Events Of Sexual Reproduction Research Articles

AFLP markers show low levels of clonal propagation and high genotypic diversity in the rare, southernmost populations of Linnaea borealis L. (Caprifoliaceae) in the Western Alps.

In plants, clonal propagation is a common reproductive strategy in parallel to sexual reproduction. It has both advantages and drawbacks, and the potential complete loss of sexual reproduction causes serious conservation concerns, especially because population maintenance then only relies on adult survival and low genetic diversity leads to decreased adaptive potential. We investigated the rare, southernmost populations of the mostly circumboreal twinflower Linnaea borealis, located in the Western Alps. Based on 105 AFLP markers and 118 leaf samples, including replicates, we estimated the genetic similarity threshold above which samples belong to a single clone. Although the species is known for extensive clonal propagation, we observed high genotypic diversity within the seven studied populations and almost all samples were genetically distinct. Nevertheless, some clonal samples were detected in two populations, separated by up to 180m. We found a strong genetic differentiation among populations (overall Fst = 0.38), which was congruent with the previously documented high plastid diversity in the region. We therefore hypothesize that Alpine populations are relicts of the Quaternary glacial periods, when the species probably survived at these lower latitudes before colonizing Northern Europe. Regarding conservation, our results suggest that most extant plants result from sexual reproduction and that populations are not highly threatened. Nevertheless, since clones can be very long-lived and almost no seedlings were observed in recent years, events of sexual reproduction may be ancient. The current reproductive dynamics should therefore be studied to estimate e.g. pollinators activity, proportions of flowering plants, and seed set.

Estimating the number of sexual events per generation in a facultatively sexual haploid population.

In populations of facultatively sexual organisms, the proportion of sexually produced offspring contributed to each generation is a critical determinant of their evolutionary potential. However, estimating this parameter in natural populations has proved difficult. Here we develop a population genetic model for estimating the number of sexual events occurring per generation for facultatively sexual haploids possessing a biallelic mating-type locus (e.g., Chlamydomonas, ascomycete fungi). Our model treats the population as two subpopulations possessing opposite mating-type alleles, which exchange genes only when a sexual event takes place. Where mating types are equally abundant, we show that, for a neutral genetic marker, genetic differentiation between mating-type subpopulations is a simple function of the effective population size, the frequency of sexual reproduction, and the recombination fraction between the genetic marker and the mating-type locus. We employ simulations to examine the effects of linkage of markers to the mating-type locus, inequality of mating-type frequencies, mutation rate, and selection on this relationship. Finally, we apply our model to estimate the number of sexual reproduction events per generation in populations of four species of facultatively sexual ascomycete fungi, which have been jointly scored for mating type and a range of polymorphic molecular markers. Relative estimates are in line with expectations based on the known reproductive biology of these species.

Boom and Bust: Life History, Environmental Noise, and the (un)Predictability of Jellyfish Blooms

Jellyfish (pelagic Cnidarians and Ctenophores) form erratic and seemingly unpredictable blooms with often large, transient effects on ecosystem structure. To rapidly capitalize on favorable conditions, jellyfish can employ different life histories, which are either a life cycle with one annual sexual reproduction event and an overwintering benthic stage (metagenic life cycle), or continuous reproduction and a holoplanktonic life cycle. However, the links between life history, blooms, and environmental variability are unclear. Here, we examine how environmental variability can drive the bloom dynamics of typical jellyfish in coastal enclosed or semi-enclosed temperate ecosystems. With a simple community model, we reproduce typical seasonalities of the two strategies and trophic cascades triggered by abundant jellyfish, demonstrating how erratic blooms can be generated by irregular changes in the environment. Consistent with literature observations, we predict that metagenic jellyfish dominate early in the season, compared to holoplanktonic organisms, and are favored by increased seasonality. Our results reveal possible mechanisms driving coastal patterns of jellyfish blooms, and factors that are important for the outcome of competition between jellyfish with different life cycles. Such knowledge is important for our understanding of jellyfish blooms, which have large consequences for human activities and well-being, and may improve our ability to predict and manage local ecosystems.

