Search

© 2014 The Authors. Plant-pollinator interactions are potential drivers of evolution in floral traits. Because nectar chemical composition is known to mediate both plant-pollinator interactions and plant reproductive success, it can be expected that chemical composition of nectar is subjected to strong pollinator-mediated selective forces. However, the extent of natural selection on different nectar components has not been studied so far. Using the Lepidoptera pollinated fragrant orchid Gymnadenia conopsea as a model species, we used high-performance anion-exchange chromatography (HPAEC) to characterize the sugar and amino acid composition of floral nectar in three calcareous grassland populations of G. conopsea. We then measured phenotypic selection on nectar composition and on other plant and floral traits through applying both linear regression and structural equation modelling. We demonstrate phenotypic selection on plant height, inflorescence height and on specific nectar amino acids, whereas spur length, total sugar and amino acid concentration were not direct targets of selection. Chemical nectar composition is thus indeed under selective pressure but nectar amino acids are much more important to fitness of G. conopsea, as compared to nectar sugars. Furthermore, as we found no evidence of selection on the total amino acid concentration, it is unlikely that amino acids increase pollinator attraction because they are a pollinator nitrogen source. To further unravel the evolutionary ecology of floral nectar, behavioural experiments with pollinators exposed to different nectar components and studies experimentally identifying the selective agents are recommended. ispartof: Oikos vol:124 issue:4 pages:421-427 status: published

Summary 1. This account presents information on all aspects of the biology of Gymnadenia conopsea (L.) R. Brown s.l. (Fragrant Orchid) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation. 2. Most available information was published before recent revisions in taxonomy split what had been known as Gymnadenia conopsea into three separate species, now designated G. borealis (Druce) R.M. Bateman, Pridgeon & M.W. Chase, G. conopsea (L.) R. Brown and G. densiflora (Wahlenb.) Dietrich. Although the three newly accepted species have at least partial reproductive isolation, they have numerous morphological and ecological similarities. Some recent work still refers to G. conopsea s.l. because of difficulties in distinguishing between the species, and inertia in adoption of the new taxonomy. Wherever possible, differences between G. borealis, G. conopsea s.s. and G. densiflora are highlighted. 3. Gymnadenia conopsea s.l. is a perennial, terrestrial orchid that is widely distributed across Eurasia. The three segregate species are all considered native. G. conopsea s.s. (Chalk Fragrant Orchid) occurs mainly in the southern half of Britain, where it is most commonly observed in dry calcareous grasslands and pastures. G. densiflora (Marsh Fragrant Orchid) occurs in damp calcareous marshes, fens and dune slacks in England and Wales; it is rare in Scotland but frequent in Ireland. G. borealis (Heath Fragrant Orchid) is mainly found on hill pastures in Wales, northern England and Scotland. The three species all avoid shade, being most abundant in open habitats. 4. Although the three segregate species cannot always be reliably distinguished on the basis of morphological characteristics, diagnostic features include plant height, leaf width and disposition, density of flowers in the inflorescence, shape of the labellum, spur width, and odour and colour of the flowers. Additionally, several cytotypes within G. conopsea s.s. have been observed in Central Europe. These often grow in mixed-ploidy populations; in contrast, the species appears to be predominantly diploid in Britain. 5. Gymnadenia conopsea s.l. is a non-bulbous geophyte. Leaves emerge in spring, and flowering takes place between the end of June and the beginning of August. Vegetative adult dormancy – the failure of above-ground parts to appear in a growing season, followed by reappearance of full-sized photosynthetic plants in subsequent years – has been observed. Such dormancy rarely lasts longer than 1 year.

Most plants attract multiple flower visitors that may vary widely in their effectiveness as pollinators. Floral evolution is expected to reflect interactions with the most important pollinators, but few studies have quantified the contribution of different pollinators to current selection on floral traits. To compare selection mediated by diurnal and nocturnal pollinators on floral display and spur length in the rewarding orchid Gymnadenia conopsea, we manipulated the environment by conducting supplemental hand-pollinations and selective pollinator exclusions in two populations in central Norway. In both populations, the exclusion of diurnal pollinators significantly reduced seed production compared to open pollination, whereas the exclusion of nocturnal pollinators did not. There was significant selection on traits expected to influence pollinator attraction and pollination efficiency in both the diurnal and nocturnal pollination treatment. The relative strength of selection among plants exposed to diurnal and nocturnal visitors varied among traits and populations, but the direction of selection was consistent. The results suggest that diurnal pollinators are more important than nocturnal pollinators for seed production in the study populations, but that both categories contribute to selection on floral morphology. The study illustrates how experimental manipulations can link specific categories of pollinators to observed selection on floral traits, and thus improve our understanding of how species interactions shape patterns of selection.

