Search Results (20)

The angiosperm seed represents a critical evolutionary breakthrough that has been shown to propel the reproductive success and radiation of flowering plants. Seeds promote the rapid diversification of angiosperms by establishing postzygotic reproductive barriers, such as hybrid seed inviability. While prezygotic barriers to reproduction tend to be transient, postzygotic barriers are often permanent and therefore can play a pivotal role in facilitating speciation. This property of the angiosperm seed is exemplified in the Mimulus genus. In order to further the understanding of the gene regulatory mechanisms important in the Mimulus seed, we performed gene regulatory network (GRN) inference analysis by using time-series RNA-seq data from developing hybrid seeds from a viable cross between Mimulus guttatus and Mimulus pardalis. GRN inference has the capacity to identify active regulatory mechanisms in a sample and highlight genes of potential biological importance. In our case, GRN inference also provided the opportunity to uncover active regulatory relationships and generate a reference set of putative gene regulations. We deployed two GRN inference algorithms—RTP-STAR and KBoost—on three different subsets of our transcriptomic dataset. While the two algorithms yielded GRNs with different regulations and topologies when working with the same data subset, there was still significant overlap in the specific gene regulations they inferred, and they both identified potential novel regulatory mechanisms that warrant further investigation. Full article

Species of the Rhodnius genus have a complex taxonomy because the events of phenotypic plasticity and cryptic speciation make it difficult to correctly classify these vectors. During the taxonomic history of the genus, five synonymization events occurred. Additionally, some authors suggest that R. milesi possibly represent only phenotypic polymorphisms of R. neglectus. Thus, we analyzed the specific status of R. milesi in relation to R. neglectus using phylogenetic studies with the mitochondrial gene cytochrome B and the study of reproductive barriers. The phylogenetic reconstruction grouped R. milesi together with R. neglectus from different localities, demonstrating that these taxa represent the same species based on the phylogenetic species concept. Experimental crosses demonstrate the absence of pre- and postzygotic barriers under laboratory conditions. Additionally, when the hatch rates of crosses are compared to intraspecific crosses, it can be noted that they are high and very similar. Finally, the mortality rate of the hybrids does not indicate hybrid inviability, the absence of chromosome pairing errors does not indicate hybrid sterility, and the proportion between male and female hybrids demonstrates that Haldane’s rule was not acting. Therefore, we perform the formal synonymization of R. milesi with R. neglectus. Full article

The study of pig preimplantation embryo development has several potential uses: from agriculture to the production of medically relevant genetically modified organisms and from rare breed conservation to acting as a physiologically relevant model for progressing human and other (e.g., endangered) species’ in vitro fertilisation technology. Despite this, barriers to the widespread adoption of pig embryo in vitro production include lipid-laden cells that are hard to visualise, slow adoption of contemporary technologies such as the use of time-lapse incubators or artificial intelligence, poor blastulation and high polyspermy rates. Here, we employ a commercially available time-lapse incubator to provide a comprehensive overview of the morphokinetics of pig preimplantation development for the first time. We tested the hypotheses that (a) there are differences in developmental timings between blastulating and non-blastulating embryos and (b) embryo developmental morphokinetic features can be used to predict the likelihood of blastulation. The abattoir-derived oocytes fertilised by commercial extended semen produced presumptive zygotes were split into two groups: cavitating/blastulating 144 h post gamete co-incubation and those that were not. The blastulating group reached the 2-cell and morula stages significantly earlier, and the time taken to reach the 2-cell stage was identified to be a predictive marker for blastocyst formation. Reverse cleavage was also associated with poor blastulation. These data demonstrate the potential of morphokinetic analysis in automating and upscaling pig in vitro production through effective embryo selection. Full article

