Pollen Exchange Research Articles

Polyploidy‐induced floral changes lead to unexpected pollinator behavior in Arabidopsis arenosa

The paradox between the ubiquity of polyploid lineages in plants and the early obstacles to the establishment of polyploids is a long‐studied yet unresolved question in evolutionary biology. It is assumed that to successfully persist after emergence, newly formed polyploids need to display certain fitness advantages and show a certain extent of reproductive isolation with their diploid progenitors. In this study, we tested whether immediate floral changes following polyploidization can improve pollinator visitation and enable pollinator preference leading to assortative mating, i.e. build a premating reproductive barrier between diploids and polyploids. For this purpose, we generated synthetic tetraploids of Arabidopsis arenosa and measured insect visitor behavior on diploids and synthetic tetraploids. We found that the increased floral size that accompanied polyploidization did not lead to a measurable increase in visitor preference, with insects visiting diploid and tetraploid plants at equal frequency. Despite this observation, tetraploids set more fruits than diploids, suggesting a positive impact of polyploidization on pollen transfer via other means. In addition, polyploidization did not lead to assortative mating but instead promoted interploidy pollen exchange, since visitors preferentially switched between cytotypes rather than preferring one. Consistent with this switching behavior, most of the progeny from tetraploid plants were triploid. Our data suggest that polyploidization has an immediate impact on mating in plants, but in a more complex way than has been assumed previously.

DO HABITAT SHIFTS ALTER FLOWERING PHENOLOGY OVERLAP IN CLOSE RELATIVES? IMPLICATIONS FOR LOCAL COEXISTENCE

Flowering time in plants is a highly variable trait that influences species' resource use and exchange of pollen with con- and heterospecifics. Levin (2009) suggested that habitat shifts within species might cause plastic shifts in flowering phenology, reducing pollen exchange across habitats. Coupled with divergent selection across habitats, diverged flowering time might thus pave the way towards ecological speciation. Some of these ideas may apply across species as well. If close heterospecific relatives share phylogenetically conserved flowering times and negatively affect each other's fitness, habitat shifts to microallopatry might provide a means for local coexistence by close relatives by reducing resource competition, shared enemies, or negative interactions via pollination. Habitat shifts might also select for diverged flowering time, or cause flowering time divergence, if phylogenetically conserved cues arrive at different times across habitats. Here, we ask if flowering phenology is phylogenetically conserved for 208 species at our coastal field site in northern California, whether flowering phenology differs systematically across habitat types, and whether habitat shifts are associated with phenological separation, especially in congeners. Because annuality and perenniality have been shown to be associated with habitat traits and flowering time, we included life history in our analyses as well. We also explore the frequency of habitat shifts between congener and noncongener pairs. We use both field observations and data from Jepson eFlora/Jepson Manual 2 (Baldwin et al. 2012) to explore patterns in flowering phenology. The two data sources were well-correlated across 59 species. Phylogeny, habitat, and life history all influenced flowering time, and habitat and life history were also phylogenetically conserved across 208 spp. Congeners differed in habitat more often than noncongener pairs, and also overlapped more in flowering time. Habitat shifts were not associated with shifts in flowering time in congeners, despite mean peak flowering time differences across habitats, and phylogenetic conservatism in habitat use. Congeners that differed in both habitat use and life history, however, did have the greatest difference in peak flowering dates. Habitat shifts likely play a role in local coexistence of close relatives, but our data do not support habitat-mediated changes in phenology as a possible mechanism. Experimental approaches may elucidate the role of phenology, resource competition, pollinators, and other associates in mediating coexistence of congeners at our coastal California field site.

Differential reward in “male” versus “female” pollen of functionally dioecious Solanum

