Selfing Rate Research Articles

Genome-wide genotyping estimates mating system parameters and paternity in the island species Tolpis succulenta.

The mating system has profound consequences, not only for ecology and evolution, but also for the conservation of threatened or endangered species. Unfortunately, small populations are difficult to study owing to limits on sample size and genetic marker diversity. Here, we estimated mating system parameters in three small populations of an island plant using genomic genotyping. Although self-incompatible (SI) species are known to often set some self-seed, little is known about how "leaky SI" affects selfing rates in nature or the role that multiple paternity plays in small populations. We generalized the BORICE mating system program to determine the siring pattern within maternal families. We applied this algorithm to maternal families from three populations of Tolpis succulenta from Madeira Island and genotyped the progeny using RADseq. We applied BORICE to estimate each individual offspring as outcrossed or selfed, the paternity of each outcrossed offspring, and the level of inbreeding of each maternal plant. Despite a functional self-incompatibility system, these data establish T. succulenta as a pseudo-self-compatible (PSC) species. Two of 75 offspring were strongly indicated as products of self-fertilization. Despite selfing, all adult maternal plants were fully outbred. There was high differentiation among and low variation within populations, consistent with a history of genetic isolation of these small populations. There were generally multiple sires per maternal family. Twenty-two percent of sib contrasts (between outcrossed offspring within maternal families) shared the same sire. Genome-wide genotyping, combined with appropriate analytical methods, enables estimation of mating system and multiple paternity in small populations. These data address questions about the evolution of reproductive traits and the conservation of threatened populations.

Albinism and inbreeding depression in seedlings of the tropical tree, Shorea laxa

ABSTRACT Investigating the level of inbreeding depression is essential to understanding population viability and extinction risk. Albino or chlorophyll-deficient mutants are one of the strongest manifestations of inbreeding depression in plant species, although it is rare to encounter them in a tropical forest. However, during January 2014, we observed a high frequency of albino seedlings in a natural population of Shorea laxa in Lambir Hills National Park in Sarawak, Malaysia. We investigated the fate and compared the cross types of these albino seedlings versus green-leaf seedlings by combining a field survey and genetic analysis using microsatellites. Overall, the albino seedlings survived at least a few months after germination, although they exhibited a 10-fold higher mortality rate than green-leaf seedlings within 19 weeks after germination. Microsatellite analysis confirmed that most albino seedlings (98.3%) were derived from self-pollination. The overall estimated selfing rate was high (61.3%), indicating that reproductive isolation occurred in the mother tree. The observed segregation rate of green:albino types was consistent with the complementation models, indicating that a combination of two dominant genes at two loci are responsible for the green-leaf phenotype in S. laxa. We also found that one albino seedling was derived from outcrossing, suggesting that at least one deleterious gene is maintained in the population. The inbreeding depression of selfed seedlings was exposed as lower initial height of seedlings, which resulted in lower seedling survival. These findings indicate that the population of S. laxa carries recessive deleterious genes and suffers inbreeding depression in selfed offspring.

The opportunity for outcrossing varies across the geographic range of the primarily selfing Clarkia xantiana ssp. parviflora.

The timing of self-fertilization has potentially important consequences for the trajectory of mating system evolution, the opportunity for outcrossing, and the maintenance of genetic variation in populations. For primarily selfing taxa, it remains poorly understood as to how floral variation influences the opportunity for outcrossing and whether those attributes vary among populations across geographic ranges. We examined variation in floral traits (herkogamy, protandry, flower size, stigma stage at anthesis, timing of stigma receptivity) in seven populations of Clarkia xantiana ssp. parviflora, a primarily selfing taxon, spanning from the western to eastern margins of its distribution. We also performed experimental emasculations and pollinations (followed by stigma severing) to quantify the extent of opportunities for outcrossing across flower development. There was marked among-population variation in all floral traits, particularly between far eastern and western populations. Emasculation experiments showed that the eastern populations had minimal autonomous selfing, but western populations had high rates of selfing within 24 h after anthesis. Population variation in autofertility was significantly predicted by floral trait variation, especially protandry and petal size. Greater protandry both extended the time over which outcrossing could potentially occur and reduced the probability of autonomous selfing, suggesting that there may be a tradeoff that results in fitness loss when pollinator visits are not common. The east-west pattern of differentiation in some floral traits parallels that of postglacial range expansion, suggesting that selection on the mating system may have been strong in the process of range expansion.

