Asexual Species Research Articles

Effects of mode of reproduction on genetic polymorphism and divergence in wild yams (Dioscoreaceae: Dioscorea)

Evolutionary transitions from sexual to asexual reproduction should have significant influences on genetic divergence and polymorphism at the genome level. Plant lineages with diverse reproductive systems provide opportunities to investigate this question using comparative approaches and studies of molecular evolution. We investigated evidence for differences among the transcriptomes of 19 Dioscorea species (wild yams) with diverse reproductive systems. These included sexual species, those that propagate primarily by bulbils, and those with mixed sexual and asexual reproductive modes. We examined how transitions between these reproductive systems affected between-species divergence and within-species polymorphism. Primarily asexual species exhibited a reduced efficacy of natural selection and accumulation of deleterious mutations for both divergence and polymorphism. In contrast, species with mixed reproductive strategies involving both seed and clonal reproduction showed no evidence of an increased fixation of harmful mutations at the divergence level, while an accumulation of genetic load present in polymorphism was evident. Our study indicates that the genetic consequences of evolutionary transitions from sexual to predominantly clonal reproduction is likely to depend on both the duration and extent of asexuality occurring in populations.

Patterns of molecular evolution in a parthenogenic terrestrial isopod (Trichoniscus pusillus).

The "paradox of sex" refers to the question of why sexual reproduction is maintained in the wild, despite how costly it is compared to asexual reproduction. Because of these costs, one might expect nature to select for asexual reproduction, yet sex seems to be continually selected for. Multiple hypotheses have been proposed to explain this incongruence, including the niche differentiation hypothesis, the Red Queen hypothesis, and accumulation of harmful mutations in asexual species due to inefficient purifying selection. This study focuses on the accumulation of mutations in two terrestrial isopods, Trichoniscus pusillus, which has sexual diploid and parthenogenic triploid forms, and Hyloniscus riparius, an obligately sexual relative. We surveyed sex ratios of both species in an upstate New York population and obtained RNA-seq data from wild-caught individuals of both species to examine within- and between-species patterns of molecular evolution in protein-coding genes. The sex ratio and RNA-seq data together provide strong evidence that this T. pusillus population is entirely asexual and triploid, while the H. riparius population is sexual and diploid. Although all the wild T. pusillus individuals used for sequencing shared identical genotypes at nearly all SNPs, supporting a clonal origin, heterozygosity and SNP density were much higher in T. pusillus than in the sexually reproducing H. riparius. This observation suggests this parthenogenic lineage may have arisen via mating between two divergent diploid lineages. Between-species sequence comparisons showed no evidence of ineffective purifying selection in the asexual T. pusillus lineage, as measured by the ratio of nonsynonymous to synonymous substitutions (dN/dS ratios). Likewise, there was no difference between T. pusillus and H. riparius in the ratios of nonsynonymous to synonymous SNPs overall (pN/pS). However, pN/pS ratios in T. pusillus were significantly higher when considering only SNPs that may have arisen via recent mutation after the transition to parthenogenesis. Thus, these recent SNPs are consistent with the hypothesis that purifying selection is less effective against new mutations in asexual lineages, but only over long time scales. This system provides a useful model for future studies on the evolutionary tradeoffs between sexual and asexual reproduction in nature.

Absence of female preference and the origin of a unisexual species, the Amazon molly (Poecilia formosa)

AbstractThe role of hybridization as a formative process in evolution has received much attention in the past few decades. A particularly fascinating outcome of hybrid speciation is the formation of asexual hybrid species. The Amazon molly (Poecilia formosa) is such a hybrid and originated from a P. mexicana mother and a P. latipinna father. Consequently, a heterospecific mating must have occurred leading to the Amazon molly, indicating a breakdown of any potential prezygotic isolation between parental species. Here we studied the female mate preferences of extant P. mexicana and P. latipinna from several populations using standard binary choice tests with males of both sexual species that were matched for size. Poecilia mexicana and P. latipinna can be crossed in the lab, however, the offspring are not asexual, but sexual F1s. In our study, we generated F1s and tested their mating preferences with sexual males of both P. mexicana and P. latipinna against F1 males. Overall, our results show that in extant P. mexicana and P. latipinna no female preference for conspecific males was detectable. Consequently, heterospecific matings are possible and not hindered by any apparent behavioral prezygotic isolation. If female preferences in these species were comparable around the time the Amazon molly originated as a hybrid species ca. 100,000 years ago, matings leading to hybrids would be very likely. F1 females also have no discernable mating preferences for either sexual males or F1 males. Such lack of prezygotic behavioral isolation could potentially lead to F2 individuals, backcrosses, and introgression.

