Pollen Vectors Research Articles

Flower scent, pollinators, and effects of proximity between plants on fruit set of the rare, threatened, and endemic Daphne rodriguezii

AbstractThis study focuses on Daphne rodriguezii, a threatened plant species that is endemic to Menorca in the Balearic Islands of the Western Mediterranean. The main objective was to investigate the volatile organic compounds (VOCs) in the floral aroma, as well as the timing and chemical variations in scent production. The primary pollinators were identified, and the relationship between their behavior and the chemical profile of the floral scent was investigated. Furthermore, the impact of plant density on fruit set rates was evaluated to obtain valuable insights for conservation and habitat‐management initiatives. The findings reveal that D. rodriguezii emits a distinct sweet floral aroma that primarily consists of benzenoids and linalool derivatives. Scent emission occurs during the evening and night, coinciding with the activity period of moths (Autographa gamma), which were identified as the primary pollen vectors for this self‐incompatible species. The fruit set values exhibit a positive correlation with the proximity between plants. These results emphasize the importance of moths and plant proximity as crucial factors to consider in the conservation management of this species.

Ambophily and evidence of hydrophily as a new pollination strategy in Eleocharis (l.) Roem. & Schult (Cyperaceae)

ABSTRACT Background Aquatic plants can reproduce through abiotic or biotic pollination. In Cyperaceae anemophily is plesiomorphic, but studies have registered floral visitors in some genera, including Eleocharis. Wind and insects, therefore, can act together in the pollination, characterising ambophily. However, so far there has been no evidence that water could also be a pollen vector in this family. Aims Expand understanding of the pollination mechanisms in Cyperaceae. Methods We analysed the floral biology, pollen to ovule ratio, floral visitors, performed pollen vector exclusion experiments, characterised the floral colour in the models of insect vision and analysed the chemical composition of floral scent of Eleocharis geniculata and E. mutata. Results Both species have anemophilous attributes. In Eleocharis mutata, wind was an effective pollen vector, increasing the fruit set. Individuals of E. geniculata exposed to water were more likely to produce fruits (p < 0.01). Eight species of insects were recorded as floral visitors of E. mutata, among which an Ephydroidea fly acting as the main pollinator. Flowers of both species had the same scent as the vegetative parts, and were shown to be visible and distinguishable from the background in both Hymenoptera and Diptera vision models. Conclusion Our results suggest a new pollination strategy (hydrophily in E. geniculata), and another case of ambophily in Cyperaceae.

Effects of anther-stigma position on cross-pollination efficiency in a hermaphroditic plant.

Evolution of cross-pollination efficiency depends on the genetic variation of flower traits, the pollen vector, and flower trait matching between pollen donors and recipients. Trait matching has been almost unexplored among nonheterostylous species, and we examined whether the match of anther length in pollen donors and stigma length in pollen recipients influences the efficiency of cross-pollination. To explore potential constraints for evolutionary response, we also quantified genetic variation and covariation among sepal length, petal length and width, stamen length, style length, and herkogamy. We created 58 experimental arrays of Turnera velutina that varied in the extent of mismatch in the position of anthers and stigmas between single-flowered plants. Genetic variation and correlations among flower traits were estimated under greenhouse conditions. Style length, but not herkogamy, influenced the efficiency of cross-pollination. Plants with stamen length that matched the style length of other plants were more efficient pollen donors, whereas those with the style protruding above the stamens of other plants were more efficient pollen recipients. Significant broad-sense heritability (0.22 > hB 2 < 0.42) and moderate genetic correlations (0.33 > r < 0.85) among floral traits were detected. Our results demonstrated that anther-stigma mismatch between flowers contributed to variation in the efficiency of cross-pollination. The genetic correlations between stamen length and other floral traits suggests that any change in cross-pollination efficiency would be driven by changes in style rather than in stamen length.

