Flower Color as Predictor for Nectar Reward Quantity in an Alpine Flower Community

Entomophilous plants have evolved colorful floral displays to attract flower visitors to achieve pollination. Although many insects possess innate preferences for certain colors, the underlying proximate and ultimate causes for this behavior are still not well understood. It has been hypothesized that the floral rewards, e.g., sugar content, of plants belonging to a particular color category correlate with the preference of the flower visitors. However, this hypothesis has been tested only for a subset of plant communities worldwide. Bumble bees are the most important pollinators in alpine environments and show a strong innate preference for (bee) “UV-blue” and “blue” colors. We surveyed plants visited by bumble bees in the subalpine and alpine zones (>1,400 m a.s.l.) of the Austrian Alps and measured nectar reward and spectral reflectance of the flowers. We found that the majority of the 105 plant samples visited by bumble bees fall into the color categories “blue” and “blue-green” of a bee-specific color space. Our study shows that color category is only a weak indicator for nectar reward quantity; and due to the high reward variance within and between categories, we do not consider floral color as a reliable signal for bumble bees in the surveyed habitat. Nevertheless, since mean floral reward quantity differs between categories, naïve bumble bees may benefit from visiting flowers that fall into the innately preferred color category during their first foraging flights.

Floral evolution and pollinator diversification in Hedychium J.Koenig (Zingiberaceae): one of Mr. Darwin’s tropical fantasies

ABSTRACTPREMISEHedychium J.Koenig (ginger lilies: Zingiberaceae) is endemic to the Indo-Malayan Realm (IMR) and is known for its fragrant flowers. Two different pollination syndromes characterize the genus: diurnal or bird pollination and nocturnal or moth pollination systems. To date, no attempt has been undertaken to understand the evolution of floral traits in this genus.METHODSWe estimated ancestral character-states, phylogenetic signals, and character correlations for thirteen discrete and eight continuous floral traits representing 75% species diversity of Hedychium. Diversification rate estimation analyses were also employed to understand trait-dependent diversification in the genus.RESULTSInflorescence structure, cincinnus capacity, and curvature of floral tubes revealed strong phylogenetic dependence, whereas number of open flowers per inflorescence per day, color of the labellum, and exertion of the stigma characterized higher ecological effects. Diversification rate estimations suggested that the labellum width, floral tube length, and labellum color played a major role in the evolutionary diversification of Hedychium.CONCLUSIONSWe identified bract type and cincinnus capacity as synapomorphies for Hedychium, while the island-specific clade III was characterized by slender cylindrical inflorescence, coiling of floral tubes, and longer bract to calyx ratio. The circum-Himalayan clade IV is the most speciose, derived, and with most variable floral traits. Although floral color and size lacked any association with pollinator-specific traits (moth and bird pollination), pale colored flowers were most common in the early diverging clades (clade I, II-el., and II-de.), indicating their ancestral nature, when compared to brightly colored flowers.

Aristolochia quiricoana (Aristolochiaceae), a new species from southern Costa Rica

Background and Aims: Aristolochia is the largest genus in Aristolochiaceae and is widely distributed in the world. A recent synopsis of Aristolochia in Costa Rica recognized 19 species; nevertheless, recent botanical exploration in southwestern Costa Rica has revealed yet another new species of this genus. Methods: The new species resulted from fieldwork in Buenos Aires, Puntarenas Province. Specimens from several herbaria were examined, as well as the type material of the most morphologically similar species. Comments about its distribution, habitat, phenology, conservation status and morphological distinction from related species are provided.Key results: Aristolochia quiricoana, a member of Aristolochia series Thyrsicae, is described and illustrated from the southern Pacific region of Costa Rica, where it is apparently endemic. It is similar to A. ornithorhyncha, from which it is distinguished by its shorter pedicels, wider, oblong perigone limbs with a shorter appendix, and a different floral color pattern.Conclusions: The new taxon described here represents the 22nd species documented in Aristolochia series Thyrsicae, as well as the 20th species of the genus from Costa Rica.

Morphometrics and Redescription of Aphyllon fasciculatum and Aphyllon franciscanum, Two Widespread but Previously Conflated Species in Western North America

Abstract— We continue the taxonomic reevaluation of Aphyllon sect. Aphyllon by describing a widespread species throughout western North America previously recognized within a polyphyletic A. fasciculatum. To support our description and revised key, we analyzed fifteen continuous and discrete characters sampled from 186 herbarium specimens and iNaturalist observations representing the geographic and host ranges. Principal component and multiple correspondence analyses reveal clear variation in floral characters. Discriminant analyses show that three aspects of floral color, corolla lobe tip shape, the calyx cup to calyx lobe ratio, calyx lobe length, and degree of bend in the corolla tube are useful distinguishing features, but not diagnostic in every case.