PremiseFive to six percent of angiosperm species exhibit a dioecious sexual system, with unisexual “male” or “female” flowers borne on separate plants. The consequent need for inter‐individual pollen exchange is a special challenge for taxa where pollen is the sole pollinator reward. Dioecious Australian Solanum assure visits from pollen‐foraging bees via production of inaperturate pollen in functionally female (morphologically bisexual) flowers. Biochemical composition of pollen from Australian Solanum has not been assessed nor compared to porate pollen from staminate flowers to reveal whether these flowers differ in their pollinator reward potential.MethodsPorate pollen from male flowers and inaperturate pollen from functionally female flowers of two functionally dioecious Australian species were compared for protein and amino acid content. We also assessed pollen from bisexual and staminate flowers of a closely related andromonoecious species, in which all pollen is porate, as a comparison across co‐occurring sexual systems.ResultsIn both functionally dioecious species, porate pollen grains from staminate flowers had significantly higher levels of proteins and amino acids than inaperturate pollen grains from functionally female flowers. Levels of proteins and amino acids were highest in bisexual and staminate flowers of the andromonoecious species.ConclusionsHigher levels of proteins and amino acids in porate pollen of “male” flowers in our functionally dioecious Solanum species suggests a greater nutritive reward for bees foraging on “male” plants than for those foraging on functionally “female” plants. Greater reward in porate pollen (including andromonoecious species) may be connected to the potential to generate a pollen tube.

Pollination biology and breeding system analysis of Ulmus wallichiana Planchon (Ulmaceae), a rare and threatened tree species of Central and Western Himalaya

Understanding the constraints on sexual reproduction of a plant species are important for predicting stability of the species in its natural habitat. In the absence of such data, any conservation efforts are arbitrary and remain ineffective. We investigated the reproductive ecology and breeding system of a rare and threatened tree species of central and western Himalaya, Ulmus wallichiana. The phenology, floral biology and pollination mechanism were observed in two populations for three consecutive years. In addition, breeding system and pollen limitation were examined using hand‐pollination experiments. Flowering in U. wallichiana begins in early March during which trees are leafless and small, pinkish‐white flowers cover the entire tree. Pollination is accomplished exclusively by wind with short average distances for pollen dispersal (~50 m). Pollination manipulation experiments showed high fruit set on outcrossing indicating U. wallichiana is xenogamous. However, a small percent of fruit set in autogamous and geitonogamous treatments indicates partial self‐incompatibility. Fruit set augmented when pollen was supplemented indicating that natural fruit set in U. wallichiana is limited due to unavailability of adequate pollen. Thus, it can be concluded that reproductive success of U. wallichiana is compromised due to scarcity of conspecifics and partial SI may partly ensure reproductive assurance in the low pollen exchange environment. The present study emphasizes on establishment of minimum population size with optimum distance between trees for effective conservation interventions.

New intergeneric orchid hybrid found in Romania × Pseudorhiza nieschalkii (Senghas) P.F.Hunt nothosubsp. siculorum H.Kertész & N.Anghelescu, 2020.

We describe the first reported intergeneric, which naturally occurs between two subspecies belonging to different genera, Dactylorhiza fuchsii subsp. sooana (genus Dactylorhiza) and Pseudorchis albida subsp. tricuspis (genus Pseudorchis), as × Pseudorhiza nieschalkii (Senghas) P.F.Hunt nothosubsp. siculorum H.Kertész & N.Anghelescu, 2020. The hybrid was found and digitally photographed for the first time by Hajnalka Kertész in June, 2020, within Terra Siculorum, in one of the Natura 2000 protected areas, known as Harghita Mădăraș, ROSCI00090. Following detailed morphometric analysis using 67 characters and molecular karyological analyses, we identified this unique specimen as an intergeneric hybrid, new to science. The hybrid, an F1 generation plant, most likely representing a single intergeneric pollination event, is phenotypically intermediate between its parental species in most of the characters scored, but it significantly closely resembles Pseudorchis albida subsp. tricuspis parent. Since several individuals of the parental species occurred in near proximity, within 1–10 meters distance, we suggest that the production of this hybrid required a minimum travel distance of ca 1–10 meters, by the pollinators and frequent exchange of pollen between the parental species was very likely. The parental species and the hybrid, which display a considerable synchronicity in their flowering time, overlap in the pollinator community, sharing various species of Hymenopterans and Dipterans, very abundant in the heathland. This Terra Siculorum hybrid is thus best described as a rarely occurring intergeneric hybrid that shows strong Pseudorchis albida subsp. tricuspis parental dominance in inheritance patterns.