Wickerhamomyces corioli f.a., sp. nov., a novel yeast species discovered in two mushroom species.

Two yeast strains, designated as 19-39-3 and 19-40-2, obtained from the fruiting bodies of Trametes versicolor and Marasmius siccus collected in Yunwu Mountain Forest Park, PR China, have been identified as representing a novel asexual ascomycetous yeast species. From the results of phylogenetic analyses of the sequences of the D1/D2 domains of the large subunit (LSU) rRNA, small subunit (SSU) rRNA and translation elongation factor 1-α (TEF1) genes, it was determined that these strains represent a member of the genus Wickerhamomyces, with Wickerhamomyces alni and Candida ulmi as the closest relatives. The novel species exhibited 6.6 and 6.7% differences in the D1/D2 domains compared with W. alni and C. ulmi, respectively. Additionally, distinct biochemical and physiological differences were observed between the novel species and its related counterparts. No sexual reproduction was observed in these strains, leading to the proposal of the name Wickerhamomyces corioli f.a., sp. nov. for this newly discovered species.

Estimating the Rate of Mutation to a Mutator Phenotype

A mutator is a variant in a population of organisms whose mutation rate is higher than the average mutation rate in the population. For genetic and population dynamics reasons, mutators are produced and survive with much greater frequency than anti-mutators (variants with a lower-than-average mutation rate). This strong asymmetry is a consequence of both fundamental genetics and natural selection; it can lead to a ratchet-like increase in the mutation rate. The rate at which mutators appear is, therefore, a parameter that should be of great interest to evolutionary biologists generally; for example, it can influence: (1) the survival duration of a species, especially asexual species (which are known to be short-lived), (2) the evolution of recombination, a process that can ameliorate the deleterious effects of mutator abundance, (3) the rate at which cancer appears, (4) the ability of pathogens to escape immune surveillance in their hosts, (5) the long-term fate of mitochondria, etc. In spite of its great relevance to basic and applied science, the rate of mutation to a mutator phenotype continues to be essentially unknown. The reasons for this gap in our knowledge are largely methodological; in general, a mutator phenotype cannot be observed directly, but must instead be inferred from the numbers of some neutral “marker” mutation that can be observed directly: different mutation-rate variants will produce this marker mutation at different rates. Here, we derive the expected distribution of the numbers of the marker mutants observed, accounting for the fact that some of the mutants will have been produced by a mutator phenotype that itself arose by mutation during the growth of the culture. These developments, together with previous enhancements of the Luria–Delbrück assay (by one of us, dubbed the “Jones protocol”), make possible a novel experimental protocol for estimating the rate of mutation to a mutator phenotype. Simulated experiments using biologically reasonable parameters that employ this protocol show that such experiments in the lab can give us fairly accurate estimates of the rate of mutation to a mutator phenotype. Although our ability to estimate mutation-to-mutator rates from simulated experiments is promising, we view this study as a proof-of-concept study and an important first step towards practical empirical estimation.

Novel Helicoma and Neohelicosporium (Tubeufiaceae, Tubeufiales) species and two new host records of Helicoma on tropical palms (Arecaceae) from China.

Asexual species of Tubeufiaceae are characterised as helicosporous hyphomycetes and are abundantly discovered in tropical and subtropical regions. The present study collected helicosporous fungal samples from rotting tissues of Caryotamitis, Elaeisguineensis and E.oleifera in Xishuangbanna, Yunan Province, China. Fungal isolates were identified, based on the morphological characteristics and multi-gene phylogeny with DNA sequence data of the internal transcribed spacer (ITS), part of the large subunit nuclear rRNA gene (LSU), translation elongation factor 1-alpha gene (tef 1-α) and RNA polymerase II second largest subunit gene (rpb2). Herein, we introduce three new species viz. Helicomaoleifera, Neohelicosporiumguineensis and N.xishuangbannaensis. In addition, we introduce two new host records of Helicomaguttulatum and H.rufum on Caryotamitis. The illustrations of all identified species, detailed descriptions and in-depth phylogenetic analyses are provided. Our results add new knowledge of fungal species associated with palm hosts in southern China. Moreover, our data will contribute to the biodiversity of fungi in tropical China.