Shedding light on overlooked pollinators: Global insights into floral interactions of velvet ants (Hymenoptera: Mutillidae and Myrmosidae)

AbstractPlant–animal interactions constitute a recurrent and central focus in ecological research, with pollination representing one of its most extensively studied aspects. While certain insect orders have traditionally received considerable attention due to their abundance as flower visitors and their efficiency in pollination, it is undeniable that the significance of other less popular and neglected flower visitors cannot be overlooked. In this regard, velvet ants (Hymenoptera: Mutillidae and Myrmosidae) constitute an excellent study model, as the knowledge of their ecology (e.g., their feeding preferences) is still very limited despite being reported as common flower visitors. In this study, we conducted a comprehensive global review of velvet ant floral visitation patterns using citizen science data, literature records and unpublished data. We used network metrics to explore their flower‐visit preferences on a global scale, as well as depending on the bioregion where the interaction was recorded and the sex of the velvet ants. In addition, we explored their potential role as pollen vectors examining the number of photographic records where velvet ants had pollen attached to their bodies. Our analyses revealed that velvet ants are generalist flower visitors of a wide range of plant families, with Apiaceae, Asteraceae, Euphorbiaceae, Rhamnaceae and Fabaceae as the most visited. Despite differences in flowering plant and velvet ant composition across bioregions causing differences in plant‐velvet ant interactions, velvet ants visited flowering plants in a generalistic way across the globe. Males and females seemed to visit different plant communities, with males being more generalist than females. Furthermore, 42.7% (likely an underestimation) of the photographic records of velvet ants visiting flowers showed pollen attached to their bodies in the same way as in other pollinating insects, suggesting the same potential role as pollinators. There remains ample scope for ongoing investigation to comprehensively assess the importance of numerous arthropods, including velvet ants, not only as flower visitors but also as potential pollinators.

Pollination by birds, non-flying mammals, and European honeybees in a heathland shrub, Banksia catoglypta (Proteaceae)

Abstract Vertebrate pollination has evolved in many plant lineages, with pollination by birds the most prevalent strategy. However, in Banksia (Proteaceae) many species are visited by a combination of nectarivorous birds, non-flying mammals (NFMs), and insects, though the relative importance of these pollen vectors for reproduction remains poorly understood. Here, we investigate the contribution to fruit set of birds, NFMs, and insects in Banksia catoglypta—a heathland shrub from south-west Australia. This species flowers in winter and produces large, golden-yellow inflorescences that are typically presented near the ground and consist of rigid, strongly scented flowers with a long stigma-nectary distance—suggesting pollination by vertebrates. The primary floral visitors were white-cheeked honeyeaters (Phylidonyris niger), honey possums (Tarsipes rostratus), house mice (Mus musculus), and introduced European honeybees (Apis mellifera), all of which carried B. catoglypta pollen. Banksia catoglypta was found to be obligately outcrossing with no evidence of pollen limitation. Selective exclusion of flying pollinators revealed that inflorescences pollinated solely by NFMs produced 50% fewer fruit than open-pollinated controls. Therefore, while mammals are pollinators of B. catoglypta, they may contribute comparatively little to fruit set in some Banksia species displaying floral traits considered adaptations to NFM pollination. Exclusion of vertebrate pollinators had no effect on fruit set, demonstrating that European honeybees can be effective pollinators of some primarily vertebrate-pollinated plants.

Pollination of Disa engleriana (Orchidaceae): Floral modifications for deposition of pollinaria on the abdomen of large bees and wasps

The evolution of complex floral morphology in orchids can be attributed largely to mechanisms that ensure precise placement of pollinaria on the bodies of animal flower visitors. Floral advertisements and rewards also play a key role in selective attraction of animals that are suitable as pollen vectors. Previous studies of the large African orchid genus Disa have demonstrated high levels of pollination system specialization and have identified functions of floral morphology for transfer of pollen, but studies of pollination in members of the tropical clade of Disa sect. Micranthae have been lacking. This clade is characterized by highly unusual floral morphology, including vertical anthers and pronounced spatial separation between a nectar-producing spur located in the centre of the dorsal sepal and the rostellum lobes that serve to attach pollinaria to flower visitors. In a study conducted in central Zambia, I found that the flowers of Disa engleriana are pollinated by large wasps (Eumeninae and Scoliidae) and carpenter bees. These insect groups carry pollinaria near the tip of their abdomen, which contacts the rostellum when the abdomen is tucked under the flower for balance during nectar-feeding. The pollinaria are rigid and project at 90˚ from the underside of the abdomen such that they contact the deeply recessed stigma during subsequent flower visits. This study reveals a new mechanism of pollen transfer in Disa and sheds light on the evolution of the highly complex floral morphology of this large orchid clade

As prey and pollinators, insects increase reproduction and allow for outcrossing in the carnivorous plant Dionaea muscipula.

