Pollen Recipient Research Articles

Effect of heterospecific pollen deposition on pollen tube growth depends on the phylogenetic relatedness between donor and recipient.

Co-flowering plant species may interact via pollinators leading to heterospecific pollen transfer with consequences for plant reproduction. What determines the severity of heterospecific pollen effect on conspecific pollen performance is unclear, but it may depend on the phylogenetic relatedness of the interactors (pollen donors and recipient). The heterospecific pollen effect might also depend on the extent to which plants are exposed to heterospecific pollen over ecological or evolutionary timescales. For instance, generalist-pollinated plant species might tolerate heterospecific pollen more than specialists. Here, we tested whether heterospecific pollen effects are stronger between closely related species than phylogenetically distant ones in a tropical highland community. Then, based on these results, we determined whether responses to heterospecific pollen were stronger in generalized vs. specialized plant species. We applied heterospecific pollen from close (congeneric) or distant (different families) donors alone or with conspecific pollen on stigmas of three recipient species (one generalist, Sisyrinchium wettsteinii; and two specialists, Fuchsia campos-portoi and Fuchsia regia) and scored pollen tube performance in styles. In all species, pollen from closely related donors grew pollen tubes to the base of the style indicating a high potential to interfere with seed set. Conversely, distantly related heterospecific pollen had no effect on either specialist Fuchsia species, whereas enhanced performance of conspecific pollen was observed in generalist S. wettsteinii. The strong effect of phylogenetic relatedness of donor and recipient might have obscured the role of pollination specialization, at least for the three species examined here. Therefore, phylogenetic relatedness mediated the effect of heterospecific pollen on post-pollination success, with possible consequences for reproductive trait evolution and community assembly for further studies to explore.

Inheritance of breeding system in Cakile (Brassicaceae) following hybridization: implications for plant invasions.

Hybridization is commonly assumed to aid invasions through adaptive introgression. In contrast, a recent theoretical model predicted that there can be non-adaptive demographic advantages from hybridization and that the population consequences will depend on the breeding systems of the species and the extent to which subsequent generations are able to interbreed and reproduce. We examined cross-fertilization success and inheritance of breeding systems of two species in order to better assess the plausibility of the theoretical predictions. Reciprocal artificial crosses were made to produce F1, F2 and backcrosses between Cakile maritima (self-incompatible, SI) and Cakile edentula (self-compatible, SC) (Brassicaceae). Flowers were emasculated prior to anther dehiscence and pollen was introduced from donor plants to the recipient's stigma. Breeding system, pollen viability, pollen germination, pollen tube growth and reproductive output were then determined. The results were used to replace the assumptions made in the original population model and new simulations were made. The success rate with the SI species as the pollen recipient was lower than when it was the pollen donor, in quantitative agreement with the 'SI × SC rule' of unilateral incompatibility. Similar outcomes were found in subsequent generations where fertile hybrids were produced but lower success rates were observed in crosses of SI pollen donors with SC pollen recipients. Much lower proportions of SC hybrids were produced than expected from a single Mendelian allele. When incorporated into a population model, these results predicted an even faster rate of replacement of the SC species by the SI species than previously reported. Our study of these two species provides even clearer support for the feasibility of the non-adaptive hybridization hypothesis, whereby the colonization of an SI species can be assisted by transient hybridization with a congener. It also provides novel insight into reproductive biology beyond the F1 generation.

Who determines the timing of inflorescence closure of a sexual dandelion? Pollen donors versus recipients

