Population Outcrossing Rate Research Articles

How does population outcrossing rate influence seed quality? A case study from a seed tree stand of Pinus massoniana

How does population outcrossing rate influence seed quality? A case study from a seed tree stand of Pinus massoniana

Outcrossing and heterozygosity rates in tropical onion populations

Outcrossing and heterogosity rates are important for defining genetic conservation and breeding strategies, and these estimates are quite rare to onion. The aim of this study was to estimate cross-pollination and heterozygosity rates in tropical onion populations to guide development of new varieties. Eight tropical onion pairs were field isolated to be open pollination by insects. Parents vernalized bulbs were used for pair crossing, in alternate rows, 1:1. Seeds were harvested from the female parent to assess the progenies outcrossing and heterogigosity rates based on color of the red bulb, partially dominant over yellow, and four microsatellite loci. The outcrossing rates estimated with morphological marker, in the ‘BRS Rio Vale’ × ‘BRS Carrancas’, ‘Botucatu’ × ‘BRS Carrancas’, ‘IPA 11’ × ‘IPA 10’ and ‘BRS Alfa São Francisco’ × ‘IPA10’ crosses, ranged from 15% to 39%, with an average of 28.2%, while with microsatellite loci, in the ‘BRS Alfa São Francisco’×’IPA 11’, ‘Alfa SF RT’ × ‘BRS A. São Francisco’, ‘BRS Rio Vale’ × ‘Botucatu’ and ‘Cascuda T6’ × ‘Botucatu’ crosses, ranged from 33% to 71%, with an average of 42.7%, indicating a mixture of cross-pollination and self-pollination within progenies. The average values ​​of heterozygosity in the eight populations ranged from 0.82 to 1.0, indicating the possibility of developing open pollinated onion varieties with greater adaptation to biotic and abiotic stresses.

Do annual and perennial populations of an insect-pollinated plant species differ in mating system?

Theory predicts that outcrossing should be more prevalent among perennials than annuals, a pattern confirmed by comparative evidence from diverse angiosperm families. However, intraspecific comparisons between annual and perennial populations are few because such variation is uncommon among flowering plants. Here, we test the hypothesis that perennial populations outcross more than annual populations by investigating Incarvillea sinensis, a wide-ranging insect-pollinated herb native to China. The occurrence of both allopatric and sympatric populations allows us to examine the stability of mating system differences between life histories under varying ecological conditions. We estimated outcrossing rates and biparental inbreeding in 16 allopatric and five sympatric populations in which both life histories coexisted using 20 microsatellite loci. In each population we measured height, branch number, corolla size, tube length and herkogamy for ~30 individuals. In a sympatric population, we recorded daily flower number, pollinator visitation and the fruit and seed set of annual and perennial plants. As predicted, outcrossing rates (t) were considerably higher in perennial (mean = 0.76) than annual (mean = 0.09) populations. This difference in mating system was also maintained at sympatric sites where plants grew intermixed. In both allopatric and sympatric populations the degree of herkogamy was consistently larger in outcrossing than selfing plants. Perennials were more branched, with more and larger flowers than in annuals. In a sympatric population, annuals had a significantly higher fruit and seed set than perennials. Genetically based differences in herkogamy between annuals and perennials appear to play a key role in governing outcrossing rates in populations, regardless of variation in local ecological conditions. The maintenance of mating system and life history trait differentiation between perennial and annual populations of I. sinensis probably results from correlated evolution in response to local environmental conditions.

Molecular genetic diversity and mating system in sacha inchi progenies1

ABSTRACT Sacha inchi (Plukenetia volubilis L.) is a species with nutraceutical benefits traditionally consumed by Amazonic indigenous and urban communities. Studies on the genetic diversity and mating system are required to preserve and make the best use of the genetic resources for this species. This study aimed to estimate the genetic diversity and mating system parameters of sacha inchi progenies using Amplified Fragment Length Polymorphism (AFLP) markers. A total of 360 progenies from 30 accessions of sacha inchi were analyzed using three AFLP primers combinations. The percentage variation between and within families and the crossing rate, among other parameters, were estimated. The AFLP markers were efficient in genetically differentiating progenies, revealing 251 (98.82 %) polymorphic fragments. The analysis of molecular variance showed that the strongest variation occurs between progenies (57.16 %). However, the genetic differentiation within progenies was considerable (42.84 %), and could be exploited in breeding programs. The estimated population outcrossing rate was high (0.957), indicating it is a predominantly allogamous species. On the other hand, 33.7 % of the crosses occurred between related individuals. The estimate for biparental crosses revealed that the progenies consisted mainly of half-siblings (66.9 %) and full-siblings (28.8 %). For purposes of breeding and ex situ genetic conservation, sacha inchi seeds should be collected from a large number of parent plants.

