Sexual Life Cycle Research Articles

If the cap fits, wear it: an overview of telomeric structures over evolution.

Genome organization into linear chromosomes likely represents an important evolutionary innovation that has permitted the development of the sexual life cycle; this process has consequently advanced nuclear expansion and increased complexity of eukaryotic genomes. Chromosome linearity, however, poses a major challenge to the internal cellular machinery. The need to efficiently recognize and repair DNA double-strand breaks that occur as a consequence of DNA damage presents a constant threat to native chromosome ends known as telomeres. In this review, we present a comparative survey of various solutions to the end protection problem, maintaining an emphasis on DNA structure. This begins with telomeric structures derived from a subset of prokaryotes, mitochondria, and viruses, and will progress into the typical telomere structure exhibited by higher organisms containing TTAGG-like tandem sequences. We next examine non-canonical telomeres from Drosophila melanogaster, which comprise arrays of retrotransposons. Finally, we discuss telomeric structures in evolution and possible switches between canonical and non-canonical solutions to chromosome end protection.

Ecological factors influencing growth of the endangered Hawaiian fern Marsilea villosa (Marsileaceae) and implications for conservation management

Conserving endangered plants is a complex task, and practitioners must often use a "triage" approach, addressing only immediate needs. Ecologists can improve this process by conducting sound science upon which to base management. Marsilea villosa is an endangered, endemic Hawaiian fern with seven remaining populations in ephemerally flooding drylands. Among its uncommon traits are long-lived sporocarps, requiring flood and drought to complete its sexual life cycle, and extensive vegetative growth. We conducted a 3-yr ecological field study, measuring percent cover of M. villosa and associated species, flooding depth, and canopy cover, to identify ecological factors with the greatest impact on M. villosa growth. Maximum flooding depth and canopy cover had strong positive relationships with M. villosa growth, and all plots with >50% threshold of either variable reached 100% cover of M. villosa by the end of the study. Interaction effects explained nuances of these relationships, including synergy between the two variables. Percent cover of nonnative functional groups (graminoids and nongraminoids) each had negative relationships with M. villosa growth, but interactions showed that nongraminoid cover was driven by particular species, and that time since flooding had greater influence on M. villosa growth than graminoid cover. We recommend planting reintroduced populations in flood-prone areas with moderate shade, experimental outplanting of native plants with M. villosa, and management of graminoids as a functional group, while nongraminoid management should be species-specific. These practices will promote self-sustaining populations and reduce the need for labor-intensive management.

Generation of an antibody that recognizes Plasmodium chabaudi cysteine protease (chabaupain-1) in both sexual and asexual parasite life cycle and evaluation of chabaupain-1 vaccine potential

Malaria cysteine proteases have been shown to be immunogenic and are being exploited as serodiagnostic markers, drug and vaccine targets. Several Plasmodium spp. cysteine proteases have been described and the best characterized of these are the falcipains, a family of papain-family enzymes. Falcipain-2 and falcipain-3 act in concert with other proteases to hydrolyze host erythrocyte hemoglobin in the parasite food vacuole. Falcipain-1 has less similarity to the other falcipains and its physiological role in parasite asexual blood stage still remains uncertain. Immunolocalization studies using an antibody developed against the Plasmodium chabaudi recombinant chabaupain-1, the falcipain-1 ortholog, were performed confirming its cellular localization in both erythrocyte and mosquito ookinete stage. Immunostaining of chabaupain-1 preferentially in apical portion of parasite ookinete suggests that this protease may be related with parasite egression from mosquito midgut. Immune responses to chabaupain-1 were evaluated using two different adjuvants, chitosan nanoparticles and hydroxide aluminum. Mice immunized with the recombinant protein alone or in association with nanoparticles were challenged with P. chabaudi showing that immunization with the recombinant protein confers partial protection to blood stage infection in BALB/c animal model.

First Report of Oregon Grape (Mahonia aquifolium) as an Alternate Host for the Wheat Stripe Rust Pathogen (Puccinia striiformis f. sp. tritici) Under Artificial Inoculation.