Floral biology and potential hybridization of three sympatric epiphytic bromeliads in Veracruz, Mexico

AbstractIn the Bromeliaceae, hybrids have been engineered for horticultural purposes; in addition, hybrids have been observed in natural habitats. We investigated the hybridization potential of three sympatric species of Tillandsia inhabiting secondary forests and shaded coffee plantations in the central mountains of Veracruz, Mexico. The studied species (T. juncea, T. polystachia and T. variabilis) show overlap in flowering phenology and are believed to share pollinators. We compared the floral morphology of the species, performed controlled intra‐ and interspecific pollinations, and recorded pollen tube growth, fruit and seed set, as well as seed germination. Flower size differed among the species, but stamen and stigma heights were similar between pairs of species, which would facilitate interspecific pollen exchange. Pollen tubes reached the ovary in interspecific crosses. The three species showed interspecific cross‐compatibility, as all crosses resulted in development of mature fruit and viable seeds. Tillandsia juncea achieved the highest fruit set, whereas T. variabilis showed the highest seed set. Seed set as a result of agamospermy, autogamy, geitonogamy and interspecific cross‐pollination did not differ among the species. The findings suggest that pre‐ and post‐pollination barriers are weak among the three species of Tillandsia, which thus could potentially hybridize in natural sympatric populations.

Optimization of Pollen Germination in Tectona grandis (Teak) for Breeding Programs

Teak has become one of the most widely planted species in tropical regions of the world, given its high price for its timber in international markets. This has motivated the development of tree improvement programs in the Latin American region and in the tropical world in general. The latest advances have achieved clonal forestry at an operational scale. Recently, important efforts are being made to advance towards the next breeding generation, since knowledge about floral biology and pollen management have become important issues. A breeding program is being developed through the Tree Improvement Cooperative GENFORES—a vinculation model between the academy and forestry companies that was initiated in Costa Rica and now involves six Latin American countries. In order to advance into the next breeding generations, building capacities in topics such as pollen banks requires pollen quality, thus enabling the exchange of pollen among cooperative members. Pollen fertility studies are of considerable value in breeding programs, in order to determine pollen viability and germination in collections of genotypes, before going into mating operational activities. In this study, we optimized pollen quality analysis protocols in terms of the viability and germination of fresh teak pollen. Results of this research show that 90% viability and 28% germination can be achieved in fresh pollen grains, both inside and outside the anther, previously dehydrated in silica gel for 2 to 4 h (40% and 33% humidity, respectively). Brewbacker and Kwack (BK) medium at 10% of its salts + 10% sucrose and at a pH of 7 must be used as the germination medium. It is possible to evaluate teak pollen quality using the parameters defined in this study, which will in turn allow pollen management and purification, providing an opportunity for carrying out controlled crosses at an operational scale as part of teak breeding programs.

Estimating the impact of divergent mating phenology between residents and migrants on the potential for gene flow.

Gene flow between populations can allow the spread of beneficial alleles and genetic diversity between populations, with importance to conservation, invasion biology, and agriculture. Levels of gene flow between populations vary not only with distance, but also with divergence in reproductive phenology. Since phenology is often locally adapted, arriving migrants may be reproductively out of synch with residents, which can depress realized gene flow. In flowering plants, the potential impact of phenological divergence on hybridization between populations can be predicted from overlap in flowering schedules—the daily count of flowers capable of pollen exchange—between a resident and migrant population. The accuracy of this prospective hybridization estimate, based on parental phenotypes, rests upon the assumptions of unbiased pollen transfer between resident and migrant active flowers. We tested the impact of phenological divergence on resident–migrant mating frequencies in experiments that mimicked a single large gene flow event. We first prospectively estimated mating frequencies two lines of Brassica rapaselected or early and late flowering. We then estimated realized mating frequencies retrospectively through progeny testing. The two estimates strongly agreed in a greenhouse experiment, where procedures ensured saturating, unbiased pollination. Under natural pollination in the field, the rate of resident–migrant mating, was lower than estimated by phenological divergence alone, although prospective and retrospective estimates were correlated. In both experiments, differences between residents and migrants in flowering schedule shape led to asymmetric hybridization. Results suggest that a prospective estimate of hybridization based on mating schedules can be a useful, although imperfect, tool for evaluating potential gene flow. They also illustrate the impact of mating phenology on the magnitude and symmetry of reproductive isolation.

Genetic variation of Gentianella campestris ssp. campestris in the Northern Alps: how important are population size and isolation?