Summary 1. Understanding the many factors that affect community composition and coexistence of species in natural environments is one of the central goals in ecology. As germination and establishment of seedlings in orchids are crucially dependent on mycorrhizal availability, the diversity and spatial distribution of orchid mycorrhizal fungi are likely factors that contribute to orchid coexistence. 2. In this study, we combined molecular identification techniques with seed germination experiments and spatial point pattern analyses to investigate to what extent differences in mycorrhizal association patterns affected spatial variation in seed germination and the above-ground distribution of three co-occurring terrestrial orchid species (Anacamptis morio, Gymnadenia conopsea and Orchis mascula). 3. The three species associated with a different set of mycorrhizal fungi, except A. morio and G. conopsea, which shared one fungal associate. The number of fungal lineages detected associating with each species also differed between species, being highest in G. conopsea, which associated with five lineages, and restricted to a single lineage in O. mascula. 4. Seed germination experiments showed that below-ground seed germination was restricted to locations where orchid individuals were most abundant, and quickly declined with increasing distance from the nearest above-ground congener. Spatial point pattern analyses indicated significant fine-scale spatial clustering that was highest in O. mascula and lowest in G. conopsea. Moreover, the spatial distributions of the three species were independent from each other, except for A. morio and G. conopsea. 5. Synthesis. Our results support previous findings that co-occurring orchid species tend to use different mycorrhizal partners. Although the possibility that variation in local environmental conditions affected seed germination could not be completely ruled out, our results suggest that the presence of specific mycorrhizal fungi contributed, at least partly, to the spatial distribution and coexistence of the investigated orchid species.

Members of the orchid genus Nigritella are widespread in European mountains, but species circumscriptions and evolutionary patterns in the genus are subjects to conflicting opinions. We analyzed a representative material of Nigritella for differentiation at nuclear and plastid marker loci. In agreement with predictions from embryological studies, diploid members of Nigritella are sexual and mostly out-crossing, whereas triploid, tetraploid and pentaploid members are apomicts. The diploid taxa were poorly differentiated in the investigated molecular markers, except for the western N. gabasiana, which was separated in plastid haplotypes. Polyploid Nigritella aggregate into three groups and within each of these groups apomictic polyploids have given rise to new species. Within the N. nigra group, the tetraploid N. nigra subsp. austriaca is somewhat differentiated from the triploid subsp. nigra at nuclear as well as plastid loci. Fusion of an unreduced egg cell from subsp. nigra with a haploid microgamete from Gymnadenia conopsea gave rise to Gymnigritella runei. Within the N. widderi group, N. archiducis-joannis is poorly separated from N. widderi in molecular markers, and the pentaploid N. buschmanniae has evolved by fusion of an unreduced egg cell from N. widderi with a haploid microgamete from a diploid Nigritella. Within the N. miniata group, N. stiriaca is somewhat differentiated from N. miniata at nuclear loci, but no other segregates of N. miniata are supported at species level. Polyploid Nigritella species accumulate genetic diversity by somatic mutations. In the widespread N. nigra subsp. austriaca and N. miniata this diversity is correlated to geography. Although some polyploids may be of recent origins, each polyploid contain genetic markers no longer encountered in diploid members of the genus. According to plastid marker data, Nigritella and Gymnadenia may constitute monophyletic sister genera. (Less)

This investigation evaluates the usage of genetic markers, microsatellites, to distinguish and re-identify individual plants in a population of the orchid Gymnadenia conopsea. The study also illust ...

Gymnadenia conopsea (L.) R. Br., or the fragrant orchid, is one of many plant species negatively influenced by new practices in agriculture and forestry during the last decades. This study describes the level of microsatellite variation within and among 10 Swedish populations of this species. It was not possible to detect strong effects of small population size or fragmentation. In general, the species had high genetic variation within and low genetic divergence among populations, although the correlation between population size and number of alleles was close to significance at the 95% level. Also, a significant isolation by distance effect was observed, indicating the presence of modest restrictions in gene dispersal between the investigated populations.

Differences in reproductive biology between two orchid species were examined: Eight Danish populations of the nectarless Dactylorhiza majalis ssp. majalis and six Swedish populations of the nectar-producing Gymnadenia conopsea ssp. densiflora. Population size varied from 24 to 1700 flowering individuals in D. majalis and from 100 to 1200 in G. conopsea. Dactylorhiza majalis had only half as many flowers per spike as G. conopsea. Fruit-set of D. majalis ranged from 16 to 39%, much lower than the fruit-set of G. conopsea (78–91%). Thus in the species with a few flowers and no nectar a lower fruit-set was observed than in the species with many flowers and presence of nectar. The low fruit-set of D. majalis was pollen-limited and fruit-set was positively correlated with pollinia removal and the latter was negatively correlated with population size. In both species, fruit-set and population size were uncorrelated.

Six polymorphic microsatellite loci were found in two genomic libraries (one unenriched and one enriched) constructed using DNA originating from the fragrant orchid, Gymnadenia conopsea. These six microsatellite loci (Gc 17, 29, 42, 49, 51 and 77) showed high levels of variation (HO= 0.65, 0.90, 0.85, 0.75, 0.90 and 0.40, respectively) when 20 individuals from one population of G. conopsea were PCR amplified and separated in 6% PAA gels.