The loss of self-incompatibility in a range expansion.

It is commonly observed that plant species' range margins are enriched for increased selfing rates and, in otherwise self-incompatible species, for self-compatibility (SC). This has often been attributed to a response to selection under mate and/or pollinator limitation. However, range expansion can also cause reduced inbreeding depression, and this could facilitate the evolution of selfing in the absence of mate or pollinator limitation. Here, we explore this idea using spatially explicit individual-based simulations of a range expansion, in which inbreeding depression, variation in self-incompatibility (SI), and mate availability evolve. Under a wide range of conditions, the simulated range expansion brought about the evolution of selfing after the loss of SI in range-marginal populations. Under conditions of high recombination between the self-incompatibility locus (S-locus) and viability loci, SC remained marginal in the expanded metapopulation and could not invade the range core, which remained self-incompatible. In contrast, under low recombination and migration rates, SC was frequently able to displace SI in the range core by maintaining its association with a genomic background with purged genetic load. We conclude that the evolution of inbreeding depression during a range expansion promotes the evolution of SC at range margins, especially under high rates of recombination.‬.

Hidden genetic variance contributes to increase the short-term adaptive potential of selfing populations.

Standing genetic variation is considered a major contributor to the adaptive potential of species. The low heritable genetic variation observed in self-fertilizing populations has led to the hypothesis that species with this mating system would be less likely to adapt. However, a non-negligible amount of cryptic genetic variation for polygenic traits, accumulated through negative linkage disequilibrium, could prove to be an important source of standing variation in self-fertilizing species. To test this hypothesis, we simulated populations under stabilizing selection subjected to an environmental change. We demonstrate that, when the mutation rate is high (but realistic), selfing populations are better able to store genetic variance than outcrossing populations through genetic associations, notably due to the reduced effective recombination rate associated with predominant selfing. Following an environmental shift, this diversity can be partially remobilized, which increases the additive variance and adaptive potential of predominantly (but not completely) selfing populations. In such conditions, despite initially lower observed genetic variance, selfing populations adapt as readily as outcrossing ones within a few generations. For low mutation rates, purifying selection impedes the storage of diversity through genetic associations, in which case, as previously predicted, the lower genetic variance of selfing populations results in lower adaptability compared to their outcrossing counterparts. The population size and the mutation rate are the main parameters to consider, as they are the best predictors of the amount of stored diversity in selfing populations. Our results and their impact on our knowledge of adaptation under high selfing rates are discussed.

Mating System in a Native Norway Spruce (Picea abies [L.] KARST.) Stand-Relatedness and Effective Pollen Population Size Show an Association with the Germination Percentage of Single Tree Progenies

Norway spruce differs little in neutral genetic markers among populations and provenances often reported, but in terms of putative adaptive traits and their candidate genes, some clear differences have been observed. This has previously been shown for crown morphotypes. Stands with mostly narrow crown shapes are adapted to high elevation conditions, but these stands are scattered, and the forest area is often occupied by planted stands with predominantly broad crowned morphotypes. This raises questions on whether this differentiation can remain despite gene flow, and on the level of gene flow between natural and planted stands growing in close neighbourhood. The locally adapted stands are a valuable seed source, the progeny of which is expected to have high genetic quality and germination ability. The presented case study is useful for spruce plantation by demonstrating evaluation of these expectations. Immigrant pollen and seeds from planted trees could be maladaptive and may alter the genetic composition of the progeny. This motivated us to study single tree progenies in a locally adapted stand with narrow crowned trees in a partial mast year at nuclear genomic simple sequence repeat (SSR) markers. Spruce is a typical open-pollinated conifer tree species with very low selfing rates, which were also observed in our study (s = 0.3–2.1%) and could be explained by efficient cross-pollination and postzygotic early embryo abortion, common in conifers. The estimated high amount of immigrant pollen found in the pooled seed lot (70.2–91.5%) is likely to influence the genetic composition of the seedlings. Notably, for individual mother trees located in the centre of the stand, up to 50% of the pollen was characterised as local. Seeds from these trees are therefore considered to retain most of the adaptive variance of the stand. Germination percentage varied greatly between half-sib families (3.6–61.9%) and was negatively correlated with relatedness and positively with effective pollen population size of the respective families. As pollen mostly originated from outside the stand and no family structures in the stand itself were found, germination differences can likely be explained by diversity differences in the individual pollen cloud.