Understanding the factors that limit reproductive success is a key component of plant biology. Carnivorous plants rely on insects as both nutrient sources and pollinators, providing a unique system for studying the effects of both resource and pollen limitation on plant reproduction. We conducted a field experiment using wild-growing Dionaea muscipula J. Ellis (Droseraceae) in which we manipulated prey and pollen in a factorial design and measured flower production, number of fruits, and number of seeds. Because understanding reproduction requires knowledge of a plant species' reproductive and pollination biology, we also examined the pollination system, per-visit pollinator effectiveness, and pollen-ovule (P/O) ratio of D. muscipula. Plants that received supplemental prey produced more flowers than control plants. They also had a higher overall fitness estimate (number of flowers × fruit set (total fruits/total flowers) × seeds per fruit), although this benefit was significant only when prey supplementation occurred in the previous growing season. Neither pollen supplementation nor the interaction between pollen and prey supplementation significantly affected overall plant fitness. This study reinforces the reliance of D. muscipula on adequate prey capture for flower, fruit, and seed production and a mobile pollen vector for reproduction, indicating the importance of considering insects as part of an effective conservation management plan for this species.

Illegitimate flower visitors and pollinators are associated with different flower morphology: Evidence from five species of Penstemon (Plantaginaceae)

The role of pollinators as drivers of morphological diversification has been extensively documented. However, how non-pollinators, such as pollen thieves and nectar robbers, affect flower morphology has received little attention. In this study, we used five species of Penstemon to investigate the relationship between pollinators and non-pollinators, and the flower morphology of the plants they visit. The results suggest that smaller flowers are more likely to be predominantly visited by small and very small pollen-collecting bees, and that larger flowers are more likely to be visited by large bees. Very small and small pollen-collecting bees rarely contacted the stigma and can thus be characterized as illegitimate visitors. However, in the absence of a more efficient pollen vector, these visitors can act as occasional pollinators. On the other hand, nectar robbing by wasps was not correlated with flower size but was associated with premature wilting. Pollinator assemblages varied geographically, but the presence and frequency of non-pollinator visitors did not, and instead they were species-specific. Finally, our results suggest that non-pollinator visitors have a detrimental effect on flower appearance from the pollinators' perspective.

Reproductive strategy of an invasive buzz-pollinated plant (Solanum rostratum)

Some plants that invade environments outside their native range of distribution often face reproductive challenges such as limited pollinators and mates. Thus, the capacity to reproduce autonomously in the absence of pollinators or mates can facilitate establishment and spread of invasive plants. Here, we study the capacity of Solanum rostratum to reproduce through autonomous self-pollination. Although this plant is self-compatible, it strongly depends on visitation of buzzing bees to reproduce in its native range. We compared floral morphology, pollen: ovule ratios, reproductive phenology, and capacity for autonomous self-pollination of two populations of native distribution (Mexico) and another two populations of the invasive range (USA). We found a reduction in anther-stigma distance, pollen: ovule ratio, and plant height in invasive populations, as well as a shift to increased resource allocation to floral vs. vegetative structures and faster flowering compared to native populations. Importantly, invasive populations show a marked increase in the capacity to produce fruits autonomously (without pollen vectors). Our results suggest that the northern invasion of S. rostratum could have been facilitated by a shift in reproductive strategy from outcrossing to autonomous self-pollination.

