Population genetics of Cordia alliodora (Boraginaceae), a neotropical tree. 2. Mating system

A multilocus mixed mating model was used to evaluate the mating system of a natural population of Cordia alliodora (Boraginaceae), a neotropical tree. The population was highly outcrossed (t_m = 0.966 ± 0.027), in agreement with results from controlled crosses. Departures from the mixed mating model were evident, suggesting some nonrandom, correlated mating. Pollen pool heterogeneity and variation in estimates of individual outcrossing rates indicated that the population may be genetically substructured. Individual outcrossing rates obtained for the samples taken from within different parts of the same tree indicated reduced levels of outcrossing due to limited sampling of the pollen pool. The incompatibility mechanism in C. alliodora, combined with variation in flowering and stand density, appears to lead to both temporal and spatial substructuring of the population.     

Nonrandom mating in an open-pollinated maize population

Randomness of fertilization was studied in an open-pollinated population of maize (Zea mays L.) through allozyme assays of seedlings from open-pollinated seeds produced on both tasseled and detasseled plants. Mixed-mating-model estimates of the amount of outcrossing (t) were not significantly different from t = 1.00 for four enzyme loci ( Adh1, Idh2, Got1 and Acp1), indicating that fertilizations were at random in the population. However, for loci Prx1 and Est4 , estimates of t were significantly smaller than unity—0.80 and 0.70 for tasseled plants and 0.81 and 0.80 for detasseled plants. The excesses of homogametic fertilizations detected on the detasseled plants could not have been due to selffertilization, s = 1 - t, because the detasseled plants shed no pollen. Analyses of allelic frequencies in the pollen that produced seed on the detasseled plants established that different maternal plants sampled genetically different populations of pollen from the outcross pollen pool. It was suggested that the causes of the differential sampling were temporal variation in the pollen pool, and/or gametophytic selection, correlated with marker-locus genotype. Two-, three- and four-locus interactions among the marker loci were often statistically significant, indicating that the factors responsible for the nonrandom gametic unions observed in the maize population studied were complexly interactive.     

A study of the mating system in Dolichandra cynanchoides (Bignoniaceae): an Argentinian Chaco woodlands liane with a late-acting self-incompatibility

We estimated the outcrossing rate in a population of 14 individuals of Dolichandra cynanchoides (Bignoniaceae), a species with late-acting self-incompatibility (LSI), at a site in Chaco woodland in Santa Fe province, Argentina. A subsample of five arbitrarily chosen loci from a total of 16 allozyme loci gave mating system parameters of t_m=0.881 (SD 0.039) and t_s=0.749 (SD 0.048), thus indicating that although predominantly outcrossing, D. cynanchoides has a mixed mating system. We draw attention to the fact that mixed mating in species with LSI is a very likely scenario, given that previous studies with diverse LSI taxa have shown that mixed cross-self pollen loads on the stigma, which is probably a common occurrence with natural pollinators, result in fruits with a proportion of selfed seeds.     

MATING SYSTEM IN NATURAL POPULATIONS OF JEFFREY PINE

The mating system and allozyme variation at 20 loci in three Klamath Mountains and two Sierra Nevada populations of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) were investigated. On average, multilocus estimates of the proportion of viable progeny due to outcrossing (t_m) were high in all populations (mean t_m = 0.935, range 0.881 to 0.971). Despite differences in stand structure, t_m did not differ (P > 0.05) between the Klamath (mean t_m = 0.933) and Sierra Nevada (mean t_m = 0.937) populations. At all but one locus in one population and at two in another, genotype frequencies fit (P > 0.05) Hardy-Weinberg expectations. Mean estimates of observed heterozygosity in Klamath (0.182) and Sierra Nevada (0.327) populations were comparable to values reported for other conifers.     

