Multilocus Estimates Of Outcrossing Rates Research Articles

Mating Systems of Single Families and Population Genetic Diversity of Endangered Ormosia hosiei in South China.

Ormosia hosiei is a tree species native to China that has been extensively used for ornamental and furniture purposes due to its valued timber. The mating system has substantial impact on genetic diversity and structure of plant natural population. Such information should be considered when planning tree planting for forest restoration. Here we used 12 microsatellite markers and described the mating system of single families and the population genetic diversity of O. hosiei. A high level of genetic diversity was observed in both adults and progenies, although slight differences existed among populations and their progenies, with the expected heterozygosity ranging from 0.763 to 0.794. Overall, O. hosiei displayed a predominantly outcrossed mating. The estimate of multi-locus outcrossing rate (tm) was high with low variations among families, ranged from 0.997 to 1.000. The value of tm-ts, ranged from 0.000 to 0.139, indicated that biparental inbreeding occurred in progenies. Therefore, to obtain a reasonable genetic representation of native tree species and prevent problems associated with inbreeding depression, we suggested effective in situ conservation by replanting seedlings, but seedling production for restoration purposes may require a much larger sampling effort than is currently used. Moreover, it is necessary to conduct further multiple population and multi-year experiments to verify our conclusions.

Outcrossing Rates and Gene Flow in Natural Population of the Endangered Endemic Aquatic Lycophyte Isoetes yunguiensis as Revealed by ISSR Markers

In this study, mating system, genetic diversity, and genetic structure of the endangered endemic aquatic Isoetes yunguiensis in China was investigated using ISSR markers. The results of ISSR analyses showed that the estimate of multilocus outcrossing rate (tm) was high at species level (tm = 0.955), indicating that diploid I. yunguiensis is a predominant outcrossing species. Nine selected ISSR primers used in the study amplified 66 reproducible bands, 41 of which were polymorphic among 37 individuals. High level of genetic diversity was detected at the species level (PPB = 62.12%), whereas, relatively low genetic diversity existed within populations (PPB = 39.39%). Analysis of molecular variance (AMOVA) revealed that 31.99% of the genetic variation was attributable to differences between populations and the rest (68.01%) to variability within populationsof I. yunguiensis. Value of Fst (0.320) indicated that genetic differentiation between populations also was significant. These results showed that I. yunguiensis predominantly favors crossing, and has a high level of genetic diversity and highly significant genetic variation between and within populations. Gene flow (Nm) among populations is equal to 1.177. High outcrossing rates may be responsible for the high levels of genetic diversity observed in the I. yunguiensis population. To maintain the current level of genetic diversity for this species, we recommend increasing in situ conservation sites.

Estimation of Mating System in the Endangered Aquatic Fern Ceratopteris pteridoides in China Based on AFLP Molecular Marker and Selfing Test: Implications for Conservation

Mating system has important implications for the genetic structure and diversity of populations, especially threatened and endangered species. In this study, mating system of the endangered aquatic fern Ceratopteris pteridoides in China was investigated using AFLP markers and selfing test. The results of AFLP analyses showed that the estimate of multilocus outcrossing rate (tm) was high at species level (tm = 0.999), indicating that C. pteridoides is a predominant outcrossing species. The small differences between tm and ts (0.136 ± 0.003) at species level showed that there is a low tendency for mating between relatives. The selfing test showed that isolated gametophytes formed the rate of normal sporophytes in three populations (BLH, ZDH, WCH) ranging from 72.9% to 77.8% with a mean value of 75.2%, indicating that C. pteridoides has a high level of intragametophytic selfing potential. Our investigation found that some of the studied populations of C. pteridoides have a prolific capacity for vegetative reproduction (clonal growth). The results revealed that the diploid homosporous pteridophyte C. pteridoides predominantly favors gametophytic crossing with a certain level of inbreeding along with clonal growth. We suggest that mating system of C. pteridoides may be adjusted to promote selfing rate in response to factors including the characteristics of hermaphrodite, and colonization events and small extant populations. As a result of the high outcrossing rate of C. pteridoides, we recommend that ex situ plantings would be most suitable for enhancing possible intermingling of the different populations thus minimizing inbreeding.