Future distribution of the epiphytic leafless orchid (Dendrophylax lindenii), its pollinators and phorophytes evaluated using niche modelling and three different climate change projections

The identification of future refugia for endangered species from the effects of global warming is crucial for improving their conservation. Because climate-driven shifts in ranges and local extinctions can result in a spatial mismatch with their symbiotic organisms, however, it is important to incorporate in niche modelling the ecological partners of the species studied. The aim of this study was to evaluate the effect of climate change on the distribution of suitable niches for the ghost orchid (Dendrophylax lindenii) and its phorophytes and pollinators. Thus, its five species of host trees and three pollen vectors were included in the analysis. Climatic preferences of all the species studied were evaluated. The modelling was based on three different climate change projections and four Shared Socio-economic Pathway trajectories. All the species analysed are characterized by narrow temperature tolerances, which with global warming are likely to result in local extinctions and range shifts. D. lindenii is likely to be subjected to a significant loss of suitable niches, but within a reduced geographical range, both host trees and pollen vectors will be available in the future. Future conservation of this orchid should focus on areas that are likely be suitable for it and its ecological partners.

Pollination by native bees achieves high fruit quantity and quality of highbush blueberry: a sustainable alternative to managed pollinators

IntroductionBlueberry is one of the most relevant buzz-pollinated crops worldwide, and Chile is the most important global producer of fresh blueberries during wintertime in the Northern Hemisphere. Non-buzzing bees, such as honey bees, may provide suboptimal services compared with bees capable of buzz pollination. The widely held contention that honey bees are inferior pollinators of blueberries drives the industry to place pressure on governments to allow bumblebee (Bombus terrestris) importation for pollination. However, the introduction of B. terrestris generates environmental problems in Chile by competing with and transmitting parasites to local bees. Despite some native Chilean bees being recently recognized as efficient pollen vectors of blueberry crops, no study has evidenced the influence of their visits on fruit yield. Therefore, we aimed to evaluate the native Chilean floral visitors' performance to improve the quantity and quality of highbush blueberry in comparison to the performance of managed visitors.MethodsPer-visit pollination performance (fruit set and fruit quality) and visitation frequency were measured, and the performance of buzzing behavior by flower visitors was evaluated in four cultivars grown in five blueberry orchards located in southern Chile.ResultsWe found that fruit set and weight were highly influenced by floral visitor taxon. Some native bee species can greatly improve the fruit set and fruit quality (greater weight) of the highbush blueberry cultivars. For instance, one single visit of C. occidentalis can increase fruit weight by a factor of 1.8 compared to an A. mellifera visit; however, visits of halictids and syrphids resulted in lower fruit sets than those of unvisited flowers. However, we found that the occurrence of sonication behavior alone was not a predictor of higher fruit set and fruit weight of highbush blueberry cultivars. Consequently, the taxonomic recognition of floral visitors, ideally to the species level, is still needed to distinguish the most efficient fruit yield promoters of blueberry.DiscussionThe conservation of the biotic pollinators, especially native pollinators, would improve blueberry fruit quality and is likely to improve overall crop productivity.

Loss of fungal symbionts and changes in pollinator availability caused by climate change will affect the distribution and survival chances of myco-heterotrophic orchid species

The first comprehensive species distribution models for orchid, its fungal symbionts and pollinator are presented. To evaluate impact of global warming on these organisms three different projections and four various climate change scenarios were analysed. The niche modelling was based on presence-only records of Limodorum abortivum, two species of Russula and three insects pollinating orchid (Anthophora affinis, Bombus terrestris, Rhodanthidium septemdentatum). Two sets of orchid predictions were examined—the first one included only climatic data and the second one was based on climate data and data on future distribution of orchid fungal symbionts. Overall, a poleward range shift is predicted to occur as a result of climate change and apparently global warming will be favorable for L. abortivum and its potential geographical range will expand. However, due to the negative effect of global warming on fungal symbionts of L. abortivum, the actual extension of the suitable niches of the orchid will be much limited. Considering future possibility of cross-pollination, the availability of A. affinis for L. abortivum will decrease and this bee will be available in the worst case scenarios only for 21% of orchid populations. On the other hand, the overlap of orchid and the buff-tailed bumblebee will increase and as much as 86.5% of plant populations will be located within B. terrestris potential range. Also the availability of R. septemdentatum will be higher than currently observed in almost all analysed climate change projections. This study showed the importance of inclusion of ecological factors in species distribution models as the climate data itself are not enough to estimate the future distribution of plant species. Moreover, the availability of pollen vectors which is crucial for long-term survival of orchid populations should be analysed in context of climate changes.

Reproductive Ecology of the Invasive Alien Shrub Pyracantha angustifolia in the Grassland Biome, South Africa.