Mating patterns and spatial distribution of conspecific neighbours in the Mediterranean shrub <Emphasis Type="Italic">Myrtus communis</Emphasis> (Myrtaceae)

Mate abundance is one of the most important sources of variation in plant mating systems. We examined within-population heterogeneity in the pollen pool at two spatial scales (sites and plants), and investigated the mating pattern variation in Myrtus communis under diverse situations of conspecific neighbourhood, using allozyme electrophoresis of naturally pollinated progeny arrays. For mating analyses, plants sampled were classified into four neighbourhood groups (from high to low) based on the local density around them and the distance to their nearest neighbour. The pollen pool was much more genetically heterogeneous among mother plants (~21%) than among sites (~2%), probably because of the high levels of selfing found (average s = 0.65). Outcrossing rates differed significantly among neighbourhood groups and showed a marked trend towards higher values from the lowest (t _m = 0.26) to the highest (t _m = 0.45) degree of conspecific aggregation. However, the lowest levels of biparental inbreeding and correlated paternity were found in the most isolated group of plants, indicating that these plants crossed with more and less genetically related fathers. Our study provides a clear demonstration of positive correlation between conspecific aggregation and the outcrossing rates. We discuss the ecological implications of these results in the context of Mediterranean ecosystems.     

Jatropha curcas L. (Euphorbiaceae) exhibits a mixed mating system, high correlated mating and apomixis

The hierarchical mating system among and within fruits of Jatropha curcas was investigated in a base population using five microsatellite loci, employing mixed mating and correlated mating models. Open-pollinated fruits were collected from 15 randomly selected seed trees, sampling seven fruits per tree for a total of 21 seeds from each tree. We detected multilocus genotypes identical to the mother tree in 13 % of offspring, implying the occurrence of apomixis in J. curcas. The presumed apomictic individuals were excluded from the analysis of the remaining results. Evidence of substantial selfing was provided by the average multilocus outcrossing rate (t _m?=?0.683), showing that the species exhibits a mixed mating system. The outcrossing rate showed a large variation among seed trees, ranging from 0.21 to 1.0, indicating that the species is not self-incompatible. Significant differences were detected between the multilocus and the single locus outcrossing rates (t _m???t _s?=?0.347) that suggested mating among related individuals, possibly because of the presence of individuals from the same progeny (sibs) in the base population. The multilocus paternity correlation was extremely high for the population (r _p(m)?=?0.999), indicating that the progenies were manly composed of full-sibs. As a consequence of selfing and a high paternity correlation, the co-ancestry coefficient within the progeny was higher (Θ?=?0.369) than expected for panmictic populations. Our results indicated that J. curcas produces seeds asexually by apomixis and sexually by a mixed mating system, combining selfing and outcrossing.     

PATTERNS OF MATING IN WILD SUNFLOWER HYBRID ZONES

Theory predicts that homoploid hybrid speciation will be facilitated by selfing, yet most well-documented hybrid species are outcrossers. One possible explanation for this puzzle is that conditions in hybrid populations may favor selfing, even in otherwise outcrossing species. For example, in self-incompatible plants, mixtures of self and interspecific pollen often induce selfing. Here, we examine patterns of mating in three hybrid zones and four “pure” populations of Helianthus annuus and H. petiolaris, wild, self-incompatible sunflower species that are thought to have parented three homoploid hybrid species. Fourteen to 16 maternal families from each pure population and 44–46 maternal families from each hybrid zone were analyzed for seven polymorphic isozyme loci. Maximum-likelihood (ML) methods were used to estimate multilocus outcrossing rates (T_m) and hybridization frequencies for each maternal family, each phenotypic group within each hybrid zone (annuus-like, hybrid, and petiolaris-like), and each population. As predicted for self-incompatible species, all four parental populations have outcrossing rate ML estimates of 1.0. Within the hybrid zones, outcrossing rates were lowest in the H. annuus–like fraction of the population (0.73, 0.72, and 0.74 in the three hybrid zones, respectively), largely intermediate in the H. petiolaris–like group (0.94, 0.90, and 0.94), and highest in the hybrid group (0.97, 0.93, and 0.97). Although outcrossing rates are lower in hybrid zones than in pure populations, it is unlikely that the observed decrease facilitates hybrid speciation because outcrossing rates in the critical hybrid fraction of the population do not differ significantly from 1.0. Dividing the outcrossed pollen pool into intraspecific and interspecific components revealed that maternal plants are largely fertilized by conspecific pollen, confirming an important role for pollen competition as a reproductive barrier. Highly sterile hybrid plants do not appear to discriminate between parental species pollen, but hybrids with higher fertility tend to be fertilized by pollen from the parental group they resemble genetically. Thus, gametic selection leads to substantial assortative mating in these hybrid zones.     