Bone morphogenetic protein and retinoic acid synergistically specify female germ-cell fate in mice.

The mechanism for sex determination in mammalian germ cells remains unclear. Here, we reconstitute the female sex determination in mouse germ cells invitro under a defined condition without the use of gonadal somatic cells. We show that retinoic acid (RA) and its key effector, STRA8, are not sufficient to induce the female germ-cell fate. In contrast, bone morphogenetic protein (BMP) and RA synergistically induce primordial germ cells (PGCs)/PGC-like cells (PGCLCs) derived from embryonic stem cells (ESCs) into fetal primary oocytes. The induction is characterized by entry into the meiotic prophase, occurs synchronously and recapitulates cytological and transcriptome progression invivo faithfully. Importantly, the female germ-cell induction necessitates a proper cellular competence-most typically, DNA demethylation of relevant genes-which is observed in appropriately propagated PGCs/PGCLCs, but not in PGCs/PGCLCs immediately after induction. This provides an explanation for the differential function of BMP signaling between PGC specification and female germ-cell induction. Our findings represent a framework for a comprehensive delineation of the sex-determination pathway in mammalian germ cells, including humans.

Dynamic transcriptomic analysis of the early response of female flowers of Populus alba\u2009\xd7\u2009P. glandulosa to pollination

Pollination is an important event in plant sexual reproduction, and post-pollination response is an essential process for reproduction. Populus alba × P. glandulosa is used widely in scientific research, especially in cross breeding as parents. Adult female P. alba × P. glandulosa flowers are highly compatible with pollen from male P. tomentosa, but the early post-pollination response of flowers at the molecular levels is unclear. In this study, RNA-seq was employed to comprehensively understand the response of female P. alba × P. glandulosa flowers to pollination. Enrichment analysis reveals that the ‘plant hormone signal transduction’ pathway is enhanced during pollen-pistil interaction. Moreover, genes related to auxin, gibberellin and ethylene biosynthesis were significantly up-regulated. Ca2+ and H+-related genes and cell wall-related genes are interrelated, and all of them are essential for pollen tube elongation in pistil, especially, free Ca2+ providing a concentration gradient for pollen tube guidance and involved in signal transduction. Furthermore, RNA-seq results indicate that genes involved in the adhesion and guidance for pollen germination and pollen tube growth are abundantly present in the extracellular matrix. Our study provides an overview and detailed information for understanding the molecular mechanism of early post-pollination response in this hybrid poplar reproduction.

Live-Cell Imaging of F-Actin Dynamics During Fertilization in Arabidopsis thaliana.

Fertilization comprises a complex series of cellular processes leading to the fusion of a male and female gamete. Many studies have been carried out to investigate each step of fertilization in plants; however, our comprehensive understanding of all the sequential events during fertilization is still limited. This is largely due to difficulty in investigating events in the female gametophyte, which is deeply embedded in the maternal tissue. Recent advances in confocal microcopy assisted by fluorescent marker lines have contributed to visualizing subcellular dynamics in real time during fertilization in vivo. In this chapter, we describe a method focusing on the investigation of F-actin dynamics in the central cell during male gamete nuclear migration. This method also allows the study of a wide range of early sexual reproduction events, from pollen tube guidance to the early stage of seed development.

Hope springs eternal in the starfish gonad: preserved potential for sexual reproduction in a single-clone population of a fissiparous starfish

Among echinoderms, asexual reproduction by fission occurs in few species. This strategy is considered a temporary response to stressful conditions and usually alternates with sexual reproduction events; thus, monoclonal populations are extremely rare. The occurrence of a single-clone population of the starfish Coscinasterias tenuispina at Llanca (NW Mediterranean) allowed us to study intra-clonal variation of the reproductive cycle during a two-year study. The few developed gonads (all male) were found in winter months, coinciding with the minimum photoperiod (ρ = −0.82; P < 0.001) and lowest temperatures (ρ = −0.75; P < 0.001), only in best-fed individuals, indicating that food availability influences individual ability for gonad development. Fissiparity happened throughout all the sampled period, but its rate increased with warm temperatures (ρ = 0.68; P < 0.0001). In contrast to what has been reported in other species, no correlation between fission rates and population density was found. The population was maintained over time by asexual reproduction and remained monoclonal. Although sexual reproduction has probably not occurred in this all-male population for a long time, the ability to yearly produce mature gonads is retained by some individuals, indicating that potential to reproduce sexually may be preserved, even in the case of strictly asexual populations.