Seasonal variation in the mating system of a selfing annual with large floral displays.

Flowering plants display considerable variation in mating system, specifically the relative frequency of cross- and self-fertilization. The majority of estimates of outcrossing rate do not account for temporal variation, particularly during the flowering season. Here, we investigated seasonal variation in mating and fertility in Incarvillea sinensis (Bignoniaceae), an annual with showy, insect-pollinated, 'one-day' flowers capable of delayed selfing. We examined the influence of several biotic and abiotic environmental factors on day-to-day variation in fruit set, seed set and patterns of mating. We recorded daily flower number and pollinator abundance in nine 3 × 3-m patches in a population at Mu Us Sand land, Inner Mongolia, China. From marked flowers we collected data on daily fruit and seed set and estimated outcrossing rate and biparental inbreeding using six microsatellite loci and 172 open-pollinated families throughout the flowering period. Flower density increased significantly over most of the 50-d flowering season, but was associated with a decline in levels of pollinator service by bees, particularly on windy days. Fruit and seed set declined over time, especially during the latter third of the flowering period. Multilocus estimates of outcrossing rate were obtained using two methods (the programs MLTR and BORICE) and both indicated high selfing rates of ∼80 %. There was evidence for a significant increase in levels of selfing as the flowering season progressed and pollinator visitation declined. Biparental inbreeding also declined significantly as the flowering season progressed. Temporal variation in outcrossing rates may be a common feature of the mating biology of annual, insect-pollinated plants of harsh environments but our study is the first to examine seasonal mating-system dynamics in this context. Despite having large flowers and showy floral displays, I. sinensis attracted relatively few pollinators. Delayed selfing by corolla dragging largely explains the occurrence of mixed mating in I. sinensis, and this mode of self-fertilization probably functions to promote reproductive assurance when pollinator service is limited by windy environmental conditions and competition from co-occurring flowering plants.

Genetic diversity and mating system of Pinus brutia var. stankewiczii Sukacz. in small localities of Sudak (Crimea)

A comparative analysis of genetic variation at 12 polymorphic isozyme loci, and the mating system has been carried out in mature trees and their seed progeny in three small localities of Pinus brutia var. stankewiczii Sukacz. near the town of Sudak--settlement of Novyi Svet in the Crimea. We found that embryos maintain the same allelic diversity as mother plants but their observed heterozygosity is lower on the average by 37.4%. The significant deviation of genotype distribution from the theoretically expected ratios caused by the deficiency of heterozygotes was observed at 8 out of 12 loci. Multilocus estimate of outcrossing rate (t(m)) in populations varied from 68.9 to 94.9% making on the average 80.7%.

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.

Polymorphic microsatellite markers in the invasive shrub Buddleja davidii (Scrophulariaceae)1

Microsatellite primers were developed for the invasive plant Buddleja davidii, a Chinese shrub that is an invader in most other continents. An invasive population was analyzed using eight di- and tetranucleotide microsatellite loci. The number of alleles per locus ranged from 5 to 14. Due to polyploidy, exact genotypes could not be determined. Progeny arrays were used to study the outcrossing rate using presence/absence data of alleles resulting in an estimate of multilocus outcrossing rate of 93%. The markers were successfully tested in five congeneric species. The results indicate the utility of these loci in future studies of population genetics and breeding systems in B. davidii and in congeneric species.

Outcrossing rates in a natural stand and in a seed orchard of Pinus peuce

The mating system parameters were studied in a natural stand and in a seed orchard of the Balkan endemic, Pinus peuce Griseb. by means of isozyme gene markers. The results indicate that the multilocus estimates of the outcrossing rates are low relative to other widespread conifers but concord to these reported for other pine species with limited area of distribution. No significant differences were detected between the natural stand and the seed orchard estimates. Multilocus estimates of outcrossing rate were within the range 0.77-0.79, while mean single-locus estimates were lower (0.69-0.73). The results indicate that at least 20% of the progeny of Pinus peuce is due to self-fertilization. Possible reasons for the results observed and the implications for tree breeding and gene conservation are discussed.