Continuity and discontinuity in evolutionary processes with emphasis on plants

The present work is aimed to review the concepts of continuity and discontinuity in the reproductive processes and their impact on the evolutionary outcome, emphasizing on the plant model. Let be stated that evolutionary changes need to pass down generation after generation through the cellular reproductive mechanisms, and these mechanisms can account for changes from single nucleotide to genome-wide mutations. Patterns of continuity and discontinuity in sexual and asexual species pose notorious differences as the involvement of the cellular genetic material from single or different individuals, the changes in the ploidy level, or the independence between nuclear and plastid genomes. One relevant aspect of the plant model is the open system for pollen donation, which can be driven from every male flower to every female flower in the neighborhood, as well as the facilitated seed dispersal patterns, that may break or restore the contact between populations. Three significative processes are distinguishable, syngenesis, anagenesis, and cladogenesis. The syngenesis refers to the reproduction between individuals, either if they pertain to the same species, from different populations or even from different species. The anagenesis refers to the pursuit of all the possible rearrangements of genes and alleles pooled in a population of individuals, and the cladogenesis represents the absence of reproduction that leads to differentiation. Recent developments on the genomic analysis of single cells, single chromosomes and fragments of homologous chromosomes could bring new insights into the processes of the evolution, in generational time and in a broad spectrum of spatial/geographic extents.

Sclerococcum pseudobactrodesmium sp. nov. from a terrestrial habitat in China

In this study, four terrestrial collections of bactrodesmium-like hyphomycetous fungi were isolated from rotten wood in Guizhou Province, China. Phylogenetic analyses based on the combined LSU, ITS, mtSSU, and SSU sequence matrix indicate that these four isolates represent one species belonging to the Sclerococcum within the Dactylosporaceae, and present a distinct lineage. Therefore, Sclerococcum pseudobactrodesmium sp. nov. was introduced with corresponding morphological descriptions. Sclerococcum pseudobactrodesmium represents the first lignicolous asexual species from a terrestrial habitat.

Danielozyma pruni sp. nov., an asexual yeast species isolated from insect frass.

Two strains (NYNU 218101 and NYNU 218104) of an asexual yeast species were isolated from insect frass collected in insect tunnels of red leaf plum trees in the Henan Province, central China. Molecular phylogenetic analysis of the D1/D2 domain of the large subunit rRNA gene and the internal transcribed spacer (ITS) region showed that these two strains belonged to the genus Danielozyma, with Danielozyma litseae as the closest known species. They differed from the type strain of D. litseae by 0.6 % substitutions (three substitutions and one gap) in the D1/D2 domain and by 5.1 % substitutions (19 substitutions and six gaps) in the ITS region, respectively. When compared with the partial ACT1, TEF1 and RPB1 gene sequences, they differed by 3 % (26 substitutions), 2.7 % (25 substitutions) and 9 %(54 substitutions) from D. litseae NRRL YB-3246T in these regions. Physiologically, they also differed from its closest known species D. litseae based on the ability to assimilate inulin and galactitol, as well as to grow in 0.1 % cycloheximide and its inability to ferment maltose and raffinose. In order to classify the two new isolates based on morphological and molecular evidence, we proposed the description of a novel species Danielozyma pruni sp. nov. with strain JCM 35735T as holotype (Mycobank MB 849101).

Acropleurophialis simplex gen. & sp. nov. from China

A new asexual ascomycete genus and species, Acropleurophialis simplex collected on dead branches of an unidentified broadleaf tree in Jiangxi Province, China, is described and illustrated. The fungus is distinguished by macronematous, unbranched, determinate or percurrently extending conidiophores, and solitary, semi-endogenous, simple, smooth, spherical or subspherical, aseptate, pale brown to subhyaline conidia seceding schizolytically from polyphialidic, integrated, terminal and intercalary, sympodial, cylindrical conidiogenous cells with conspicuous collarettes.