Male–male competition for mating or fertilization opportunities may in theory select for male manipulative adaptation that can harm males’ mates, leading to sexual conflict. Evolutionary theory predicts that selection will favor the manipulation by pollen of the duration of its recipients’ receptivity. However, there is insufficient evidence to show that pollen can exert effects on the duration of receptivity, a prerequisite for the evolution of pollen manipulative adaptation. Using a sexual diploid dandelion, Taraxacum japonicum, we conducted hand pollination experiments within and between populations to examine the effects of pollen on the timing of inflorescence (flower head) closure. We also examined the potential fitness consequences to the pollen recipients by field observation of seed production in populations with different inflorescence closure timing. Within-population experiments showed that pollination induced inflorescence closure even when some of the florets in the inflorescence were not yet pollinated with compatible pollen. Furthermore, between-population crosses revealed that pollen donors, recipients, and their interaction all influenced the timing of inflorescence closure. Different populations differed in the timing of inflorescence closure, which could affect the availability to the recipients of pollen for fertilization and thereby seed production. However, there were no significant differences in the rates of natural seed production in these populations. Our results demonstrate that pollen donors, as well as recipients, contribute to the duration of floral receptivity. We discuss the implications of our findings to the evolutionary theory of plant reproduction.

Hermaphroditism promotes mate diversity in flowering plants.

PremiseGenetically diverse sibships are thought to increase parental fitness through a reduction in the intensity of sib competition, and through increased opportunities for seedling establishment in spatially or temporally heterogeneous environments. Nearly all research on mate diversity in flowering plants has focused on the number of fathers siring seeds within a fruit or on a maternal plant. Yet as hermaphrodites, plants can also accrue mate diversity by siring offspring on several pollen recipients in a population. Here we explore whether mate composition overlaps between the dual sex functions, and discuss the implications for plant reproductive success.MethodsWe established an experimental population of 49 Mimulus ringens (monkeyflower) plants, each trimmed to a single flower. Following pollination by wild bees, we quantified mate composition for each flower through both paternal and maternal function. Parentage was successfully assigned to 240 progeny, 98% of the sampled seeds.ResultsComparison of mate composition between male and female function revealed high mate diversity, with almost no outcross mates shared between the two sexual functions of the same flower.ConclusionsDual sex roles contribute to a near doubling of mate diversity in our experimental population of Mimulus ringens. This finding may help explain the maintenance of hermaphroditism under conditions that would otherwise favor the evolution of separate sexes.

Water influences how seed production responds to conspecific and heterospecific pollen.

Outcrossing species depend on pollen from conspecific individuals that may not be exposed to the same abiotic conditions as maternal plants. Additionally, many flowers receive heterospecific pollen, which can also influence seed production. Studies aimed to understand how abiotic conditions influence seed production tend to focus on maternal conditions and leave unexplored the effect of abiotic conditions experienced by pollen donors. We tested how water availability to pollen donors, both conspecific and heterospecific, influenced the seed production of recipient plants exposed to different water availability regimes. In a greenhouse setting we manipulated the water availability (low- or high-water treatment) to potted recipient plants (Phacelia parryi), to conspecific pollen donors, and to heterospecific pollen donors (Brassica nigra). We hand pollinated recipient plants with different pollen mixes that represented all combinations of conspecific pollen mixed with heterospecific pollen. From these hand pollinations we determined the amount of pollen that was transferred, pollen volume, pollen shape, and seed production. Higher water availability to conspecific pollen donors led to higher seed production. Under low water availability to heterospecific pollen donors, seed production was unaffected by recipient or conspecific pollen donor treatment. Under high water availability to heterospecific pollen donors, seed production was highest when conspecific pollen donors and pollen recipients also received the high-water treatment. Environmental conditions of pollen donors can influence the seed production of maternal plants. These results illustrate potential impacts of environmental heterogeneity on post-pollination events that lead to seed production and thus impact a pollinator's contribution to plant fitness.

