High Rates Of Self-fertilization Research Articles

Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata

The transition to self-compatibility from self-incompatibility is often associated with high rates of self-fertilization, which can restrict gene flow among populations and cause reproductive isolation of self-compatible (SC) lineages. Secondary contact between SC and self-incompatible (SI) lineages might re-establish gene flow if SC lineages remain capable of outcrossing. By contrast, intrinsic features of SC plants that reinforce high rates of self-fertilization could maintain evolutionary divergence between lineages. Arabidopsis lyrata subsp. lyrata is characterized by multiple origins of self-compatibility and high rates of self-fertilization in SC-dominated populations. It is unclear whether these high rates of selfing by SC plants have intrinsic or extrinsic causes. We estimated outcrossing rates and examined patterns of pollinator movement for 38 SC and 40 SI maternal parents sampled from an admixed array of 1509 plants sourced from six SC and six SI populations grown under uniform density. Although plants from SI populations had higher outcrossing rates (mean tm = 0.78 ± 0.05 SE) than plants from SC populations (mean tm = 0.56 ± 0.06 SE), outcrossing rates among SC plants were substantially higher than previous estimates from natural populations. Patterns of pollinator movement appeared to contribute to lower outcrossing rates for SC plants; we estimated that 40% of floral visits were geitonogamous (between flowers of the same plant). The relatively high rates of outcrossing for SC plants under standardized conditions indicate that selfing rates in natural SC populations of A. lyrata are facultative and driven by extrinsic features of A. lyrata, including patterns of pollinator movement.

The distribution of mutational effects on fitness in Caenorhabditis elegans inferred from standing genetic variation.

The distribution of fitness effects (DFE) for new mutations is one of the most theoretically important but difficult to estimate properties in population genetics. A crucial challenge to inferring the DFE from natural genetic variation is the sensitivity of the site frequency spectrum to factors like population size change, population substructure, genome structure, and nonrandom mating. Although inference methods aim to control for population size changes, the influence of nonrandom mating remains incompletely understood, despite being a common feature of many species. We report the DFE estimated from 326 genomes of Caenorhabditis elegans, a nematode roundworm with a high rate of self-fertilization. We evaluate the robustness of DFE inferences using simulated data that mimics the genomic structure and reproductive life history of C. elegans. Our observations demonstrate how the combined influence of self-fertilization, genome structure, and natural selection on linked sites can conspire to compromise estimates of the DFE from extant polymorphisms with existing methods. These factors together tend to bias inferences toward weakly deleterious mutations, making it challenging to have full confidence in the inferred DFE of new mutations as deduced from standing genetic variation in species like C. elegans. Improved methods for inferring the DFE are needed to appropriately handle strong linked selection and selfing. These results highlight the importance of understanding the combined effects of processes that can bias our interpretations of evolution in natural populations.

Apis mellifera visitation enhances productivity in rapeseed

Rapeseed (Brassica napus L.) is the second most produced oilseed crop in the world. It provides a high-quality nutrient for pollinating insects, and pollination, in many cases, increases crop yield. Although a large number of species visit rapeseed crops, Apis mellifera (Hymenoptera: Apidae) is the most frequent, abundant, and with the highest pollination potential. Our aim was to evaluate the effect of A.mellifera on the different yield components of Brassica napusL. (cv. Rivette). The hypothesis of the study was that the presence of pollinators would increase rapeseed crop yield and improves maturation uniformity. Four trials were conducted (one in 2013, two in 2015, and one in 2016) in commercial rapeseed crops, using pollinator exclusion tents placed during the flowering period. A randomized complete block design with two treatments and six replications during 2013 and three replications during 2015 and 2016 was used. Treatments consisted of exclusion tents with the addition of an active beehive (WITH) and without a beehive (EXCLUDED). WITH treatments showed greater uniformity on siliques maturation and a lower proportion of flowers at maturity. Rapeseed yield was determined by the site (season and farm) (P < 0.0005) and treatments (WITH or EXCLUDED) (P = 0.0482), with no interaction between them (P = 0.1217). Grain yield in WITH treatments was 14% higher than in EXCLUDED treatments (2089 vs. 1836 kg ha−1). In 12 out of 15 (80%) experimental units, WITH treatment yields were higher than EXCLUDED treatments. Results show that A.mellifera can increase rapeseed yields, despite a high rate of self-fertilization.