In this study, we analysed the impact of population size and isolation on the genetic variation of the short-lived alpine plant species Gentianella campestris ssp. campestris from two study regions (Allgau and Karwendel) in the Northern calcareous Alps in Germany. We determined the size and isolation of the study populations and analysed genetic variation using amplified fragment length polymorphisms. Genetic variation of G. campestris ssp. campestris differed significantly between the two study regions. Genetic variation did not depend on population size. However, the level of genetic variation within populations was about three times lower in the Karwendel, where the species is much more isolated than in the Allgau. Conversely, genetic variation among populations was much stronger in the Karwendel than in the Allgau. Our results support the observation that the level of genetic variation within populations of alpine plant species may not only be affected by population size, but also by population isolation. Depending on the distance among populations, gene flow by exchange of pollen and seeds triggers the influx of genetic variation, thereby sometimes superimposing the effects of population size. Our results suggest that for seed collections in conservation projects, not only population size, but also isolation should be considered.

Pollen flow and pollinator sharing among synchronopatric species of Psychotria (Rubiaceae)

Sympatric plant species that flower at the same time in highly seasonal environments are subject to competitive interference. Many species of the genus Psychotria (Rubiaceae) are sympatric and have an aggregated flowering period, which may have a strong influence on interactions among these species and their pollinators. We assessed the strategies of sympatric species of Psychotria to segregate or share pollinators, and the consequences for intra- and interspecific pollen flow. We sampled pollinators and analyzed flowering phenology, floral tube length, pollinator tongue length and floral nectar production of three sympatric species of Psychotria in the understory of a tropical forest in Brazil. We also marked flowers with fluorescent powder to monitor the flow of pollen. The studied species of Psychotria exhibited a short synchronous flowering period, with the sharing of pollinators and interspecific pollen exchange. The prevalence of shared or unshared pollinators and of intra- or interspecific pollen exchange varied among the studied species. Variation in floral tube length and nectar was not enough to hamper the sharing of most pollinators and pollen flow between Psychotria nitidula and P. hoffmannseggiana. Non-shared pollinators were more common in flowers of P. prunifolia, probably due to its longer floral tube, which can impede the access of shared pollinators. The higher offer of floral nectar by P. prunifolia makes this species more attractive to a greater number of flower visitors. Pollinator sharing seems to have no negative effect on intraspecific pollen flow and on the reproductive success of the studied synchronopatric species of Psychotria.

Histoire de la vigne sauvage, Vitis vinifera ssp. sylvestris, en Camargue / Wild grapevine Vitis vinifera ssp. sylvestris in Camargue, southern France

La vigne sauvage (Vitis vinifera ssp. sylvestris) est en déclin marqué depuis la fin du XIXe siècle. Depuis 2000, l’espèce est considérée en danger critique d’extinction. Des prospections dans la vallée du Rhône ont montré qu’il existait quelques micropopulations jusque dans le delta. Une population de 52 pieds de grandes dimensions et présentant un phénotype sauvage a récemment été découverte en rive gauche du Grand Rhône, dans le boisement privé du mas Saint-Georges. Une recherche pluridisciplinaire a été entreprise sur cette population de vignes afin de reconstituer leur histoire ; les outils utilisés ont été la génétique (effectuée sur 37 individus), l’écologie (dimensions des pieds, identification des porteurs), et la dendrochronologie effectuée sur 5 pieds. L’habitat forestier a également été analysé du point de vue architectural et dynamique de la lumière. Trente et un (31) individus ont été déterminés comme étant de véritables vignes sauvages, dont la diversité est légèrement inférieure à celle des autres populations européennes. Quatre sont des individus hybrides ou introgressés : deux entre vignes sauvages et vignes américaines, et deux entre vignes sauvages et vignes cultivées. Trois haplotypes typiques des vignes sauvages ont été déterminés, indiquant que ce site est à un point de convergence entre populations méditerranéennes du sud, de l’ouest et du centre de la Méditerranée. Le boisement a été suffisamment fermé pour éviter les échanges de pollen avec les vignes américaines échappées. À partir de ces données et de l’analyse des cartes anciennes, il a pu être déduit que ce boisement s’était développé au début du XXe siècle à partir d’un marais asséché par les aménagements hydrauliques. L’âge des vignes, estimé par la dendrochronologie à une fourchette de 38 à 50 ans, pourrait cependant être de l’âge de la forêt. Les vignes se seraient installées lors de la succession forestière. Les caractéristiques architecturales du boisement (à la fois dense et lumineux) ont permis à la vigne de s’y établir sur une longue durée. Actuellement, cette population ne se reproduit plus. Les conditions actuelles ne sont donc plus favorables à l’espèce, à l’inverse des populations échappées de porte-greffes, très abondantes en Camargue. Une protection forte de ces derniers pieds de vigne forestière devrait être mise en place avec l’accord des propriétaires.