Watermelon general and specific combining ability

The combining ability of six watermelon genotypes was estimated in a diallel cross scheme (6x6), including genotypes JNY (1), ‘ORA’ (2), ‘KOD’ (3), ‘SOL’ (4), ‘CHG’ (5), ‘PEA’ (6) and all possible hybrids between them. A randomized complete block design (RCB) was used, with 36 treatments, three blocks, and plots with five plants. The following traits were evaluated: days before female flower anthesis, main branch length, fruit mass, number of fruits per plant, yield, fruit length, fruit width, pulp firmness, soluble solids content, average rind thickness, seed length, seed width, and seed mass. The data obtained were submitted to analysis of variance, and a diallel analysis was performed according to Griffing’s experimental method I. According to the general combining ability estimates obtained, genotypes ‘KOD’ (3) and ‘JNY’ (1) were the most likely ones to produce hybrids with smaller-sized fruits and smaller seeds. The reciprocal effects confirmed that the results indicate that these genotypes should be used as pollen donors and pollen recipients, respectively. On the other hand, genotypes ‘ORA’ (2) and ‘CHG’ (5) can be used for the commercial exploitation of sliced ​​watermelons. According to the specific combining ability estimates obtained, the combinations ‘ORA’ (2) x ‘PEA’ (6), ‘ORA’ (2) x ‘JNY’ (1), ‘CHG’ (5) x ‘KOD’ (3), ‘PEA’ (6) x ‘KOD’ (3), and ‘CHG’ (5) x ‘SOL’ (4) stood out as being the genotypes most likely to produce the smallest fruits and smallest seeds.

Interactive effects between donor and recipient species mediate fitness costs of heterospecific pollen receipt in a co-flowering community.

Evaluation of pollen transfer in wild plant communities revealing heterospecific pollen receipt is common, yet experimental hand pollinations have revealed high among-species variation in the magnitude of its effect on recipient fitness. The causes of this among-species variation are unknown, however, prompting the investigation of underlying factors. Here, we conducted a hand-pollination experiment with ten co-flowering species to determine whether the effects of heterospecific pollen receipt are mediated by the pollen donor or recipient species alone, or whether the effects are determined by the interaction between them. We further assessed species traits potentially mediating interactive effects in heterospecific pollen receipt by evaluating the relationship between heterospecific pollen effect size and three different predictors reflecting a unique combination of pollen donor and recipient characteristics. Our results show, for the first time, that the magnitude of the heterospecific pollen receipt effect is determined by the specific combination of donor and recipient species (i.e., interactive effects). However, we were unable to uncover the specific combination of traits mediating these effects. Overall, our study provides strong evidence that an understanding of heterospecific pollen receipt effects based on recipient or donor characteristics alone may be insufficient. This study is an important step toward an understanding of consequences of heterospecific pollen receipt in co-flowering communities.

Production and performance of sugarcane seeds (caryopses) from different hybridizations involving RB92579.

A major challenge in sugarcane breeding program is the obtaining of enough number of seeds (caryopses) for the development of new improved cultivars. Genotypes differ in their function as pollen recipient and pollen donor, which also affect the seed performance. Thus, the aim of this study was to verify the production and performance of sugarcane seeds from different hybridizations involving RB92579 as pollen recipient and pollen donor. Twelve bi-parental crossings were carried out involving RB92579 and other different genotypes randomly chosen. Seed production potential was evaluated by percentage of fertile spikelets and caryopsis fresh weight. The seed physiological potential was determined by evaluating germination and vigor (index of germination rate, number of normal seedlings per gram of fuzz, and seedling dry weight). The results showed better performance for RB92579 as pollen donor for all characteristics studied. Therefore, RB92579 sugarcane cultivar should be used as pollen donor during hybridizations, condition that permits a greater production and physiological performance of seeds for the sugarcane breeding programs.

Molecular evidence of bidirectional introgression between Quercus suber and Quercus ilex

Abstract: Cork oak and holm oak share a large part of their natural range, and are known to hybridize in mixed stands. This hybridization is supposed to have played a relevant role in the past history of cork oak. Previous research has reported that F1 hybrids are produced with holm oak acting as pollen recipient, therefore carrying holm oak chloroplast. Additionally, F1 hybrids have been assumed to be pollinated mostly by cork oak. Continued backcrossing of F1 hybrids with cork oak (supported by flowering phenology) could have created the organellar introgression patterns observed nowadays in Eastern Spain and Southern France cork oak populations. On the contrary, no organellar introgression has been detected in holm oak and multiple generation backcross individuals to holm oak have not been reported so far. In this work, we examined whether hybrids preferentially backcross with cork oak or with holm oak. To reach this goal, we genotyped by using eight microsatellite loci the progeny of four cork and four holm oak trees (33 and 44 half-siblings, respectively), and of four hybrids (468 half-siblings) collected over three years from a natural mixed population. We used the STRUCTURE software to estimate the proportion of the genotype of each seedling inherited from cork oak (qs) or from holm oak (qi). The ratio of the offspring q value over the mother q value helped determine the source of pollen that originated each acorn. Our results show for the first time that hybrid trees can be effectively pollinated by both parental species. Additionally, each hybrid tree was predominantly pollinated by the most abundant oak species in its vicinity. These results confirm the occurrence of bidirectional introgression, previously suggested for adult hybrid trees in the field, and point out the pattern of introgression in the seedlings could be most affected by the abundance of the parental species.