Embryo rescue (ER) techniques are among the oldest and most successful in vitro tissue culture protocols used with plant species. ER refers to a series of methods that promote the development of an immature or lethal embryo into a viable plant. Intraspecific, interspecific, or intergeneric crosses allow the introgression of important alleles of agricultural interest from wild species, such as resistance or tolerance to abiotic and biotic stresses or morphological traits in crops. However, pre-zygotic and post-zygotic reproductive barriers often present challenges in achieving successful hybridization. Pre-zygotic barriers manifest as incompatibility reactions that hinder pollen germination, pollen tube growth, or penetration into the ovule occurring in various tissues, such as the stigma, style, or ovary. To overcome these barriers, several strategies are employed, including cut-style or graft-on-style techniques, the utilization of mixed pollen from distinct species, placenta pollination, and in vitro ovule pollination. On the other hand, post-zygotic barriers act at different tissues and stages ranging from early embryo development to the subsequent growth and reproduction of the offspring. Many crosses among different genera result in embryo abortion due to the failure of endosperm development. In such cases, ER techniques are needed to rescue these hybrids. ER holds great promise for not only facilitating successful crosses but also for obtaining haploids, doubled haploids, and manipulating the ploidy levels for chromosome engineering by monosomic and disomic addition as well substitution lines. Furthermore, ER can be used to shorten the reproductive cycle and for the propagation of rare plants. Additionally, it has been repeatedly used to study the stages of embryonic development, especially in embryo-lethal mutants. The most widely used ER procedure is the culture of immature embryos taken and placed directly on culture media. In certain cases, the in vitro culture of ovule, ovaries or placentas enables the successful development of young embryos from the zygote stage to maturity. Full article

Key message. The success of interspecific hybridization in hardy geranium (Geranium sp.) can be predicted by considering the genetic distance between parental genotypes and using the logistic regression model developed in this study. Hardy geranium is a popular ornamental plant known for its architecture, hardiness, prolonged flowering, and diverse colors in leaves and flowers. In ornamental breeding, the pursuit of novel trait combinations is never-ending. Even in Geranium, certain combinations of valuable traits have not yet been achieved. Interspecific hybridization can increase diversity; however, success remains low due to pre- and postzygotic barriers. Crossing success can be predicted by response criteria such as pollen tube growth (tube_length), seed development (seed_dev), and seed setting (seed_set). Within a collection of 42 Geranium genotypes and during two consecutive breeding seasons (years), we evaluated tube_length, seed_dev, and seed_set for 150, 1155, and 349 crosses, respectively. These crosses varied in four parental differences (variables): chromosome number (Chrom), DNA/chromosome (DNA), style length (Style), and genetic distance expressed as the Jaccard distance (cJaccard = 1 − Jaccard). Using logistic regression models has confirmed that most often, the success rate decreased with increasing parental distance. The most consistent association was seen in seed_dev in combination with cJaccard. The model was used to predict the number of crosses necessary to have 10 successful crossing products by taking into account the uncertainty in the model. These findings provide valuable guidance for future planning of interspecific breeding experiments in Geranium. By incorporating the genetic distance between parental genotypes, breeders can enhance the efficiency and success of hybridization efforts. Full article

Genome editing, as exemplified by the CRISPR/Cas9 system, has recently been employed to effectively generate genetically modified animals and cells for the purpose of gene function analysis and disease model creation. There are at least four ways to induce genome editing in individuals: the first is to perform genome editing at the early preimplantation stage, such as fertilized eggs (zygotes), for the creation of whole genetically modified animals; the second is at post-implanted stages, as exemplified by the mid-gestational stages (E9 to E15), for targeting specific cell populations through in utero injection of viral vectors carrying genome-editing components or that of nonviral vectors carrying genome-editing components and subsequent in utero electroporation; the third is at the mid-gestational stages, as exemplified by tail-vein injection of genome-editing components into the pregnant females through which the genome-editing components can be transmitted to fetal cells via a placenta-blood barrier; and the last is at the newborn or adult stage, as exemplified by facial or tail-vein injection of genome-editing components. Here, we focus on the second and third approaches and will review the latest techniques for various methods concerning gene editing in developing fetuses. Full article