Knowledge on reproductive traits of problematic invasive alien plants, such as the woody invasive shrub Pyracantha angustifolia of temperate Chinese origin, can help better manage invasive species. To determine factors contributing to its invasion, we investigated floral visitors and pollen loads, self-compatibility, seed set, seed rain, soil seed banks, and seed longevity in the soil. Generalist insects were recorded visiting flowers and all carried pollen loads of high purity (>70%). Floral visitor exclusion experiments showed that P. angustifolia can set seed (66%) without pollen vectors, although natural pollination resulted in higher fruit set (91%). Fruit count surveys and seed set showed an exponentially increased relationship between seed set and plant size with high natural seed yield (±2 million seeds m-2). Soil core samples revealed a high seed density of 46,400 ± (SE) 8934 m-2 under shrubs, decreasing with distance away from the shrub. Bowl traps stationed under trees and fences confirmed that seeds were efficiently dispersed by animals. Buried seeds survived for less than six months in the soil. Due to high seed production, self-compatibility augmented by generalist pollen vectors, and effective seed dispersal by local frugivores, it is difficult to manage the spread manually. Management of this species should focus on the short life span of seeds.

Reproductive Biology and Pollination Ecology of Fritillaria michailovskyi Fomin (Liliaceae), Endemic to East Anatolia (Turkey)

Fritillaria is highly endangered in their natural habitats, and these species are perennial bulbous plants with an important medicinal and ornamental value whose reproductive strategies and adaptive evolution mechanisms are still not fully clear. Therefore, the reproductive strategies of endemic species, like Fritillaria michailovskyi Fomin are important to detect the community structure and the diversity patterns of ornamental plants. The current paper on the reproductive strategy of F. michailovskyi, a rare endemic species, was carried out at the Erzincan Horticultural Research Institute, Turkey. Our results indicate that the flowering stages of F. michailovskyi may be divided into eight phases. According to pollination experiments and the pollen/ovule ratio, and the self-incompatibility index (SII) in an ex-situ population, F. michailovskyi indicated high levels of xenogamy and self-incompatibility. It was determined that the pollination of F. michailovskyi mostly depended on pollen vectors, and the effective pollinators of F. michailovskyi were Apis mellifera and Bombus terrestris. In addition, average seed number, seed germination, and average seed viability were found as 144, 46%, and 67%, respectively. The stigma receptivity, pollen grains, and pollen viability were detected as 83%, 252,000, and 95%, respectively. Our study is the first report providing a detailed explanation of the reproductive strategy of this rare endemic species, which could aid in the genetic evolution and conservation of this valuable taxa.

The effect of global warming on the Australian endemic orchid Cryptostylis leptochila and its pollinator.

Ecological stability together with the suitability of abiotic conditions are crucial for long-term survival of any organism and the maintenance of biodiversity and self-sustainable ecosystems relies on species interactions. By influencing resource availability plants affect the composition of plant communities and ultimately ecosystem functioning. Plant-animal interactions are very complex and include a variety of exploitative and mutualistic relationships. One of the most important mutualistic interactions is that between plants and their pollinators. Coevolution generates clustered links between plants and their pollen vectors, but the pollination and reproductive success of plants is reduced by increase in the specialization of plant-animal interactions. One of the most specialized types of pollination is sexual deception, which occurs almost exclusively in Orchidaceae. In this form of mimicry, male insects are attracted to orchid flowers by chemical compounds that resemble insect female sex pheromones and pollinate the flowers during attempted copulations. These interactions are often species-specific with each species of orchid attracting only males of one or very few closely related species of insects. For sexually deceptive orchids the presence of a particular pollen vector is crucial for reproductive success and any reduction in pollinator availability constitutes a threat to the orchid. Because global warming is rapidly becoming the greatest threat to all organisms by re-shaping the geographical ranges of plants, animals and fungi, this paper focuses on predicting the effect of global warming on Cryptostylis leptochila, a terrestrial endemic in eastern Australia that is pollinated exclusively via pseudo copulation with Lissopimpla excelsa. As a species with a single pollinator this orchid is a perfect model for studies on the effect of global warming on plants and their pollen vectors. According to our predictions, global warming will cause a significant loss of suitable niches for C. leptochila. The potential range of this orchid will be 36%-75% smaller than currently and as a result the Eastern Highlands will become unsuitable for C. leptochila. On the other hand, some new niches will become available for this species in Tasmania. Simultaneously, climate change will result in a substantial expansion of niches suitable for the pollinator (44-82%). Currently ca. 71% of the geographical range of the orchid is also suitable for L. excelsa, therefore, almost 30% of the areas occupied by C. leptochila already lack the pollen vector. The predicted availability of the pollen vector increased under three of the climate change scenarios analysed. The predicted habitat loss is a serious threat to this orchid even with the potential colonization of Tasmania by this plant. In the reduced range of C. leptochila the pollen vector will also be present assuring fruit set in populations of this orchid. The genetic pool of the populations in New South Wales and Queensland will probably be lost.

