High Levels Of Outcrossing Research Articles

Genetic characterization of global collection of flax (L. Usitatissimum L.) utilizing molecular marker

In assess the sufficient knowledge of genetic diversity, population structure and linkage disequilibrium were estimated among the three representative sub-population: Pop 1 (Indian accessions), Pop 2 (different species of Linum genus) and Pop 3 (exotic accessions) of flax using ISSR marker systems. A total of 118 number of alleles were amplified by eleven primers, with an average of 10.64 alleles per primer (100 bp −2072 bp). The maximum PIC value (0.25) was observed in the primer combination UBC808, which indicated that it as the most informative primer among the eleven primers to study genetic diversity among flax genotypes. The results of the AMOVA indicated that genetic variation within sub-populations (92%) was significantly higher than the variation among the sub-population (8%). According to the results of split network tree analysis, population structure and PCA, the total 264 flax accessions were distinctly clustered into eight genetic groups. Overall the mean LD value was less than the threshold level (r2 < 0.1) explaining that the population has a high level of outcrossing or gene flow. The knowledge generated through ISSR fingerprinting in this study has enhanced our conception of population structure and LD of the flax population, which has high implications for genetic improvement and association mapping.

Temporal diversification and no geographic population structure in the most abundant European ectomycorrhizal fungus Russula ochroleuca

Abstract Although Russula ochroleuca is a common ectomycorrhizal (ECM) species in European forests, its reproduction mode, dispersal range, and population structure remains unknown. Altogether, 462 fruit bodies from three spruce forests (two 15 km apart, one 230 km distant from the first two) were analysed using AFLP markers. A mixed mode of reproduction, with several large genets accompanied by a majority of single fruit body genets, was found. Low level of inbreeding (Fis = 0.0021–0.0072), low level of genetic differentiation among subpopulations (PhiPT = 0.037–0.190) and negligible isolation by distance (r = 0.033, P = 0.005) indicates effective spore dispersal and a high level of outcrossing across the sampled area. Finally, we discovered temporal diversification within this species, as evidenced by genetic differentiation between early (August) and late (September) fruiting genotypes.

Migrant pool model of dispersal explains strong connectivity of Avicennia officinalis within Sundarban mangrove areas: Effect of fragmentation and replantation

The ability of mangrove trees to reproduce and disperse in highly dynamic tidal environments is reflected in the contemporary genetic diversity and structure of their populations. Resilience and establishment may occur through either local recruitment (propagule pool model) or over longer distances with mixed origins (migrant pool model), thereby affecting the connectivity between natural populations. Anthropogenic activities such as encroachment and fragmentation or from mitigating reforestation could cause strategy switches and thus the connectivity and genetic structure of populations. In this study, we considered Avicennia officinalis, a dominant component of the Sundarban mangrove forest in Bangladesh to estimate dispersal dynamics over various distances within estuaries. A total of 423 individuals of A. officinalis, distributed over thirteen sites in the Sundarbans were sampled at both large and fine-scaled spatial level, the latter for comparison of natural and dense with fragmented sites. Up to 62 alleles showed a comparable level of allele diversity and gene diversities at both juvenile and adult life stages, assuming overall high levels of outcrossing. Significant inbreeding levels and high kinship values were solely observed at a reforested A. officinalis site. Genetic variables revealed high levels of connectivity between sites at close vicinity, with only a weak structure over larger geographic distances, between natural core Sundarban and coastal edge populations. Kinship coefficients were mostly low though significant up to several kilometers along estuarine branches, thereby suggesting propagule dispersal beyond each site. A fine-scaled analysis of kinship levels estimated for fragmented and natural forest plots along both sides of a river revealed that fragmentation induced higher kinship levels over 25–50 m distance, whereas dense natural populations were composed of less related individuals at shortest distances. A. officinalis populations might stay resilient through a mixture of unrelated propagules, clearly adhering a migrant pool model in natural sites and propagule pool model in fragmented sites. A poor gene diversity of planted trees might jeopardize the sustainability of mangrove plantation practices. Furthermore, high levels of diversity and connectivity indicated that the core Sundarban populations are a relevant source of germplasm in afforestation programmes.