Intensive and efficient egg-laying tempo of the parthenogenesis mourning gecko Lepidodactylus lugubris

Although suffered from many evolutionary disadvantages, asexual species benefit from their high efficiency to build clonal populations in a novel habitat. Here we report that a parthenogenetic mourning gecko Lepidodactylus lugubris continuously laid 12 clutches within two years. The egg-laying period lasted from mid-April to late October, and the egg-laying interval ranged between 24 and 73 days with a mean of 34.4 days. Referring to this fecundity, a female gecko could reproduce up to 24 clonal female offspring every year, and expand the population size in an efficient way much faster than most bisexual species. The intensive and efficient egg-laying tempo, associated with the parthenogenetic breeding mode, are crucial factors which facilitated their successful colonisation into many islands. Keywords: clonal population, cost of sex, invariant clutch size, invasive species

Sperm-dependent asexual species and their role in ecology and evolution.

Sexual reproduction is the primary mode of reproduction in eukaryotes, but some organisms have evolved deviations from classical sex and switched to asexuality. These asexual lineages have sometimes been viewed as evolutionary dead ends, but recent research has revealed their importance in many areas of general biology. Our review explores the understudied, yet important mechanisms by which sperm-dependent asexuals that produce non-recombined gametes but rely on their fertilization, can have a significant impact on the evolution of coexisting sexual species and ecosystems. These impacts are concentrated around three major fields. Firstly, sperm-dependent asexuals can potentially impact the gene pool of coexisting sexual species by either restricting their population sizes or by providing bridges for interspecific gene flow whose type and consequences substantially differ from gene flow mechanisms expected under sexual reproduction. Secondly, they may impact on sexuals' diversification rates either directly, by serving as stepping-stones in speciation, or indirectly, by promoting the formation of pre- and postzygotic reproduction barriers among nascent species. Thirdly, they can potentially impact on spatial distribution of species, via direct or indirect (apparent) types of competition and Allee effects. For each such mechanism, we provide empirical examples of how natural sperm-dependent asexuals impact the evolution of their sexual counterparts. In particular, we highlight that these broad effects may last beyond the tenure of the individual asexual lineages causing them, which challenges the traditional perception that asexual lineages are short-lived evolutionary dead ends and minor sideshows. Our review also proposes new research directions to incorporate the aforementioned impacts of sperm-dependent asexuals. These research directions will ultimately enhance our understanding of the evolution of genomes and biological interactions in general.

Metschnikowia ahupensis f.a., sp. nov., a new yeast species isolated from the gut of the wood-feeding termite Nasutitermes sp.

The gut of xylophagous insects such as termites harbours various symbiotic micro-organisms, including many yeast species. In a taxonomic study of gut-associated yeasts, two strains (ATS2.16 and ATS2.18) were isolated from the gut of the wood-feeding termite Nasutitermes sp. in Maharashtra, India. Morphological and physiological characteristics and sequence analyses of the ITS and D1/D2 region of the large subunit rRNA gene revealed that these two strains represent a novel asexual ascomycetous yeast species in the genus Metschnikowia. The species differs from some of its close affiliates in the genus in its inability to utilize ethanol and succinate as the sole carbon source and growth in high sugar concentrations (up to 50 % glucose). In contrast to most members of Metschnikowia, the formation of ascospores was not observed on various sporulation media. Moreover, whole-genome sequencing was used to further confirm the novelty of this species. When compared with other large-spored Metschnikowia species, average nucleotide identity values of 79-80 % and digital DNA-DNA hybridization values of 16-17 % were obtained. The name Metschnikowia ahupensis f.a., sp. nov. is proposed to accommodate this novel yeast species, with ATS2.16 as the holotype and strains NFCCI 4949, MTCC 13085 and PYCC 9152 as isotypes. The MycoBank number is MB 844210.

Why do hybrids turn down sex?

