Limited phenological and pollinator-mediated isolation among selfing and outcrossing Arabidopsis lyrata populations

Transitions from outcrossing to selfing have been a frequent evolutionary shift in plants and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are pre-zygotic pre-pollination mechanisms (e.g. changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation isolate selfing populations of Arabidopsis lyrata from outcrossing populations, we conducted a common garden experiment with plants from selfing and outcrossing populations as well as their between-population hybrids. Specifically, we asked whether there was isolation between outcrossing and selfing plants and their between-population hybrids through differences in (1) the timing or intensity of flowering; and/or (2) pollinator visitation. We found that phenology largely overlapped between plants from outcrossing and selfing populations. There were also no differences in pollinator preference related to mating system. Additionally, pollinators preferred to visit flowers on the same plant rather than exploring nearby plants, creating a large opportunity for self-fertilization. Overall, this suggests that pre-zygotic pre-pollination mechanisms do not strongly reproductively isolate plants from selfing and outcrossing populations of Arabidopsis lyrata .

Studies on Phenology and Reproductive Biology of Khejri [Prosopis cineraria (L.) Druce]

Background: Khejri [Prosopis cineraria (L.) Druce] belongs to the family Leguminosae and subfamily Mimosoideae. The rural communities encourage the growth of Khejri in their agricultural fields as it improves grain yield and storage biomass production. It is the true multipurpose species and also called as ‘Golden Tree of Desert’, ‘Kalpvriksha’ of the desert, ‘King of desert’, ‘Love Tree’, and ‘Pride of the Desert’. For any tree improvement programme, knowledge of phenology and breeding system is pre-requisite, which also helps in understanding the evolutionary dynamics of a species. The range of genetic variability is controlled by reproductive system, which in turn controls the adaptive change. Pollination mechanisms affect seed set, fertility, gene flow, breeding systems, hybridization and genetic constitutions of tree populations. Methods: In this investigation during 2014-15, ten trees of [Prosopis cineraria (L.) Druce] growing at the research area of Forestry Department of CCS Haryana Agricultural University, Hisar were randomly selected and phenological observations were made on the selected trees at different phenophases. Through selfing, breeding behaviour was examined, by covering the inflorescence with muslin cloth bags before opening. Approximately, an equal number of buds were kept open in close vicinity of the covered branch. Reproductive capacity was estimated from the percentage of fruit setting in marked inflorescence. Result: In present study of Prosopis cineraria, the average fruit set under self-pollination was nil whereas it was 2.03 per cent in open natural pollination. This study confirms previous studies that Prosopis cineraria is a cross-pollinated species.

Rotating Arrays of Orchid Flowers: A Simple and Effective Method for Studying Pollination in Food Deceptive Plants

Floral deception has been observed in several genera in angiosperms, but is most common in the Orchidaceae. Pollination mechanisms in food deceptive plants are often difficult to assess, as visitation frequency by insects requires numerous hours of field observations to ascertain. Here, for the first time, we describe in detail and validate a simple and effective method that extends previous approaches to increase the effectiveness of pollination studies of food deceptive orchids. We used an orchid of southwest Australia, Diuris brumalis (Orchidaceae), that visually mimics model plants belonging to the genus Daviesia (Faboideae). Arrays of orchid flowers were placed and moved systematically in proximity to model plants, resulting in rapid attraction of the pollinators of D. brumalis. We compared pollinaria removal (as an indicator of pollination success) in naturally growing orchids with pollinaria removal in arrays of orchid flowers in the same sites. We showed that the proposed method greatly enhances pollinator attractiveness in food deceptive systems with very low pollination rates, and we compared its efficiency with other similar methods. The approach can be used for observing pollinator behavioural patterns and confirming effective pollinators for food deceptive species with low insect visitation rates.

An ancient push-pull pollination mechanism in cycads

Most cycads engage in brood-site pollination mutualisms, yet the mechanism by which the Cycadales entice pollination services from diverse insect mutualists remains unknown. Here, we characterize a push-pull pollination mechanism between a New World cycad and its weevil pollinators that mirrors the mechanism between a distantly related Old World cycad and its thrips pollinators. The behavioral convergence between weevils and thrips, combined with molecular phylogenetic dating and a meta-analysis of thermogenesis and coordinated patterns of volatile attraction and repulsion suggest that a push-pull pollination mutualism strategy is ancestral in this ancient, dioecious plant group. Hence, it may represent one of the earliest insect/plant pollination mechanisms, arising long before the evolution of visual floral signaling commonly used by flowering plants.

Butterfly-wing pollination in Scadoxus and other South African Amaryllidaceae

Understanding the evolution of floral morphology requires information about the identity of pollinators as well as the specific mechanisms of pollen transfer. Based on preliminary field observations and floral structure, we hypothesized that pollination mechanisms involving the transfer of pollen on butterfly wings occur in several lineages of South African Amaryllidaceae. Here we report findings from a detailed study of butterfly-wing pollination in two subspecies of Scadoxus multiflorus and review the prevalence of this pollination mechanism among other Amaryllidaceae in southern Africa. We established that S. multiflorus subsp. katherinae is genetically self-incompatible and thus entirely reliant on pollinators for seed production. We determined that this subspecies is pollinated almost exclusively by large swallowtail butterflies, principally males of the mocker swallowtail Papilio dardanus cenea. Flowers of S. multiflorus subsp. multiflorus are pollinated by pierid and swallowtail butterflies. Pollen is deposited on the ventral surface of the wings of butterflies as they flutter over the strongly exserted stamens. We predict that butterfly-wing pollination occurs in at least nine species of South African Amaryllidaceae, which may reflect several independent origins of this mechanism. The flowers of these species are red or orange with strong herkogamy and are either bowl-brush or open-brush in shape. We provide maps of the distribution of pollen on the ventral surface of the wings of pollinators for four of these species. All four appear to be pollinated via the ventral surface of large butterfly wings, with the floral structure facilitating the process. These findings illustrate the importance of investigating pollen transfer mechanisms in order to understand patterns of floral diversification and floral convergence.