Divergent Responses of Floral Traits of Lonicera nervosa to Altitudinal Gradients at the Eastern Margin of Hengduan Mountains

Understanding phenotypic responses is crucial for predicting and managing the effects of environmental change on native species. Color and display size are typically used to evaluate the utilization value of ornamental plants, which are also important ornamental characters of Lonicera nervosa Maxim. (L. nervosa). However, there is limited documentation of its floral environmental adaptation. The environmental conditions for the development of an organism changes with altitudinal variation. The aim of this research was to find flower trait variability maintenance and the tradeoff among the organs in five different populations of L. nervosa growing at distinct altitudes. We investigated the distribution patterns of floral color, floral display, and biomass tradeoff along a 700-m altitude gradient from 2,950 to 3,650 m. One-way ANOVA analysis was performed to assess the variability of flower traits and floral color across different altitudes. Moreover, correlations and tradeoffs between flowers and vegetative organs were also observed at different altitude ranges. The results indicated that L. nervosa flowers had a strong adaptability along the elevation and divergent altitude-range-specific patterns, which was divided by an altitude breakpoint at around 3,300 m. Below 3,300 m, petal lightness (petal L) decreased, but total floral display area (TFDA), individual floral dry mass (IFDM), and total floral dry mass (TFDM) increased with an increase in altitude. Whereas, above 3,300 m no significant difference was observed in petal L, TFDA, IFDM, and TFDM decreased slightly with an increase in altitude. The responsibility for the selection on floral color at a lower altitude was stronger than that at a higher altitude, while the selection agents on floral biomass had significant effects within the entire altitude range. However, the effects on floral biomass were opposite on both sides of 3,300 m. Thus, floral trait and floral color can be useful indicators for the domestication of horticultural plants and help to evaluate and initiate management and conservation actions.

Transcriptome-Based WGCNA Analysis Reveals Regulated Metabolite Fluxes between Floral Color and Scent in Narcissus Tazetta Flower

A link between the scent and color of Narcissus tazetta flowers can be anticipated due to their biochemical origin, as well as their similar biological role. Despite the obvious aesthetic and ecological significance of these colorful and fragrant components of the flowers and the molecular profiles of their pigments, fragrant formation has addressed in some cases. However, the regulatory mechanism of the correlation of fragrant components and color patterns is less clear. We simultaneously used one way to address how floral color and fragrant formation in different tissues are generated during the development of an individual plant by transcriptome-based weighted gene co-expression network analysis (WGCNA). A spatiotemporal pattern variation of flavonols/carotenoids/chlorophyll pigmentation and benzenoid/phenylpropanoid/ monoterpene fragrant components between the tepal and corona in the flower tissues of Narcissus tazetta, was exhibited. Several candidate transcription factors: MYB12, MYB1, AP2-ERF, bZIP, NAC, MYB, C2C2, C2H2 and GRAS are shown to be associated with metabolite flux, the phenylpropanoid pathway to the production of flavonols/anthocyanin, as well as related to one branch of the phenylpropanoid pathway to the benzenoid/phenylpropanoid component in the tepal and the metabolite flux between the monoterpene and carotenoids biosynthesis pathway in coronas. It indicates that potential competition exists between floral pigment and floral fragrance during Narcissus tazetta individual plant development and evolutionary development.

Genetic analysis and population structure of wild and cultivated wishbone flower (Torenia fournieri Lind.) lines related to specific floral color

Background The wishbone flower or Torenia fournieri Lind., an annual from tropical Indochina and southern China, is a popular ornamental plant, and many interspecific (T. fournieri × T. concolor) hybrid lines have been bred for the international market. The cultivated lines show a pattern of genetic similarity that correlates with floral color which informs on future breeding strategies. This study aimed to perform genetic analysis and population structure of cultivated hybrid lines comparing with closely related T. concolor wild populations. Methods We applied the retrotransposon based iPBS marker system for genotyping of a total of 136 accessions from 17 lines/populations of Torenia. These included 15 cultivated lines of three series: Duchess (A, B, C); Kauai (D, E, F, G, H, I, J); Little Kiss (K, L, M, N, P) and two wild T. concolor populations (Q and R). PCR products from each individual were applied to estimate the genetic diversity and differentiation between lines/populations. Results Genotyping results showed a pattern of genetic variation differentiating the 17 lines/populations characterized by their specific floral colors. The final PCoA analysis, phylogenetic tree construction, and Bayesian population structural bar plot all showed a clear subdivision of lines/populations analysed. The 15 cultivated hybrid lines and the wild population Q that collected from a small area showed the lowest genetic variability while the other wild population R which sampled from a larger area had the highest genetic variability. Discussion The extremely low genetic variability of 15 cultivated lines indicated that individual line has similar reduction in diversity/heterozygosity from a bottleneck event, and each retained a similar (but different from each other) content of the wild genetic diversity. The genetic variance for the two wild T. concolor populations could be due to our varied sampling methods. The two wild populations (Q, R) and the cultivated hybrid lines (I, K, M, N, P) are genetically more closely related, but strong positive correlations presented in cultivated lines A, C, E, M, and N. These results could be used to guide future Torenia breeding. Conclusions The genetic variation and population structure found in our study showed that cultivated hybrid lines had similar reduction in diversity/heterozygosity from a bottleneck event and each line retained a similar (but different from each other) content of the wild genetic diversity, especially when strong phenotypic selection of floral color overlaps. Generally, environmental factors could induce transposon activation and generate genetic variability which enabled the acceleration of the evolutionary process of wild Torenia species. Our study revealed that wild Torenia populations sampled from broad geographic region represent stronger species strength with outstanding genetic diversity, but selective breeding targeting a specific floral color decreased such genetic variability.