Two HAP2-GCS1 homologs responsible for gamete interactions in the cellular slime mold with multiple mating types: Implication for common mechanisms of sexual reproduction shared by plants and protozoa and for male-female differentiation

Fertilization is a central event in sexual reproduction, and understanding its molecular mechanisms has both basic and applicative biological importance. Recent studies have uncovered the molecules that mediate this process in a variety of organisms, making it intriguing to consider conservation and evolution of the mechanisms of sexual reproduction across phyla. The social amoeba Dictyostelium discoideum undergoes sexual maturation and forms gametes under dark and humid conditions. It exhibits three mating types, type-I, -II, and -III, for the heterothallic mating system. Based on proteome analyses of the gamete membranes, we detected expression of two homologs of the plant fertilization protein HAP2-GCS1. When their coding genes were disrupted in type-I and type-II strains, sexual potency was completely lost, whereas disruption in the type-III strain did not affect mating behavior, suggesting that the latter acts as female in complex organisms. Our results demonstrate the highly conserved function of HAP2-GCS1 in gamete interactions and suggest the presence of additional allo-recognition mechanisms in D. discoideum gametes.

Late progamic phase and fertilization affect calreticulin expression in the Hyacinthus orientalis female gametophyte.

Key messageCalreticulin expression is upregulated during sexual reproduction ofHyacinthus orientalis, and the protein is localized both in the cytoplasm and a highly specialized cell wall within the female gametophyte.Several evidences indicate calreticulin (CRT) as an important calcium (Ca2+)-binding protein that is involved in the generative reproduction of higher plants, including both pre-fertilization and post-fertilization events. Because CRT is able to bind and sequester exchangeable Ca2+, it can serve as a mobile intracellular store of easily releasable Ca2+ and control its local cytosolic concentrations in the embryo sac. This phenomenon seems to be essential during the late progamic phase, gamete fusion, and early embryogenesis. In this report, we demonstrate the differential expression of CRT within Hyacinthus female gametophyte cells before and during anthesis, during the late progamic phase when the pollen tube enters the embryo sac, and at the moment of fertilization and zygote/early endosperm activation. CRT mRNA and the protein localize mainly to the endoplasmic reticulum (ER) and Golgi compartments of the cells, which are involved in sexual reproduction events, such as those in sister synergids, the egg cell, the central cell, zygote and the developing endosperm. Additionally, immunogold research demonstrates selective CRT distribution in the filiform apparatus (FA), a highly specific component of the synergid cell wall. In the light of our previous data showing the total transcriptional activity of the Hyacinthus female gametophyte and the results presented here, we discuss the possible functions of CRT with respect to the critical role of Ca2+ homeostasis during key events of sexual plant reproduction. Moreover, we propose that the elevated expression of CRT within the female gametophyte is a universal phenomenon in the cells involved in double fertilization in higher plants.

Cross-species fertilization: the hamster egg receptor, Juno, binds the human sperm ligand, Izumo1.

Fertilization is the culminating event in sexual reproduction and requires the recognition and fusion of the haploid sperm and egg to form a new diploid organism. Specificity in these recognition events is one reason why sperm and eggs from different species are not normally compatible. One notable exception is the unusual ability of zona-free eggs from the Syrian golden hamster (Mesocricetus auratus) to recognize and fuse with human sperm, a phenomenon that has been exploited to assess sperm quality in assisted fertility treatments. Following our recent finding that the interaction between the sperm and egg recognition receptors Izumo1 and Juno is essential for fertilization, we now demonstrate concordance between the ability of Izumo1 and Juno from different species to interact, and the ability of their isolated gametes to cross-fertilize each other in vitro. In particular, we show that Juno from the golden hamster can directly interact with human Izumo1. These data suggest that the interaction between Izumo1 and Juno plays an important role in cross-species gamete recognition, and may inform the development of improved prognostic tests that do not require the use of animals to guide the most appropriate fertility treatment for infertile couples.