Promising options for improving performance and proanthocyanidins of the forage legume sainfoin (Onobrychis viciifolia Scop.)

Sainfoin (Onobrychis viciifolia Scop.) is an underutilized perennial forage legume with high potential as a forage source for ruminants in grassland based livestock production systems. The species is also particularly valued for its content of proanthocyanidins (PA; also known as condensed tannins), which have been shown to improve animal health by reducing bloat, and by diminishing gastro-intestinal parasites, can reduce nitrogen losses through excreted urine and may also have the potential to lower methane emissions. However, sainfoin cultivation is not widespread today, mainly due to the limited availability of high performing cultivars and agronomic constraints such as slow establishment, poor competitive ability and limited yield stability. In this paper, we give an overview on the importance and the potential of sainfoin and review recent findings regarding cultivation practices and the variability observed for agronomic and quality traits. A special focus is placed on the potential and implications for targeted improvement through breeding. Results show that stability of sainfoin yields can be significantly improved when grown in mixtures with appropriate companion species and it was shown that the choice of cultivar, management practices and drought could have an impact on PA content and composition. Various studies demonstrate large variability in agronomic performance, PA concentration and PA composition among and within sainfoin accessions, highlighting the big potential to improve this species by breeding. In addition, we highlight recent advances in breeding research such as high rates of self-fertilization in this generally allogamous species and the development of molecular genetic resources, which build the basis for novel breeding strategies and the targeted exploitation of sainfoin germplasm in the future.

High Rates of Self-Fertilization in a Marine Ribbon Worm (Nemertea).

Organisms capable of self-fertilization ("selfing") typically exhibit two evolutionary syndromes: uniting high inbreeding depression with low levels of selfing, or low inbreeding depression with high levels of selfing. We examined the effect of inbreeding on fecundity and time to first reproduction in an apparently self-compatible, simultaneously hermaphroditic marine nemertean worm Prosorhochmus americanus. Adult and juvenile worms were raised in isolation or in pairs. Isolated worms produced significantly more offspring than paired worms (in the adult experiment), and did not exhibit inbreeding avoidance (in the juvenile experiment). The selfing rate of six natural populations was evaluated using 17 species-specific, microsatellite markers, and was consistent with preferential selfing (mean: 0.843, SD: 0.027). Our results showed that P. americanus exhibited an interesting suite of life-history traits, uniting high colonization potential through self-fertilization and high fecundity, with no dispersive larval stage, and with moderate levels of gene flow. We believe that P. americanus is an ideal model system for studies of mating system evolution, inbreeding, and sex allocation.

Informativeness of minisatellite and microsatellite markers for genetic analysis in papaya.

The objective of this study was to evaluate information on minisatellite and microsatellite markers in papaya (Carica papaya L.). Forty minisatellites and 91 microsatellites were used for genotyping 24 papaya accessions. Estimates of genetic diversity, genetic linkage and analyses of population structure were compared. A lower average number of alleles per locus was observed in minisatellites (3.10) compared with microsatellites (3.57), although the minisatellites showed rarer alleles (18.54 %) compared with microsatellite (13.85 %). Greater expected (He = 0.52) and observed (Ho = 0.16) heterozygosity was observed in the microsatellites compared with minisatellites (He = 0.42 and Ho = 0.11), possibly due to the high number of hermaphroditic accessions, resulting in high rates of self-fertilization. The polymorphic information content and Shannon-Wiener diversity were also higher for microsatellites (from 0.47 to 1.10, respectively) compared with minisatellite (0.38 and 0.85, respectively). The probability of paternity exclusion was high for both markers (>0.999), and the combined probability of identity was from 1.65(-13) to 4.33(-38) for mini- and micro-satellites, respectively, which indicates that both types of markers are ideal for genetic analysis. The Bayesian analysis indicated the formation of two groups (K = 2) for both markers, although the minisatellites indicated a substructure (K = 4). A greater number of accessions with a low probability of assignment to specific groups were observed for microsatellites. Collectively, the results indicated higher informativeness of microsatellites. However, the lower informative power of minisatellites may be offset by the use of larger number of loci. Furthermore, minisatellites are subject to less error in genotyping because there is greater power to detect genotyping systems when larger motifs are used.