Floral traits and mating system of Hibiscus trionum (Malvaceae)

Variations in floral traits and floral structures influence plant mating systems. Hibiscus trionum produces large, showy flowers typical of an outcrossing species, yet flowers are autonomously self-pollinated. In this study, we measured floral morphology, breeding system and outcrossing rate estimated by ISSR markers. Results indicate that two types of flowers were observed in H. trionum, and the type I with bigger petals appears to be much more visible to pollinators, demonstrated by than type II flowers with smaller petals. The flowers with hand pollination were closed 1h earlier than intact flowers, whether they were type I or II. The relationship between the amount of pollen deposited on the stigma and the number of seeds per capsule was highly significant, and 80 or more pollens per flower can make the mean number of seeds (mean=37) in H. trionum. Delayed selfing in H. trionum did not provide a large contribution to seed production, since reproductive assurance were only 0.025. However, successful reproduction of 72.5% flowers in the absence of pollinators suggested that selfing provides reproductive assurance during seasons, in which pollinators were limiting. The multilocus outcrossing rates in different populations varied from 0.982 to 1.200, with a mean of 1.116. Our data provide an empirical demonstration of a predominantly outcrossing species with potential delayed selfing when pollinators are absent or scarce.

Postpollination discrimination between self and outcross pollen covaries with the mating system of a self-compatible flowering plant.

Variation in the mating system of hermaphroditic plant populations is determined by interactions between genetic and environmental factors operating via both pre- and postmating processes. Models predicting the maintenance of intermediate outcrossing rates in animal-pollinated plants often assume that the mating system is primarily controlled by floral morphology and pollinator availability, but rarely has the influence of postpollination processes on variation in outcrossing been examined. We investigated the influence of stylar discrimination between illegitimate and legitimate pollen-tube growth and the pollen-load capacity of stigmas on mating-system variation in the annual, tristylous species Eichhornia paniculata using controlled crosses and genetic markers. This species exhibits an exceptionally broad range of outcrossing rates in natural populations. There was significant variation among populations in the pollen-load capacity of stigmas and the ability of styles to discriminate between illegitimate vs. legitimate pollen. There was strong correspondence between stylar-discrimination ability and variation in outcrossing rate among populations and style morphs. The combination of stigmatic pollen-load capacity and stylar discrimination explained more than 80% of the variation in outcrossing rates among populations. The finding that stigmatic pollen-load capacity and stylar-discrimination ability contributed significantly to explaining the wide range of outcrossing rates in E. paniculata suggests that postpollination mechanisms play an important role in governing mating patterns in this species. The difference in levels of stylar discrimination between outcrossing and selfing populations may reflect a trade-off between selection for increased outcrossing and greater reproductive assurance.

Sexual antagonism in the pistil varies among populations of a hermaphroditic mixed-mating plant.

Sexual conflicts and their evolutionary outcomes may be influenced by population-specific features such as mating system and ecological context; however, very few studies have investigated the link between sexual conflict and mating system. The self-compatible, mixed-mating hermaphrodite Collinsia heterophylla (Plantaginaceae) is thought to exhibit a sexual conflict over timing of stigma receptivity. This conflict involves (i) delayed stigma receptivity, which intensifies pollen competition, and (ii) early fertilization forced by pollen, which reduces seed set. We investigated the potential for the conflict to occur under field conditions and performed glasshouse crosses within eight populations to assess its consistency across populations. Flowers were visited, and produced seeds after pollination, at all developmental stages, suggesting that the conflict can be of significance under natural conditions. In the glasshouse, early pollination imposed costs in all populations. Overall, the timing of first seed set was most strongly affected by the maternal parent, denoting stronger female than male ability to influence the onset of stigma receptivity. Crosses also revealed a negative relationship between donor- and recipient-related onset of receptivity within individuals, a novel result hinting at trade-offs in sex allocation or a history of antagonistic selection. Neither timing of stigma receptivity, timing of first seed set, nor pollen competitive ability covaried with population outcrossing rate. In conclusion, these results indicate that sexually antagonistic selection may be present in varying degrees in different populations of C. heterophylla, but this variation does not appear to be directly related to mating system variation.

The role of hermaphrodites in the experimental evolution of increased outcrossing rates in Caenorhabditis elegans.