Genetic Diversity of Natural Crossing in Six Cotton Cultivars

We have previously shown genetic diversity in mature cotton (Gossypium hirsutum L.) pollen sensitivity to low humidity. In vitro studies showed reduced pollen germination and pollen tube growth under low humidity. The present study investigated the impact of pollen sensitivity to low humidity on the amount of outcrossing to neighboring plants. We utilized “red” and “green” pigmented cotton, in addition to gossypol glanded and glandless cotton cultivars, to study pollen movement in the field. Genetic diversity in outcrossing was observed among the six cultivars tested. Differences in outcrossing of 5 to 15% were observed under both irrigated and dryland production systems. Higher levels of outcrossing were observed within a row compared to outcrossing between rows. Cotton cultivars with mature pollen sensitive to low humidity exhibited reduced outcrossing compare to cultivars that were less sensitive to low humidity. These results suggest that cultivars with pollen sensitive to low humidity can be used to reduce natural outcrossing and subsequently adventitious presence in adjacent fields throughout the Southwest.

English

&nbsp; Genetic relationships of two wild&nbsp;Vigna&nbsp;species,&nbsp;Vigna mungo&nbsp;var.&nbsp;silvestris&nbsp;andVigna hainiana,&nbsp;with accessions of a cultivated species,&nbsp;V. mungo&nbsp;known as urdbean or blackgram was studied with a view of using them as a donor of alien stress resistance genes in future breeding. POPGENE analysis conducted on a total of 375 individuals of 25 accessions using sequence tag microsatellite markers (STMS) revealed effective number of alleles varying from 3.0 to 1.7. The mean values of observed and expected heterozygosity were 0.084 and 0.335, respectively. Average Wright&rsquo;s fixation indices were: FIT&nbsp;= 0.710, FST&nbsp;= 0.840 and FIS&nbsp;= -0.84, indicating high level of outcrossing and genetic differentiation with limited gene flow between and within the three taxa studied. The&nbsp;Nm&nbsp;value for the accessions was found to be negligible, suggesting no gene flow within populations. For the groups,&nbsp;Nm&nbsp;value for&nbsp;V. mungo&nbsp;was 0.464, which was more than that of both&nbsp;V. radiata&nbsp;var.&nbsp;silvestris&nbsp;and&nbsp;V. hainiana. Since&nbsp;V. mungo&nbsp;is a cultivated species, it showed the highest within-species gene flow. Ewens-Watterson test for neutrality was done using 1000 simulated samples. All the loci were neutral to selection pressure as their observed F value was between lower and upper 95% limit. &nbsp; Key words:&nbsp;Species relationships,&nbsp;Vigna mungo,&nbsp;microsatellite marker, blackgram.

Mating system in Mexican populations of the annual herb Solanum rostratum Dunal (Solanaceae)

Traditionally, annual colonising species are expected to have high rates of self-fertilisation, although recent theoretical and empirical studies have shown that cross-fertilisation can be selected for under heterogeneous pollination environments. Solanum rostratum is a self-compatible annual herb that colonises disturbed habitats. Despite the lack of physiological mechanisms to prevent self-fertilisation, pollen transfer between individuals is expected to be favoured because of its complex floral morphology. In previous studies of S. rostratum it has been shown that anther dimorphism within flowers results in precise pollen placement on the pollinator's body, and the presence of mirror-image floral morphs within plants promotes outcrossing in experimental arrays. However, the mating system of natural populations of S. rostratum has never been assessed, and thus whether it is predominantly selfing or outcrossing remains unknown. We hypothesise that floral and inflorescence morphology of S. rostratum should facilitate cross-fertilisation, making it a predominantly outcrossing despite its lack of a self-incompatibility system. To test this hypothesis, we estimated outcrossing rates by genotyping 700 individuals at 13 microsatellite loci, sampled from four populations across a 690-km transect in the species' native range. We found that populations had mean outcrossing rates of 0.70±0.03, with multiple sires contributing to paternity of each progeny array (average effective number of sires=8.97±0.57). This indicates that natural populations S. rostratum have relatively high levels of outcrossing, probably facilitated by its floral and inflorescence morphology. We speculate that partial selfing in this species may be an unavoidable consequence of displaying multiple flowers at the same time (geitonogamy), as well as the result of self-pollen transfer by illegitimate visitors.