Flexible mating system in a logged population of <Emphasis Type="Italic">Swietenia macrophylla</Emphasis> King (Meliaceae): implications for the management of a threatened neotropical tree species

Microsatellites were used to evaluate the mating system of the remaining trees in a logged population of Swietenia macrophylla, a highly valuable and threatened hardwood species, in the Brazilian Amazon. A total of 25 open pollinated progeny arrays of 16 individuals, with their mother trees, were genotyped using eight highly polymorphic microsatellite loci. Genotypic data analysis from the progeny arrays showed that 373 out of the 400 seedlings (93.25%) were unambiguously the result of outcrossed matings and that the remaining 6.75% had genotypes consistent with self-fertilisation. Apomixis could be ruled out, since none of the 400 seedlings analysed had a multi-locus genotype identical to its mother tree. The high estimate of the multi-locus outcrossing rate (t _m = 0.938 ± 0.009) using the mixed mating model also indicated that the population in this remnant stand of S. macrophylla was predominantly allogamous. The relatively large difference between the multi-locus and single-locus outcrossing estimates (t _m −t _s = 0.117 ± 0.011) provides evidence that, in spite of the high outcrossing rate, a considerable degree of biparental inbreeding has contributed to the genetic structure of this population. Levels of outcrossing were not evenly distributed among maternal trees (t _m ranging from 0.39 to 1.00), suggesting the occurrence of a variable degree of self-incompatibility and/or dichogamy among individual trees of this monoecious species. Due to its generalist pollination system and some level of tolerance for selfing, S. macrophylla seems to be resilient to environmental disturbances such as those caused by logging, since it sets fruits with predominantly outcrossed seeds even at low stand densities. Therefore, the remaining individuals in logged areas or in relict fragments may be very important for long-term population recovery and genetic conservation programmes.     

Estimation of mating system parameters in plant populations using marker loci with null alleles

Summary An Expectation-Maximization (EM)-algorithm procedure is presented that extends Cheliak et al. (1983) method of maximum-likelihood estimation of mating system parameters of mixed mating system models. The extension permits the estimation of the rate of self-fertilization (s) and allele frequencies (Pi) at loci in outcrossing pollen, at marker loci having recessive null alleles. The algorithm makes use of maternal and filial genotypic arrays obtained by the electrophoretic analysis of cohorts of progeny. The genotypes of maternal plants must be known. Explicit equations are given for cases when the genotype of the maternal gamete inherited by a seed can (gymnosperms) or cannot (angiosperms) be determined. The procedure can accommodate any number of codominant alleles, but only one recessive null allele at each locus. An example, using actual data from Pinus banksiana, is presented to illustrate the application of this EM algorithm to the estimation of mating system parameters using marker loci having both codominant and recessive alleles.Issued as AECL-8745     

Short-distance pollen dispersal for an outcrossed, wind-pollinated southern beech (Nothofagus nervosa (Phil.) Dim. et Mil.)

The mating system (outcrossing, selfing, and biparental inbreeding) and the extent of pollen flow are two of the most important genetic features that determine the genetic structure of plant populations, and both are crucial for the design of conservation strategies. The objectives here were to estimate mating system parameters and to fit the pollen dispersal kernel for the southern beech, Nothofagus nervosa. We sampled 25 mothers and 372 progeny from two stands in the Tromen Lake region of Argentina. We registered spatial positions of the maternal trees, and genotyped mothers and offspring for five simple sequence repeat markers. We estimated single-locus (t _s?=?0.95) and multilocus (t _m?=?0.99) outcrossing rates and biparental inbreeding (t _m-t _s?=?0.04). The species is strongly outcrossing, but correlated paternity within maternal sibships (r _p?=?0.10) indicates that each maternal parent is sampling a different and restricted array of pollen donors. We used two protocols (twogener and kindist) to fit an exponential power dispersal kernel to the structure of pollen clouds sampled by different mothers. The estimated effective number of pollen donors contributing to a single mother was N _ep?=?9.9. The twogener and kindist analyses yielded slightly different estimates, but both indicated short average distances for pollen dispersal (<35?m), indicating that the dispersal kernel was strongly leptokurtic (???=?0.36). While short-distance pollen dispersal predominates, there remains a nontrivial probability of long-distance dispersal. The results are discussed in the context of ongoing conservation and management programs.     