Reproductive Ecology of Mangrove Flora: Conservation and Management

ABSTRACT Mangroves are dynamic and unique inter-tidal ecosystems, common in tropical and subtropical coastal environments. They are among the world’s most productive ecosystems and are important in protecting coasts from erosion by fierce tides, in promoting the diversity of marine organisms and fisheries by contributing a quantity of food and providing favourable habitats for animals. These economic uses of mangroves indicate that they play an important role in the lives and economies in the coastal regions of different countries. Mangrove forests are under immense threat worldwide due to their multiple economic uses and alterations of freshwater inflows by various upstream activities in catchment areas. Mangrove plants with unique adaptations play a crucial role in sustaining life in mangrove forests. Their reproductive biology is central to understanding the structural and functional components of mangrove forests. The success of sexual reproduction and subsequent population expansion in mangrove plants is linked to flowering timings, pollinators and tidal currents. Viviparous and cryptoviviparous plants are true mangroves while non-viviparous ones are mangrove associates. The dispersal propagule is seedling in viviparous and non-viviparous plants while it is seed in nonviviparous plants. In this study, viviparous and crypto-viviparous species were included for study. These species are self-compatible, self-pollinating and also cross-pollinating; such a breeding system is a requirement for the success of sexual reproduction and subsequent build up and expansion of population. They are entomophilous in the study region. The viviparous plants include Ceriops tagal, C. decandra, Rhizophora apiculata, R. mucronata, Bruguiera gymnorrhiza and B. cylindrica. The non-viviparous plants include Avicennia alba, A. marina, A. officinalis, Aegiceras corniculatum and Aegialitis rotundifolia. Sexual reproduction and regeneration events are annual in these plants and are dependent on local insects, tidal currents and nutrient content in estuarine environment. In recent times, erratic and insufficient rainfall together with industrial pollutants released into rivers is causing negative effects on the growth, development and regeneration of mangrove flora. In effect, there is a gradual decrease in mangrove cover. Added to this is continuous exploitation of mangrove plants for fuel wood, creation of shelters for cattle and changes for industrial establishments and aquaculture development in estuarine regions. As a consequence, the existing mangrove cover is struggling to survive and also not in a position to support local needs and provide livelihood opportunities through fishery resources. Further, reduced mangrove cover is showing catastrophic effects on fishing communities who live along the shore line during the period of cyclonic surges and tsunami events.

Sexual reproduction of the pentaploid, short‐styled Oxalis pes‐caprae allows the production of viable offspring

Reproduction is a key factor for the successful establishment and spread of introduced species. Oxalis pes-caprae is a tristylous species with a self- and morph-incompatibility sexual system that, in the invaded range of the western Mediterranean Basin, has been found to reproduce asexually because only the pentaploid, short-styled morph (5x S-morph) was introduced. The objective of this study was to test the ability of the 5x S-morph of O.pes-caprae to produce viable offspring in the absence of compatible mates, exploring the hypothesis that new morphs could have emerged by sexual reproduction events of the initially introduced morph. Pollen germination, pollen tube development, fruit and seed production, seed germination and offspring ploidy levels were analysed after controlled hand-pollinations to assess self- and morph-incompatibility and production of viable gametes by the 5x S-morph. The self-incompatibility system is still operating, but a partial breakdown in the morph-incompatibility system combined with the production of viable gametes was observed, allowing sexual reproduction of the 5x S-morph in the invaded range. The ability of the 5x S-morph to reproduce sexually may have major consequences for the dynamics of invasive populations of O.pes-caprae and could be one of the factors involved in the occurrence of new floral morphs in this invaded range.

Polyploidy and microsatellite variation in the relict tree Prunus lusitanica L.: how effective are refugia in preserving genotypic diversity of clonal taxa?