Self-interference is reduced in a secondary pollen presentation species, Duperrea pavettifolia (Rubiaceae)

Occurrence of secondary pollen presentation (SPP) is evidenced for Duperrea pavettifolia. For this, self-pollen was presented on the stigma and reduced fertilization was observed in this case. The receptive area located in the furrow of the stigma becomes receptive from the third day of elongation growth. Fruit set upon hand pollination with pollen from other individuals was significantly higher than the results of selfed, bagged, emasculated and control treatments. However there was no difference in pollen tube growth rate between selfed and crossed pollen on a receptive stigma. Hawkmoths and butterflies were effective pollinators for D. pavettifolia, but the visiting frequencies were very low. Stingless bees removed pollen from the unreceptive stigma which had no contribution to reproductive success. High level of outcrossing in D. pavettifolia was demonstrated by molecular analyses using the simple sequence repeats (SSR) method. Although the wild populations of D. pavettifolia are small and with fragmented distribution, the genetic diversity of seedlings was high, with fluctuations among years. Our results indicated that protandry and the visitation of stingless bees reduced the amount of self-pollen on the still unreceptive stigma and self-incompatibility prevented fertilization by un-removed self-pollen.

Reproductive Ecology of Male and Female Strobili and Mating System in Two Different Populations ofPinus roxburghii

We studied several flowering traits, namely, male-female cone phenology, male-female cone production per tree, mating system, sex ratio, air-borne pollen grains and pollen migration, over four successive years in two different natural populations of P. roxburghii from Garhwal Himalaya, India. Assessment of each trait mentioned except pollen dispersion was done by selecting five representative trees randomly in each population. The pollen migration was studied on naturally isolated source trees. The pollen trapping was done in all directions up to 2.5 km. The average reproductive period in P. roxburghii was 36 days with 3–5 days protandry. There were significant year and population effects for male and female cone output and pollen grains production per tree. In mass production year (1999), an average production of pollen cone per tree was estimated as 42.44 ± 8.32 × 103 at lower altitude and 28.1 ± 0.89 × 103 at higher altitude. The controlled pollination results in high level of outcrossing with 90% seed setting. We conclude that the high male-female ratio and tremendous pollen production capacity in P. roxburghii indicate high male competition among trees within populations. The isolation strip of 600 m is considered minimal for the management of seed orchard.

Genetic diversity and relationship among faba bean (Vicia faba L.) germplasm entries as revealed by TRAP markers

Target region amplification polymorphism markers were used to assess the genetic diversity and relationship among 151 worldwide collected faba bean (Vicia faba L.) entries (137 accessions maintained at the USDA–ARS, Pullman, WA, 2 commercial varieties and 12 elite cultivars and advanced breeding lines obtained from Link of Georg-August University, Germany). Twelve primer combinations (six sets of polymerase chain reaction) amplified a total of 221 markers, of which 122 (55.2%) were polymorphic and could discriminate all the 151 entries. A high level of polymorphism was revealed among the accessions with an estimated average pairwise similarity of 63.2%, ranging from 36.9 to 90.2%. Cluster analysis divided the 151 accessions into five major groups with 2–101 entries each and revealed a substantial association between the molecular diversity and the geographic origin. All 101 accessions in Group V are originated from China and 13 of the 15 accessions in Group II were from Afghanistan. Thirty-two individual plants were sampled from two entries to assess the intra-accession variation. It was found that the advanced inbred line (Hiverna/5-EP1) had very little variation (5.0%), while the original collection (PI 577746) possessed a very high amount of variation (47.1%). This is consistent with the previous reports that faba bean landraces have a high level of outcrossing in production fields and thus contain larger amount variation within each landrace. One implication of this observation for germplasm management is that a relatively larger population is needed in regeneration to mitigate the possible loss of genetic variation due to genetic drift.

High Levels of Outcrossing in a Family Trial of Western Australian Sandalwood (Santalum spicatum)

AbstractThe mating system of Western Australian sandalwood (Santalum spicatum) was investigated in seed collections from a family trial. The mean outcrossing rate was high (95.2%) although there was variation among families and one family showed particularly low outcrossing, high bi-parental inbreeding and high correlated paternity. Variation in flowering time between this family and others in the trial was the most likely cause of the high inbreeding and low number of fathers contributing to the seed crop in trees from this family. The high level of outcrossing in the rest of the families indicated that S. spicatum has a preferentially outcrossed mating system, but that it is capable of selfing when conditions are unsuitable for outcrossing. The seedling progeny showed no influence of inbreeding on seedling height at 4 months. Analysis of genetic diversity revealed high levels of genetic diversity have been captured in the seed crop from the trial, and this diversity is comparable to that identified in a previous study of natural populations from throughout the range of the species. These results indicated that production of seed through seed orchards will be a successful means of deployment of breeding gains in the species, however it is essential to ensure overlap in flowering times among different families planted in a seed orchard.

