Reproductive Isolation Research Articles

Analysis of the variations within Q. ilex L. and the evaluation of morphological types based on chloroplast and nuclear DNA sequences

Q. ilex evaluated within evergreen has wide geographic distribution in Mediterranean basin. Hybridization and gene flow are effective and frequently observed mechanisms in Q. ilex. Moreover, weak reproductive barrier between closely related taxa in the zones with geographical contact is another important state that increase genetic diversity within Q. ilex and then taxonomic problems. Two morphological types known as rotundifolia and ilex are defined based on the variations between Q. ilex populations appearing as a result of all these factors. However, it is still controversial situation whether morphological types: ilex and rotundifolia are subspecies of Q. ilex or two separate species. In this study, short DNA sequences that consist of matK gene-partial trnK gene intron of chloroplast DNA and ITS1-5.8S rRNA gene-ITS2 of nuclear DNA were used to overcome such difficulties and to reveal the variations between Q. ilex populations. All populations belonging to Q. ilex based on both barcoding regions were determined and examined using the Molecular Evolutionary Genetics Analysis (MEGA 11). The analysis such as base substitutions, variable and parsim-info sites, transitional and transversional base substitution ranges (%) and nucleotide frequencies (%) were performed and finally, Maximum Parsimony (MP) dendrograms for both barcoding regions were drawn to evaluate the populations belonging to Q. ilex in terms of their variations, phylogenetic-evolutionary relationships and taxonomic statues. Although both barcoding regions support the separation of Q. ilex populations based on different morphological types, especially, matK gene-partial trnK gene intron sequences exhibited more clear and informative results than ITS1-5.8S rRNA gene-ITS2 sequences.

What Predicts Gene Flow During Speciation? The Relative Roles of Time, Space, Morphology and Climate.

The processes that restrict gene flow between populations are fundamental to speciation. Here, we develop a simple framework for studying whether divergence in morphology, climatic niche, time and space contribute to reduced gene flow among populations and species. We apply this framework to a model system involving a clade of spiny lizards (Sceloporus) occurring mostly in northeastern Mexico, which show striking variation in morphology and habitat among closely related species and populations. We developed a new time-calibrated phylogeny for the group using RADseq data from 152 individuals. This phylogeny identified 12 putative species-level clades, including at least two undescribed species. We then estimated levels of gene flow among 21 geographically adjacent pairs of species and populations. We also estimated divergence in morphological and climatic niche variables among these same pairs, along with divergence times and geographic distances. Using Bayesian generalised linear models, we found that gene flow between pairs of lineages is negatively related to divergence time and morphological divergence among them (which are uncorrelated), and not to geographic distance or climatic divergence. The framework used here can be applied to study speciation in many other organisms having genomic data but lacking direct data on reproductive isolation. We also found several other intriguing patterns in this system, including the parallel evolution of a strikingly similar montane blue-red morph from more dull-coloured desert ancestors within two different, nonsister species.

A new species of Diacheopsis (Myxomycetes) and a new habitat for myxomycetes

ABSTRACT We describe a new species, Diacheopsis resinae (Myxomycetes), collected from a microhabitat new for myxomycetes: stem wounds of coniferous trees (Norway spruce) where the resin is overgrown with a community of resinicolous fungi. The 80 known collections come from the Vosges (France), the Black Forest (Germany), Swabian Alp (Germany), and several localities in Denmark and Norway. Observations, but as well as metabarcoding of substrate samples with fungal (ITS [internal transcribed spacer]), bacterial (16S rDNA), and myxomycete (18S nuc rDNA) primers from eight trunks, revealed the new myxomycete to co-occur with resin-degrading ascomycetes (Infundichalara microchona, Lophium arboricola, Zythia resinae). The gram-negative bacterial genera Endobacter and Sphingomonas were found to be abundant in the substrate and may be a food source for the myxomycete. Fruit bodies were found mostly during the more humid winter season, with a peak in January/February. Partial sequences of two independent molecular markers (18S nuc rDNA, EF1α [elongation factor 1-alpha] gene) were obtained for 41 accessions, which form a monophyletic cluster in a two-gene phylogeny of Stemonititidales but do not group with other species of Diacheopsis, thus rendering this genus paraphyletic. The new species, although exclusively developing sessile sporocarps and morphologically undoubtedly falling into the genus Diacheopsis, is most closely related to species of Lamproderma, especially L. album, L. zonatum, and L. zonatopulchellum. Within D. resinae, three groups can be differentiated, which show nearly complete reproductive isolation, as judged from a recombination analysis of the two unlinked markers and the allelic combinations of the EF1α gene.