Refugia are expected to preserve genetic variation of relict taxa, especially in polyploids, because high gene dosages could prevent genetic erosion in small isolated populations. However, other attributes linked to polyploidy, such as asexual reproduction, may strongly limit the levels of genetic variability in relict populations. Here, ploidy levels and patterns of genetic variation at nuclear microsatellite loci were analysed in Prunus lusitanica, a polyploid species with clonal reproduction that is considered a paradigmatic example of a Tertiary relict. Sampling in this study considered a total of 20 populations of three subspecies: mainland lusitanica (Iberian Peninsula and Morocco), and island azorica (Azores) and hixa (Canary Islands and Madeira). Flow cytometry results supported an octoploid genome for lusitanica and hixa, whereas a 16-ploid level was inferred for azorica. Fixed heterozygosity of a few allele variants at most microsatellite loci resulted in levels of allelic diversity much lower than those expected for a high-order polyploid. Islands as a whole did not contain higher levels of genetic variation (allelic or genotypic) than mainland refuges, but island populations displayed more private alleles and higher genotypic diversity in old volcanic areas. Patterns of microsatellite variation were compatible with the occurrence of clonal individuals in all but two island populations, and the incidence of clonality within populations negatively correlated with the estimated timing of colonization. Our results also suggest that gene flow has been very rare among populations, and thus population growth following founder events was apparently mediated by clonality rather than seed recruitment, especially in mainland areas. This study extends to clonal taxa the idea of oceanic islands as important refugia for biodiversity, since the conditions for generation and maintenance of clonal diversity (i.e. occasional events of sexual reproduction, mutation and/or seed immigration) appear to have been more frequent in these enclaves than in mainland areas.

Reproductive strategy of the invasive Oxalis pes-caprae: distribution patterns of floral morphs, ploidy levels and sexual reproduction

Oxalis pes-caprae, a tristylous flowering plant native to South Africa, is described in the western Mediterranean basin as an asexual—only 5x short-styled morph (5x S-morph) invasive weed losing all mating partners after introduction. The objective of this study was to reassess the patterns of floral morph and cytotype distribution and the sexual reproduction ability in this invaded range. For that, floral morph and cytotype composition were evaluated in 39 populations of O. pes-caprae in a methodical sampling. The reproductive success of natural populations was assessed as fruit and seed production and seed germination for all floral morphs and cytotypes detected. Self- and morph-incompatibility were also studied with controlled hand pollinations. A remarkable diversity in floral morph and cytotype composition was observed. Furthermore, we observed successful sexual reproduction in several localities across the surveyed area. The S-morph is still dominant in this invaded area, and although it was mostly 5x, an additional cytotype (4x) was also recorded. Records of both a mid-styled morph (M-morph) and an area with trimorphic populations of this species are reported here for the first time in the invasive range of the Mediterranean basin. The long-styled morph appears to occur randomly across the surveyed area, while the M-morph is concentrated mainly in Estremadura province (Portugal), where a breakdown in the incompatibility system was observed. These distribution patterns may result from events of sexual reproduction after incompatibility breakdown and/or from multiple introduction events from the native area. The ability to reproduce sexually, undetected so far, may have important impacts in the population dynamics and major consequences for the adaptation and selection potential of O. pes-caprae in this invaded area.

Asexual reproduction induces a rapid and permanent loss of sexual reproduction capacity in the rice fungal pathogen Magnaporthe oryzae: results of in vitroexperimental evolution assays