Selfing and correlated paternity in relation to pollen management in western red cedar seed orchards

We used microsatellite genetic markers to evaluate the mating system of western red cedar (Thuja plicata Donn ex D. Don) under various seed orchard pollen management schemes. We primarily examined whether supplemental mass pollination (SMP) can reduce the observed selfing rates. Pollen blowing and “hooding” were also examined in smaller tests. Only SMP was consistently effective in reducing the selfing rate, from 30% to 20%. The correlation of paternity was quite high (60%–90%) in two of three orchards, and in these two orchards the application of SMP reduced this correlation by about 10% as well. The correlation of paternity is the fraction of full-sibling vs. half-sibling progeny, and unbiased estimates can be obtained with few loci, even single loci, in contrast to other types of paternity analysis. We also find the microsatellite amplicon sizes should be pooled into “bins” of 2–4 nucleotides, owing to unintended errors of assay; otherwise the estimates are biased. This new feature of mating system estimation was incorporated into the computer program MLTR.

Fine-scale spatial genetic structure, mating, and gene dispersal patterns in Parkia biglobosa populations with different levels of habitat fragmentation.

PremiseA good understanding of genetic variation and gene dispersal in tree populations is crucial for their sustainable management, particularly in a context of rapid environmental changes. West African Sudanian savannahs are being fragmented and degraded, partly due to expansion of crop cultivation and monocultures that reduce tree density and may impact pollinators. The population dynamics of important indigenous trees could also be affected. We investigated the influence of habitat fragmentation on patterns of genetic diversity and gene dispersal of a key Sudanian agroforestry tree species, Parkia biglobosa.MethodsUsing 10 highly polymorphic nuclear microsatellites, we genotyped 2475 samples from reproductive trees, seedlings, and embryos in four tree populations presenting different levels of habitat fragmentation.Results Parkia biglobosa presented similar high genetic diversity across the four populations studied. Genetic diversity and inbreeding were similar between adults and embryo cohorts. In all four populations, the selfing rate was less than 1%. The effective number of pollen donors per tree was high (N EP~ 18–22), as was the pollen immigration rate (from 34 to 74%). Pollen dispersal was characterized by a fat‐tailed distribution with mean estimates exceeding 200 m. In three populations, stem diameter had a pronounced effect on male reproductive success. Here, the highest male reproductive success was observed in trees with a diameter at breast height between 60 and 75 cm.ConclusionsAt the scale analyzed, fragmentation does not seem to pose limitations to gene flow in any of the sites investigated, regardless of the landscape configuration associated with the different tree stands. The study provides useful insights on the reproductive biology of an important tree species in the West African savannahs.

The wave of gene advance under diverse systems of mating.

Mating systems will influence gene spread across the natural distribution of a plant species. Existing theories have not fully explored the role of mating systems on the wave of advance of an advantageous gene. Here, we develop a theory to account for the rate of spread of both advantageous and neutral genes under different mating systems, based on migration-selection processes. We show that a complex relationship exists between selfing rate and the speed of gene spread. The interaction of selfing with gametophytic selection shapes the traveling wave of the advantageous gene. Selfing can impede (or enhance) the spread of an advantageous gene in the presence (or absence) of gametophytic selection. The interaction of selfing with recombination shapes the spread of a neutral gene. Linkage disequilibrium, mainly generated by selfing, enhances the traveling wave of the neutral gene that is tightly linked with the selective gene. Recombination gradually breaks down the genetic hitchhiking effects along the direction of advantageous gene spread, yielding decreasing waves of advance of neutral genes. The stochastic process does not alter the pattern of selfing effects except for increasing the uncertainty of the waves of advance of both advantageous and neutral genes. This theory helps us to explain how mating systems act as a barrier to spread of adaptive and neutral genes, and to interpret species cohesion maintained by a low level of adaptive gene flow.