Hybridization between Cucumis species, including cultivated melon (C. melo), is hampered by Interspecific Reproductive Barriers (IRBs). However, the nature of IRBs in Cucumis is largely unknown. This study explores locations, timing, and contribution to reproductive isolation (RI) of pre- and post-zygotic IRBs in Cucumis. To do this, we assessed crossability among Cucumis African wild species and C. melo at the pre-zygotic level by visualizing pollen tubes under fluorescence microscopy and, post-zygotically, by evaluating fruit/seed set and F₁ hybrid fertility. Genetic distances among Cucumis species were inferred from Genotyping-by-Sequencing, and its correlation with RI stages was analyzed. Observed pre- and post-zygotic IRBs included pollen tube arrest, fruit set failure, and hybrid male sterility. Unilateral cross-incongruity/incompatibility (UCI) was detected in some hybridizations, and dominant gene action is suggested for pistil-side UCI in interspecific F₁ hybrids. Notably, the allotetraploid C. ficifolius was very fertile as a seed parent but infertile in all reciprocal crosses. Contribution to RI was found significant for both pre- and post-zygotic IRBs. Additionally, a significant positive correlation was detected between genetic distance and pre- and post-zygotic RI stages. Interestingly, UCI offers an accessible system to dissect the genetics of IRBs in Cucumis, which may facilitate the use of wild relatives in breeding. Full article

The world-wide fauna of the genus Cardiocondyla is assessed to have 79 currently recognized species and is subdivided into 14 informal species groups plus three monotypical clades. It is argued that the phylogenetic placement of Cardiocondyla next to the genus Ocymyrmex Emery, 1886 as proposed by Blaimer et al. (2018) is doubtful. The main body of the paper is a species-level taxonomic revision of those six species groups and the one monotypical clade which have their centers of origin in the Oriental and Australasian regions. The fauna of this area comprises 26 species eleven of which are described as new: Cardiocondyla schulzi n.sp., C. argentea n.sp., C. semiargentea n.sp., C. argyrotricha n.sp., C. latifrons n.sp., C. micropila n.sp., C. allonivalis n.sp., C. excavata n.sp., C. goroka n.sp., C. subspina n.sp. and C. sulcata n.sp. Recognized as junior synonyms were: Cardiocondyla tsukuyomi Terayama, 1999 and C. breviscapus Seifert, 2003 of C. minutior Forel, 1899 and C. brevispinosa (Donisthorpe, 1948) of C. paradoxa Emery, 1897. Each confirmed species is characterized by verbal descriptions, 18 numerically recorded phenotypic characters, z-stack images in three viewing positions, the key, a differential diagnosis and, if available, a brief life history. Exploratory and hypothesis-driven data analyses of phenotypic characters support the separation of the cryptic species Cardiocondyla minutior Forel, 1899, C. goa Seifert, 2003 and C. tjibodana Karavajev, 1935, two of which have dispersed as tramp species to the New World. Missing development of postzygotic isolation due to very strong prezygotic barriers is indicated in the closely related species Cardiocondyla latifrons n.sp. and C. micropila n.sp. which produce fertile hybrids in laboratory rearings but apparently do not hybridize in a natural context even if nesting in close neighborhood. The strong prezygotic isolation is supposed to be generated by the prevalence of intranidal mating and the difficulty for a mated heterospecific gyne to become accepted in a foreign colony. Full article

The continuous nature of speciation implies that different species are found at different stages of divergence, from no- to complete reproductive isolation. This process and its underlying mechanisms are best viewed in incipient species. Moreover, the species complex can offer unique insight into how reproductive isolation (RI) has evolved. The royal irises (Iris section Oncocyclus) are a young group of species in the course of speciation, providing an ideal system for speciation study. We quantified pre- and post-zygotic reproductive barriers between the eight Israeli species of this complex and estimated the total RI among them. We tested for both pre-pollination and post-pollination reproductive barriers. Pre-pollination barriers, i.e., eco-geographic divergence and phenological differentiation were the major contributors to RI among the Iris species. On the other hand, post-pollination barriers, namely pollen–stigma interactions, fruit set, and seed viability had negligible contributions to total RI. The strength of RI was not uniform across the species complex, suggesting that species may have diverged at different rates. Overall, this study in a young, recently diverged group of species provides insight into the first steps of speciation, suggesting a crucial role of the pre-zygotic barriers. Full article