BackgroundSexual reproduction is common in eukaryotic microorganisms, with few species reproducing exclusively asexually. However, in some organisms, such as fungi, asexual reproduction alternates with episodic sexual reproduction events. Fungi are thus appropriate organisms for studies of the reasons for the selection of sexuality or clonality and of the mechanisms underlying this selection. Magnaporthe oryzae, an Ascomycete causing blast disease on rice, reproduces mostly asexually in natura. Sexual reproduction is possible in vitro and requires (i) two strains of opposite mating types including (ii) at least one female-fertile strain (i.e. a strain able to produce perithecia, the female organs in which meiosis occurs). Female-fertile strains are found only in limited areas of Asia, in which evidence for contemporary recombination has recently been obtained. We induced the forced evolution of four Chinese female-fertile strains in vitro by the weekly transfer of asexual spores (conidia) between Petri dishes. We aimed to determine whether female fertility was rapidly lost in the absence of sexual reproduction and whether this loss was controlled genetically or epigenetically.ResultsAll the strains became female-sterile after 10 to 19 rounds of selection under asexual conditions. As no single-spore isolation was carried out, the observed decrease in the production of perithecia reflected the emergence and the invasion of female-sterile mutants. The female-sterile phenotype segregated in the offspring of crosses between female-sterile evolved strains and female-fertile wild-type strains. This segregation was maintained in the second generation in backcrosses. Female-sterile evolved strains were subjected to several stresses, but none induced the restoration of female fertility. This loss of fertility was therefore probably due to genetic rather than epigenetic mechanisms. In competition experiments, female-sterile mutants produced similar numbers of viable conidia to wild-type strains, but released them more efficiently. This advantage may account for the invasion of our populations by female-sterile mutants.ConclusionsWe show for the first time that, in the absence of sexual reproduction, female-sterile mutants of M. oryzae rice strains can arise and increase in abundance in asexual generations. This change in phenotype was frequent and probably caused by mutation. These results suggest that female fertility may have been lost rapidly during the dispersion of the fungus from Asia to the rest of the world.

Whole-organ analysis of calcium behaviour in the developing pistil of olive (Olea europaea L.) as a tool for the determination of key events in sexual plant reproduction.

BackgroundThe pistil is a place where multiple interactions between cells of different types, origin, and function occur. Ca2+ is one of the key signal molecules in plants and animals. Despite the numerous studies on Ca2+ signalling during pollen-pistil interactions, which constitute one of the main topics of plant physiology, studies on Ca2+ dynamics in the pistil during flower formation are scarce. The purpose of this study was to analyze the contents and in situ localization of Ca2+ at the whole-organ level in the pistil of olive during the whole course of flower development.ResultsThe obtained results showed significant changes in Ca2+ levels and distribution during olive pistil development. In the flower buds, the lowest levels of detectable Ca2+ were observed. As flower development proceeded, the Ca2+ amount in the pistil successively increased and reached the highest levels just after anther dehiscence. When the anthers and petals fell down a dramatic but not complete drop in calcium contents occurred in all pistil parts. In situ Ca2+ localization showed a gradual accumulation on the stigma, and further expansion toward the style and the ovary after anther dehiscence. At the post-anthesis phase, the Ca2+ signal on the stigmatic surface decreased, but in the ovary a specific accumulation of calcium was observed only in one of the four ovules. Ultrastructural localization confirmed the presence of Ca2+ in the intracellular matrix and in the exudate secreted by stigmatic papillae.ConclusionsThis is the first report to analyze calcium in the olive pistil during its development. According to our results in situ calcium localization by Fluo-3 AM injection is an effective tool to follow the pistil maturity degree and the spatial organization of calcium-dependent events of sexual reproduction occurring in developing pistil of angiosperms. The progressive increase of the Ca2+ pool during olive pistil development shown by us reflects the degree of pistil maturity. Ca2+ distribution at flower anthesis reflects the spatio-functional relationship of calcium with pollen-stigma interaction, progamic phase, fertilization and stigma senescence.

RSPO1/β-Catenin Signaling Pathway Regulates Oogonia Differentiation and Entry into Meiosis in the Mouse Fetal Ovary

Differentiation of germ cells into male gonocytes or female oocytes is a central event in sexual reproduction. Proliferation and differentiation of fetal germ cells depend on the sex of the embryo. In male mouse embryos, germ cell proliferation is regulated by the RNA helicase Mouse Vasa homolog gene and factors synthesized by the somatic Sertoli cells promote gonocyte differentiation. In the female, ovarian differentiation requires activation of the WNT/β-catenin signaling pathway in the somatic cells by the secreted protein RSPO1. Using mouse models, we now show that Rspo1 also activates the WNT/β-catenin signaling pathway in germ cells. In XX Rspo1−/− gonads, germ cell proliferation, expression of the early meiotic marker Stra8, and entry into meiosis are all impaired. In these gonads, impaired entry into meiosis and germ cell sex reversal occur prior to detectable Sertoli cell differentiation, suggesting that β-catenin signaling acts within the germ cells to promote oogonial differentiation and entry into meiosis. Our results demonstrate that RSPO1/β-catenin signaling is involved in meiosis in fetal germ cells and contributes to the cellular decision of germ cells to differentiate into oocyte or sperm.