Will Greenland be the last refuge for the continental European small-white orchid?Niche modeling of future distribution of Pseudorchis albida

Climate change affects populations of plants, animals, and fungi not only by direct modifications of their climatic niches but also by altering their ecological interactions. In this study, the future distribution of suitable habitats for the small-white orchid (Pseudorchis albida) was predicted using ecological niche modeling. In addition, the effect of global warming on the spatial distribution and availability of the pollen vectors of this species was evaluated. Due to the inconsistency in the taxonomic concepts of Pseudorchis albida, the differences in the climatic preferences of three proposed subspecies were investigated. Due to the overlap of both morphological and ecological characters of ssp. albida and ssp. tricuspis, they are considered to be synonyms, and the final analyses were carried out using ssp. albida s.l. and ssp. straminea. All of the models predict that with global warming, the number of suitable niches for these orchids will increase. This significant increase in preferred habitats is expected to occur in Greenland, but habitat loss in continental Europe will be severe. Within continental Europe, Pseudorchis albida ssp. albida will lose 44%–98% of its suitable niches and P. albida ssp. straminea will lose 46%–91% of its currently available habitats. An opposite effect of global warming was predicted for pollinators of P. albida s.l., and almost all insects studied will be subject to habitat loss. Still, within the predicted potential geographical ranges of the orchid studied, some pollen vectors are expected to occur, and these can support the long-term survival of the small-white orchid.

Insect Pollinator Monitoring in and around a Netted Plot of Apple Trees—Biosafety Implications for Genetically Engineered Fruit Trees

The complete netting of orchards is one strategy to protect fruit trees from pest and pathogen damage by reducing insect movement. When the cultivated trees were derived from genetic engineering (GE), reduced pollinator movement may also reduce outcrossing to cultivated or wild non-GE trees. We report on a field study over four years in a plot of apple tress supplied with insect side nets and covered with hail nets that were closed from shortly before flowering to harvest. A reduced number of arthropods in general, and large bees in particular, were recorded inside the netted plot compared with outside. However, wild bees colonized the plot before the net was closed and built up populations inside. An additional experiment demonstrated that small bees were able to cross the hail net. While the nets were effective in excluding large bees as active pollen vectors, the proportion of small bees acting as such remained unquantified. Furthermore, a companion study showed occasional cross-pollination events through the netting. For the field release of GE apple trees, acceptable levels of outcrossing thus need to be defined.

Flower morphology variation in five species of Penstemon (Plantaginaceae) displaying Hymenoptera pollination syndrome

Background: Geographic distance promotes phenotypic variation by facilitating environmental distance, limiting gene flow, and exposing plants to different pollen vectors. Therefore, understanding how plant morphology changes across a geographic range improves our understanding of the drivers of morphological diversification both on a macro- and micro-evolutionary scale.&#x0D; Questions: 1) How do geographic location and abiotic factors affect flower morphology between populations? 2) Is there a geographic pattern of flower morphology variation? and 3) How does yearly variation in temperature and precipitation affect flower morphology within populations?&#x0D; Studied species: Penstemon albidus, P. fruticosus, P. glandulosus, P. speciosus, and P. whippleanus&#x0D; Study site and dates: The continental USA, summers of 2017 and 2018&#x0D; Methods: Fifty-seven populations and 496 individuals were selected at random to measure ten floral traits. Bioclimatic variables were extracted from the WorldClim database and NOAA. Linear models, partial least squares regression, Mantel tests and canonical correlation analysis were used to analyze the data.&#x0D; Results: Geographic variables alone explained a significant portion of the variation in flower morphology in two species, while in others, flower morphology did not vary despite large geographic distances. Penstemon albidus and P. whippleanus flowers increase in size from south-north, while P. glandulosus and P. speciosus exhibited an east-west increasing trend. Additionally, mean annual precipitation was the most important variable influencing P. glandulosusflower morphology.&#x0D; Conclusions: Geographic distance facilitates isolation-by-distance and isolation-by-phenology as well as abiotic differences between populations; however, other factors such as pollinators might be keeping populations morphologically homogeneous despite large geographic distance.

