nectar microbial communities

   https://doi.org/10.1111/1442-1984.12446  

   Luizzi, Victoria_J ; Harrington, Alison_H ; Bronstein, Judith_L ; Arnold, A_Elizabeth ( January 2024 , Plant Species Biology)

   Floral nectar contains microbes that can influence nectar chemistry and pollinator visitation, and these microbial communities can be affected by pollinators in turn. Some flowers are also visited by nectar robbers, which feed on nectar through holes cut in floral tissue. If nectar robbers alter nectar microbial communities, they might have unexpected impacts on pollinator visitation. We investigated whether robbing could affect nectar microbial communities directly, by introducing microbes, or indirectly, by triggering a plant response to floral damage. We applied four treatments to flowers ofTecoma× “Orange Jubilee” (Bignoniaceae) in an arboretum setting: flowers were (1) covered to exclude all visitors; (2) available to both pollinators and nectar robbers and robbed naturally by carpenter bees; (3) available to pollinators only but cut at the base to simulate nectar robbing damage; or (4) available to pollinators only. We found that nectar in flowers accessible to any visitors was more likely to contain culturable microbes than flowers from which visitors were excluded. Microbial community composition and beta diversity were similar across treatments. Among flowers containing culturable microbes, flowers available to pollinators and nectar robbers had higher microbial abundance than flowers with simulated robbing, but there were no differences between flowers available to pollinators and robbers and unwounded flowers from which robbers were excluded. Overall, our results suggest that floral damage can affect some features of nectar microbial communities, but specific effects of nectar robbing are limited compared with the influence of visitation in general.

    

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