Unravelling intermediate migration patterns in gull hybrids: insights from ring re-encounters

Hybridization is a common phenomenon in birds, particularly between closely related species, when reproductive isolation mechanisms are insufficiently developed. Hybrids differ from the parental species in genetic, morphological, and behavioural traits. However, the migration patterns of hybrids have been scarcely studied. Examining hybrid migration behaviour is essential as it may reveal their role as a “gene bridge” between species and enhance our understanding of speciation mechanisms and the genetics of migration. Most research focuses on tracking the migration of long-distance migrants, but the effect of hybridization on migration is poorly understood also in short-distance migrants. The study aimed to verify whether the migratory movements of interspecific hybrids between the Herring (Larus argentatus) and the Caspian Gull (L. cachinnans) are intermediate, as predicted by the genetic basis of migration. Migration patterns, based on distance and direction, were determined from re-encounter data of individuals ringed in Poland, for over 20 years (2002–2023). These included both allopatric (parental species) and sympatric (both parental species and hybrids) populations. The results indicated that large gull hybrids exhibit an intermediate migration patterns, similarly to other hybridizing species. Unlike many cases where intermediacy may select against hybrids, the absence of significant environmental barriers along gulls’ migration routes and their wide wintering range likely mitigates selective pressures. This finding underscores the need for further investigation into the ecological implications of hybrid migration patterns. By using bird re-encounter data, we demonstrated that it provides a sufficient basis for analysing migration patterns and detecting intermediacy, even in within-continental and short-distance migrants.

Mycorrhizal specialization toward each distinct Oliveonia fungus in two closely related photosynthetic Dactylostalix orchids

Abstract Although rhizoctonias from Ceratobasidiaceae, Tulasnellaceae and Serendipitaceae are typical orchid mycobionts, orchid mycorrhizal fungi exhibit vast taxonomic and ecological diversity. This diversity stems from the high specificity of orchid mycorrhizal associations and the remarkable diversity of over 28,000 orchid species. The subtribe Calypsoinae is particularly notable for its diverse mycorrhizal partnerships, including rhizoctonias, ectomycorrhizal and saprotrophic non‐rhizoctonia fungi. However, the mycobionts within certain Calypsoinae lineages, such as the genus Dactylostalix, remain understudied. This study explores the physiological ecology of two photosynthetic Calypsoinae species, Dactylostalix ringens and Dactylostalix uniflora, to gain insight into potentially novel associations and their ecological implications. We analysed the mycorrhizal communities of both Dactylostalix species using high‐throughput ITS metabarcoding of root samples collected from multiple locations. Additionally, we measured the natural abundances of 13C and 15N isotopes in the leaves of the two Dactylostalix species and their co‐occurring autotrophic reference plants, as well as in fungal pelotons isolated from D. ringens, to assess the potential for partial mycoheterotrophy. Our findings revealed that D. ringens and D. uniflora form specialized mycorrhizal associations predominantly with distinct lineages of Oliveonia (Oliveoniaceae, Auriculariales), even in sympatric populations. Stable isotope analysis showed that both Dactylostalix species exhibited conflicting isotopic signals: elevated δ15N values, supporting partial mycoheterotrophy, but lower δ13C values compared to autotrophic plants, suggesting autotrophy. Peloton samples from D. ringens displayed only modest 13C enrichment relative to autotrophic references. These conflicting isotopic signals make it difficult to precisely determine whether both Dactylostalix species are autotrophic or partially mycoheterotrophic. Intriguingly, the 13C and 15N signatures of Dactylostalix species and their pelotons resemble those of many rhizoctonia‐associated orchids. This isotopic evidence implies a niche overlap with endophytic tendencies between rhizoctonias and Oliveonia, suggesting that potential endophytic traits may have facilitated the recruitment of Oliveonia as novel mycorrhizal partners. Furthermore, the mycorrhizal segregation between D. ringens and D. uniflora likely promotes their sympatric coexistence and may contribute to reproductive isolation through ecological specialization. Read the free Plain Language Summary for this article on the Journal blog.

