Search Results (6)

Insects are renowned for their remarkable diversity of reproductive modes. Among these, the largest non-holometabolous order, Hemiptera, stands out with one of the most diversified arrays of parthenogenesis modes observed among insects. Although there are extensive reviews on reproduction without fertilization in some hemipteran higher taxa, no such analysis has been conducted for the large suborders Fulgoromorpha (planthoppers) and Cicadomorpha (leafhoppers). In both groups, there are species that reproduce by true parthenogenesis, specifically thelytoky, and in Fulgoromorpha, there are species that reproduce by pseudogamy or, more specifically, sperm-dependent parthenogenesis. In this review paper, we give and discuss the only currently known examples of true parthenogenesis in Fulgoromorpha and Cicadomorpha, mainly from the planthopper family Delphacidae and the leafhopper family Cicadellidae. We analyze patterns of distribution, ecology, mating behavior, acoustic communication, and cytogenetic and genetic diversity of parthenoforms and discuss hypotheses about the origin of parthenogenesis in each case. We also highlight examples in which natural populations show a shift in sex ratio toward females and discuss possible causes of this phenomenon, primarily the influence of endosymbiotic bacteria capable of altering the reproductive strategies of the hosts. Our review is mainly based on studies in which the authors have participated. Full article

Reproduction studies, particularly embryology, represent basic information of any plant. However, the current embryological information is fragmentary for Kentucky bluegrass (Poa pratensis L.). Here, paraffin sections were used to examine the cyto-embryological characteristics, including microsporogenesis, microgametogenesis, megasporogenesis, megagametogenesis, and apomixis, of wild Kentucky bluegrass germplasm from Gannan (GN) and Longnan (LN) in Gansu Province. The study found no significant differences in pollen diameter, characteristics, viability, and stigma receptivity between the two germplasm materials. The Kentucky bluegrass consisted of three anthers, and each contained four pollen sacs that were divided into left and right halves. After meiosis, the microspore mother cells formed dyads and tetrads, which were primarily symmetrical and underwent mitosis to form three-celled pollen. Kentucky bluegrass has a one-locular ovary, two-feathery stigmas, thick nucleolar and anatropous ovules, and a typical polygonum embryo sac as its reproductive organs. The main type of apomixis observed was apospory, resulting in the coexistence of multiple embryo sacs. Polyembryonic seeds were frequently observed in Kentucky bluegrass due to apospory. Most importantly, our research found that apospory caused early embryogenesis during fertilization, which is a vital embryological feature for identifying sexual reproduction and apomixis in Kentucky bluegrass. Sexual reproduction followed strict double fertilization, while in apomixis a complete seed was only formed through pseudogamy. These embryological characteristics are documented here, and their study can aid in understanding the evolution of Kentucky bluegrass. Full article

The remarkable species diversity of the genus Sorbus is a result of polyploidization and frequent hybridization between interacting species of different cytotypes. Moreover, hybridization is possible between several parental taxa. Gametophytic apomixis, which is common among polyploid Sorbus taxa, indicates the role of clonal reproduction in the evolutionary stabilization of hybridogeneous genotypes. The precise determination of the origin of seeds and their quantitative evaluation may elucidate inter-cytotype interactions, the potential role of mixed-cytotype populations in evolutionary success, and the long-term survival of some hybrid species. We investigated the reproduction modes of selected species of Sorbus in mixed-cytotype populations in eastern Slovakia, Central Europe. We determined the pollen quality, seed production rate, and the ploidy level of mature trees, as well as the origin of the embryo and endosperm in seeds of the stenoendemics S. amici-petri, S. dolomiticola, and S. hornadensis. The tetraploids S. amici-petri and S. hornadensis are characterized by regular and highly stainable pollen grains and reproduce predominantly via pseudogamous apomixis. In contrast, triploid S. dolomiticola usually has oval, heterogenous, and weakly stainable pollen grains, suggesting male meiotic irregularities. Although seeds originate via pseudogamous apomixis in S. dolomiticola as well, the ploidy level of sperm cells participating in the fertilization of central cells is usually determined by co-occurring species of different cytotypes. This suggests that maintaining mating partners is necessary for the long-term survival of a triploid species. We documented rare B_III hybrids and the residual sexuality in tetraploids. The distribution of seeds of meiotic and apomeiotic origins in S. amici-petri shows bimodal characteristics; however, genotypes with predominantly sexual seed types are rare. Reproduction modes documented in polyploid stenoendemics of Sorbus and inferred microevolutionary intercytotype relationships highlight the mixed-cytotype populations as the source of biodiversity in apomictic plant complexes. We suggest that conservation efforts should focus on maintaining the species and cytotypic diversity of Sorbus populations, especially when it comes to the conservation of triploid species. Full article