High outcrossing and random pollen dispersal in a planted stand of Acacia saligna subsp. saligna revealed by paternity analysis using microsatellites

The mating system, patterns of pollen mediated gene flow and levels of genetic contamination were investigated in a planted stand of Acacia saligna subsp. saligna via paternity analysis using microsatellite markers. High levels of outcrossing were detected within the stand (tm = 0.98), and the average pollen dispersal distance was 37 m with the majority of progeny sired by paternal trees within a 50-m neighbourhood of the maternal tree. Genetic contamination from the natural background population of A. saligna subsp. lindleyi was detected in 14% of the progeny of A. saligna subsp. saligna and varied among maternal trees. Long distance inter-subspecific pollen dispersal was detected for distances of over 1,500 m. The results provide information for use in the breeding and domestication programme aimed at developing A. saligna as an agroforestry crop for the low rainfall areas of southern Australia.

Population genetic studies on indigenous conifers in Korea

Studies on the genetic variation in tree populations have been greatly facilitated by the development of molecular markers. Allozyme and DNA markers have been employed to estimate the level of genetic diversity and characterize the distribution patterns of genetic variation within and among populations. They have also been applied to examine the dispersal patterns and mating systems influencing the degree of population differentiation. We reviewed 18 population genetic studies on 8 native Korean conifers (Pinus densiflora, P. thunbergii, P. koraiensis, P. pumila, Abies holophylla, A. koreana, Taxus cuspidata, and Torreya nucifera), which appeared in the literature between 1992 and 2005. The level and distribution patterns of genetic variation observed in the 8 conifers were comparable with those reported in studies on other conifers. From studies on allozyme markers, the expected heterozygosity ranged from 0.168 to 0.262 for Taxus cuspidata and Pinus densiflora, and the degree of genetic differentiation between populations (GST) ranged from 0.031 to 0.067 for Pinus densiflora and Taxus cuspidata, respectively. From studies on the DNA markers of I‐SSR, the genetic diversity (Shannon's Index) ranged from 0.306 to 0.478 for Pinus koraiensis and Taxus cuspidata, respectively, and most of genetic variations were allocated within populations with FST values (i.e., degree of population differentiation) ranging from 0.066 to 0.198 for Pinus densiflora and Abies holophylla, respectively. Although the multilocus outcrossing rate (t m) of Pinus densiflora was 0.860, based on allozymes, suggesting a high level of outcrossing, highly correlated outcrossed paternity (r p=0.874) and evidence of biparental inbreeding (t m‐t s=0.115) were also verified. A study on the spatial autocorrelation of a scattered Korean pine (Pinus koraiensis) stand with relatively low density revealed a significant spatial genetic structure at distances between 24 and 32 m. At the allozyme level, the species with limited distributions tended to show less genetic diversity, but a higher level of genetic differentiation (G ST). For DNA markers, this tendency was not marked.

Competition‐dependent incompatibility in Phormium tenax: Does self‐fertilisation provide reproductive assurance?

New Zealand flax (Phormium tenax) has a reproductive system in which the early abscission of selfed flowers is determined by the degree of competition with crossed fruits on the same plant. It has been suggested that this functions as a form of reproductive assurance, allowing for high levels of outcrossing when pollinators are abundant, while ensuring seedset when pollinators are scarce. We performed experimental crosses and mating system estimation in natural populations to determine whether P. tenax can set seed in the absence of pollinators, and how pure and mixed pollen loads influence reproductive success and population‐level selfing rates. Phormium tenax can set seed autonomously, although if other flowers on the plant are available for outcrossing, resources are preferentially allocated to maturing those fruits. Experimental crosses suggest that flowers pollinated with mixtures of selfed and outcrossed pollen can result in fruitset, although fruitset is reduced if flowers pollinated with mixed pollen loads compete with cross‐pollinated flowers. Despite the potential for geitonogamy in P. tenax, outcrossing rates from five populations showed that these populations were universally outcrossing (t = 0.83–1.06). In P. tenax, self‐compatibility in the absence of competition from outcrossed pollen can provide some reproductive assurance, but in large populations, selfing and mixed mating rarely occur.

High nuclear genetic diversity, high levels of outcrossing and low differentiation among remnant populations of Quercus petraea at the margin of its range in Ireland.