Effect of pollination on dropping of flowers and fruits in new quince ( Cydonia oblonga Mill.) cultivar and promising genotypes

Abstract Access to sufficient and good quality fruits and solving problems such as early abscission of the fruitlets depends on the status of self-fertility and self-incompatibility in cultivars and genotypes and determination of the best pollinizer for them. This research was carried out to study the best pollinizer for some quince cultivars and promising genotypes from the collection of germplasm at the Horticultural Research Station of Isfahan, Iran in 2015 and 2016. For this, the effects of the pollen donor parent, including ‘Vidoja’, KVD2, KVD4, ‘Isfahan’, ‘Torsh’ and also open pollination were studied on quantitative and qualitative characteristics of the pollen recipient parent, including ‘Vidoja’, KVD2 and KVD4 as a factorial experiment in a randomized complete block design with four replications. To determine the best pollinizer, flowers of pollen recipient parents were emasculated at the balloon stage and were covered with isolation bags. Emasculated flowers were crossed with the pollen of donor parents during receptability of stigmas as well as hand self-pollination for each female parent. Results showed that some traits such as percentage of fruit set, seed numbers and total soluble solids (TSS) were affected by the pollen source. Phenol and pectin were not affected by the foreign pollen sources. According to the results, self-pollination did not have acceptable fruit set. The best pollen source for the ‘Vidoja’ was KVD2, for KVD4 was ‘Torsh’ and ‘Vidoja’ and for KVD2 was KVD4 and ‘Vidoja’, therefore the cultivation of all three female parents together in the quince orchards is recommended.

Study on Pollination and Selection of the Most Suitable Pollinizers for Commercial Pear Cultivars (Pyrus communisL.) in Iran

AbstractThe cultivated pear is an economically important fruit tree species of genusPyrusin which often gametophytic self-incompatibility occurs. Therefore, this species need to be pollinated by cross-compatible cultivars that bloom in the same time. Selection of appropriate pollinizers for pear cultivars is very important to produce commercial yield. ‘Sebri’, ‘ Shahmiveh’ and ‘Natanzi’ are the best commercial cultivars in Iran, but the lack of a suitable source of pollen can reduce productivity. In order to select the most suitable pollinizer for these pear cvs, an experiment was conducted in which they were considered as pollen recipients and ‘Coscia’, ‘Bartlett’ and ‘Sardroud’ along with ‘Sebri’, ‘Shahmiveh’ and ‘Natanzi’ were evaluated as pollen donors. This research was conducted as a factorial experiment in randomized complete block design for four years. Recipient and donor cultivars had almost overlapping flowering time. The flower buds on selected branches were emasculated at balloon stage and then were counted and isolated with cotton tissue bags. Pollen grains of these pollinizers were collected in the laboratory. Isolation bags were taken off from the branches and emasculated flowers were pollinated with pollen grains of listed pollinizers during receptibility of stigma. The number of pollinated flowers was counted, and branches were covered again with the bags. The results showed that for ‘Sebri’ the best pollinizer was ‘Coscia’ with 5.7% fruit set, for ‘Shahmiveh’ ‘Bartlett’ cv. with 5.8% of fruit set and for ‘Natanzi’, ‘Shahmiveh’ with 5.5% of fruit set.