Indicator Candidate Traits for Autonomous Fruit Set Ability Under High Temperatures in Capsicum

Abstract “Autonomous fruit set” refers to self-pollination and fruit set without pollen vectors such as vibration or insects. Autonomous fruit set under high-temperature stress is an important breeding goal as climate change can reduce fruit yields in Capsicum. We screened Capsicum cultivars for autonomous fruit set ability in a greenhouse environment and investigated pollen germination, viability, pollen grains number, chlorophyll fluorescence (Fv/Fm), style length, anther cone length, and anthesis stage under high temperatures in order to identify indicator traits for screening more genotypes with autonomous fruit set ability. The fruit set of the ‘Takanotsume’ (57.7 ± 20.6%) and ‘Goshiki Kyokko’ (52.2 ± 14.2%) cultivars (both C. annuum) were higher than those of other cultivars. Correlation analysis showed that pollen germination had the highest correlation with fruit set in C. annuum cultivars (r = 0.63). These results indicate that ‘Takanotsume’ and ‘Goshiki Kyokko’ are useful cultivars for novel breeding programs focusing on autonomous fruit sets under high temperatures, and pollen germination in C. annuum was a convincing candidate for an indicator trait of autonomous fruit set ability under high temperatures.

Transition model for the hermaphroditism-dioecy continuum in higher plants

Dioecy, characterized by the presence of distinct male and female individuals in the breeding population, has evolved independently numerous times, suggesting that a simple common mechanism may prevail behind the evolution of dioecy from hermaphroditism. In the present study, a floral sex allocation model is demonstrated for the presence of a hermaphroditism-dioecy continuum in higher plants using an N-player game model. In the continuum, we pay attention to the emergence of gynodioecy in which both hermaphroditic and female individuals coexist in the breeding population, and trioecy which includes hermaphroditic, male and female individuals in the breeding population, as these have often been considered as an intermediate step in the evolution of dioecy from hermaphroditism and vice versa. In the N-player game model, we assumed a local breeding population containing N players with different reproductive investment, and there is a trade-off between the reproductive investment to male function and female function at individual level. Furthermore, we focused on the uncertainty of pollen transportation, as dioecy is often linked to both the unreliable pollen vectors and harsh environment for pollinators. The pollen transport efficiency was explained by the probability of the pollen hitting ovules or stigmata. In the model, setting hypothetical populations with different population sizes, we showed the Nash solutions for dioecy appeared at a smaller pollen transport efficiency than for hermaphroditism in all hypothetical populations. Since the low pollen transport efficiency equals the low reliability of pollen vectors, the result is comparable with the pollinators of real dioecy such as water, wind and opportunistic species. The Nash solution for gynodioecy and trioecy was obtained at the transition zone between dioecy and hermaphroditism in the continuum. The number of male and female individuals in dioecy were almost stable in the range of low pollen transport efficiency. If the number of males decreased with increasing pollen transport efficiency, hermaphroditic individuals emerged in the population (establishment of trioecy). Gynodioecy established as soon as no males were left in the population. Finally, hermaphroditism established at the time no females were left in the population. These results imply that pollen transport efficiency played an important role of obtaining a variety of Nash solutions in the model. Though the Darwinian paradigm in evolutionary ecology of dioecy is based on the various aspects of the interaction between environment and species-specific characters, our model is composed of numerical interactions between and within individuals. In this paper, we argue that the association between the continuum and the pollen transport efficiency is reflected in the real world.