Quercus petraea colonized Ireland after the last glaciation from refugia on mainland Europe. Deforestation, however, beginning in Neolithic times, has resulted in small, scattered forest fragments, now covering less than 12,000 ha. Plastid (three fragments) and microsatellite variation (13 loci) were characterized in seven Irish populations sampled along a north-south gradient. Using Bayesian approaches and Wright's F-statistics, the effects of colonization and fragmentation on the genetic structure and mating patterns of extant oak populations were investigated. All populations possessed cytotypes common to the Iberian Peninsula. Despite the distance from the refugial core and the extensive deforestation in Ireland, nuclear genetic variation was high and comparable to mainland Europe. Low population differentiation was observed within Ireland and populations showed no evidence for isolation by distance. As expected of a marker with an effective population size of one-quarter relative to the nuclear genome, plastid variation indicated higher differentiation. Individual inbreeding coefficients indicated high levels of outcrossing. Consistent with a large effective population size in the historical migrant gene pool and/or with high gene flow among populations, high within-population diversity and low population differentiation was observed within Ireland. It is proposed that native Q. petraea populations in Ireland share a common phylogeographic history and that the present genetic structure does not reflect founder effects.

Comparative analysis of late floral development and mating‐system evolution in tribe Collinsieae (Scrophulariaceae s.l.)

Species of Collinsia and Tonella, the two sister genera of self-compatible annuals that constitute tribe Collinsieae, show extensive variation in floral size and morphology and in patterns of stamen and style elongation during the life of the flower (anthesis). We used a nuclear ribosomal ITS phylogeny, independent contrasts, and phylogenetically corrected path analysis to explore the patterns of covariance of the developmental and morphological traits potentially influencing mating system. Large-flowered taxa maintain herkogamy (spatial separation of anthers and stigmas) early in anthesis by differential elongation of staminal filaments, which positions each of the four anthers at the tip of the "keel" upon dehiscence. Small-flowered taxa do not show this pattern of filament elongation. The styles of large-flowered taxa elongate late in the 2-5 d of anthesis, resulting in late anther-stigma contact and delayed self-pollination. Anther-stigma contact and self-pollination occur early in anthesis in small-flowered species/populations. Thus, we found complex covariation of morphological and developmental traits that can be interpreted as the result of multitrait adaptation for early selfing and high levels of autogamy, delayed selfing and higher levels of outcrossing, or intermediate levels of outcrossing. Continuous variation in these traits suggests the operation of continuous variation in selective optima or the combined effects of divergent selection and phylogenetic inertia.

A comparison of methods for hybrid seed production using self-incompatibility in swedes (Brassica napus ssp. napobrassica)

Procedures for producing seed of hybrid swedes using self-incompatibility were examined. Single-cross, double-cross and modified double-cross hybrids were compared in isolation plots using natural pollinators and in polythene tunnels using blow-flies. With good coincidence of flowering and the same flower colour, nearly 100% hybrid seed was produced by natural pollinators with the single-crosses, the double-cross and one of the two modified double-cross hybrids; the other modified double-cross hybrid produced 87%hybrid seed. With poor coincidence of flowering and different flower colours the proportion of hybrids dropped to 61%. Using different flower colours and blow-flies as pollinators in polythene tunnels, higher levels of outcrossing were produced than in isolation plots with natural pollinators; the opposite result was obtained when the same flower colour was used.

Out-crossing rates for 10 Canadian spring wheat cultivars

The genetic purity of pedigreed wheat seed can be compromised by inter-cultivar cross-pollination. Common wheat (Triticum aestivum L.) is assumed to be highly self-pollinated, an assumption that has not been verified for more recent western Canadian spring wheat cultivars. This field study was designed to estimate the outcrossing (OC) rate in three market classes of spring wheat in each of 2 yr and to determine whether OC rates were associated with specific spike characteristics. Highest OC rates were detected for the cultivar Oslo (6.05%) followed by Rongotea (2.30%), Roblin (1.43%), Wildcat (1.35%), Biggar (1.05%) and Glenlea (0.95%). In contrast Katepwa and CDC Makwa had OC rates of 0.38 and 0.30%, respectively. The cultivars Oslo, Columbus, Roblin and Glenlea tended to have lower iodine pollen viabilities. Of those four cultivars, three had higher-than-average OC rates. No single spike characteristic was correlated with OC rate. However, the cultivars Oslo, Wildcat and Glenlea had high OC rates, low pollen staining and spikes which tapered at the extremeties. Furthermore, cultivars with higher OC rates tended to have a greater degree of spikelet opening at anthesis. The high levels of OC observed in this study could result in obvious off-types if morphologically diverse cultivars were grown in adjacent pedigreed seed fields. The current 3 to 10 m isolation distance for pedigreed wheat seed production may not be enough to ensure that OC is minimized. Key words: Cross-pollination, spring wheat, market class

MATING SYSTEM AND ASYMMETRIC HYBRIDIZATION IN A MIXED STAND OF EUROPEAN OAKS.