Coexistence in Oilseed Rape: Effect of Donor Variety Type and Discarding Field Edges

Oilseed rape is one of the most important sources of vegetable oil worldwide. Approximately 24% of the world’s total cultivation area in 2015 was planted with genetically modified (GM) varieties. Until now the cultivation of GM oilseed rape in the EU is not approved since coexistence of GM and non-GM oilseed rape is a matter of significant public concern. One reason is the differing information about pollen-mediated gene flow in this crop species. Therefore, in a 3-year field trial we investigated gene flow using a GM-free marker system consisting of a high erucic acid oilseed rape (HEAR) variety as pollen donor and a low erucic acid oilseed rape (LEAR) variety as pollen recipient. Donor and receptor fields were equally-sized (75 by 100 m or 0.75 ha) and separated by an isolation distance of 20 m clover-grass. Two different HEAR varieties, a hybrid variety and a line variety, were compared as pollen donor. Generally, outcrossing rates at 1 m field depth were significantly highest. A significant decrease in outcrossing was observed in the first donor-facing 20 m of recipient fields, with no further significant decrease in field depths > 20 m. Outcrossing rates of the total field harvest never exceeded 0.25%. Due to irregular patterns of outcrossing, a separated harvest of the receptor field edge facing the donor plot only marginally reduced the GM content in the total harvest.

Estimation of outcrossing rates in intraspecific (Oryza sativa) and interspecific (Oryza sativa × Oryza glaberrima) rice under field conditions using agro-morphological markers

Rice is mainly a self-pollinating crop, but some outcrossing has been reported. Outcrossing with an undesirable donor would lead to the creation of segregants or off-types, which would adversely affect genetic purity and uniformity of the crop. Outcrossing rates in rice under field conditions were investigated using cultivar WAB96-1-1 as a pollen donor and WAB56-104, NERICA 2, NERICA 4 and NERICA 7 as pollen recipients. Levels of outcrossing were investigated up to 30 m from the pollen donor. Dominant morphological markers of red kernel colour and pubescent leaves of the donor were used to identify hybrids. A total of 721 134 plants were investigated. There was an average outcrossing rate of 0.7 ± 0.51%, with a potential outcrossing rate of 2.45 ± 0.86%. Outcrossing rates decreased with increase in distance. It ranged from 2.45% at 0.2 m from the donor to 0.05% at 25 m from the donor. Differences were observed between genotypes and seasons. In season 1 the highest average outcrossing rate of 1.2 ± 0.63% was with WAB56-104 and in season 2 it was 1.1 ± 0.69% with NERICA 4. Outcrossing occurred up to 30 m from the donor. This has implications for germplasm management and conservation and the production of high quality seed. Spatial isolation remains the most practical method to prevent undesirable gene flow. The study indicated that red kernel colour and leaf pubescence can be used to effectively assess outcrossing under field conditions in rice.

Pollen-Mediated Movement of Herbicide Resistance Genes in Lolium rigidum

The transfer of herbicide resistance genes by pollen is a major concern in cross-pollinated species such as annual ryegrass (Lolium rigidum). A two-year study was conducted in the greenhouse, under favorable conditions for pollination, to generate information on potential maximum cross-pollination. This maximum cross-pollination rate was 56.1%. A three-year field trial was also conducted to study the cross-pollination rates in terms of distance and orientation to an herbicide-resistant pollen source. Under field conditions, cross-pollination rates varied from 5.5% to 11.6% in plants adjacent to the pollen source and decreased with increasing distances (1.5 to 8.9% at 15 m distance and up to 4.1% at 25 m in the downwind direction). Environmental conditions influenced the cross-pollination both under greenhouse and field conditions. Data were fit to an exponential decay model to predict gene flow at increasing distances. This model predicted an average gene flow of 7.1% when the pollen donor and recipient plants were at 0 m distance from each other. Pollen-mediated gene flow declined by 50% at 16.7 m from the pollen source, yet under downwind conditions gene flow of 5.2% was predicted at 25 m, the farthest distance studied. Knowledge of cross-pollination rates will be useful for assessing the spread of herbicide resistance genes in L. rigidum and in developing appropriate strategies for its mitigation.