Maintenance of high inbreeding depression in selfing populations: Two-stage effect of early- and late-acting mutations

High estimates of inbreeding depression have been obtained in many plant populations with high selfing rates. However, deleterious mutations might be purged from such populations as a result of selfing. I developed a simulation model assuming the presence of mutations at two sets of loci, namely, early- and late-acting loci, and the selective abortion of embryos coupled with ovule overproduction. In the model, early-acting loci are expressed during embryo initiation, and less vigorous embryos are aborted. Late-acting loci are expressed after selective abortion ends; the surviving embryos (seeds) compete, and some of them form the next generation. If mutations are allowed to occur in both early- and late-acting loci, both types increase in frequency in populations with high selfing rates. However, this phenomenon does not occur if mutations occur only in the early- or only in the late-acting loci. Consistent results are observed even if the total number of loci in which mutations are allowed to occur is the same for simulations with both early- and late-acting loci, only early-acting loci, or only late-acting loci, indicating that the presence of both types of loci is the causal factor. Thus, the two-stage effect, or occurrence of both early- and late-acting mutations, promotes the maintenance of these mutations in populations with high selfing rates.

Patterns of pollen dispersal and mating in a population of the clonal plant Sagittaria latifolia

Abstract Increased plant size is generally expected to have negative consequences for mating by increasing pollen transfer between flowers of the same plant. Such geitonogamous self‐pollination would then reduce sexual fitness through both female and male function. However, recent theoretical work has indicated that when plants grow clonally, the outward expansion of plants caused by clonal growth might have positive effects on siring without substantially increasing rates of self‐pollination. We investigated patterns of pollen dispersal, selfing and siring in a monoecious population of the clonal plant Sagittaria latifolia, in which clones varied in size and the extent of intermingling with other clones. A spatially explicit statistical model based on the inferred pollen dispersal kernel was constructed to examine the mechanisms underlying observed mating patterns. Pollen dispersal typically occurred over distances that exceeded the spatial extent of clones. There was a positive association between clone size (measured as the number of ramets per genet) and the likelihood that clones were intermingled with the shoots of other clones. Together, these patterns of pollen dispersal and clonal intermingling resulted in a weak positive association between clone size and selfing rates and a strong positive association between clone size and outcross siring success. These patterns were replicated in the spatially explicit model, indicating that the intermingling of clones is an important determinant of mating patterns in this population. Synthesis. Our study provides the first examination of the pollen dispersal kernel for a clonal plant. It is the first study providing empirical support for model predictions that potentially negative effects of increased selfing in large clones might be offset by increased siring success. This implies that the negative consequences of becoming large do not necessarily apply to clonal plants.

Inference of past demography, dormancy and self-fertilization rates from whole genome sequence data.

Several methods based on the Sequential Markovian coalescence (SMC) have been developed that make use of genome sequence data to uncover population demographic history, which is of interest in its own right and is a key requirement to generate a null model for selection tests. While these methods can be applied to all possible kind of species, the underlying assumptions are sexual reproduction in each generation and non-overlapping generations. However, in many plants, invertebrates, fungi and other taxa, those assumptions are often violated due to different ecological and life history traits, such as self-fertilization or long term dormant structures (seed or egg-banking). We develop a novel SMC-based method to infer 1) the rates/parameters of dormancy and of self-fertilization, and 2) the populations' past demographic history. Using simulated data sets, we demonstrate the accuracy of our method for a wide range of demographic scenarios and for sequence lengths from one to 30 Mb using four sampled genomes. Finally, we apply our method to a Swedish and a German population of Arabidopsis thaliana demonstrating a selfing rate of ca. 0.87 and the absence of any detectable seed-bank. In contrast, we show that the water flea Daphnia pulex exhibits a long lived egg-bank of three to 18 generations. In conclusion, we here present a novel method to infer accurate demographies and life-history traits for species with selfing and/or seed/egg-banks. Finally, we provide recommendations for the use of SMC-based methods for non-model organisms, highlighting the importance of the per site and the effective ratios of recombination over mutation.