The sessile (Quercus petraea [Matt.] Liebl.) and pedunculate (Quercus robur L.) oaks are two closely related species having a wide sympatric distribution over Europe. Under natural conditions, they frequently form mixed forests, where hybridization is suspected to occur. In this paper, two different approaches have been applied to the study of the mating system and the interspecific gene flow in a mixed stand formed by the two species. The mating systems of both species have been studied separately by means of the mixed-mating model. The relative contribution of the parental species to the progenies have been estimated with two different methods. The first uses the admixture model. The second is an extension of the mixed-mating model and subdivides the outcrossing rate into intra- and interspecific components. The two species were almost completely outcrossing. This high level of outcrossing and interspecific gene flow could play an important role in the maintenance of the genetic diversity in these long-lived forest tree species. The contribution of the sessile oak to the pedunculate oak progenies varied from 17% to 48%. In contrast, ovules of sessile oak trees appear to be preferentially fertilized by other extreme sessile genotypes. We suggest that interspecific and directional gene flow was responsible for such patterns. Pedunculate oak is considered as a pioneer species and is progressively replaced by sessile oak. Our present findings add a further genetic component to this succession scheme, suggesting that unidirectional gene flow reinforces succession between the two species.

CONTRIBUTION OF CRYPTIC INCOMPATIBILITY TO THE MATING SYSTEM OF EICHHORNIA PANICULA TA (PONTEDERIACEAE).

Tristylous populations of the annual aquatic Eichhornia paniculata have high levels of outcrossing and intermorph mating despite being fully self- and intramorph compatible. Experimental studies of pollen germination, ∗∗∗pollen-tube growth, and pollinations with mixtures of genetically marked pollen were used to determine whether postpollination processes contribute to the observed mating patterns. Differences in pollen germination were small and did not contribute to differences in pollen siring ability. The fraction of pollen tubes first entering the ovary, however, was greater for legitimate outcross pollen than for either of the other two pollen types (self or outcross illegitimate pollen) in all recipient morphs. Moreover, legitimate pollen had higher siring success when in competition with illegitimate pollen types (self or outcross) in each recipient style morph. The ranking of pollen performance for different pollen-style combinations was the same for both the pollen-tube growth and marker-gene experiments indicating that differences in pollen-tube growth rate are the principal cause of differences in pollen siring ability. Cryptic incompatibility in E. paniculata may represent a weak heteromorphic incompatibility system because the observed patterns of pollen-tube growth parallel pollen-tube growth and seed-set patterns that occur in related species with strong trimorphic incompatibility. The ability to produce mostly outcrossed progeny when pollinators are abundant, but to reliably produce seed under a variety of environmental and demographic conditions may be favored in E. paniculata because of its colonizing life history and occurrence in ephemeral habitats. Cryptic incompatibility may be more likely to occur in species subject to wide fluctuations in population size and levels of pollinator service.

EXPERIMENTAL STUDIES ON THE FUNCTIONAL SIGNIFICANCE OF HETEROSTYLY.

Heterostyly has been viewed as both an antiselfing device and a mechanism that increases the proficiency of pollen transfer between plants. We used experimental manipulation of the morph structure of garden populations of self-compatible, tristylous Eichhornia paniculata to investigate the function of floral polymorphism. Outcrossing rates (t), levels of intermorph mating (d), and morph-specific male and female reproductive success were compared in replicate trimorphic and monomorphic populations. In trimorphic populations, t and d averaged 0.81 (2 SE = 0.03) and 0.77 (2 SE = 0.03) respectively, with no difference in either parameter among morphs. Ninety-five percent of outcrossed seeds were therefore the result of intermorph fertilizations. Male reproductive success of the long-styled morph was low, especially in comparison with plants of the short-styled morph. Outcrossing rates for each morph were higher in trimorphic than monomorphic populations where t averaged 0.71 (2 SE = 0.01), 0.30 (2 SE = 0.04) and 0.43 (2 SE = 0.1) for the long-, mid-, and short-styled morphs, respectively. Seed set was lower in monomorphic populations, particularly those composed of the L morph, reflecting reduced pollen deposition. Floral polymorphism therefore increased both outcrossing rate and fecundity but the magnitude of the differences varied among morphs. If the ancestral condition in heterostylous groups resembled the L morph, as has been suggested, data from this study suggests that the selective basis for the establishment of floral polymorphism could have been increased pollen transfer rather than higher levels of outcrossing.