Clonal-row versus random seed orchard designs: interior spruce mating system evaluation

Mating system pattern (selfing or outcrossing and correlated matings levels) comparisons between two interior spruce seed orchard designs (clonal-row and random) managed under intensive crown and pollen management were conducted. Crown manipulation consisted of tree topping and branch pruning, while pollen management involved multiple supplemental mass-pollination applications during peak seed-cone reproductive receptivity and pollen agitation using helicopters. Significant differences between orchards’ multilocus outcrossing rate estimates were observed, and both estimates significantly departed from complete outcrossing (t = 1.0). Clonal arrangements in the clonal-row design permitted higher chances for selfing (t = 0.948) in comparison with those of the random design (t = 0.989). Intensive pollen management, while effective, still produced a minor component of selfing. Both orchard designs produced similar individual tree's outcrossing rate trends with the majority showing high outcrossing, while few individuals showed high selfing propensity. Estimates of correlated mating varied substantially between the two seed orchard designs with 9.3% and 4.3% for the clonal-row and random seed orchards, respectively. While small but significant differences in the genetic quality of the seed crops were observed between the two orchard designs, the establishment of clonal-row seed orchards should be given serious considerations specifically under committed pollen and crown management. The ease of crop and orchard management in the clonal-row design outweighs the observed differences in the seed crop genetic quality. A slight modification to the clonal-row design is proposed and is expected to reduce the observed minor genetic quality differences between the two orchard designs.

In situ estimation of outcrossing rate in sorghum landraces using microsatellite markers

Summary We assessed the outcrossing rate of sorghum landraces sampled in situ from two fields under traditional cultivation in north-western Morocco using genotypic data from five microsatellite loci. Assuming a mixed mating model, we estimated outcrossing parameters by two methods that are based on progeny analyses. With both methods, the multilocus estimate of outcrossing rate for the overall sample was in the order of 0.1, meaning that sorghum landraces are predominantly autogamous, but with a significant proportion of outcrossing. The estimated outcrossing rate is about two times higher in field 1 (tm = 0.161) than in field 2 (tm = 0.069). This difference could be explained by distinct morphological characteristics of the inflorescence in the two fields, with predominance of loose panicles in field 1 and of very compact panicles in field 2. The distribution of outcrossing rate among progeny families showed that 30% of them were completely self-fertilized but some families showed substantial outcrossing. These results are at odds with the very low genetic differentiation observed previously among Moroccan landraces and suggest that morphological differences are maintained despite gene flow through seed exchanges among farmers.

Taxas de cruzamento em uma população natural de Cryptocarya Moschata Nees (Lauraceae)

O sistema de cruzamento da espécie arbórea de dossel da Mata Atlântica brasileira, Cryptocarya moschata, foi estudado a partir de material proveniente do Parque Estadual Carlos Botelho, São Miguel Arcanjo, São Paulo, Brasil. As taxas de cruzamento foram determinadas através de marcadores alozímicos obtidos de plântulas germinadas de coortes de sementes coletadas de 35 árvores. O valor médio da taxa de cruzamento de equilíbrio (estimador indireto) foi t^eq = 0.51. As estimativas das taxas de cruzamento uniloco e multilocos (estimadores diretos) foram t^s = 0.725± 0,041 e t^m = 0,884 ± 0,034, respectivamente, indicando um sistema de cruzamento predominantemente alogâmico. As taxas de cruzamento de árvores individuais variaram de 27 a 100 ( x¯ = 87,8) porcento, a partir de t^m calculado com as freqüências gênicas de pólen mantidas constantes ao nível populacional. A partir do modelo de "par de irmãos" (modelo de cruzamento correlacionado) de Ritland, a correlação entre duas progênies irmãs oriundas de autofecundação (r^s) e a correlação entre duas progênies irmãs oriundas de paternidade por exocruzamento (r^p) foram 35,7% e 99,0%, respectivamente. Esses resultados corroboram o fato de haver variação nas taxas de autocruzamento entre as diferentes árvores, podendo também indicar que quando há endogamia, a maior parte das sementes nas árvores são provavelmente irmãs-germanas.