Pollen pool heterogeneity in jack pine (Pinus banksiana Lamb.): a problem for estimating outcrossing rates?

Summary Pollen pool heterogeneity, which violates an assumption of the mixed-mating model, is a major potential problem in measuring plant mating systems. In this study, isozyme markers were used to examine pollen pool heterogeneity in two natural populations of jack pine, Pinus banksiana Lamb., in northwestern Ontario, Canada. Population multilocus estimates of outcrossing rate ranged from 0.83 to 0.95 and differed significantly between populations. Single-tree multilocus outcrossing rates were found to be homogeneous among trees in both populations. Computer simulation studies indicated that a consanguineous pollen pool (pollen gametes related to the mother tree) was capable of biasing population outcrossing estimates downward. Random pollen pool heterogeneity (uncorrelated with maternal genotypes) did not appear to affect population outcrossing estimates in the simulations. Heterogeneity G-tests and Spearman rank tests showed that pollen pool heterogeneity existed in the two natural populations examined; however, it did not have a major effect on population outcrossing estimates, since the consanguineous pollen pool detected was probably a relatively minor component of the outcross pollen pool in both populations. In addition, heterogeneity G-tests were found to be not sensitive in detecting pollen pool heterogeneity caused by consanguineous pollen pool.     

Mating Systems of Psychotria tenuinervis (Rubiaceae): Distance from Anthropogenic and Natural Edges of Atlantic Forest Fragment

The aim of this study was to determine and compare the mating systems among Psychotria tenuinervis populations at anthropogenic edges, natural edges, and the forest interior using allozyme electrophoresis of naturally pollinated progeny arrays. P. tenuinervis showed low outcrossing rates, varying from 37% to 50% of the mating attributable to outcrossing and 50% to 63% attributable to self-fertilization, in the three habitats. The forest interior had the highest outcrossing rate (t _m = 0.50 and t _s = 0.43) among the three habitats. However, there were no differences in either multilocus or single-locus rates among the three habitats, indicating that the contribution of biparental inbreeding to the apparent selfing rate in these populations was very low. The multilocus (t _m) and single-locus (t _s) outcrossing rates for the P. tenuinervis in the sample plots within each habitat showed great heterogeneity. In conclusion, edge creation seems not to influence its mating systems. Additionally, although P. tenuinervis is a distylous species, the population’s inbreeding can be attributed almost entirely to self-fertilization.     

EVIDENCE FOR AN EXTREME BOTTLENECK IN A RARE MEXICAN PINYON: GENETIC DIVERSITY,DISEQUILIBRIUM, AND THE MATING SYSTEM IN PINUS MAXIMARTINEZII

Maxipiñon (Pinus maximartinezii Rzedowski), which is confined to a single population of approximately 2000 to 2500 mature trees, covers about 400 ha in southern Zacatecas, Mexico. Genetic diversity measured by expected heterozygosity was 0.122, which is moderate for pines. However, percentage polymorphic loci was low, 30.3%. The fixation index (F) of 0.081 indicated only slight heterozygote deficiency. Mating system analysis indicated a significant but low level of selling; the multilocus outcrossing rate, t_m, was 0.816. The mean of single locus estimates, t_s, was smaller (0.761), perhaps suggesting mating among relatives, although the difference between t_m and t_s was not statistically significant. The most striking features of maxipiñon's genetic structure were that no polymorphic locus had more than two alleles and most alleles at polymorphic loci were at intermediate frequencies. This is in contrast to other pines, which often have three to five or more alleles at some loci and in which the distribution of allele frequencies is U-shaped, most alleles being present at frequencies less than 10% or greater than 90%. A population with only two alleles per locus and at intermediate frequencies could occur if the population had been reduced to an extreme bottleneck and then expanded rapidly before random drift modified allele frequencies. A novel origin from a hybridization event would also explain the results. Significant gametic disequilibrium was detected at several pairs of loci in both maternal and paternal gametes. The presence of disequilibrium is in agreement with an origin from an extreme bottleneck, perhaps even a single seed. Furthermore, it demands that the event be relatively recent. The number of generations, as calculated from the observed mean disequilibrium, suggested that maxipiñon derived from an extreme bottleneck four to five generations ago, which is less than 1000 years in this species.     