Triatoma bassolsae, T. longipennis, T. mazzottii, T. pallidipennis, T. phyllosoma and T. picturata are species that have great epidemiological importance in the transmission of Chagas disease in Mexico. However, there is no consensus regarding the specific status of these species, since they appear in various articles as species, subspecies and even subgenera. Thus, we revisited genetic, taxonomic and evolutionary data that allowed us to assess and discuss the specific status of these six species of the T. phyllosoma subcomplex. Phylogenetic studies were performed with nuclear (18S, 28S, ITS-2) and mitochondrial (16S, cytb, COI, COII, 12S) markers deposited in GenBank. In addition, data from experimental crosses were pooled and the genetic distance to the cytb gene was calculated. The phylogenetic reconstruction enabled us to rescue the six species as independent lineages. Post-zygotic reproductive isolation barriers (sterility and/or hybrid collapse) were observed for some experimental crosses. Although the other experimental crosses did not allow us to characterize reproductive barriers, these species showed high genetic distances in relation to the cytb gene (ranging from 4.6% to 14.9%). Thus, based on the revisited literature data, we confirmed the specific status of these six species of the T. phyllosoma subcomplex based on the phylogenetic and biological concepts of the species. Full article

Ancient lakes are known speciation hotspots. One of the most speciose groups in the ancient Lake Baikal are gammaroid amphipods (Crustacea: Amphipoda: Gammaroidea). There are over 350 morphological species and subspecies of amphipods in Baikal, but the extent of cryptic variation is still unclear. One of the most common species in the littoral zone of the lake, Eulimnogammarus verrucosus (Gerstfeldt, 1858), was recently found to comprise at least three (pseudo)cryptic species based on molecular data. Here, we further explored these species by analyzing their mitogenome-based phylogeny, genome sizes with flow cytometry, and their reproductive compatibility. We found divergent times of millions of years and different genome sizes in the three species (6.1, 6.9 and 8 pg), further confirming their genetic separation. Experimental crossing of the western and southern species, which are morphologically indistinguishable and have adjacent ranges, showed their separation with a post-zygotic reproductive barrier, as hybrid embryos stopped developing roughly at the onset of gastrulation. Thus, the previously applied barcoding approach effectively indicated the separate biological species within E. verrucosus. These results provide new data for investigating genome evolution and highlight the need for precise tracking of the sample origin in any studies in this morphospecies. Full article

Cultivated yam (D. rotundata) is a staple tuber crop in West Africa whose sexual reproduction control remains largely unknown despite its importance for plant breeding programs. In this paper, we compared self-pollination, intracultivar cross-pollination and intercultivar cross-pollination in three monoecious cultivars (Amoula, Heapala and Yassi). Results showed that pollen viability (49%) and stigma receptivity (40%) were similar in monoecious and dioecious plants, suggesting that autogamy could occur in monoecious plants. However, fruit and seed sets were significantly lower after self-pollination compared to cross-pollination. Overall, autogamy reached 11% and pollen lability was almost zero (<1%). The low percentage of pollen grains germinating on the stigma (37%) and pollen tubes reaching the ovules (25%) after self-pollination partly explained the low seed set. Strong inbreeding depression was observed after self-pollination and almost all fruits and about 75% of the seeds resulting from self-pollination showed malformations. Seed germination was also 20 times lower after self-pollination compared to cross-pollination. Sexual reproduction remained low in D. rotundata even after cross-pollination as fruit and seed set did not exceed 18% and 13% respectively. Moreover, comparison between intracultivar cross-pollination and self-pollination revealed intravarietal genetic diversity inside the analyzed yam cultivars. Overall, our results showed that D. rotundata has a very low tolerance to autogamy in monoecious cultivars and has developed pre- and postzygotic mechanisms to limit selfing. Full article