Proteasomal degradation of ubiquitinated proteins in oocyte meiosis and fertilization in mammals

Gametogenesis and fertilization are the key events in sexual reproduction. In the female, meiosis results in a large oocyte that is competent for fertilization and fundamental for the success of early embryonic development. Progression through meiosis is monitored by fine regulatory mechanisms. In this review, we focus on one of the most well-known regulatory elements, the E3 ligase APC/C, which mediates proteolytic degradation of a number of important substrates via the ubiquitin proteasome pathway (UPP). The UPP also indirectly regulates protein synthesis by affecting proteins involved in RNA metabolism, a process that is paramount for the transcriptionally silent oocyte. During the past few years, more evidence has accumulated to suggest that the UPP has an important role in zona pellucida penetration and gamete fusion in mammals. This review focuses on the function of the UPP in regulating oocyte meiotic maturation in mammals, with special attention to its role in chromosome segregation and polar body extrusion, its role in the acquisition of meiotic/developmental competence and recent advances in our understanding of the UPP role in fertilization.

Genetic signature of amphimixis allows for the detection and fine scale localization of sexual reproduction events in a mainly parthenogenetic nematode

Asexuality is an important mode of reproduction in eukaryotic taxa and has a theoretical advantage over sexual reproduction because of the increased ability to propagate genes. Despite this advantage, hidden signs of cryptic sex have been discovered in the genomes of asexual organisms. This has provided an interesting way to address the evolutionary impact of sex in plant and animal populations. However, the identification of rare sexual reproduction events in mainly asexual species has remained a challenging task. We examined the reproductive history in populations of the plant parasitic nematode Xiphinema index by genotyping individuals collected from six grapevine fields using seven microsatellite markers. A high level of linkage disequilibrium and heterozygous excess suggested a clonality rate of 95-100%. However, we also detected rare sexual reproduction events within these highly clonal populations. By combining highly polymorphic markers with an appropriate hierarchical sampling, and using both Bayesian and multivariate analysis with phylogenetic reconstructions, we were able to identify a small number of sexually produced individuals at the overlapping zones between different genetic clusters. This suggested that sexual reproduction was favoured when and where two nematode patches came into contact. Among fields, a high degree of genetic differentiation indicated a low level of gene flow between populations. Rare genotypes that were shared by several populations suggested passive dispersal by human activities, possibly through the introduction of infected plants from nurseries. We conclude that our method can be used to detect and locate sexual events in various predominantly asexual species.

Gene flow between sexual and facultatively asexual lineages of an aphid species and the maintenance of reproductive mode variation

Many organisms considered as strictly clonal may in fact experience some rare events of sexual reproduction with their sexual relatives. However, the rate of sexual-asexual gene flow has rarely been assessed mainly because its evaluation is difficult to achieve in the field. In the cyclically parthenogenetic aphid Rhopalosiphum padi, two main sets of lineages, differing in their investment in sexual reproduction and in their genetic attributes, co-exist even at a very fine scale: the 'sexual' lineages which have a full commitment to the sexual reproduction, and the 'facultatively asexual' lineages, which allocate investment in the sexual and parthenogenetic reproduction. This system offers a unique opportunity to tackle the genetic interactions between two contrasting reproductive modes. Here, we provide evidence that gene flow occurred between sexual and facultatively asexual lineages of R. padi. We carefully examined the shuffling in phenotypic and genotypic variation following a sexual reproduction event that took place in the field. Combining genotypic data and phenotypic measurements showed that this gene mixing led to the production of a wide array of reproductive modes, including strictly asexual lineages. Finally, we discuss the central role played by facultatively asexual lineages on the maintenance of reproductive mode variation.