Digest: Scarce pollen resources and asymmetric reproductive isolation.

What mechanisms cause asymmetries in reproductive success in crosses between closely related species that differ in floral style length? Feller et al. (2024) found that in five Phlox species, short-styled species produced smaller pollen grains than long-styled species. The smaller pollen of short-styled species lacked the resources to grow pollen tubes long enough to reach the ovules of long-styled species. This asymmetric pollen-style-length incompatibility may considerably affect patterns of gene flow among species.

Sperm as a speciation phenotype in promiscuous songbirds.

Sperm morphology varies considerably among species. Sperm traits may contribute to speciation if they diverge fast in allopatry and cause conspecific sperm precedence upon secondary contact. However, their role in driving prezygotic isolation has been poorly investigated. Here we test the hypothesis that, early in the speciation process, female promiscuity promotes a reduction in overlap in sperm length distributions among songbird populations. We assembled a data set of 20 pairs of populations with known sperm length distributions, a published estimate of divergence time, and an index of female promiscuity derived from extrapair paternity rates or relative testis size. We found that sperm length distributions diverged more rapidly in more promiscuous species. Faster divergence between sperm length distributions was caused by the lower variance in the trait in more promiscuous species, and not by faster divergence of the mean sperm lengths. The reduced variance is presumably due to stronger stabilizing selection on sperm length mediated by sperm competition. If divergent sperm length optima in allopatry causes conspecific sperm precedence in sympatry, which remains to be shown empirically, female promiscuity may promote prezygotic isolation and rapid speciation in songbirds.

Sex Pheromone Mediates Resource Partitioning Between Drosophila melanogaster and D. suzukii.

The spotted-wing drosophila, Drosophila suzukii and the cosmopolitan vinegar fly D. melanogaster feed on soft fruit and berries and widely overlap in geographic range. The presence of D. melanogaster reduces egg-laying in D. suzukii, possibly because D. melanogaster outcompetes D. suzukii larvae feeding in the same fruit substrate. Flies use pheromones to communicate for mating, but pheromones also serve a role in reproductive isolation between related species. We asked whether a D. melanogaster pheromone also modulates oviposition behaviour in D. suzukii. A dual-choice oviposition assay confirms that D. suzukii lays fewer eggs on blueberries exposed to D. melanogaster flies and further shows that female flies have a stronger effect than male flies. This was corroborated by treating berries with synthetic pheromones. Avoidance of D. suzukii oviposition is mediated by the female D. melanogaster pheromone (Z)-4-undecenal (Z4-11Al). Significantly fewer eggs were laid on berries treated with synthetic Z4-11Al. In comparison, the male pheromone (Z)-11-octadecenyl acetate (cVA) had no effect on D. suzukii oviposition. Z4-11Al is a highly volatile compound that is perceived via olfaction and it is accordingly behaviourally active at a distance from the source. D. suzukii is known to engage in mutual niche construction with the yeast Hanseniaspora uvarum, which strongly attracts flies. Adding Z4-11Al to fermenting H. uvarum significantly decreased D. suzukii flight attraction in a laboratory wind tunnel and a field trapping assay. That a D. melanogaster pheromone regulates oviposition in D. suzukii demonstrates that heterospecific pheromone communication contributes to reproductive isolation and resource partitioning in cognate species. Stimulo-deterrent diversion or push-pull methods, building on combined use of attractant and deterrent compounds, have shown promise for control of D. suzukii. A pheromone that specifically reduces D. suzukii attraction and oviposition adds to the toolbox for D. suzukii integrated management.

Gene Flow Between Populations With Highly Divergent Mitogenomes in the Australian Stingless Bee, Tetragonula hockingsi.