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 (t _m = 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.     

Mating Systems of Three Tropical Dry Forest Tree Species1

Polymorphic allozyme loci were used to estimate outcrossing rates for three tree species from a disturbed dry forest in southern Costa Rica. Estimates of the multilocus outcrossing rates of Cedrela odorata and Jacaranda copaia were 0.969 and 0.982, respectively, and suggest that these species may be self-incompatible. The subcanopy tree Stemmadenia donnell-smithii also demonstrated little self-fertilization based on an estimated outcrossing rate of 0.896. Significant heterogeneity in pollen allele frequencies among maternal trees was detected for at least two enzyme loci for each species. A test of correlated mating between progeny of S. donnell-smithii revealed that all seeds within a fruit were singly sired. In addition, the low estimates of biparental inbreeding and significant differences in pollen and ovule allele frequencies for this species suggest that gene flow into the sampled forest fragment may occur. The implications of deforestation on the mating systems of these tropical tree taxa are discussed.     

Wild sorghum from different eco-geographic regions of Kenya display a mixed mating system

Knowledge of mating systems is required in order to understand the genetic composition and evolutionary potential of plant populations. Outcrossing in a population may co-vary with the ecological and historical factors influencing it. However, literature on the outcrossing rate is limited in terms of wild sorghum species coverage and eco-geographic reference. This study investigated the outcrossing rates in wild sorghum populations from different ecological conditions of Kenya. Twelve wild sorghum populations were collected in four sorghum growing regions. Twenty-four individuals per population were genotyped using six polymorphic simple sequence repeat (SSR) markers to compute their indirect equilibrium estimates of outcrossing rate as well as population structure. In addition, the 12 populations were planted in a field in a randomised block design with five replications. Their progeny (250 individuals per population) were genotyped with the six SSR markers to estimate multi-locus outcrossing rates. Equilibrium estimates of outcrossing rates ranged from 7.0 to 75.0%, while multi-locus outcrossing rates (t _m) ranged from 8.9 to 70.0% with a mean of 49.7%, indicating that wild sorghum exhibits a mixed mating system. The wide range of estimated outcrossing rates in wild sorghum populations indicate that environmental conditions may exist under which fitness is favoured by outcrossing and others under which selfing is more advantageous. The genetic structure of the populations studied is concordant with that expected for a species displaying mixed mating system.     

Individual and Temporal Variation in Outcrossing Rates and Pollen Flow Patterns in Ceiba pentandra (Malvaceae: Bombacoidea)

Ceiba pentandra is a tropical tree with high rates of selfing in some populations. In mixed‐mating species, variation in selfing is due to changes in adult density or variability of incompatibility systems. The effect of spatial isolation and phenology on selfing rates and pollen flow distances was analyzed using microsatellites in a fragmented population of Ceiba pentandra, in southern Costa Rica. Adult trees within a heterogeneous landscape were classified as grouped or isolated. We compared selfing rates at the individual level, between isolation conditions and 2 yr (2007, 2009), which differed in the number of flowering individuals. Mixed mating was estimated in both years (t_m = 0.624–0.759). Trees mated predominantly by outcrossing, while only a few trees reproduced through selfing. Spatial isolation did not significantly affect outcrossing rates. The progeny of grouped trees was mostly sired by near‐neighbors (<1 km) and by long‐distance pollen flow events in isolated trees. A reduction in the number of flowering individuals in 2009 reduced near‐neighbor matings, increased selfing in grouped trees, and decreased the number of unsampled sires in the progeny. Comparing selfing rates on individuals that flowered in both reproductive periods suggests a flexible mating system. Variation in self‐fertilization rates in this population appears to depend on variation of individual traits, such as genetic variability in self‐incompatibility genes, but it is independent of landscape heterogeneity. In contrast, pollen flow distances depend on local tree density as bats concentrate their foraging between near individuals to maximize energy efficiency.     