A multi-faceted approach for assessing evolutionary significant conservation units in the endangered Omphalodes littoralis subsp. gallaecica (Boraginaceae)

Genetic diversity is now regarded as a key component of biodiversity and its assessment has become a frequent addition to conservation studies. However, due to practical limitations, most studies assess genetic variation using neutral markers while the variability of evolutionary relevant quantitative traits is typically overlooked. Here, we simultaneously assessed neutral and quantitative variation in an endangered plant to identify the mechanism behind their spatial arrangement and to propose conservation guidelines for maximizing mid- to long-term survival. Omphalodes littoralis subsp. gallaecica is a self-fertilizing therophyte with an extremely narrow and fragmented distribution. Regardless of the marker set (non-coding sequences of cpDNA or Amplified Fragment Length Polymorphism loci), the five extant populations of O. littoralis subsp. gallaecica showed minimal to none neutral genetic diversity and a lack of gene flow between them. Moreover, genetic structure was identical in samples collected on two consecutive years suggesting that the seed bank cannot buffer against genetic loss. High rates of self-fertilization together with a strongly fragmented distribution and recurrent bottlenecks seem the likely mechanisms that may have led to a dramatic loss of genetic variation in a classic scenario drawn by genetic drift. Despite the extremely narrow distribution range, reciprocal transplant experiments revealed that the populations differed in several quantitative traits and that these differences likely have a genetic basis. Nevertheless, the pattern of differences among populations did not fit the expectations of local adaptation. Instead, phenotypic variation seemed another outcome of genetic drift with important implications for conservation because each population should be designated as an independent evolutionary significant unit (ESU). Our study evidences the benefits of combining neutral markers with appropriate assessments of phenotype variation, and shows that even endemics with extremely narrow ranges can contain multiple conservation units.

Microsatellite markers for the native Texas perennial grass, Panicum hallii (Poaceae)

We developed microsatellites for Panicum hallii for studies of gene flow, population structure, breeding experiments, and genetic mapping. Next-generation (454) genomic sequence data were used to design markers. Eighteen robust markers were discovered, 15 of which were polymorphic across six accessions of P. hallii var. hallii. Fourteen of the markers cross-amplified in a P. capillare accession. For the 15 polymorphic markers, the total number of alleles per locus ranged from two to 26 (mean: 11.0) across six populations (11-19 individuals per population). Observed heterozygosity (mean: 0.031) was 13.7 times lower than the expected heterozygosity (mean: 0.426). The deficit of heterozygous individuals is consistent with P. hallii having a high rate of self-fertilization. These markers will be useful for studies in P. hallii and related species.

Selection and habitat-specific allozyme variation in the self-fertilizing land snail Cochlicopa lubrica (O. F. Müller)

Allozyme variation of aspartate-aminotransferase locus Aat 1 is analysed in the land snail Cochlicopa lubrica (O. F. Müller, 1774). Two alleles, denoted ‘20’ and ‘80’, have been found in 29 Central European populations investigated. This species reproduces under a high rate of self-fertilization. Only three out of 787 individuals were heterozygous (enzyme pattern Aat 1 ‘20’/‘80’). The homozygous individuals with Aat 1 ‘80’ were frequent in moist and shady habitats. In exposed and open habitats, however, the homozygous individuals with Aat 1 ‘20’ occurred frequently. These results give strong evidence for habitat-specific selection inferred from allozyme variation. Moreover, a tight interlocus correlation of isocitrate-dehydrogenase patterns (Idh 1) and Aat 1 patterns has been observed. Two groups of homozygous genotypes are commonly found: (1) the group Idh 1 ‘145’/Aat 1 ‘80’, and (2) the group Idh 1 ‘155’/Aat 1 ‘20’. The Aat data for Cochlicopa lubrica are complemented by morphometric measurements of the shells. The homozygous types of Aat 1 ‘20’ (common in exposed/open habitats) possessed, on average, slightly smaller shells than the homozygous types with Aat 1 ‘80’ (common in moist/shady habitats). This slight mean difference in shell size might be due to the living conditions in the habitats. In the last part of the study, the allozyme variation of snails was assessed for spatial selection processes, and a compilation of the available papers is shown.

Plasmodium falciparum parasites in French Guiana: limited genetic diversity and high selfing rate.