Coadaptation of mitochondrial and nuclear genes is essential for proper cellular function. When populations become isolated, theory predicts that they should maintain mito-nuclear coadaptation in each population, even as they diverge in genotype. Mito-nuclear incompatibilities may therefore arise when individuals from populations with divergent co-evolved mito-nuclear gene sets are re-united and hybridise, contributing to selection against inter-population hybrids and, potentially, to speciation. Here, we explored genetic divergence and gene flow between populations of a stingless bee (Tetragonula hockingsi) that have highly divergent mitogenomes. We identified three distinct populations across the species' 2500 km range on the east coast of Queensland (Australia): 'Cape York', 'Northern', and 'Southern'. The mitogenomes of each population showed > 12% pairwise nucleotide divergence from each other, and > 7% pairwise amino acid divergence. Based on nuclear SNPs from reduced representation sequencing, we identified at least two zones of gene flow between populations: a narrow natural zone between Northern and Southern populations (coinciding with a biogeographic barrier, the Burdekin Gap), and an artificial zone at the southern edge of the species' distribution, where Cape York, Northern, and Southern mito-lineages have been brought together in recent decades due to beekeeping. In the artificial hybrid zone, we also confirmed that males of all three mito-lineages were attracted to the mating aggregations of Southern queens, consistent with inter-population hybridisation. Populations of T. hockingsi thus appear to be in the 'grey zone' of the speciation continuum, having strong genetic differentiation but incomplete reproductive isolation. Among the nuclear SNPs most differentiated between Northern and Southern populations, several were associated with genes involved in mitochondrial function, consistent with populations having co-diverged mito-nuclear gene sets. Our observations suggest that coadapted sets of mitochondrial and nuclear genes unique to each population of T. hockingsi may play a role in maintaining population boundaries, though more study is needed to confirm the fitness costs of mito-nuclear incompatibilities in hybrid individuals.

A Next Generation of Hierarchical Bayesian Analyses of Hybrid Zones Enables Model-Based Quantification of Variation in Introgression in R.

Hybrid zones, where genetically distinct groups of organisms meet and interbreed, offer valuable insights into the nature of species and speciation. Here, we present a new R package, bgchm, for population genomic analyses of hybrid zones. This R package extends and updates the existing bgc software and combines Bayesian analyses of hierarchical genomic clines with Bayesian methods for estimating hybrid indexes, interpopulation ancestry proportions, and geographic clines. Compared to existing software, bgchm offers enhanced efficiency through Hamiltonian Monte Carlo sampling and the ability to work with genotype likelihoods combined with a hierarchical Bayesian approach, enabling inference for diverse types of genetic data sets. The package also facilitates the quantification of introgression patterns across genomes, which is crucial for understanding reproductive isolation and speciation genetics. We first describe the models underlying bgchm and then provide an overview of the R package and illustrate its use through the analysis of simulated and empirical data sets. We show that bgchm generates accurate estimates of model parameters under a variety of conditions, especially when the genetic loci analyzed are highly ancestry informative. This includes relatively robust estimates of genome-wide variability in clines, which has not been the focus of previous models and methods. We also illustrate how both selection and genetic drift contribute to variability in introgression among loci and how additional information can be used to help distinguish these contributions. We conclude by describing the promises and limitations of bgchm, comparing bgchm to other software for genomic cline analyses, and identifying areas for fruitful future development.

Cytogenetic and <i>ISSR</i>-Markers Polymorphism in the Population of Local Ukrainian Lebedyn Cows

Preservation of the fund of local breeds of agricultural animals, which are breeding material for the creation of new ones and the improvement of existing ones, meets the requirements of the FAO - the protection of biological diversity. The study of the genetic structure of cows of the local Lebedyn breed, which was bred in Ukraine, with the use of cytogenetic and molecular genetic methods, is aimed at establishing information about the structure of the gene pool of these animals and the uniqueness of their genotype. Cytogenetic monitoring showed that the modal number of chromosomes corresponded to the species norm and was 2n=60, no constitutional abnormalities in the form of Robertsonian translocations were detected, the average frequency of genomic disorders (aneuploidy) was 10,2±2,10%, polyploidy was not manifested. structural disorders (chromosomal breaks) accounted for 3,1±1,88% and asynchronous separation of the centromeric regions of chromosomes – 0,8±0,10%. The average share of cytogenetic parameters of cells was determined: lymphocytes with micronucleus – 3,6±0,61‰, binucleus lymphocytes – 4,3±0,97‰ and mitotic index – 3,7±1,20‰. An analysis of the genetic structure of the local, small-numbered Lebedyn cattle breed of Ukraine was carried out using 8 ISSR-systems. All 8 microsatellite primers showed high efficiency. ISSR labeling revealed 88 amplified DNA fragments, of which only 18 were polymorphic. The total share of polymorphic loci was 25,45%. 11 species-specific loci for (ACC)6G, 5 loci for (CTC)6C, 10 for (GAG)6C, 7 for (GA)6CC, 10 for (AG)8CG, 9 for (AG)8CA, 13 for (GA)9C and 14 for (AG)9C. It was established that the studied animals were characterized by karyotype stability, reduced sensitivity to mutagenic factors of various nature, absence of inbreeding depression and reproductive isolation.