Tychoparthenogenesis and mixed mating in natural populations of the mayfly Stenonema femoratum.

Tychoparthenogenesis is a breeding system characterized by low population mean hatching success (usually < 10%) of unfertilized eggs from females of typically sexually reproducing species. I used progeny-array analysis to estimate outcrossing and parthenogenetic rates for two tychoparthenogenetic populations of the mayfly, Stenonema femoratum. Based on multilocus outcrossing rate estimates (t(m)), populations exhibited moderate rates of tychoparthenogenetic reproduction (population LD: 1 - t(m)=0.266; population RBG: 1 - t(m)=0.495). Differences between multilocus and average single-locus outcrossing rates indicated some biparental inbreeding in population LD, but not in population RBG. Family outcrossing rates ranged from 0 to 1.0, indicating mixed mating in which some females generated a mixture of sexually and parthenogenetically produced offspring. Outcrossing rates showed substantial heterogeneity among families. Correlation with paternity was high, indicating that outcrossed sibs within families were sired by the same father. Progeny-array sex ratios were significantly female biased for both populations and did not differ significantly between populations. However, family outcrossing rate was not significantly correlated with family sex ratio. Results indicate that substantial amounts of parthenogenetic reproduction are occurring in these natural S. femoratum populations and that some females produce mixed broods of sexually and parthenogenetically produced offspring.

Effects of Density on Mixed Mating Systems and Reproduction in Natural Populations ofImpatiens capensis

Understanding the role of plant density in natural populations necessitates evaluation of density effects on both mating system and reproduction. I estimated parameters of the mixed mating system of Impatiens capensis, including plant outcrossing rate (t) and level of biparental inbreeding (mb), along with reproductive components at three densities typically found within three natural populations. As a result of coexisting cleistogamous (CL) and chasmogamous (CH) flowers on individual I. capensis, an estimate of t at each density was obtained by multiplying the percentage of CH seeds and the multilocus estimate of outcrossing rate among CH seeds (tCH). Estimation of mb was based on the relationships between fixation indices of selfed and outcrossed progeny. These estimates led to evaluation of average inbreeding coefficients in seeds (f) and at equilibrium (fe). When plant density decreased from high (>100 plants/m2) to low (ca. 20–30 plants/m2), the estimated tCH increased significantly from 0.44 to 0.62. The estimated mb and tCH were not correlated, but lower mb and higher tCH were significantly associated with higher fruit set and more seeds per CH fruit. I extended Ritland's estimation of inbreeding depression to the case of biparental inbreeding and found that mb affects inbreeding depression positively; the effect of t on inbreeding depression can be negative or positive, depending on the level of mb; magnitudes of both effects rely on the level of f. Plant mixed mating system not only responds to densities but also assists in maintaining population density through its association with reproduction and inbreeding depression.

Paternal bottlenecks in fragmented populations of the grassland daisy Rutidosis leptorrhynchoides

Allozyme markers were used to estimate mating system parameters in nine fragmented populations of the grassland daisy Rutidosis leptorrhynchoides that differed in size and spatial isolation. Multilocus estimates of outcrossing rate did not differ significantly among populations, all indicating a high level of outcrossing (tm=0·84–1·0). Small populations showed greater divergence than large populations between the allele frequencies in the population and those in the pollen pool, indicating paternal bottlenecks. Isolated populations of fewer than 200 individuals also exhibited higher correlations of outcrossed paternity (rp) than larger populations, indicating the production of more full-sibs within families. The combination of paternal bottlenecks and correlated paternity increases the genetic identity of progeny across families and predisposes populations to biparental inbreeding in subsequent generations. As over half the remaining populations of R. leptorrhynchoides contain fewer than 200 plants, such second-order inbreeding may threaten the viability of the species if it is associated with significant inbreeding depression.