Asexual reproduction is ancestral in prokaryotes; the switch to sexuality in eukaryotes is one of the major transitions in the history of life. The study of the maintenance of sex in eukaryotes has raised considerable interest for decades and is still one of evolutionary biology's most prominent question. The observation that many asexual species are of hybrid origin has led some to propose that asexuality in hybrids results from sexual processes being disturbed because of incompatibilities between the two parental species' genomes. However, in some cases, failure to produce asexual F1s in the lab may indicate that this mechanism is not the only road to asexuality in hybrid species. Here, we present a mathematical model and propose an alternative, adaptive route for the evolution of asexuality from previously sexual hybrids. Under some reproductive alterations, we show that asexuality can evolve to rescue hybrids' reproduction. Importantly, we highlight that when incompatibilities only affect the fusion of sperm and egg's genomes, the two traits that characterize asexuality, namely unreduced meiosis and the initiation of embryogenesis without the incorporation of the sperm's pronucleus, can evolve separately, greatly facilitating the overall evolutionary route. Taken together, our results provide an alternative, potentially complementary explanation for the link between asexuality and hybridization.

Revising Clonostachys and allied genera in Bionectriaceae.

Clonostachys (Bionectriaceae, Hypocreales) species are common soil-borne fungi, endophytes, epiphytes, and saprotrophs. Sexual morphs of Clonostachys spp. were placed in the genus Bionectria, which was further segregated into the six subgenera Astromata, Bionectria, Epiphloea, Myronectria, Uniparietina, and Zebrinella. However, with the end of dual nomenclature, Clonostachys became the single depository for sexual and asexual morph-typified species. Species of Clonostachys are typically characterised by penicillate, sporodochial, and, in many cases, dimorphic conidiophores (primary and secondary conidiophores). Primary conidiophores are mononematous, either verticillium-like or narrowly penicillate. The secondary conidiophores generally form imbricate conidial chains that can collapse to slimy masses, particularly on sporodochia. In the present study, we investigated the species diversity within a collection of 420 strains of Clonostachys from the culture collection of, and personal collections at, the Westerdijk Fungal Biodiversity Institute in Utrecht, the Netherlands. Strains were analysed based on their morphological characters and molecular phylogeny. The latter used DNA sequence data of the nuclear ribosomal internal transcribed spacer regions and intervening 5.8S nrDNA (ITS) and partial 28S large subunit (LSU) nrDNA and partial protein encoding genes including the RNA polymerase II second largest subunit (RPB2), translation elongation factor 1-alpha (TEF1) and β-tubulin (TUB2). Based on these results, the subgenera Astromata, Bionectria, Myronectria and Zebrinella are supported within Clonostachys. Furthermore, the genus Sesquicillium is resurrected to accommodate the former subgenera Epiphloea and Uniparietina. The close relationship of Clonostachys and Sesquicillium is strongly supported as both are inferred phylogenetically as sister-genera. New taxa include 24 new species and 10 new combinations. Recognition of Sesquicillium distinguishes species typically forming a reduced perithecial stroma superficially on plant tissue from species in Clonostachys often forming well-developed, through bark erumpent stromata. The patterns of observed perithecial wall anatomies, perithecial wall and stroma interfaces, and asexual morph diversifications described in a previously compiled monograph are used for interpreting ancestral state reconstructions. It is inferred that the common ancestor of Clonostachys and Sesquicillium may have formed perithecia superficially on leaves, possessed a perithecial wall consisting of a single region, and formed intercalary phialides in penicilli of conidiophores. Character interpretation may also allow hypothesising that diversification of morphs occurred then in the two genera independently and that the frequently stroma-linked Clonostachys morphs evolved together with the occupation of woody host niches and mycoparasitism. Taxonomic novelties: New species: Clonostachys aurantiaca L. Zhao & Crous, Clonostachys australiana L. Zhao & Crous, Clonostachys bambusae L. Zhao & Crous, Clonostachys buxicola L. Zhao & Crous, Clonostachys cylindrica L. Zhao & Crous, Clonostachys ellipsoidea L. Zhao & Crous, Clonostachys flava L. Zhao, Crous & Schroers, Clonostachys fujianensis L. Zhao & Crous, Clonostachys fusca L. Zhao, Crous & Schroers, Clonostachys garysamuelsii L. Zhao & Crous, Clonostachys hongkongensis L. Zhao & Crous, Clonostachys longiphialidica L. Zhao, Crous & Schroers, Clonostachys obovatispora, L. Zhao & Crous, Clonostachys palmae L. Zhao, Crous & Schroers, Clonostachys parasporodochialis L. Zhao & Crous, Clonostachys penicillata L. Zhao, Crous & Schroers, Clonostachys reniformis L. Zhao & Crous, Clonostachys vacuolata L. Zhao, Crous & Schroers, Clonostachys venezuelae L. Zhao, Crous & Schroers, Mycocitrus synnematus L. Zhao & Crous, Nectriopsis didymii L. Zhao & Crous, Sesquicillium intermediophialidicum L. Zhao & Crous, Sesquicillium neerlandicum L. Zhao & Crous, Sesquicillium symmetricum L. Zhao & Crous. New combinations: Mycocitrus coccicola (J.A. Stev.) L. Zhao & Crous, Mycocitrus coxeniae (Y.P. Tan et al.) L. Zhao & Crous, Sesquicillium essexcoheniae (Y.P. Tan et al.) L. Zhao & Crous, Sesquicillium lasiacidis (Samuels) L. Zhao, Crous & Schroers, Sesquicillium phyllophilum (Schroers) L. Zhao, Crous & Schroers, Sesquicillium rossmaniae (Schroers) L. Zhao, Crous & Schroers, Sesquicillium saulense (Lechat & J. Fourn.) L. Zhao & Crous, Sesquicillium sesquicillii (Samuels) L. Zhao, Crous & Schroers, Sesquicillium spinulosisporum (Lechat & J. Fourn.) L. Zhao & Crous, Sesquicillium tornatum (Höhn.) Schroers. New synonyms: Clonostachys aranearum W.H. Chen et al., Clonostachys chuyangsinensis H. Yu & Y. Wang, Clonostachys eriocamporesiana R.H. Perera & K.D. Hyde, Clonostachys granuligera (Starbäck) Forin & Vizzini, Clonostachys indica Prasher & R. Chauhan, Clonostachys spinulosa R.H. Perera et al., Clonostachys squamuligera (Sacc.) Forin & Vizzini, Clonostachys wenpingii (J. Luo & W.Y. Zhuang) Z.Q. Zeng & W.Y. Zhuang. Epitypes (basionyms): Fusidium buxi J.C. Schmidt ex Link, Verticillium candelabrum Bonord. Citation: Zhao L, Groenewald JZ, Hernández-Restrepo M, Schroers H-J, Crous PW (2023). Revising Clonostachys and allied genera in Bionectriaceae. Studies in Mycology 105: 205-266. doi: 10.3114/sim.2023.105.03.