BackgroundWhy most organisms reproduce via outcrossing rather than selfing is a central question in evolutionary biology. It has long ago been suggested that outcrossing is favoured when it facilitates adaptation to novel environments. We have previously shown that the experimental evolution of increased outcrossing rates in populations of the male-hermaphrodite nematode Caenorhabditis elegans were correlated with the experimental evolution of increased male fitness. However, it is unknown whether outcrossing led to adaptation, and if so, which fitness components can explain the observed increase in outcrossing rates.ResultsUsing experimental evolution in six populations with initially low standing levels of genetic diversity, we show with head-to-head competition assays that population-wide fitness improved during 100 generations. Since outcrossing rates increased during the same period, this result demonstrates that outcrossing is adaptive. We also show that there was little evolution of hermaphrodite fitness under conditions of selfing or under conditions of outcrossing with unrelated tester males. We nonetheless find a positive genetic correlation between hermaphrodite self-fitness and population-wide fitness, and a negative genetic correlation between hermaphrodite mating success and population-wide fitness. These results suggest that the several hermaphrodite traits measured are fitness components. Tradeoffs expressed in hermaphrodites, particularly noticed between self-fitness and mating success, may in turn explain their lack of change during experimental evolution.ConclusionsOur findings indicate that outcrossing facilitates adaptation to novel environments. They further indicate that the experimental evolution of increased outcrossing rates depended little on hermaphrodites because of fitness tradeoffs between selfing and outcrossing. Instead, the evolution of increased outcrossing rates appears to have resulted from unhindered selection on males.

The effect of bird and bee visitation on pollination and reproductive success in Phormium tenax

To study how pollinator composition and abundance influence reproduction of Phormium tenax, we compared pollen deposition by bees and birds to unvisited flowers, and plant reproductive success and outcrossing rates in populations on island and mainland sites that vary in bird abundance. Bees deposited pollen on stigmas if stigmas were close to the anthers but deposited little pollen on stigmas of emasculated flowers, suggesting that they are largely depositing self pollen. Birds deposit pollen on both intact and emasculated flowers with well-exserted stigmas, suggesting they are depositing more outcross pollen. High frequencies of bird claw marks on inflorescences were associated with high fruit set, but not seed set. Seed set and seed outcrossing rates were positively correlated with the number of unique maternal allozyme genotypes in a population and seedlings also showed higher outcrossing rates than seeds, suggesting that genetic diversity, selfing and inbreeding depression limit reproductive success. These results highlight the interplay of pollination and breeding systems in determining plant reproductive success.

A multidimensional approach to understanding floral function and form1

Variation in plant mating systems is a fundamental component of the diversity of floral form and function. Mating systems have a strong influence on the distribution and expression of genetic variation, which in turn can influence the course of mating system evolution. It has long been appreciated, however, that ecological interactions may provide much of the impetus behind these evolutionary changes. • This commentary reviews the Special Section in the American Journal of Botany (vol. 100, issue 6) that features novel research on the role of interactions between plants and their pollinators, seed dispersers, herbivores, and interspecific competitors in the evolution of selfing rates and gender. These studies vary in approach from empirical experiments, to phylogenetic comparisons, to theoretical models, to literature reviews as they each attempt to shed new light on longstanding questions about the selective forces and evolutionary pathways that have led to the diversified means by which plants promote or discourage self-fertilization. • Evidence is provided that indicates that ecological interactions (e.g., herbivory and heterospecific pollen deposition by pollinators) can strongly influence the relative advantages of selfing and outcrossing. Ecological interactions can also influence allocation to sexual functions, which will influence individual and population outcrossing rates and possibly the evolutionary path of gender expression. • Mating systems evolution is clearly a multidimensional problem. Research that places the study of mating and sexual systems within a more realistic ecological context will no doubt reveal more complexity as we move toward a better understanding of plant diversity.

Comparison of mating system parameters and genetic structure in three natural scenarios of Acacia visco (Leguminosae, Mimosoideae)

Acacia visco is a native South American tree species that has been extensively used for ornamental purposes and in carpentry, bodywork and parquet due to the hardness and durability of its wood. Little is known about genetic diversity and mating system of A. visco. The main aims of this study were to (1) estimate outcrossing rates in natural Argentinean populations using AFLP markers, (2) test for any difference in mating patterns among a large a patchy and relict population, and (3) compare the mating system of A. visco with other Acacia species. The three primer pairs used in the AFLP analysis revealed a total of 569 variable loci. Most genetic variation was observed among individuals within families (61.2 %). The estimate of multilocus outcrossing rate (t m) was high (≥0.971) in all populations. Average pairwise coancestry between progenies within families for each population ranged from 0.082 to 0.105 or from 0.125 to 0.136, depending on the method θ was estimated. In the three populations studied, the progenies of open pollination were constituted mainly for half-sibs (94.3 %). This work shows a similar mating system in all populations of A. visco in spite of their size differences, hypothesizing that the entire species has a similar mating system of outcrossing preferential. Considering the results obtained here where a high percentage of individuals were half-sibs, sampling large numbers of pods from individual trees for ex situ conservation will result in a genetically diverse sample as a consequence of high outcrossing rates.