Comparative analysis of the mating system of the rare woodland shrub Daviesia suaveolens and its common congener D. mimosoides

Controlled pollinations and allozyme markers were used to compare mating system parameters among three populations of the rare woodland shrub Daviesia suaveolens Crisp. and five populations of its common relative D. mimosoides R. Br. Pollination results show that both species require a vector to facilitate pollination and have strong self-incompatibility mechanisms. Multilocus estimates of outcrossing rates confirm this, with all populations being highly outcrossed (D. suaveolens tm=0.78−1.0; D. mimosoides tm=0.71−0.96). Smaller and less dense D. mimosoides populations had higher correlations of outcrossed paternity than larger ones. The divergence of pollen pool allele frequencies from population frequencies was greater in smaller populations than in larger ones, in keeping with a lower effective size of the male source. Regression analyses generally failed to show effects of either plant size or local flowering environment on estimates of single-plant outcrossing rates. Most variation in these rates probably reflects the combined effects of sampling error, correlated mating and the influence of marker diversity on outcross detectability.

Comparative analysis of the mating system of the rare woodland shrub Daviesia suaveolens and its common congener D. mimosoides

Controlled pollinations and allozyme markers were used to compare mating system parameters among three populations of the rare woodland shrub Daviesia suaveolens Crisp. and five populations of its common relative D. mimosoides R. Br. Pollination results show that both species require a vector to facilitate pollination and have strong self-incompatibility mechanisms. Multilocus estimates of outcrossing rates confirm this, with all populations being highly outcrossed (D. suaveolens tm=0.78−1.0; D. mimosoides tm=0.71−0.96). Smaller and less dense D. mimosoides populations had higher correlations of outcrossed paternity than larger ones. The divergence of pollen pool allele frequencies from population frequencies was greater in smaller populations than in larger ones, in keeping with a lower effective size of the male source. Regression analyses generally failed to show effects of either plant size or local flowering environment on estimates of single-plant outcrossing rates. Most variation in these rates probably reflects the combined effects of sampling error, correlated mating and the influence of marker diversity on outcross detectability.

Outcrossing Rate, Yield, and Selective Fruit Abscission in `Ettinger' and `Ardith' Avocado Plots

The reciprocal effect of two avocado (Persea americana Mill.) cultivars—Ardith and Ettinger—on outcrossing rate and yield was studied in several orchards in Israel. Multilocus estimates of outcrossing rates were made using the isozyme loci Mdh-1 (malate dehydrogenase) and Aat-1 (aspartate aminotransferase) for `Ettinger' progeny and Lap-2 (leucine aminopeptidase), Pgm-1 (phosphoglucomutase) and Tpi-1 (triosephosphate isomerase) for `Ardith' progeny. When the two cultivars were in close proximity, estimated yields ranged from 10 to 20 t·ha-1 and outcrossing rates ranged from 0.71 to 0.89 and from 0.87 to 0.90 for `Ettinger' and `Ardith', respectively. The effect of `Ettinger' as a pollenizer was not restricted to adjacent `Ardith' trees; it also reached more distant `Ardith' trees. Thus, outcrossing rate in `Ardith' was 0.82 at a distance of 30 m from `Ettinger' in one orchard and 0.91 at a distance of 36 m in another orchard. These results confirm previous observations that `Ettinger' is a highly potent pollenizer. Outcrossing rates in `Ardith' and `Ettinger' were found to increase from the young fruitlet stage to that of mature fruit. These findings provide evidence for selective abscission of selfed fruitlets. In addition, parentage analysis of abscised versus retained `Ardith' fruit showed that `Ardith' selfed fruit abscised at a much higher rate than outcrossed ones. The survival advantage of outcrossed fruit is probably related to the fact that selfed progeny have less-vigorous embryos than outcrossed progeny due to inbreeding depression.