Performance-based habitat choice can drive rapid adaptive divergence and reproductive isolation

Theory predicts that performance-based habitat choice1,2,3-where individuals select environments based on their local performance-should be widespread in nature and significantly influence ecological and evolutionary processes, including local adaptation, population divergence, reproductive isolation, and speciation.2,4,5,6,7,8,9 However, experimental evidence supporting these predictions has been largely lacking. In this study, we addressed this by inducing performance-based habitat choice in wild tree sparrows (Passer montanus) through the manipulation of differential access to transponder-operated feeders in two adjacent woodland areas. Sparrows overwhelmingly chose to move to and breed in the area where their feeding performance was highest, leading to local adaptation and increased reproductive success. Moreover, this non-random movement led to a high degree of assortative mating for transponder type and to reproductive isolation with respect to this ecological trait-all within a single generation. Our findings provide an empirical proof of principle that performance-based habitat choice can drive adaptive population divergence, even in the absence of divergent natural selection, underscoring its potential role as a key mechanism in ecological and evolutionary dynamics. This highlights the importance of integrating performance-based habitat choiceinto broader frameworks of adaptation and speciation, especially in the context of rapidly changing environments.

Temperature affects conspecific and heterospecific mating rates in Drosophila.

Behavioral mating choices and mating success are important factors in the development of reproductive isolation during speciation. Environmental conditions, especially temperature, can affect these key traits. Environmental conditions can vary across, and frequently delimit species' geographic ranges. Pairing suboptimal conditions with relative rarity of conspecifics at range margins may set the stage for hybridization. Despite the importance of mating behaviors as a reproductive barrier, a general understanding of the interaction between behavioral choices and the environment is lacking, in part because systematic studies are rare. With this report, we begin to bridge that gap by providing evidence that temperature has a significant - but not consistent influence on mating choices and success, and thus on reproductive isolation in Drosophila . We studied mating propensity and success at four different temperatures among 14 Drosophila species in non-choice conspecific mating trials and in heterospecific trials among two Drosophila species triads that are known to regularly hybridize in the wild. We show that mating frequency varies significantly across a 10°C range (from 18ºC to 28ºC), both in 1:1 mating trials and in high-density en-masse trials, but that the effect of temperature is highly species-specific. We also show that mating frequency is consistently low and that temperature has a moderate effect in some heterospecific crosses. As conspecific mating propensity decreases outside of the optimal thermal range, while heterospecific matings remain constant, the proportion of heterospecific matings at suboptimal temperatures is relatively high. This result indicates that temperature can modulate behavioral choices that impose reproductive barriers and influence the rate of hybridization. More broadly, our results demonstrate that to truly understand how mating choice and reproductive isolation occur in nature, they need to be studied in an environmental context.

Opening the species box: what parsimonious microscopic models of speciation have to say about macroevolution.

In the last two decades, lineage-based models of diversification, where species are viewed as particles that can divide (speciate) or die (become extinct) at rates depending on some evolving trait, have been very popular tools to study macroevolutionary processes. Here, we argue that this approach cannot be used to break down the inner workings of species diversification and that "opening the species box" is necessary to understand the causes of macroevolution, but that too detailed speciation models also fail to make robust macroevolutionary predictions. We set up a general framework for parsimonious models of speciation that rely on a minimal number of mechanistic principles: (a) reproductive isolation is caused by excessive dissimilarity between genotypes; (b) dissimilarity results from a balance between differentiation processes and homogenizing processes; and (c) dissimilarity can feed back on these processes by decelerating homogenization. We classify such models according to the main homogenizing process: (a) clonal evolution models (ecological drift), (b) models of genetic isolation (gene flow), and (c) models of isolation by distance (spatial drift). We review these models and their specific predictions on macroscopic variables such as species abundances, speciation rates, interfertility relationships, or phylogenetic tree structure. We propose new avenues of research by displaying conceptual questions remaining to be solved and new models to address them: the failure of speciation at secondary contact, the feedback of dissimilarity on homogenization, and the emergence in space of breeding barriers.