To expand the gene pool and introduce new traits to the tetraploid cultivars of Vaccinium corymbosum from wild diploid species V. myrtillus, it is necessary to double the chromosome number in diploid species in order to overcome a post zygotic crossing barrier and a strong triploid block, existing within the genus Vaccinium. Five genetically diverse bilberry genotypes were selected from 21 accessions taken from the breeding collection of the National Institute of Horticultural Research (Skierniewice, Poland) for this study. The bilberry genotypes were derived from the Polish locations of Bolimów Landscape Park, Budy Grabskie and forest complex Zwierzyniec (Łódź Province), and habitats in Norway. The selection of genotypes was made based on the analysis of amplified fragment length polymorphism (AFLP-PCR). Analysis of the Jaccard similarity indexes and the UPGMA method revealed that the examined accessions formed two main groups on the dendrogram. The first group consisted of accessions from Norway, while the second group agglomerated Polish accessions. A further two classes were distinguished in the Polish group: the first included accessions from Budy Grabskie and the second from Zwierzyniec, located ca. 9 km from Budy Grabskie. In order to obtain plant material for in vitro polyploidisation, in vitro shoot cultures of the selected accessions were initiated and multiplied. Both antimitotics used, colchicine and APM, induced tetraploids for all of the accessions. The obtained tetraploids were multiplied, rooted ex vitro and grown in a greenhouse and then in a field. The first flowering was observed in 1.5-year-old plants, either diploid or tetraploid. Diploids bloomed slightly earlier and more profusely than tetraploid plants. Compared to diploids, autotetraploids had significantly larger flowers by ca. 64% and larger pollen tetrads by ca. 35%. The germination capacity of pollen tetrads was high in tetraploids (87.8%), although slightly lower than in diploids (94.3%). After pollinating the flowers of three highbush blueberry cultivars with pollen from the bilberry tetraploid accession, J-4-4x, the plants formed fruits, some of which contained properly formed seeds. The effectiveness of interspecific crossing between V. corymbosum and tetraploid V. myrtillus, defined as the percentage of obtained seedlings in relation to the number of pollinated flowers, was highest (53.3%) in the blueberry ‘Liberty’, and lower in ‘Bluecrop’ and ‘Northland’, 14.8% and 10.0%, respectively. Before using the seedlings for further breeding, their hybridity will be confirmed by molecular markers and the phenotype will be evaluated. Full article

Hybridization in flowering plants depends, in the first place, on the delivery of pollen to a receptive stigma and the subsequent growth of pollen tubes through the style to the ovary, where the sperm nucleus of the pollen grain can ultimately fertilize the egg cell. However, reproductive failure is often observed in distant crosses and is caused by pre- and/or post-zygotic barriers. In this study, the reproductive pre-fertilization barriers of intertribal crosses between Anemone coronaria L. and Ranunculus asiaticus L., both belonging to the Ranunculaceae, were investigated. Despite the incongruity of intertribal crosses between A. coronaria and R. asiaticus having been of low intensity at the stigmatic level, interstylar obstructions of the pollen tube growth occurred, which confirmed the presence of pre-fertilization barriers. We show that these barriers could be partially bypassed by combining pollination with a stigma treatment. More specifically, a significantly higher ratio of the pollen tube length to the total style length and a better seed set were observed when the stigma was treated with the auxin 2,4-dichlorophenoxyacetic acid (2,4-D, 1 mg·mL⁻¹) together with the cytokinin kinetin (KIN, 0.5 mg·mL⁻¹) 24 h after pollination, irrespective of the cross direction. More specifically, the stigma treatments with any form of auxin (combined or not combined with cytokinin) resulted in a full seed set, assuming an apomictic fruit set, because no pollination was needed to obtain these seeds. Full article

Chromosomal polymorphism plays a major role in speciation processes in mammals with high rates of karyotypic evolution, as observed in the family Cervidae. One remarkable example is the genus Mazama that comprises wide inter- and intra-specific chromosomal variability. To evaluate the impact of chromosomal polymorphisms as reproductive barriers within the genus Mazama, inter-specific hybrids between Mazama gouazoubira and Mazama nemorivaga (MGO × MNE) and intra-specific hybrids between cytotypes of Mazama americana (MAM) differing by a tandem (TF) or centric fusion (Robertsonian translocations—RT) were evaluated. MGO × MNE hybrid fertility was evaluated by the seminal quality and testicular histology. MAM hybrids estimation of the meiotic segregation products was performed by sperm-FISH analysis. MGO × MNE hybrids analyses showed different degrees of fertility reduction, from severe subfertility to complete sterility. Regarding MAM, RT, and TF carriers showed a mean value for alternate segregation rate of 97.74%, and 67.23%, and adjacent segregation rate of 1.80%, and 29.07%, respectively. Our results suggested an efficient post-zygotic barrier represented by severe fertility reduction for MGO × MNE and MAM with heterozygous TF. Nevertheless, RT did not show a severe effect on the reproductive fitness in MAM. Our data support the validity of MGO and MNE as different species and reveals cryptic species within MAM. Full article