Genetic consequences of specialization: yucca moth behavior and self-pollination in yuccas.

Reciprocal specialization in interspecific interactions, such as plant-pollinator mutualisms, increases the probability that either party can have detrimental effects on the other without the interaction being dissolved. This should be particularly apparent in obligate mutualisms, such as those that exist between yucca and yucca moths. Female moths collect pollen from yucca flowers, oviposit into floral ovaries, and then pollinate those flowers. Yucca moths, which are the sole pollinators of yuccas, impose a cost in the form of seed consumption by the moth larvae. Here we ask whether there also is a genetic cost through selfish moth behavior that may lead to high levels of self fertilization in the yuccas. Historically, it has been assumed that females leave a plant immediately after collecting pollen, but few data are available. Observations of a member of the Tegeticula yuccasella complex on Yucca filamentosa revealed that females remained on the plant and oviposited in 66% of all instances after observed pollen collections, and 51% of all moths were observed to pollinate the same plant as well. Manual cross and self pollinations showed equal development and retention of fruits. Subsequent trials to assess inbreeding depression by measuring seed weight, germination date, growth rate, and plant mass at 5 months revealed significant negative effects on seed weight and germination frequency in selfed progeny arrays. Cumulative inbreeding depression was 0.475, i.e., fitness of selfed seeds was expected to be less than half that of outcrossed seeds. Single and multilocus estimates of outcrossing rates based on allozyme analyses of open-pollinated progeny arrays did not differ from 1.0. The discrepancy between high levels of behavioral self-pollination by the moths and nearly complete outcrossing in mature seeds can be explained through selective foreign pollen use by the females, or, more likely, pollen competition or selective abortion of self-pollinated flowers during early stages of fruit development. Thus, whenever the proportion of pollinated flowers exceeds the proportion that can be matured to ripe fruit based on resource availability, the potential detrimental genetic effects imposed through geitonogamous pollinations can be avoided in the plants. Because self-pollinated flowers have a lower probability of retention, selection should act on female moths to move among plants whenever moth density is high enough to trigger abortion.

Estimation of mating system parameters in two Italian natural populations of Fagussylvatica

Mating system parameters were estimated in two Italian natural populations of European beech (Fagussylvatica L.) using a mixed mating model and considering seven allozyme loci (Idh-A, Lap-A, Mdh-B, Pgd-A, Pgd-B, Pgd-C, Skd-A). High values of multilocus estimates of the outcrossing rate were found in both populations, ranging from 94 to 98%. Comparison of single- and multi-locus estimates of outcrossing rates seems to indicate the presence of consanguineous matings, probably because the populations are substructured. This hypothesis seems to be confirmed by the presence of a heterogeneity of the pollen allele frequencies across female parent trees and by the significant coefficient of the regression of pollen allele frequencies on ovule genotype. Variation in the fixation indices in different life-cycle phases was observed, indicating possible presence of selective processes between seed set and sexual maturity. Possible explanations of these results are presented.

Mating system dynamics of Ocotea tenera (Lauraceae), a gynodioecious tropical tree

Progeny arrays of Ocotea tenera (Lauraceae), a gynodioecious tree endemic to Costa Rica, were electrophoretically surveyed for allozyme variation to estimate the outcrossing rate in the overall population and to test for differences in outcrossing rates between hermaphroditic and female trees. Multilocus outcrossing rate estimates across 3 yr indicated O. tenera predominantly outcrosses. However, significant heterogeneity in single‐locus outcrossing rates was found among loci. Two loci (Fe1, Fe2) gave high outcrossing estimates, and a third locus (Gdh) gave much lower outcrossing estimates. Heterogeneity in Gdh pollen allele frequencies, consanguineous matings, and selection against homozygous zygote genotypes at the Fe1 and Fe2 loci are factors contributing to the discrepancy in outcrossing rate estimates among loci. There were no differences in the mating systems of hermaphroditic and female trees, which suggests that factors beyond prevention of self‐fertilization may have also promoted the evolution of gynodioecy in O. tenera.