Differential gender selection on flower size in two Neotropical savanna congeneric species

Larger flowers greatly increase among-individual pollen exchange within populations. However, water costs associated to transpirational cooling also increase with increasing flower size. Overall, the interplay between pollen and resource limitation determines the intensity of selection on flower size and this process is mostly dependent on gender and ecological context. To examine how pollinators and water use affect flower size, we determined corolla transpiration, pollen limitation, and selection through male and female fitness in two Kielmeyera species from the Brazilian cerrado flowering at different seasons. Hand-pollination experiments suggested pollen limitation through female fitness in both species, but K. coriacea showed lower limitation levels than K. regalis. For male fitness, the percentage of pollen removal was 1.5-times higher in K. coriacea. Higher air temperature and water deficit during flowering season of K. coriacea resulted in 4-fold higher corolla transpiration rates compared to K. regalis. Selection on flower size through male function was positive and significantly higher than selection through female components in both species. We also detected stabilizing selection in K. coriacea and positive selection in K. regalis on flower size through seed number. Our results suggest that selection on flower size in K. coriacea was mainly limited by water, whereas in K. regalis it was more limited by pollen. We demonstrate that differences in pollen and abiotic resource limitation determine gender-specific selection on flower size.

Functional differentiation in pollination processes among floral traits in Serapias species (Orchidaceae).

Floral displays, influencing attractiveness to insects, increase the number of pollinator visits and the efficiency of each visit in terms of pollen exchange and thus affect the plant reproductive success. Here, we conducted an in situ manipulation experiment to investigate whether the floral modifications affect reproductive success in natural orchid populations of Serapias lingua and Serapias vomeracea. We estimated male and female reproductive success of three treatment groups, disassembly of floral tube, cutting of lip, and painting of the callus surface, in terms of pollinaria removed/deposited and fruit production. Results revealed that phenotypic modification had opposite effects on reproductive success of two examine species. Indeed, reproductive success was significantly increased by the detached of the petals and sepals, and decreased, due to callus painting and lip removal, in S. lingua. On the contrary, unmanipulated plants of S. vomeracea showed significantly higher value of pollinaria removed and deposited and fruit set than manipulated ones. The differences between S. lingua and S. vomeracea agree to the different pollination strategy of examined species. S. vomeracea shows shelter imitation strategy, and thus, the disassembly of tunnel‐like corolla does not allow the insects to use the flower as a refuge, while S. lingua is a sexually deceptive orchid and therefore the opening of the flower made more visible callus (visible at a greater distance) increasing the pollinators attraction. This study provides evidence that pollinators were largely sensitive to the experimental modification of the flower phenotype, which is consistent with the presence of significant selection on individual floral characters. Our experimental investigations of the effects of variation in display on pollinator visitation provide insights into the evolution of floral morphology in orchid with shelter imitation strategy.

Estimating contemporary migration rates: effect and joint inference of inbreeding, null alleles and mistyping

Summary Microsatellite‐based genetic assignment is used broadly to monitor contemporary effective dispersal among populations. The need to investigate the robustness of this method to common genotyping errors was emphasized more than a decade ago, but it remains unaddressed. We evaluate here for the first time the effect of mistaken and null alleles on estimates of contemporary seed and pollen migration rates obtained with genetic assignment methods. We also introduce a novel Bayesian approach to jointly estimate seed and pollen migration rates, genotyping error rates and null allele frequencies, not requiring independent reference or duplicate genotypic data. Unaccounted‐for mistaken alleles caused positive bias and increased the root mean square error (RMSE) of pollen migration rate estimates, whereas seed migration rate estimates were weakly sensitive to mistyping. Jointly estimating mistyping rates minimized the bias and RMSE they introduce on pollen migration estimates, while yielding seed migration rate estimates with similar or slightly larger bias and RMSE than those obtained when ignoring mistyping. Ignoring genotyping errors can be especially problematic when there is no actual migration, because it can lead to the wrong conclusion that there is statistically significant exchange of pollen and/or seeds among populations that are actually isolated. Unaccounted‐for null alleles are problematic when among‐population pollen dispersal is present, leading to underestimation of pollen migration rates and overestimation of seed migration rates. Jointly estimating null allele frequencies minimized these two biases, reduced the RMSE of seed migration rate estimates and produced relatively small changes in the RMSE of pollen dispersal estimates. Synthesis. Disregarding genotyping errors and null alleles can produce biased and less accurate estimates of the rates at which present‐day plant populations are exchanging seed and pollen. An approach is proposed here to minimize the effect of genotyping problems on contemporary migration rate estimates, which should help avoiding erroneous migration inference, monitoring and management, especially when dealing with low migration rates and their associated uncertainty.

