Visibility and attractiveness of Fritillaria (Liliaceae) flowers to potential pollinators

Visual floral characters play an important role in shaping plant-pollinator interactions. The genus Fritillaria L. (Liliaceae), comprising approximately 140 species, is described as displaying a remarkable variety of flower colours and sizes. Despite this variation in visual floral traits of fritillaries, little is known about the potential role of these features in shaping plant-pollinator interactions. Here, we seek to clarify the role of visual attraction in species offering a robust food reward for pollinators early in the spring, which is the case for Fritillaria. We also searched for potential tendencies in the evolution of floral traits crucial for plant-pollinator communication. The generality of species with green and purple flowers may indicate an influence of environmental factors other than pollinators. The flowers of the studied species seem to be visible but not very visually attractive to potential pollinators. The food rewards are hidden within the nodding perianth, and both traits are conserved among fritillaries. Additionally, visual floral traits are not good predictors of nectar properties. When in the flowers, pollinators are navigated by nectar guides in the form of contrasting nectary area colouration. Flower colour does not serve as a phenotypic filter against illegitimate pollinators—red and orange bird-pollinated fritillaries are visible to bees.

The regulatory network for petal anthocyanin pigmentation is shaped by the MYB5a/NEGAN transcription factor in Mimulus

Much of the visual diversity of angiosperms is due to the frequent evolution of novel pigmentation patterns in flowers. The gene network responsible for anthocyanin pigmentation, in particular, has become a model for investigating how genetic changes give rise to phenotypic innovation. In the monkeyflower genus Mimulus, an evolutionarily recent gain of petal lobe anthocyanin pigmentation in M. luteus var. variegatus was previously mapped to genomic region pla2. Here, we use sequence and expression analysis, followed by transgenic manipulation of gene expression, to identify MYB5a—orthologous to the NEGAN transcriptional activator from M. lewisii—as the gene responsible for the transition to anthocyanin-pigmented petals in M. l. variegatus. In other monkeyflower taxa, MYB5a/NEGAN is part of a reaction-diffusion network that produces semi-repeating spotting patterns, such as the array of spots in the nectar guides of both M. lewisii and M. guttatus. Its co-option for the evolution of an apparently non-patterned trait—the solid petal lobe pigmentation of M. l. variegatus—illustrates how reaction-diffusion can contribute to evolutionary novelty in non-obvious ways. Transcriptome sequencing of a MYB5a RNAi line of M. l. variegatus reveals that this genetically simple change, which we hypothesize to be a regulatory mutation in cis to MYB5a, has cascading effects on gene expression, not only on the enzyme-encoding genes traditionally thought of as the targets of MYB5a but also on all of its known partners in the anthocyanin regulatory network.

Petal epidermal micromorphology in holoparasitic Orobanchaceae and its significance for systematics and pollination ecology

Flowers of holoparasitic plants have evolved several adaptations for pollination as part of their parasitic strategies. A study of the petal epidermis may be useful to systematics as well as to the knowledge of ecological and co-evolutionary adaptations between the parasites and their pollinators. The present work is a comparative study of the microsculpture of nectar guides and landing platforms in the flowers of holoparasitic species in the family Orobanchaceae. In total, 285 samples of 39 species from 10 holoparasitic genera (Boschniakia C.A.Mey. ex Bong., Boulardia F.W.Schultz, Cistanche Hoffmanns. & Link, Conopholis Wallr., Diphelypaea Nicolson, Epifagus Nutt., Mannagettaea H.Sm., Orobanche L., Phacellanthus Siebold & Zucc. and Phelipanche Pomel) and as an outgroup, of six additional hemiparasitic genera (Castilleja Mutis ex L.f., Euphrasia L., Orthantha (Benth.) A.Kern., Parentucellia Viv., Rhinanthus L., and Striga Lour.) were analysed using both light and scanning electron microscopy. Types of epidermal cells were characterised, and their distribution on the adaxial and abaxial surfaces of the petals determined. The following four major epidermal types were recognised: tabular rugose striate cells (TRS), areolate cells (AS), papillose conical cells (PCS) and lobular striate cells (PLS). Two main types of trichomes were observed, namely glandular and non-glandular. Our results showed that petal micromorphology may be useful to systematics; its influence in relation to the pollinators is discussed.

Micromorphology of trichomes in the flowers of the horse chestnut Aesculus hippocastanum L.

<em>Aesculus hippocastanum </em>L. is an ornamental tree appreciated for its beautiful flowers and leaves. The flowers of this species contain secondary metabolites exhibiting pharmacological activity. They also produce essential oils and coloured “nectar guides”, which enable insects to reach nectar and pollen. The aim of the study was to investigate the types and characteristics of chestnut flower trichomes, which may contain biologically active substances. The analyses were performed using light, fluorescence, and scanning electron microscopy. Three types of trichomes were found on the sepals and the surface of the ovary, whereas the corolla petals exhibited two types of hairs and papillae. The hairs differ in terms of their length and number of cells. The perianth and pistil had no capitate hairs, whereas the ovary exhibited the presence of colleters. Histochemical assays revealed that all the types of trichomes and papillae contained lipids or essential oils; hence, they can be classified as glandular structures. The “nectar guides” were characterised by higher density of secretory hairs than that on the rest of the petal surface, which implies that these petal fragments may emit stronger fragrance.