Parentage and relatedness reconstruction in Pinus sylvestris using genotyping-by-sequencing

Estimating kinship is fundamental for studies of evolution, conservation, and breeding. Genotyping-by-sequencing (GBS) and other restriction based genotyping methods have become widely applied in these applications in non-model organisms. However, sequencing errors, depth, and reproducibility between library preps could potentially hinder accurate genetic inferences. In this study, we tested different sets of parameters in data filtering, different reference populations and eight estimation methods to obtain a robust procedure for relatedness estimation in Scots pine (Pinus sylvestris L.). We used a seed orchard as our study system, where candidate parents are known and pedigree reconstruction can be compared with theoretical expectations. We found that relatedness estimates were lower than expected for all categories of kinship estimated if the proportion of shared SNPs was low. However, estimates reached expected values if loci showing an excess of heterozygotes were removed and genotyping error rates were considered. The genetic variance-covariance matrix (G-matrix) estimation, however, performed poorly in kinship estimation. The reduced relatedness estimates are likely due to false heterozygosity calls. We analyzed the mating structure in the seed orchard and identified a selfing rate of 3% (including crosses between clone mates) and external pollen contamination of 33.6%. Little genetic structure was observed in the sampled Scots pine natural populations, and the degree of inbreeding in the orchard seed crop is comparable to natural stands. We illustrate that under our optimized data processing procedure, relatedness, and genetic composition, including level of pollen contamination within a seed orchard crop, can be established consistently by different estimators.

Management Practices and Breeding History of Varieties Strongly Determine the Fine Genetic Structure of Crop Populations: A Case Study Based on European Wheat Populations

As the effects of climate change begin to be felt on yield stability, it is becoming essential to promote the use of genetic diversity in farmers’ fields. The presence of genetic variability in variety could fulfil this purpose. Indeed, the level of intra-varietal genetic diversity influences the spatio-temporal stability of yields and the disease susceptibility of crop species. Breeding history of varieties and their management practices are two factors that should influence intra-varietal genetic diversity. This paper describes the genetic diversity of eight wheat samples covering a gradient from modern single varieties to on-farm mixtures of landraces. This gradient discriminates between landrace, historical and modern varieties, considering the breeding history of varieties, between single-varieties and mixtures of varieties, and between ex situ and in situ de facto strategy in terms of management practices. Genetic diversity of these samples was analyzed with the help of 41 single nucleotide polymorphism markers located in neutral regions, through computing genetic indices at three different levels: Allelic, haplotypic and genetic group level. Population structure and kinship were depicted using discriminant analysis and kinship network analysis. Results revealed an increase in the complexity of the genetic structure as we move on the gradient of variety types (from modern single variety to in situ on-farm mixtures of landraces). For the landraces, the highest levels of genetic diversity have been observed for a landrace (Solina d’Abruzzo) continuously grown on-farm in the region of Abruzzo, in Italy, for many decades. This landrace showed an excess of haplotypic diversity compared to landraces or the historical variety that were stored in genebanks (ex situ conservation). Genetic analyses of the mixtures revealed that, despite a very high selfing rate in wheat, growing in evolutionary mixtures promotes recombination between different genetic components of the mixture, a second way to increase the level of haplotype diversity. When management practices such as growing in mixture and on-farm management are combined, they substantially increase the different levels of genetic diversity of the populations (allelic, haplotypic, genetic group diversity), and consequently promote their adaptability. Our results confirm the need to develop and manage evolving diversified large populations on-farm. These results invite crop diversity managers such as genebank curators, community seed bank managers and farmers’ organizations to adapt their management strategies to the type of variety they wish to manage, because we have shown that their choices have a strong influence on the genetic composition of the crop populations.