Floral morphology and morphogenesis in Sanguisorba (Rosaceae): flower diversification despite petal reduction and spatial constraints

Most Rosaceae flowers are pentamerous and have petals, but subtribe Sanguisorbinae have small tetramerous (or trimerous) flowers without petals, and their floral morphology and morphogenesis remain poorly known. We investigated the floral development of three Sanguisorba spp. using scanning electron microscopy to clarify the relationship between floral development and mature flowers, with emphasis on floral constraints affecting reduction of petals, diversity of androecial patterns and the development of the gynoecium and ovule, and to clarify the pollination mechanisms in the absence of petals. All species have botryoids, with numerous flowers initiated acropetally, and the maturation of flowers follows different directions. All flowers are tetramerous and sepals emerge pairwise. No petal primordia appear. Antesepalous stamens are initiated in a pairwise manner; only S. hakusanensis has a second whorl. The ovary appears inferior by development of a cystiform hypanthium. There is only one ovule with a single integument by reduction of the inner. The space occupied by the larger sepals forces the stamens to develop sequentially. Our data demonstrate that petals are basically absent and that there is a possible shift of pollination mechanisms in Sanguisorba among the mainly wind-pollinated Sanguisorbinae, as both anemophilous and entomophilous characters are found in this genus.

Limited phenological and pollinator-mediated isolation among selfing and outcrossing Arabidopsis lyrata populations

Transitions from outcrossing to selfing have been a frequent evolutionary shift in plants and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are prezygotic pre-pollination mechanisms (e.g. changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation isolate selfing populations of Arabidopsis lyrata from outcrossing populations, we conducted a common garden experiment with plants from selfing and outcrossing populations as well as their F1 hybrids. Specifically, we asked whether there was isolation between outcrossing and selfing plants and their F1 hybrids through differences in 1) the timing or intensity of flowering; and/or 2) pollinator visitation. We found that phenology largely overlapped between plants from outcrossing and selfing populations. There were also no differences in pollinator preference related to mating system. Additionally, pollinators preferred to visit flowers on the same plant rather than exploring nearby plants, creating a large opportunity for self-fertilization. Overall, this suggests that prezygotic pre-pollination mechanisms do not strongly reproductively isolate plants from selfing and outcrossing populations of Arabidopsis lyrata.

Rubus glaucus Benth.: morphology and floral biology aimed at plant breeding processes

Rubus glaucus is widely distributed throughout the three mountain ranges of Colombia, where the blackberry growers have highlighted the need to standardize the supply of planting material, starting with plant breeding schemes that lead to more productive varieties with morphological characteristics that ease agricultural activities. Plant breeding activities have improved by considering the pollination mechanisms of plants. The implementation of controlled sexual hybridization depends on these pollination mechanisms, and several plant breeding methods have been adapted to crop pollination patterns. Morphological characteristics and studies on the floral biology of R. glaucus Benth were conducted to improve plant breeding processes. In addition, a study on pollen viability and stigma receptivity were performed. The reported morphological characteristics of R. glaucus enabled characterization of its flowers as complete and perfect with a regular, actinomorphic, perianth heterochlamydeous, dialipetalous, and dialisepalous structure. Meanwhile, the evaluation of different collection times for pollen viability revealed significant differences. The highest pollen viability occurred at 10:00 am, followed by 9:00 am. Qualitative evaluation of stigma receptivity led to the conclusion that the highest stigma receptivity is at anthesis at 12:00 m.

Hidden in plain sight: a new species of Pleurothallis (Orchidaceae: Pleurothallidinae) from Colombia previously misidentified as Pleurothallis luctuosa

Pleurothallis tenuisepala, a new species in subsection Acroniae, is described and compared to Pleurothallis luctuosa with which it has previously been confused. While the two species are superficially similar, they can be very easily distinguished by the size of the flowers, which are approximately 60 mm long in P. tenuisepala versus approximately 29 mm long in P. luctuosa, or the length of the sepals, which are approximately four-times the length of the petals in P. tenuisepala versus less than twice the length of the petals in P. luctuosa. The two species can also be discriminated by their nuclear internal transcribed spacer (nrITS) sequences. Pleurothallis tenuisepala occurs on Isla Gorgona off the Pacific coast of Colombia and on the western slopes of the Cordillera Occidental of the Colombian Andes, while P. luctuosa is restricted to the Cordillera de Tilarán of Costa Rica. Labellar micromorphology of both species is discussed in relation to possible pollination mechanisms. Key words: Acroniae, cryptic species, labellum, morphology, taxonomy