Incomplete barriers to heterospecific mating among Somatochlora species (Odonata: Corduliidae) as revealed in multi-gene phylogenies.

Mating between species occurs within many insect orders. The result of heterospecific mating depends upon the effectiveness of pre- and post-reproductive barriers. Incomplete reproductive barriers lead to introgression of DNA into one species or both. Intricate genital morphology among dragonflies provides little assurance of species specificity given that heterospecific mating or mating attempts have been observed among many species. The genetic consequence is unknown for many heterospecific matings. For example, Somatochlora species mating and genetic exchange have been hypothesized based on observational records and individuals with hybrid morphology. We investigate the potential of heterospecific mating between North American Somatochlora species as inferred from multi-gene phylogenies. We used mitochondrial genes (COI and ND3) and nuclear genes (EF1-α and ITS2) to construct phylogenies using maximum parsimony. Observation of non-monophyletic mtDNA lineages but monophyletic nDNA lineages between Somatochlora sister-species would indicate mtDNA introgression and suggest heterospecific matings. Our results highlighted three instances of non-monophyly of mtDNA clades in the following groups: (i) S. hineana + S. tenebrosa; (ii) S. kennedyi + S. forcipata + S. franklini; and (iii) S. calverti + S. provocans + S. filosa. Analysis of partitioned Bremer support indicates that mtDNA COI largely contributed to the non-monophyly of these species, thus suggesting mtDNA introgression resulting from heterospecific matings. Additionally, the topology resulting from the combined data analysis was concordant with previous taxonomic understanding of Somatochlora species groups. These multi-gene phylogenies of North American Somatochlora are the first, providing a foundation for future ecological and evolution studies and knowledge for effective decision-making and public policy, which is especially important for the endangered species, S. hineana.

Wait, What? What's Going On?- Pregnancy Experiences of Deaf and Hard of Hearing Mothers Who Do Not Sign.

Deaf and hard of hearing (DHH) women experience higher rates of reproductive healthcare barriers and adverse birth outcomes compared to their hearing peers. This study explores the pregnancy experiences of DHH women who do not sign to better understand their barriers and facilitators to optimal perinatal health care. Qualitative study using thematic analysis. Semi-structured, individual remote, or in-person interviews in the United States. Twenty-two DHH English speakers (non-signers) who gave birth in the United States within the past 5 years. Semi-structured interviews explored how DHH women experienced pregnancy and birth, including access to perinatal information and resources, relationships with healthcare providers, communication access, and their involvement with the healthcare system throughout pregnancy. A thematic analysis was conducted. The barriers and facilitators related to a positive perinatal care experience among DHH women. Five key themes emerged. For barriers, healthcare communication breakdowns and loss of patient autonomy highlighted DHH women's struggle with perinatal health care. In contrast, DHH participants outlined the importance of accessible health communication practices and accommodations, use of patient advocacy or self-advocacy, and assistive technologies for DHH parents for more positive perinatal care experiences. Perinatal healthcare providers and staff should routinely inquire about ways to ensure an inclusive and accessible healthcare experience for their DHH patients and provide communication accommodations for optimal care. Additionally, healthcare providers should be more aware of the unique parenting needs and resources of their DHH patients.

Hybrid incompatibility emerges at the one-cell stage in interspecies Caenorhabditis embryos.

Intrinsic reproductive isolation occurs when genetic differences between populations disrupt the development of hybrid organisms, preventing gene flow and enforcing speciation.1-4 While prior studies have examined the genetic origins of hybrid incompatibility,5-18 the effects of incompatible factors on development remain poorly understood. Here, we investigate the mechanistic basis of hybrid incompatibility in Caenorhabditis nematodes by capitalizing on the ability of C. brenneri females to produce embryos after mating with males from several other species. Contrary to expectations, hybrid incompatibility was evident immediately after fertilization, suggesting that post-fertilization barriers to hybridization originate from physical incompatibility between sperm and oocyte-derived factors rather than from zygotic transcription, which starts after the 4-cell stage.19-22 Sperm deliver chromatin, which expands to form a pronucleus, and a pair of centrioles, which form centrosomes that attach to the sperm-derived pronucleus and signal to establish the embryo's anterior-posterior axis.23,24 In C. brenneri oocytes fertilized with C. elegans sperm, sperm pronuclear expansion was compromised, frequent centrosome detachment was observed, and cortical polarity was disrupted. Live imaging revealed that defective polar body extrusion contributes to defects in mitotic spindle morphology. C. brenneri oocytes fertilized with C. remanei or C. sp. 48 sperm showed similar defects, and their severity and frequency increased with phylogenetic distance. Defective expansion of the sperm-derived pronucleus and unreliable polar body extrusion immediately after fertilization generally underlie the inviability of hybrid embryos in this clade. These results indicate that physical mismatches between sperm and oocyte-derived structures may be a primary mechanism of hybrid incompatibility.