Considerations for Managing Agricultural Co-Existence between Transgenic and Non-Transgenic Cultivars of Outcrossing Perennial Forage Plants in Dairy Pastures

Many of the major forage species used in agriculture are outcrossing and rely on the exchange of pollen between individuals for reproduction; this includes the major species used for dairy production in grazing systems: perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.). Cultivars of these species have been co-existing since contrasting cultivars were developed using plant breeding, but the consequences and need for strategies to manage co-existence have been made more prominent with the advent of genetic modification. Recent technological developments have seen the experimental evaluation of genetically modified (GM) white clover and perennial ryegrass, although there is no current commercial growing of GM cultivars of these species. Co-existence frameworks already exist for two major cross-pollinated grain crops (canola and maize) in Europe, and for alfalfa (Medicago sativa L.) in the US, so many of the principles that the industry has developed for co-existence in these crops such as detection techniques, segregation, and agronomic management provide lessons and guidelines for outcrossing forage species, that are discussed in this paper.

Unusually limited pollen dispersal and connectivity of Pedunculate oak (Quercus robur) refugial populations at the species' southern range margin.

Low-latitudinal range margins of temperate and boreal plant species typically consist of scattered populations that persist locally in microrefugia. It remains poorly understood how their refugial habitats affect patterns of gene flow and connectivity, key components for their long-term viability and evolution. We examine landscape-scale patterns of historical and contemporary gene flow in refugial populations of the widespread European forest tree Pedunculate oak (Quercus robur) at the species' southwestern range margin. We sampled all adult trees (n=135) growing in a 20km long valley and genotyped 724 acorns from 72 mother trees at 17 microsatellite loci. The ten oak stands that we identified were highly differentiated and formed four distinct genetic clusters, despite sporadic historical dispersal being detectable. By far most contemporary pollination occurred within stands, either between local mates (85.6%) or through selfing (6.8%). Pollen exchange between stands (2.6%) was remarkably rare given their relative proximity and was complemented by long-distance pollen immigration (4.4%) and hybridization with the locally abundant Quercus pyrenaica (0.6%). The frequency of between-stand mating events decreased with increasing size and spatial isolation of stands. Overall, our results reveal outstandingly little long-distance gene flow for a wind-pollinated tree species. We argue that the distinct landscape characteristics of oaks' refugial habitats, with a combination of a rugged topography, dense vegetation and humid microclimate, are likely to increase plant survival but to hamper effective long-distance pollen dispersal. Moreover, local mating might be favoured by high tree compatibility resulting from genetic purging in these long-term relict populations.

Reproductive biology of Pentadesma butyracea (Clusiaceae), source of a valuable non timber forest product in Benin

Background and aims – The main reproductive traits of the native African food tree species, Pentadesma butyracea Sabine (Clusiaceae), which is threatened in Benin and Togo, were examined in Benin to gather basic data necessary to develop conservation strategies in these countries. Methodology – Data were collected on phenological pattern, floral morphology, pollinator assemblage, seed production and germination conditions on 77 adult individuals from three natural populations occurring in the Sudanian phytogeographical zone. Key results – In Benin, Pentadesma butyracea flowers once a year during the dry season from September to December. Flowering entry displayed less variation among populations than among individuals within populations. However, a high synchrony of different floral stages between trees due to a long flowering period (c. 2 months per tree), might still facilitate pollen exchange. Pollen-ovule ratio was 577 ± 213 suggesting facultative xenogamy. The apical position of inflorescences, the yellowish to white greenish flowers and the high quantity of pollen and nectar per flower (1042 ± 117 μL) represent floral attractants that predispose the species to animal-pollination. The main pollinators were two sunbirds (Cyanomitra verticalis, Cinnyris coccinigastrus) and three Hymenoptera (Apis mellifera, Meliponula togoensis, Hypotrigona sp.). Mean fruit set reached 49%, and absolute fruit production increased with tree size. Seeds were desiccation-sensitive (i.e. recalcitrant) with a maximum duration of hydrated storage of three months. Germination of seeds was most successful and rapid at 30°C (50% after nine days). Conclusions – Our results indicate that the natural reproduction of P. butyracea is not limited by its ecology so that we hypothesize anthropogenic activities to be the reason for the threatened status of P. butyracea in Benin and Togo. However, due to its recalcitrant seeds, the conservation of its genetic resources is not feasible through ex situ conservation of seed banks but in situ strategies and/or ex situ conservation in orchards should be successful.