New insights on Salvia platyphylla (Lamiaceae) and description of S. pugana and S. albiterrarum, two new species from Jalisco, Mexico

An expanded description of Salvia platyphylla with new insights based on the examination of recent herbarium specimens and observations made in the field is provided. Additionally, are included descriptions and illustrations of two new species morphologically similar to S. platyphylla. The first, S. pugana, can be distinguished from S. platyphylla by its larger calyces, magenta corollas with larger and internally epapillate tubes, longer filaments and connectives, and wider nutlets. The second, S. albiterrarum, differs from the latter by its longer corolla tubes, absence of patent white nectar guides on the lower lip, longer filaments, longer and not geniculate connectives, longer styles, with the branches and 3–5.3 mm of the apical portion exserted from the upper lip, and lower stigmatic branch straight rather than sigmoid or arquate. The three taxa are sympatric and represent western Mexico endemisms. Lastly, floral morphology differences between these species suggest valuable considerations on pollination syndromes.

The structure of the spur nectary in Dendrobium finisterrae Schltr. (Dendrobiinae, Orchidaceae)

To date, the structure of the nectary spur of <i>Dendrobium finisterrae</i> has not been studied in detail, and the present paper compares the structural organization of the floral nectary in this species with the spurs of other taxa. The nectary spur of <i>D. finisterrae</i> was examined by means of light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is composed of a single layer of secretory epidermis and several layers of small and compactly arranged subepidermal secretory cells. The secretory cells have thick cellulosic cell walls with primary pits. The secretory tissue is supplied by vascular bundles that run beneath in ground parenchyma and are additionally surrounded by strands of sclerenchymatous fibers. The flowers of the investigated species displayed morphological features characteristic of bee-pollinated taxa, as they are zygomorphic, creamy-green coloured with evident nectar guides. They also emit a weak but nice scent. However, they possess some characters attributed to bird-pollinated flowers such as a short, massive nectary spur and collenchymatous secretory tissue that closely resembles the one found in the nectaries of certain species that are thought to be bird-pollinated. This similarity in anatomical organization of the nectary, regardless of geographical distribution and phylogeny, strongly indicates convergence and appears to be related to pollinator-driven selection.

The structure of some floral elements and the nectar production rate of Polemonium caeruleum L.

The present study, carried out in the period 2008 - 2009, covered some morphological and anatomical features of the flowers of <i>Polemonium caeruleum</i> L. and their nectar production rate in the climatic conditions of the Lublin region. Observations were made with stereoscopic, light and scanning electron microscopy. Nectar production in the flowers was determined using the pipette method. The flowers of <i>Polemonium caeruleum</i> develop a calyx covered by an epidermis with numerous non-glandular and glandular trichomes. The secretory trichomes are composed of a several-celled stalk and a four-celled head. At the boundary of the corolla tube and the lobes, there is white colouration with violet nectar guides. The epidermis in this region produces several-celled living trichomes that close the entry into the corolla tube, thereby protecting the nectar accumulated in it. These hairs are at the same time glistening colour attractants for insects. The tripartite stigma of the pistil is covered, from the adaxial side, by unicellular papillae with striated cuticular ornamentation, growing at high density. Around the ovary there is located a nectariferous disc, in the form of a free projection, which secrets nectar with sugar concentration of 29 - 52% and sugar weight ranging 1.1 - 1.8 mg/flower.

Floral signposts: testing the significance of visual ‘nectar guides’ for pollinator behaviour and plant fitness

Nectar guides, contrasting patterns on flowers that supposedly direct pollinators towards a concealed nectar reward, are taxonomically widespread. However, there have been few studies of their functional significance and effects on plant fitness. Most previous studies focused on pollinator behaviour and used artificial flowers in laboratory settings. We experimentally investigated the role of putative nectar guides in a natural system: the South African iris Lapeirousia oreogena , whose flowers have a clearly visible pattern of six white arrow-markings pointing towards the narrow entrance of the long corolla tube, and its sole pollinator, a long-proboscid nemestrinid fly. We painted over none, some or all of the white arrow-markings with ink that matched the colour of the corolla background. Although arrow-marking removal had little effect on the approaches by flies to flowers from a distance, it dramatically reduced the likelihood of proboscis insertion. Export of pollen dye analogue (an estimate of male fitness) was reduced to almost zero in flowers from which all nectar guides had been removed, and fruit set (a measure of female fitness) was also significantly reduced. Our results confirm that the markings on L. oreogena flowers serve as nectar guides and suggest that they are under strong selective maintenance through both male and female fitness components in this pollination system.

Advertisements 1: Visual Signals and Floral Color

This chapter examines how color interacts with the other visual signals from floral size, shape, and outline in enhancing floral attraction to visitors. Visual attraction by flowers is linked to floral shape and size. For most pollinators, color and color patterns are attractive. Most of today’s key pollinating taxa have good color vision, and flowers should have been selected to interact with their visitors’ visual abilities. The chapter first considers floral pigments and floral color before discussing the problems of defining and measuring color in flowers. It then explains how animals perceive flower color and proceeds by analyzing color preferences in animals, along with the ecology and evolution of flower color and color preferences. It also explores nectar guides, how floral color change can control pollinators, and other visual cues used for advertisement. Finally, it asks why flower colors diverge, citing the role of selection.