NpCIPK6–NpSnRK1 module facilitates inter-subgeneric hybridization barriers in water lily (nymphaea) by reducing abscisic acid content

Abstract Pre-fertilization hybridization barriers are the main causes of inter-subgeneric hybridization challenges in water lily. However, the mechanism underlying low compatibility between pollen and stigma of water lily remains unclear. This study demonstrates that CBL-interacting protein kinase 6 (CIPK6) responded to the signaling exchange between incompatible pollen and stigma through interactions with SNF1-related kinase 1 (SnRK1) and promotes the accumulation of SnRK1 protein. Activated SnRK1 interacted with 9-cis-epoxycarotenoid dioxygenase 2 (NCED2) to promote its degradation, thereby inhibiting abscisic acid (ABA) synthesis. A decrease in ABA content in the stigma impaired the ABA-mediated removal of reactive oxygen species (ROS), ultimately resulting in the rejection of the incompatible pollen by the stigma. Our results highlight the essential role of the NpCIPK6–NpSnRK1–NpNCED2 module in conferring inter-subgeneric hybridization barriers in water lily by interfering with ABA synthesis and promoting ROS accumulation. This study offers valuable mechanistic insights into cellular signaling and reproductive barriers in water lily as well as across other biological contexts.

Increased Evolutionary Rate in the Z chromosome of Sympatric and Allopatric Species of Morpho Butterflies.

Divergent evolution of genomes among closely related species is shaped by both neutral processes and ecological forces, such as local adaptation and reinforcement. These factors can drive accelerated evolution of sex chromosomes relative to autosomes. Comparative genomic analyses between allopatric and sympatric species with overlapping or divergent ecological niches offer insights into reinforcement and ecological specialization on genome evolution. In the butterfly genus Morpho, several species coexist in sympatry, with specialization across forest strata and temporal niches. We analyzed the genomes of eight Morpho species, along with previously published genomes of three others, to compare chromosomal rearrangements and signs of positive selection in the Z chromosome vs. autosomes. We found extensive chromosomal rearrangements in Z chromosome, particularly in sympatric species with similar ecological niches, suggesting a role for inversions in restricting gene flow at a postzygotic level. Z-linked genes also exhibited significantly higher dN/dS ratios than autosomal genes across the genus, with pronounced differences in closely related species living in sympatry. Additionally, we examined the evolution of eight circadian clock genes, detecting positive selection in Period, located on the Z chromosome. Our findings suggest that the Z chromosome evolves more rapidly than autosomes, particularly among closely related species, raising questions about its role in prezygotic and postzygotic isolation mechanisms.

Prezygotic barriers effectively limit hybridization in a rapid evolutionary radiation.

Hybridization is increasingly recognized as an important evolutionary process across the tree of life. In many clades, phylogenomic approaches have permitted unparalleled insight into the extent and frequency of hybridization. However, we continue to lack a deep understanding of the factors that limit and shape patterns of hybridization, especially in evolutionary radiations. In this study, we characterized patterns of introgression across Costus (Costaceae), a young evolutionary radiation of tropical understory plants that maintain widespread interfertility despite exhibiting strong prezygotic reproductive isolation. We analyzed a phylogenomic dataset of 756 genes from 54 Costus species using multiple complementary approaches - D-statistics, gene-tree-based tests, and phylogenetic network analyses - to detect and characterize introgression events throughout the evolutionary history of the radiation. Our results identified a moderate number of introgression events, including a particularly ancient, well-supported event spanning one of the deepest divergences in the clade. Most introgression events occurred between taxa or ancestral lineages that shared the same pollination syndrome (bee-pollinated or hummingbird-pollinated). These findings suggest that prezygotic barriers, including pollinator specialization, have been key to the balance between introgression and reproductive isolation in Costus.