Comparative genomics of smut fungi suggest the ability of meiosis and mating in asexual species of the genus Pseudozyma (Ustilaginales)

BackgroundThe Ustilaginales comprise hundreds of plant-parasitic fungi with a characteristic life cycle that directly links sexual reproduction and parasitism: One of the two mating-type loci codes for a transcription factor that not only facilitates mating, but also initiates the infection process. However, several species within the Ustilaginales have no described parasitic stage and were historically assigned to the genus Pseudozyma. Molecular studies have shown that the group is polyphyletic, with members being scattered in various lineages of the Ustilaginales. Together with recent findings of conserved fungal effectors in these non-parasitic species, this raises the question if parasitism has been lost recently and in multiple independent events or if there are hitherto undescribed parasitic stages of these fungi.ResultsIn this study, we sequenced genomes of five Pseudozyma species together with six parasitic species from the Ustilaginales to compare their genomic capability to perform two central functions in sexual reproduction: mating and meiosis. While the loss of sexual capability is assumed in certain lineages and asexual species are common in Asco- and Basidiomycota, we were able to successfully annotate potentially functional mating and meiosis genes that are conserved throughout the whole group.ConclusionOur data suggest that at least the key functions of a sexual lifestyle are maintained in the analyzed genomes, challenging the current understanding of the so-called asexual species with respect to their evolution and ecological role.

Range expansions of sexual versus asexual organisms: Effects of reproductive assurance and migration load.