Population genetics shed light on species delimitation and life history of the Dyckia pernambucana complex (Bromeliaceae)

AbstractIn the Atlantic Rainforest located north of the São Francisco River (northeast Brazil), the humid enclaves called brejos de altitude play a significant role in the diversity dynamics of local flora and fauna. The related species Dyckia pernambucana and D. limae (Bromeliaceae) are characterized by their narrow endemic occurrence in such brejos, and their species status remains unclear. In order to understand the species delimitation in those assigned taxonomic entities, patterns of gene flow and genetic variability were calculated using nuclear and plastid microsatellites and AFLP markers. In this regard, we collected populations of the Pernambuco complex (D. limae and D. pernambucana, from the Borborema Plateau) and the closest relative D. dissitiflora (from the northern Espinhaço Range). Genetic diversity was moderate, despite the possible influence of genetic drift and selfing rates. Dyckia limae could not be undoubtedly discriminated from the remaining populations of Pernambuco, and we propose the synonymization of these species. Thus, the conservation of D. limae as a formerly single species would not reflect the conservation of the minimal gene pool of the studied lineage (D. pernambucana). We also propose the revalidation of the conservation status of this species, endemic to anthropomorphic island-like mountains environments. Finally, the associations found here were consistent with the historical patterns of colonization and fragmentation of the Atlantic Rainforest.

Gametophytic competition games among relatives: When does spatial structure select for facilitativeness or competitiveness in pollination?

Abstract Determining whether pollination occurs competitively or rather facilitatively among co‐flowering plants is a central question in plant reproductive ecology. Kobayashi [2018; Journal of Ecology 107: 1433–1438] theoretically investigated the scenario in which intraspecific pollen tube competition (male–male competition) can lead to regulation of population growth due to reduced female success. Kobayashi (2018) showed that evolutionary dynamics in intraspecific pollen tube competition can reduce female success and consequently generate negative density‐dependence of population growth, which allows for numerous species to coexist in a spatially subdivided metacommunity. Kobayashi (2018) hypothesized that trait evolution driven by sexual selection may maintain biodiversity. However, the models proposed by Kobayashi (2018) allow for the assumptions to be relaxed; he assumed: (i) fully global seed dispersal (instead of limited dispersal, albeit the spatial subdivision), (ii) fully local pollination (i.e., pollination occurred exclusively within patches), (iii) selfing rate was exactly proportionate (i.e., pollen grains distributed equally among all individuals within a patch, irrespective of their parental origins), (iv) haploid mode of inheritance, and most importantly, (v) each individual was mutually competitive, rather than facilitative for pollination. Here, I extend the models of Kobayashi (2018) and show that when I relax assumptions (i)–(v), facilitativeness, as opposed to competitiveness, is more likely to be favoured by selection. The present results are attributed to kin selection in gametopythic competition among relatives in spatially subdivided populations. If facilitativeness for pollination is favoured by kin selection, then the premise that the evolution of pollen traits can generate negative density‐dependence does not necessarily follow. I also discuss the potential mechanisms by which pollen phenotypes can either strengthen or attenuate intraspecific and interspecific competition.

Breeding system and inbreeding depression in a translocated population of the endangered plant Dianthus morisianus (Caryophyllaceae)

Know the breeding system of endemic plants is important to design conservation strategies. Translocations are actions to improve the survival prospects of the species, but nowadays there are only a few studies that analyse their success and make a comparison between translocation and the natural populations. Dianthus morisianus is a threatened narrow endemic plant species growing on sand dunes in SW Sardinia (Italy). The objective of this study was to assess the breeding system, the presence of inbreeding depression and pollen limitation, as well as the success of the plant translocation. All these results were compared with those from the single natural population. The breeding system was tested through five pollination treatments and the reproductive success was analysed by the fruit set, seed set, seed weight, germination and mortality rate. The translocated population behaved like the natural one on fruit and seed formation. Autonomous self-pollination was lower than the other treatments regarding fruit set and seed/ovule ratio in the two studied populations. The species is self-compatible and presents partial self-fertility. The selfing rate was higher in the translocated population and the inbreeding depression presented low values for the natural population, while the translocated population presented negative values. Neither of the populations suffered pollen limitation. The species did not present reproductive problems and it is pollinator dependent. Moreover, the translocated population demonstrated high success after five years, as an increase of the population area and new recruited plants was observed; the offspring were able to flower, fruiting and reproduce. This translocation success increases the survival prospects of the species.

Multiple founder events explain the genetic diversity and structure of the model allopolyploid grass Brachypodium hybridum in the Iberian Peninsula hotspot.