A Bayesian method for the joint estimation of outcrossing rate and inbreeding depression

The population outcrossing rate (t) and adult inbreeding coefficient (F) are key parameters in mating system evolution. The magnitude of inbreeding depression as expressed in the field can be estimated given t and F via the method of Ritland (1990). For a given total sample size, the optimal design for the joint estimation of t and F requires sampling large numbers of families (100-400) with fewer offspring (1-4) per family. Unfortunately, the standard inference procedure (MLTR) yields significantly biased estimates for t and F when family sizes are small and maternal genotypes are unknown (a common occurrence when sampling natural populations). Here, we present a Bayesian method implemented in the program BORICE (Bayesian Outcrossing Rate and Inbreeding Coefficient Estimation) that effectively estimates t and F when family sizes are small and maternal genotype information is lacking. BORICE should enable wider use of the Ritland approach for field-based estimates of inbreeding depression. As proof of concept, we estimate t and F in a natural population of Mimulus guttatus. In addition, we describe how individual maternal inbreeding histories inferred by BORICE may prove useful in studies of inbreeding and its consequences.

Mating System Analysis of Alnus maritima (Seaside Alder), a Rare Riparian Tree

Abstract Effective conservation requires an understanding of the genetic interactions among populations and individuals of a species, particularly those with fragmented, isolated distributions. Alnus maritima (seaside alder) is a rare tree species with an extremely fragmented distribution of highly isolated populations in the Delmarva Peninsula, Georgia, and Oklahoma. We conducted a mating system study to estimate the outcrossing rate, inbreeding coefficient, biparental inbreeding rate, and correlation of paternity in progeny from a Georgia and an Oklahoma population to investigate the effects of isolation on the A. maritima mating system. Data from nine microsatellite loci showed similarly high multilocus outcrossing rates in both populations (tm = 0.94). Individual tree outcrossing rates were also high (tm = 0.873–1.047). There was no significant biparental inbreeding in either population, but there was significantly higher correlated paternity in the Oklahoma population. Results showed the high out...

Disentangling the effects of breakdown of self‐incompatibility and transition to selfing in North American Arabidopsis lyrata

AbstractA breakdown of self‐incompatibility (SI) followed by a shift to selfing is commonly observed in the evolution of flowering plants. Both are expected to reduce the levels of heterozygosity and genetic diversity. However, breakdown of SI should most strongly affect the region of the SI locus (S‐locus) because of the relaxation of balancing selection that operates on a functional S‐locus, and a potential selective sweep. In contrast, a transition to selfing should affect the whole genome. We set out to disentangle the effects of breakdown of SI and transition to selfing on the level and distribution of genetic diversity in North American populations of Arabidopsis lyrata. Specifically, we compared sequence diversity of loci linked and unlinked to the S‐locus for populations ranging from complete selfing to fully outcrossing. Regardless of linkage to the S‐locus, heterozygosity and genetic diversity increased with population outcrossing rate. High heterozygosity of self‐compatible individuals in outcrossing populations suggests that SI is not the only factor preventing the evolution of self‐fertilization in those populations. There was a strong loss of diversity in selfing populations, which was more pronounced at the S‐locus. In addition, selfing populations showed an accumulation of derived mutations at the S‐locus. Our results provide evidence that beyond the genome‐wide consequences of the population bottleneck associated with the shift to selfing, the S‐locus of A. lyrata shows a specific signal either reflecting the relaxation of balancing selection or positive selection.

Potential Inbreeding in a Small Population of a Mass Flowering Species, <i>Xanthorrhoea johnsonii</i> (Xanthorrhoeaceae): Is Your Mother My Father?