It is generally considered that sexual organisms show faster evolutionary adaptation than asexual organisms because sexuals can accumulate adaptive mutations through recombination. Yet, empirical evidence often shows that the geographic range size of sexual species is narrower than that of closely related asexual species, which may seem as if asexuals can adapt to more varied environments. Two potential explanations for this apparent contradiction considered by the existing theory are reproduction assurance and migration load. Here, we consider both reproductive assurance and migration load within a single model to comparatively examine their effects on range expansions of sexuals and asexuals across an environmental gradient. The model shows that higher dispersal propensity decreases sexuals' disadvantage in reproductive assurance while increasing their disadvantage in migration load. Moreover, lower mutation rate constrains adaptation more strongly in asexuals than in sexuals. Thus, high dispersal propensity and high mutation rates promote that asexuals have wider range sizes than sexuals. Intriguingly, our model reveals that sexuals can have wider geographic range sizes than asexuals under low dispersal propensity and low mutation rates, a pattern consistent with a few exceptional empirical cases. Combining reproductive assurance and migration load provides a useful perspective to better understand the relationships between species' mating systems and their geographic ranges.

Two New Species and a New Record of Microdochium from Grasses in Yunnan Province, South-West China.

Microdochium species are frequently reported as phytopathogens on various plants and also as saprobic and soil-inhabiting organisms. As a pathogen, they mainly affect grasses and cereals, causing severe disease in economically valuable crops, resulting in reduced yield and, thus, economic loss. Numerous asexual Microdochium species have been described and reported as hyphomycetous. However, the sexual morph is not often found. The main purpose of this study was to describe and illustrate two new species and a new record of Microdochium based on morphological characterization and multi-locus phylogenetic analyses. Surveys of both asexual and sexual morph specimens were conducted from March to June 2021 in Yunnan Province, China. Here, we introduce Microdochium graminearum and M. shilinense, from dead herbaceous stems of grasses and report M. bolleyi as an endophyte of Setaria parviflora leaves. This study improves the understanding of Microdochium species on monocotyledonous flowering plants in East Asia. A summary of the morphological characteristics of the genus and detailed references are provided for use in future research.

Asexual male production by ZW recombination in Artemia parthenogenetica.

In some asexual species, parthenogenetic females occasionally produce males, which may strongly affect the evolution and maintenance of asexuality if they cross with related sexuals and transmit genes causing asexuality to their offspring ("contagious parthenogenesis"). How these males arise in the first place has remained enigmatic, especially in species with sex chromosomes. Here, we test the hypothesis that rare, asexually produced males of the crustacean Artemia parthenogenetica are produced by recombination between the Z and W sex chromosomes during non-clonal parthenogenesis, resulting in ZZ males through loss of heterozygosity at the sex determination locus. We used RAD-sequencing to compare asexual mothers with their male and female offspring. Markers on several sex-chromosome scaffolds indeed lost heterozygosity in all male but no female offspring, suggesting that they correspond to the sex-determining region. Other sex-chromosome scaffolds lost heterozygosity in only a part of the male offspring, consistent with recombination occurring at a variable location. Alternative hypotheses for the production of these males (such as partial or total hemizygosity of the Z) could be excluded. Rare males are thus produced because recombination is not entirely suppressed during parthenogenesis in A. parthenogenetica. This finding may contribute to explaining the maintenance of recombination in these asexuals.

Four New Species of Aspergillus Subgenus Nidulantes from China.

Aspergillus subgenus Nidulantes includes species with emericella-like ascomata and asexual species. Subgenus Nidulantes is the second largest subgenus of Aspergillus and consists of nine sections. In this study, agricultural soils were sampled from 12 provinces and autonomous regions in China. Based on primary BLAST analyses, seven of 445 Aspergillus isolates showed low similarity with existing species. A polyphasic investigation, including phylogenetic analysis of partial ITS, β-tubulin, calmodulin, and RNA polymerase II second largest subunit genes, provided evidence that these isolates were distributed among four new species (Aspergillus guangdongensis, A. guangxiensis, A. sichuanensis and A. tibetensis) in sections Aenei, Ochraceorosei, and Sparsi of subgenus Nidulantes. Illustrated morphological descriptions are provided for each new taxon.