The genetic characteristics of Plasmodium falciparum isolates collected in French Guiana, where malaria transmission is low and occurs in isolated foci, were studied. Blood samples were collected from 142 patients with symptomatic malaria and typed using a polymerase chain reaction-based strategy for merozoite surface protein-(MSP-1) block 2, the MSP-2 central domain, and glutamate-rich protein (GLURP) repeat domain polymorphism. This showed that the parasite population circulating in French Guiana presented a limited number of allelic forms (4, 2, and 3 for MSP-1 block 2, MSP-1, and GLURP, respectively) and a small number of mixed infections, contrasting with the large genetic diversity of parasite populations and infection complexity reported for Africa, Asia, and other parts of South America. Two groups of isolates displaying identical 3 loci allele combinations were further studied for the Pf332 antigen, histidine-rich protein-1, thrombospondin-related anonymous protein, and Pf60 multigene family polymorphism. Within each group, most isolates were identical for all markers tested. This suggests a high rate of self-fertilization of P. falciparum parasites in French Guiana, resulting in homogenization of the population. The implications of these findings for malaria control in areas of low endemicity are discussed.

BREEDING STRUCTURE OF A YUCCA FILAMENTOSA (AGAVACEAE) POPULATION.

Yucca filamentosa and its species-specific pollinator, the yucca moth, Tegeticula yuccasella (Lepidoptera: Prodoxidae), form a relationship that is often cited as a classic example of a coevolved plant-pollinator mutualism. Observations of the moth's behavior have led to predictions that moth dispersal is relatively limited and that, as a consequence, the self-compatible Y. filamentosa should experience relatively high rates of self-fertilization. In contrast, analyses of its mating system indicated that Y. filamentosa was predominantly outcrossed. To better understand effective breeding patterns in Y. filamentosa populations, 10 polymorphic allozyme loci were investigated to analyze the breeding structure of a natural Y. filamentosa population. Analyses revealed that Y. filamentosa is predominantly outcrossed, has multiply sired fruits, and that each fruit was sired by a different set of pollen donors. The effective number of pollen donors per fruit ranged from 1.56 to 3.13, indicating that some correlated mating exists within fruits. Paternity analyses revealed that pollen moved from 6 m to 293 m (mean = 118 m) within the study population and that a minimum of 10% of the progeny were sired by pollen originating outside of the population. These results are discussed in the context of the yucca-yucca moth mutualism.

The reduction of neutral gene flow caused by a selected gene in plant population models

The neutral gene flow among populations of higher plants in the presence of a simple zygotic isolating mechanism is studied theoretically. Partial reproductive isolation is caused by a gene subject to selection. The population model is an island model with very small interpopulation migration rates. General solutions have been obtained and verified by numerical tests. It has been observed that the reduction of gene flow caused by the isolating mechanism is stronger—other things being equal—for: (1) greater intensity of selection; (2) lower values of the frequency of recombination between the selected locus and the neutral locus; (3) higher values of the level of partial self-fertilization. The last result is particularly interesting and needs to be considered in discussing speciation processes in plants with high rates of self-fertilization.

A high rate of self-fertilization and increased seed fertility of homostyle primroses

There has been extensive theoretical study of the evolution of self-fertilization in hermaphroditic or monoecious flowering plants because self-compatible species with high rates of self-fertilization are often derived from outcrossing ancestors1–4. Such studies have shown that a gene causing an increased rate of self-fertilization has an advantage because the mother transmits genes via both pollen and egg to selfed progeny5, and thereby evades the ‘cost of meiosis’6–8. Selfing also may be advantageous if the amount of pollen available to fertilize ovules by outcrossing is limited1,2,4,6. However, these advantages are offset, at least partially, if the fitness of selfed progeny is lower than that of outcrossed progeny, due to inbreeding depression1,2,6,7,9,10. Biogeographical evidence suggests that reduced pollinator activity may be sufficient to counteract this disadvantage and permit the evolution of selfing in populations in ecologically marginal areas1–4, but direct evidence is usually lacking. Here we show that the self-fertile homostyle variant of the primrose Primula vulgaris, which reaches high frequencies in certain populations11, experiences a fertility advantage, in terms of seeds per plant, as a result of its high rate of self-fertilization.