Xanthorrhoea johnsonii is a long lived slow growing perennial understorey species, that produces a large quantity of passively dispersed seed every 3 - 5 years. Reproductive maturity is not reached until 20 - 30 years of age. The temporal asynchrony of the flowering event in this population was analogous to geographic isolation through fragmentation. A small population of plants flowering in isolation provided the opportunity to examine outcrossing rates, genetic diversity and the paternity of progeny at a small spatial scale (0.2 ha). The geographic location and physical characteristics of the adult plants were recorded, and both adults and their seed were sampled for genetic analysis. Four microsatellite loci were screened for genetic diversity and spatial structure analysis. A population outcrossing rate was estimated, as well as the number of paternal parents required to resolve the progeny multilocus genotypes. High genetic diversity was found in both adults and progeny with an estimated 97% outcrossing rate. All maternal lines required several paternal contributors, with no evidence of dominant paternal genotypes. Pollen transfer occurred between both geographically close and distant plants.

Determination of the mating system of Tucumã palm using microsatellite markers

The Amazonian Tucumã palm (Astrocaryum aculeatum) produces edible fruit, traditionally consumed in indigenous communities and increasingly in urban centers. The species is incipiently domesticated and little studied, despite its growing economic importance for smallholder farmers and gatherers. Studies on the mating system are required for the conservation and use of the species' genetic resources. Our objective was to estimate mating system parameters of the Tucumã palm using microsatellite markers. Plants of 11 progenies of a spontaneous population were genotyped with eight microsatellite loci and the mating system parameters estimated. The population outcrossing rate was estimated at 0.978, and ranged from 0.774 to 1at the family level. The estimates of the correlation of paternity (0.176 and 0.205) suggest a low probability of full-sibs within progenies. Tucumã palm is a predominantly allogamous species and the open-pollinated progenies consist predominantly of half-sibs.

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.

ANALISIS SISTEM PERKAWINAN MERBAU (Intsia bijuga O. Ktze) DI PAPUA BERDASARKAN PENANDA ISOENZIM

Merbau (Intsia bijuga O. Ktze) is an important species to supply wood in Indonesia. Mating system on natural population of merbau can influence genetic diversity of merbau. The objectives of this study were to investigate mating system on natural forest of merbau in Papua. The research used 200 samples of merbau from 10 mother trees in Gunung Meja Forest Research Manokwari-Papua. Isoenzyme analysis was done using four enzyme systems i. e. Peroxidase (POD), Esterase (EST), Glutamate Oxaloacetate Transaminase (GOT) dan Diaphorase (DIA). Data were analysed using MLTR program. The result showed that average genetic diversity (He) 0.463 and total heterozygosity (HT) 0.496. The multilocus population outcrossing rate (t m ) and singlelocus population outcrossing rate (t s ) were t m = 1.00 and t s = 0.992. Probability of inbreeding rate (t m - t s ) = 0.008.

Estimation of out-crossing rate in a natural breeding population of Warburgia ugandensis using AFLP marker

Warburgia ugandensis Sprague (Canellaceae) occurs in East and Central Africa, and the species is of great medicinal importance to the local communities where it occurs. As the wild populations diminish, planted stands will in future be used as the source of medicinal products as well as germplasm. This study investigated the levels of out-crossing rates to provide knowledge for proper planning in future cultivation programmes. The mating parameters estimated using the mixed mating model (software MLTR) showed the species to be predominantly out-crossing (89%) with significant levels of selfing. The multi-locus population out-crossing rate was higher than the single-locus population out-crossing rate (tm- ts= 0.023; SE = 0.010), implying that there was less likelihood of mating between relatives (biparental inbreeding). Low values were also obtained for the correlation of paternity, rp(s) = 0.028 (SE = 0.040) and correlation of selfing among family, rs = 0.016 (SE = 0.015). For most loci, allele frequencies of pollen and ovule contributions to the progeny genotypes were significantly different (P

Estimation of out-crossing rate in a natural breeding population of Warburgia ugandensis using AFLP marker

Warburgia ugandensis Sprague (Canellaceae) occurs in East and Central Africa, and the species is of great medicinal importance to the local communities where it occurs. As the wild populations diminish, planted stands will in future be used as the source of medicinal products as well as germplasm. This study investigated the levels of out-crossing rates to provide knowledge for proper planning in future cultivation programmes. The mating parameters estimated using the mixed mating model (software MLTR) showed the species to be predominantly out-crossing (89%) with significant levels of selfing. The multi-locus population out-crossing rate was higher than the single-locus population out-crossing rate (tm- ts= 0.023; SE = 0.010), implying that there was less likelihood of mating between relatives (biparental inbreeding). Low values were also obtained for the correlation of paternity, rp(s) = 0.028 (SE = 0.040) and correlation of selfing among family, rs = 0.016 (SE = 0.015). For most loci, allele frequencies of pollen and ovule contributions to the progeny genotypes were significantly different (P