It is accepted that contemporary allopolyploid species have originated recurrently, but very few cases have been documented using multiple natural formations of the same species. To extend our knowledge, we have investigated the multiple origins, genetic variation and structure of the allotetraploid grass Brachypodium hybridum with respect to its progenitor diploid species B. distachyon (D genome) and B. stacei (S genome). For this, our primary focus is the Iberian Peninsula, an evolutionary hotspot for the genus Brachypodium. We analysed 342 B. hybridum individuals from 36 populations using ten nuclear SSR loci and two plastid loci. The B. hybridum genetic profiles were compared with those previously reported for B. stacei and B. distachyon. In addition, phylogenetic analysis of the plastid data was performed for a reduced subset of individuals. The nuclear simple sequence repeat (SSR) genetic analysis detected medium to high genetic diversity, with a strong south-to-north genetic structure cline, and a high selfing rate in B. hybridum. Comparative genetic analysis showed a close relatedness of current B. hybridum D allelic profiles with those of B. distachyon, but a lack of similarity with those of B. stacei, suggesting another B. stacei source for the B. hybridum S alleles. Plastid analysis detected three different bidirectional allopolyploidization events: two involved distinct B. distachyon-like ancestors and one involved a B. stacei-like ancestor. The south-eastern Iberian Peninsula B. hybridum populations were more genetically diverse and could have originated from at least two hybridization events whereas north-eastern/north-western Iberian Peninsula B. hybridum populations were less diverse and may have derived from at least one hybridization event. The genetic and evolutionary evidence supports the plausible in situ origin of the south-eastern and northern Iberian Peninsula B. hybridum allopolyploids from their respective local B. distachyon and unknown B. stacei ancestors. The untapped multiple origins and genetic variation detected in these B. hybridum populations opens the way to future evolutionary analysis of allopolyploid formation and genomic dominance and expression in the B. hybridum-B. distachyon-B. stacei grass model complex.

Self-compatibility and autonomous selfing of plants in meadow communities.

One of the most fundamental, although controversial, questions related to the evolution of plant mating systems is the distribution of outcrossing rates. Self-compatibility, and especially autonomous self-pollination, can become particularly beneficial in anthropogenically degraded habitats with impoverished pollinator assemblages and increased pollen limitation. In a hand-pollination experiment with 46 meadow plants from the Železné hory Mts., Czech Republic, we evaluated the species' ability to adopt different mating systems. For a subset of the species, we also tested seed germination for inbreeding depression. Subsequently, we analysed relationships between the species' mating systems and 12 floral and life-history traits. We found a relatively discrete distribution of the studied species into four groups. Fully and partially self-incompatible species formed the largest group, followed by self-compatible non-selfers and mixed mating species. The germination experiment showed an absence of inbreeding depression in 19 out of 22 examined species. Nectar sugar per flower, nectar sugar per shoot and dichogamy were significant associated with the mating system. Spontaneous selfing ability and self-incompatibility in species of the meadow communities had a discrete distribution, conforming to the general distribution of mating and breeding systems in angiosperms. The low frequency of spontaneous selfers and the lack of inbreeding depression at germination suggest the existence of a selection against selfing at the later ontogenetic stages. Some floral traits, such as the level of dichogamy and amount of nectar reward, may strongly impact the balance between selfing and outcrossing rates in the self-compatible species and thus shape the evolution of mating systems.

Effect of partial selfing and polygenic selection on establishment in a new habitat

This article analyzes how partial selfing in a large source population influences its ability to colonize a new habitat via the introduction of a few founder individuals. Founders experience inbreeding depression due to partially recessive deleterious alleles as well as maladaptation to the new environment due to selection on a large number of additive loci. I first introduce a simplified version of the inbreeding history model to characterize mutation‐selection balance in a large, partially selfing source population under selection involving multiple nonidentical loci. I then use individual‐based simulations to study the eco‐evolutionary dynamics of founders establishing in the new habitat under a model of hard selection. The study explores how selfing rate shapes establishment probabilities of founders via effects on both inbreeding depression and adaptability to the new environment, and also distinguishes the effects of selfing on the initial fitness of founders from its effects on the long‐term adaptive response of the populations they found. A high rate of (but not complete) selfing is found to aid establishment over a wide range of parameters, even in the absence of mate limitation. The sensitivity of the results to assumptions about the nature of polygenic selection is discussed.