Variability in seed oil content and fatty acid composition, phenotypic traits and self-incompatibility among selected niger germplasm accessions

AbstractNiger (Guizotia abyssinica, L.) is a desirable oilseed crop for birdseed, especially for finches (Spinusspp.) because of its high ratio of unsaturated to saturated fatty acids and relatively high oil content. In 2012, phenotypic traits, seed oil and fatty acid content measurements were made on 14 plant introductions (PIs) from the United States Department of Agriculture germplasm collection. The PIs originated in Ethiopia (ten), India (three) and USA (one). The phenotypic traits analysed included seed/plant, branches/plant, capitula/plant1, average seed/capitulum and plant height. After initial assessments of the 14 PIs, three were selected for use as parents to produce two one-way and two two-wayF1crosses for the purpose of evaluating self-incompatibility (SI). Parent andF1progeny seeds were planted in a greenhouse and transplanted to a field site at the East Tennessee Research and Education Center (2012, 2013 and 2014). Comparisons from 2012 showed seed oil of the 14 PIs ranging from 32.9 to 37.9% (PI 508076 (Ethiopia) and PI 509436 (India), respectively). Major fatty acids included stearic, palmitic, oleic and linoleic; with linoleic acid in highest amount. PI508079 (Ethiopia) had the best combination of seed yield, seed oil and linoleic acid content. Over 2013 and 2014, SI ranged from 91.1 to 100.0%. W6 18860 (USA) had the most self-compatibility, and theF1plants generated from crosses between W6 18860 and other plants tended to be self-compatible when the former was used as a pollen recipient. The results obtained from this study should be useful for niger breeding and production purposes.

Pollen competition in style: Effects of pollen size on siring success in the hermaphroditic common morning glory, Ipomoea purpurea.

Pollen size varies greatly among flowering plant species and has been shown to influence the delivery of sperm cells to the eggs. Relatively little is known, however, about the functional significance of within-species genetic variation in pollen size. This study tests whether pollen size influences the relative siring success of a pollen donor during in vivo pollen competition experiments. We used two groups of Ipomoea purpurea plants genetically divergent in their pollen sizes and applied equal number of pollen grains from one large-pollen and one small-pollen donor onto the same stigma. Using microsatellite genetic markers, we identified the pollen parent of each of the resulting progeny to determine the relative siring success of the competing donors. Competitions between donors of equal-sized pollen served as a control. Differences in pollen size significantly affected the relative siring success of a pollen donor; larger-grained individuals outcompeted smaller-grained competitors but not equal-sized competitors. Relative siring success, however, sometimes varied across different pollen recipients. Pollen size can influence the relative siring success of different individuals competing on the same stigma during postpollination processes. However, other factors, such as pollen-pistil interaction and environmental conditions, are likely to influence these competitions as well.

Gene flow from herbicide resistant genetically modified rice to conventional rice (Oryza sativa L.) cultivars

Rice (Oryza sativa L.) is an important feeding crop in Asia, and utilization of genetically modified (GM) rice is highly demanding. For co-existence of GM rice and non-GM rice, the proper confinement measures should be provided. Thus, we surveyed gene flow from herbicide resistant GM rice to the conventional rice cultivars in the field tests. Gene flow frequency decreased with increasing distance between the pollen donor and recipients and did not exceed more than 1% even at the nearest distance. In single recipient model plot, a maximum gene flow frequency was observed at the shortest distance and hybrid was detected up to 12 m from the pollen donor. The direction of gene was coincided with the dominant wind direction. Gene flow assessment to multiple recipient plots was conducted under the high raining season by chance, and abrupt decline of gene flow frequency and maximum distance were resulted. According to the survey results, current regulation for isolation distance is reasonable for environmental safety or for general crop production. However, we suggest an alternative measure for GM rice cultivation that should be supplemented to overcome the out of estimation and in the environment asking higher security levels.