The role of apomeiosis, parthenogenesis, and pseudogamy in the asexual reproduction of some plant groups has not been fully elucidated in relation to species diversification. Quantitative analyses of seed origin may help in gaining better understanding of intercytotypic interactions. Asexual reproduction associated with polyploidy and frequent hybridization plays a crucial role in the evolutionary history of the genus Crataegus in North America. In Europe, the genus represents a taxonomically complex and very difficult species group not often studied using a modern biosystematic approach. We investigated the reproduction pathways in mixed-cytotype populations of selected taxa of Crataegus in eastern Slovakia, Central Europe. The investigated accessions were characterized by seed production data and the ploidy level of mature plants as well as the embryo and endosperm tissues of their seeds determined via flow cytometry. Diploid and polyploid hawthorns reproduce successfully; they also produce high numbers of seeds. An exception is represented by an almost sterile triploid. Diploids reproduce sexually. Polyploids shift to asexual reproduction, but pseudogamy seems to be essential for regular seed development. In rare cases, fertilization of unreduced gametes occurs, which offers opportunity for the establishment of new polyploid cytotypes between diploid sexuals and polyploid asexuals. Opposite to sexual diploids, triploids are obligate, and tetraploids almost obligate apomicts. Apomixis is considered to help stabilize individual weakly differentiated polyploid microspecies. Pseudogamy is a common feature and usually leads to unbalanced maternal to paternal contribution in the endosperm of triploid accessions. Parental contribution to endosperm gene dosage is somehow relaxed in triploids. Our Crataegus plant system resembles reproduction in the diploids and polyploids of North American hawthorns. Our data provide support for the hypothesis that polyploidization, shifts in reproduction modes, and hybridization shape the genus diversity also in Central Europe. Full article

Background: Engineering apomixis in sexually reproducing plants has been long desired because of the potential to fix hybrid vigor. Validating the functionality of genes originated from apomictic species that contribute to apomixis upon transfer to sexually reproducing species is an important step. The PsASGR-BABYBOOM-like (PsASGR-BBML) gene from Pennisetum squamulatum confers parthenogenesis in this apomict, and its functionality was demonstrated in several sexually reproducing monocots but not in any dicots. Methods: We introduced the PsASGR-BBML gene regulated by egg cell-specific promoters, either AtDD45 or AtRKD2, into tobacco, and analyzed progeny of the transgenic lines resulting from self-pollination and crossing by flow cytometry. Results: We identified haploid progeny at a frequency lower than 1% in the AtDD45_pro lines, while at a frequency of 9.3% for an octoploid (2n = 8x) AtRKD2_pro line. Haploid production in the T₂ generation, derived from the tetraploid T₁ offspring of this original octoploid AtRKD2_pro line, was also observed. Pollinated by homozygous transgenic tobacco carrying a DsRed marker gene, 4x progeny of the AtRKD2_pro line yielded parthenogenetic embryos identified as DsRed negative. We verified that the DsRed negative seedlings recovered were haploid (2x). Conclusion: The PsASGR-BBML gene regulated by egg cell-specific promoters could enable parthenogenesis in tobacco, a dicotyledon species. Full article

Background and Objectives: Polyploidisation and frequent hybridisation play an important role in speciation processes and evolutionary history and have a large impact on reproductive systems in the genus Crataegus. Reproductive modes in selected diploid and polyploid taxa in eastern Slovakia were investigated and analysed for the first time. Materials and Methods: Diploid, triploid, and tetraploid hawthorns were tested for self-pollination, self-compatibility, and self-fertilisation. Pollination experiments were performed within and between diploid and triploid species to determine the possibilities and directions of pollen transfer under natural conditions. Seeds from crossing experiments and open pollinations were analysed using the flow cytometric seed screen method. Results: These experiments demonstrated that sexual reproduction, cross-pollination, and self-incompatibility are typical of the diploid species Crataegus monogyna and C. kyrtostyla. Seeds produced by self-fertile tetraploid C. subsphaerica were derived from both meiotically reduced and unreduced megagametophytes. Conclusions: Experimental results concerning triploid C. subsphaerica and C. laevigata × C. subsphaerica are ambiguous but suggest that seeds are almost exclusively created through apomixis, although a few sexually generated seeds were observed. In the genus Crataegus, pseudogamy is a common feature of polyploid taxa, as in all cases pollination is essential for regular seed development. Research Highlights: We suggest that all studied Crataegus taxa produce reduced pollen irrespective of ploidy level. Moreover, we emphasise that triploids produce apparently aneuploid pollen grains as a result of irregular meiosis. They are also capable of utilising pollen from 2x, 3x, or 4x donors for pseudogamous formation of endosperm. Full article