Aspects of Orchid Conservation: Seed and Pollen Storage and their Value in Re-introduction Projects

Dry seeds of many orchid species, when stored at low temperatures, are capable of maintaining high levels of viability for many years, supporting orchid seed banking as a valuable part of emerging integrated conservation strategies. The Orchid Seed Science and Sustainable Use (OSSSU) network has already stored over 300+ species across 26 countries around the world. Its future ambition to store seeds representing a minimum of one thousand species in the next five years, and to expand the network to include more institutes and countries, provides an example of what can be achieved by a small dedicated group, willing to share their technical expertise and to develop a deeper understanding of the underlying science. Recent work indicates that it may also be possible to store orchid pollen of some species for a minimum of six years under similar conditions to those used for orchid seeds, thereby facilitating pollen exchange between collections. OSSSU partners in a number of countries have already demonstrated that raising plants from stored seeds can be used successfully in reintroduction projects.

Electrical signals in prayer plants (marantaceae)? Insights into the trigger mechanism of the explosive style movement.

The explosive pollination mechanism of the prayer plants (Marantaceae) is unique among plants. After a tactile stimulus by a pollinator, the style curls up rapidly and mediates pollen exchange. It is still under discussion whether this explosive movement is released electrophysiologically, i.e. by a change in the membrane potential (as in Venus flytrap), or purely mechanically. In the present study, electrophysiological experiments are conducted to clarify the mechanism. Artificial release experiments (chemical and electrical) and electrophysiological measurements were conducted with two phylogenetically distant species, Goeppertia bachemiana (E. Morren) Borchs. & S. Suárez and Donax canniformis (G. Forst.) K. Schum. Electric responses recorded after style release by extracellular measurements are characterised as variation potentials due to their long repolarization phase and lack of self-perpetuation. In both species, chemical and electric stimulations do not release the style movement. It is concluded that the style movement in Marantaceae is released mechanically by relieving the tissue pressure. Accordingly, the variation potential is an effect of the movement and not its cause. The study exemplarily shows that fast movements in plants are not necessarily initiated by electric changes of the membrane as known from the Venus flytrap.

On the potential strength and consequences for nonrandom gene flow caused by local adaptation in flowering time.

Gene flow is generally considered a random process, that is the loci under consideration have no effect on dispersal success. Edelaar and Bolnick (Trends Ecol Evol, 27, 2012 659) recently argued that nonrandom gene flow could exert a significant evolutionary force. It can, for instance, ameliorate the maladaptive effects of immigration into locally adapted populations. I examined the potential strength for nonrandom gene flow for flowering time genes, a trait frequently found to be locally adapted. The idea is that plants that successfully export pollen into a locally adapted resident population will be a genetically biased subset of their natal population - they will have resident-like flowering times. Reciprocally, recipients will be more migrant-like than the resident population average. I quantified the potential for biased pollen exchange among three populations along a flowering time cline in Brassica rapa from southern California. A two-generation line cross experiment demonstrated genetic variance in flowering time, both within and among populations. Calculations based on the variation in individual flowering schedules showed that resident plants with the most migrant-like flowering times could expect to have up to 10 times more of the their flowers pollinated by immigrant pollen than the least migrant-like. Further, the mean flowering time of the pollen exporters that have access to resident mates differs by up to 4weeks from the mean in the exporters' natal population. The data from these three populations suggest that the bias in gene flow for flowering time cuts the impact on the resident population by as much as half. This implies that when selection is divergent between populations, migrants with the highest mating success tend to be resident-like in their flowering times, and so, fewer maladaptive alleles will be introduced into the locally adapting gene pool.