Outcrossing Potential between U.S. Blackhull Red Rice and Indica Rice Cultivars

Weedy red rice is a major weed pest of rice in the southern United States. Outcrossing between red rice and commercial tropical japonica rice cultivars has resulted in new weed biotypes that further hinder the effectiveness of weed management. In recent years, indica rice has been used increasingly as a germplasm source for breeding and for reduced-input systems in the United States, but little is known about its outcrossing potential with U.S. weedy red rice biotypes. In a 2-yr study, simple sequence repeat marker analysis was used to show that blackhull (BH) red rice (PI 653424) outcrossing to four, late-maturing indica cultivars averaged 0.0086% and ranged from 0.002% for ‘TeQing’ to 0.0173% for ‘4484’ (PI 615022). Rates of outcrossing to a tropical japonica cultivar standard, ‘Kaybonnet’ (0.032%), were substantially greater than for the indica cultivars. These differences in outcrossing were due largely to synchronization of flowering times between rice and red rice, with Kaybonnet and TeQing exhibiting the greatest and least synchronization, respectively. Outcrossing rates also may have been affected by rice–red rice flower density differences within the rice plots. Outcrossing from cultivated rice to the red rice (as pollen recipient), which was taller than all rice cultivars, was undetectable in these studies, and environmental conditions (e.g., temperature, humidity, solar radiation, and rainfall) were not strongly correlated with the outcrossing rates observed. Grain yields of the original BH red rice line were greatest in the Kaybonnet plots, demonstrating that the indica cultivars were superior competitors against this weed. Collectively, these results suggest that red rice biotypes that flower synchronously with rice cultivars are a potential source of pollen for outcrossing and gene flow in rice fields in the southern United States.

High male fertility in males of a subdioecious shrub in hand-pollinated crosses.

Female reproductive success in females versus hermaphrodites has been well documented. However, documenting a potential advantage in male fertility of male versus hermaphrodite individuals in subdioecious species is also essential for understanding the evolutionary pathway toward dioecy from hermaphroditism via gynodioecy. Siring success in terms of fruit set, fruit mass, number of seeds and mean seed mass was compared by hand-pollinated crosses in the subdioecious shrub Eurya japonica The pollen was from male and hermaphrodite individuals, and the pollen recipients were females and hermaphrodites. Seed quality was also evaluated in terms of seed germination rate, seed germination day and seedling survival. Overall, pollen from males sired more fruits of larger size and more seeds than did pollen from hermaphrodites. The male advantage was observed when pollen recipients were females, whereas no effect was found in hermaphrodite recipients. Pollen from males also produced better quality seeds with higher germination rate and sooner germination day. Although these results could also be explained by a higher pollen load for crosses with male pollen donors, we took care to saturate the stigma regardless of the pollen donor. Therefore, these results suggest that male individuals of E. japonica have advantages in male fertility in terms of both quantity and quality. Our previous studies indicated that females exhibit higher female reproductive success compared with hermaphrodites. Thus, both the female and male functions of hermaphrodites are outperformed by females and males, respectively, raising the possibility that the subdioecious E. japonica at this study site is entering the transitional phase to dioecy along the gynodioecy-dioecy pathway.

Spatial dynamics of pollination in dioecious Shepherdia canadensis (Elaeagnaceae)

The immobility of plants and the need for third-party vectors to enact pollen transfer render pollination an inherently spatial process. Little is known about the spatial scales over which pollen transfer and plant reproductive success are dependent on mate availability in natural plant populations. Dioecious plants provide useful study systems for examining the dependence of reproductive success on spatial patterns of mate availability because potential pollen donors and recipients are unambiguous. We examined the spatial dynamics of pollination in the dioecious shrub Shepherdia canadensis (L.) Nutt. (Elaeagnaceae) at a range of spatial scales in Ivvavik National Park, Canada. On average, males occurred at higher frequencies than females across ten study sites with at least 60 S. canadensis plants per site. Although we detected substantial variation in sex ratios across sites, there was no association between sex ratio and fruit set. Instead, patterns of fruit set were significantly correlated with male density within sites, over distances of 4–6 m. The density of females and males was spatially cross correlated. Therefore, density effects appear to be driven by pollinator responses to the overall density of shrubs. A pollinator exclusion experiment indicated that syrphid flies (Family: Syrphidae) were the most important pollinators in these populations. This study demonstrates that female reproductive success in S. canadensis is limited by plant density over small spatial scales, corresponding with the short foraging distances characteristic of its fly pollinators.