The mating system and genetic significance of polycarpy in the neem tree (Azadirachta indica)

The objectives of this study were to estimate the outcrossing rate and to explain genetic consequences of the development of seed in the endocarp in a natural population of neem in Bangladesh. Cotyledons of germinated open-pollinated seeds of individual trees were analyzed by starch-gel electrophoresis to examine allozymes. Three loci with clear Mendelian segregation were used to estimate outcrossing rate. A multilocus mixed mating model was used to evaluate the mating system. The population exhibited high outcrossing rates both for multilocus (t_m=0.90±0.024) and mean single-locus (t_s=0.92±0.020) estimates. The difference between these two parameters (t_m–t_s=0±SE 0.038) was insignificant, indicating that there was no ’biparental inbreeding’ in the population. The degree of variance of the estimates of multilocus outcrossing rates decreased when two or more loci were included. In order to elucidate the significance of polycarpy a total of 471 seeds were counted out of 440 endocarps. This mechanism appears to be a possible way of avoiding inbreeding. The results indicated that the studied neem population was predominantly allogamous. Received: 10 January 1999 / Accepted: 10 April 1999     

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

Mating systems have long been recognized as key factors determining genetic structure within and between populations. Outcrossing promotes genetic diversity and gene flow between populations, while inbreeding, on the other hand, decreases recombination rates, facilitating fixation of co-adapted genes. In small populations, selfing moderates pollen limitation because of low mate availability, but at the cost of increased inbreeding depression. These conflicts are of more than theoretical interest; they are critical for the management of endangered species. In order to help designing conservation strategies for the management of the gene pool of fragmented populations of Pinus cembra, a protected species in Poland, we have characterized pollen flow and mating structure using nuclear microsatellite markers. We demonstrated that P. cembra in the studied stands of the Tatra Mts. is characterized by an average outcrossing rate (t) of 0.72. Unlike with the existing approaches, using the newly developed Bayesian method, we found that population size and seasonal variation had confounding effects on outcrossing rates. In concordance with predictions, large populations showed significantly higher outcrossing rates (t?=?0.89) than smaller ones (t?=?0.51). Temporal variation revealed in the outcrossing rate might be linked with masting behavior of the species. On the other hand, we showed that outcrossing rates were not associated with a trunk diameter of a mother tree. Our study also demonstrated that biparental inbreeding is a significant component of mating system. However, we further show that pollen dispersal follows a fat-tailed distribution (with the average dispersal distance of 1,267 m) so that at least some long-distance pollen dispersal must be occurring. Overall, we conclude that the high inbreeding (both selfing and mating between relatives) found in P. cembra buffers for pollen limitation. We argue that small, isolated stands can be at risk of gene pool erosion, despite the potential for long-distance pollen and seed dispersal.     

Influence of asymmetrical mating patterns and male reproductive success on the maintenance of sexual polymorphism in Acer pictum subsp. mono (Aceraceae)

Populations of Acer species often contain more than three sex phenotypes with complex sexual polymorphism including duodichogamy, protandry and protogyny. We identified the mechanisms that maintain sexual polymorphism in Acer pictum subsp. mono, a temperate tree from northern China, by investigating maternal mating patterns and male reproductive success. We used paternity analyses to estimate rates of outcrossing and disassortative mating, as well as male outcrossed siring success, in a population of A. pictum subsp. mono with uneven sex phenotype ratios (duodichogamous 69.1%, protandrous 19.6%, protogynous 11.3%). We used a pollen‐transfer model to investigate whether the unequal ratios of sex phenotypes could be explained by the observed patterns of mating. Most progeny resulted from outcrossing, particularly disassortative among the sex phenotypes. Although the duodichogamous phenotype showed a significant amount of intraphenotypic mating, the frequency did not exceed that of disassortative mating. We detected no significant differences in male outcrossed siring success among the sex phenotypes. The pollen‐transfer model demonstrated that sex phenotype ratios could be maintained by the observed mating pattern in the population. Our results indicate that disassortative mating among the sex phenotypes can maintain sexual polymorphism in A. pictum subsp. mono and that ratios biased towards duodichogamy can result from frequent intraphenotypic mating in this phenotype.