Whole-genome resequencing of Osmanthus fragrans provides insights into flower color evolution

Osmanthus fragrans is a well-known ornamental plant that has been domesticated in China for 2500 years. More than 160 cultivars have been found during this long period of domestication, and they have subsequently been divided into four cultivar groups, including the Yingui, Jingui, Dangui, and Sijigui groups. These groups provide a set of materials to study genetic evolution and variability. Here, we constructed a reference genome of O. fragrans ‘Liuyejingui’ in the Jingui group and investigated its floral color traits and domestication history by resequencing a total of 122 samples, including 119 O. fragrans accessions and three other Osmanthus species, at an average sequencing depth of 15×. The population structure analysis showed that these 119 accessions formed an apparent regional cluster. The results of linkage disequilibrium (LD) decay analysis suggested that varieties with orange/red flower color in the Dangui group had undergone more artificial directional selection; these varieties had the highest LD values among the four groups, followed by the Sijigui, Jingui, and Yingui groups. Through a genome-wide association study, we further identified significant quantitative trait loci and genomic regions containing several genes, such as ethylene-responsive transcription factor 2 and Arabidopsis pseudoresponse regulator 2, that are positively associated with petal color. Moreover, we found a frameshift mutation with a 34-bp deletion in the first coding region of the carotenoid cleavage dioxygenase 4 gene. This frameshift mutation existed in at least one site on both alleles in all varieties of the Dangui group. The results from this study shed light on the genetic basis of domestication in woody plants, such as O. fragrans.

Genetic architecture of floral traits in bee- and hummingbird-pollinated sister species of Aquilegia (columbine)

Interactions with animal pollinators have helped shape the stunning diversity of flower morphologies across the angiosperms. A common evolutionary consequence of these interactions is that some flowers have converged on suites of traits, or pollination syndromes, that attract and reward specific pollinator groups. Determining the genetic basis of these floral pollination syndromes can help us understand the processes that contributed to the diversification of the angiosperms. Here, we characterize the genetic architecture of a bee-to-hummingbird pollination shift in Aquilegia (columbine) using QTL mapping of 17 floral traits encompassing color, nectar composition, and organ morphology. In this system, we find that the genetic architectures underlying differences in floral color are quite complex, and we identify several likely candidate genes involved in anthocyanin and carotenoid floral pigmentation. Most morphological and nectar traits also have complex genetic underpinnings; however, one of the key floral morphological phenotypes, nectar spur curvature, is shaped by a single locus of large effect.

Evolution of the Subgroup 6 R2R3-MYB Genes and Their Contribution to Floral Color in the Perianth-Bearing Piperales

Flavonoids, carotenoids, betalains, and chlorophylls are the plant pigments responsible for floral color. Anthocyanins, a class of flavonoids, are largely responsible for the red, purple, pink, and blue colors. R2R3-MYB genes belonging to subgroup 6 (SG6) are the upstream regulatory factors of the anthocyanin biosynthetic pathway. The canonical members of these genes in Arabidopsis include AtMYB75, AtMYB90, AtMYB113, and AtMYB114. The Aristolochiaceae is an angiosperm lineage with diverse floral groundplans and perianth colors. Saruma henryi exhibits a biseriate perianth with green sepals and yellow petals. All other genera have sepals only, with colors ranging from green (in Lactoris) to a plethora of yellow to red and purple mixtures. Here, we isolated and reconstructed the SG6 R2R3-MYB gene lineage evolution in angiosperms with sampling emphasis in Aristolochiaceae. We found numerous species-specific duplications of this gene lineage in core eudicots and local duplications in Aristolochiaceae for Saruma and Asarum. Expression of SG6 R2R3-MYB genes examined in different developmental stages and plant organs of four Aristolochiaceae species, largely overlaps with red and purple pigments, suggesting a role in anthocyanin and flavonoid synthesis and accumulation. A directed RNA-seq analysis corroborated our RT-PCR analyses, by showing that these structural enzymes activate during perianth development in Aristolochia fimbriata and that the regulatory genes are expressed in correlation with color phenotype. Finally, the reconstruction of the flavonoid and anthocyanin metabolic pathways using predicted peptides from transcriptomic data show that all pivotal enzymes are present in the analyzed species. We conclude that the regulatory genes as well as the biosynthetic pathway are largely conserved across angiosperms. In addition, the Aristolochiaceae emerges as a remarkable group to study the genetic regulatory network for floral color, as their members exhibit an outstanding floral diversity with elaborate color patterns and the genetic complement for SG6 R2R3-MYB genes is simpler than in core eudicot model species.