As the primary host of the stripe rust pathogen, Puccinia striiformis f. sp. tritici (Pst), wheat can be infected by both aeciospores and urediniospores, and later is the host that gives rise to urediniospores and teliospores. Barberry species (e.g., Berberis vulgaris) can be infected by basidiospores, produced from the teliospores of wheat plants, and later gives rise to pycniospores and aeciospores, which has been demonstrated through artificial inoculation (3). Oregon grape (Mahonia aquifolium), closely related to Berberis, is a native evergreen shrub that is also grown as an ornamental plant in the Pacific Northwest. To determine if M. aquifolium can also serve as an alternate host for Pst, we conducted artificial inoculations under controlled conditions. Seeds of M. aquifolium collected from Pullman, WA, were sown in pots filled with soil mixture, and plants were grown in a greenhouse under wheat-growing conditions (1). In the first experiment, conducted in May to June 2011, the inoculum was telia collected from artificially inoculated wheat cv. Avocet S with urediniospores of isolate 09-134 (race PST-127) from the greenhouse. In the second experiment, conducted in July to August 2011, the inoculum was telia collected from naturally infected wheat cv. Nugaines with urediniospores from isolate 11-292 (race PST-127) from an experimental field near Pullman. For each experiment, mature teliospores of 60 telia from a single wheat plant were suspended in 1.0 ml of distilled water and inoculated with a fine paint brush onto the leaves of seven or eight 10- to 15-day-old plants of M. aquifolium. Plants were incubated initially in a dew chamber at 10°C for 72 h in darkness, then transferred to a growth chamber with a diurnal temperature cycle of 10 to 24°C and a 16 h light/8 h dark cycle (1). Reddish pycnia with nectar appeared on adaxial surfaces of inoculated leaves at 12 days post-inoculation (DPI), and reddish aecia were produced on the baxial surface at 16 DPI. All 15 M. aquifolium leaves of the 15 plants inoculated with teliospores produced pycnia and aecia. Seedlings of Nugaines and Avocet S, wheat cultivars that are susceptible to all Pst races (1), were then inoculated with a water suspension of aeciospores of 30 aecia collected from the M. aquifolium plants. Wheat plants were incubated as described above for M. aquifolium. Uredinia appeared at 15 DPI, and telia were produced after an additional 15 days. From these uredinia that formed on inoculated wheat, a total of 30 single-uredinium isolates were obtained using the standard procedure (1). Virulence tests were carried out on 20 wheat differentials for 10 randomly selected urediniospore isolates, revealing six virulence patterns. When tested with four selected Pst SSR markers (PstP001, PstP003, PstP005, PstP029) (2) and compared to other race PST-127 isolates, all 10 progeny isolates were homozygous, as were the parental isolates (09-134, 11-292). The virulence tests and marker genotypes verified that the urediniospore isolates resulted from infection by aecia, produced by parental isolate 09-134 through its sexual cycle on M. aquifolium. The study exhibited the completed sexual lifecycle of Pst through the five spore stages on wheat and M. aquifolium in a controlled setting, and suggests that under appropriate weather conditions, M. aquifolium may serve as an alternate host for Pst. Due to the wide distribution of M. aquifolium, further studies are needed to determine if the species can be infected by Pst under natural conditions.

Effects of Light, Flooding, and Weeding on Experimental Restoration of an Endangered Hawaiian Fern

AbstractConservation of rare plants can be accomplished by the restoration practice of reintroduction, but subsequent management is often required. In species with narrow habitat requirements, it is especially difficult to predict which management methods will be successful at new locations. Marsilea villosa is an endangered endemic Hawaiian fern with only seven remaining populations in ephemerally flooding drylands. Among its uncommon traits are long‐lived sporocarps, a requirement of flood and drought to complete its sexual life cycle, and the potential for extensive vegetative growth. An experiment was performed to determine which restoration techniques might best facilitate growth of outplanted M. villosa. The following effects were tested in a split‐plot factorial design: flooding (once/none), light (50% shade/full sun), weeding (bi‐monthly/none), and all interactions. We hypothesized that flooding would have the largest single‐factor effect and that there would be interactions among treatments. As hypothesized, flooding had the greatest positive effect on percent cover and sporocarp production. However, shade also increased cover over full sun when the plants began to experience drought. There was an interaction of light × flooding because M. villosa grew best in flooded, shaded plots. Weeding had no significant effect except in combination with flooding. Beyond protected status, current management of M. villosa only includes weed management at some populations. This study shows that if reintroducing new populations, the need for labor‐intensive weed management might be reduced if M. villosa is planted under conditions of flooding and moderate shade.

Collecting, rearing, spawning and inducing regeneration of the starlet sea anemone, Nematostella vectensis

Over the past 20 years, the starlet sea anemone, Nematostella vectensis, a small estuarine animal, has emerged as a powerful model system for field and laboratory studies of development, evolution, genomics, molecular biology and toxicology. Here we describe how to collect Nematostella, culture it through its entire sexual life cycle and induce regeneration for the production of clonal stocks. In less than 1 h at a suitable field site, a researcher on foot can collect hundreds of individual anemones. In a few months, it is possible to establish a laboratory colony that will be reliable in generating hundreds or thousands of fertilized eggs on a roughly weekly schedule. By inducing regeneration roughly every 2 weeks, in less than 6 months, one can establish a clonal stock consisting of hundreds of genetically identical anemones. These results can be achieved very inexpensively and without specialized equipment.

Overview of some recent research developments in fusarium head blight of wheat

This article reviews the recent progress of research on fusarium head blight (FHB) of wheat. It addresses the broad areas of strategies for disease management, biological control, the pathogen (Fusarium graminearum (teleomorph Gibberella zeae)), mycotoxins, the effects of dwarfing genes on FHB severity, quantitative trait loci (QTLs) and new perspectives. Where there are recent reviews on this subject, we have deliberately examined the subsequent literature to provide an update on research. With few resistant cultivars available even now, the main tools to manage the disease remain rotation, varietal selection, disease forecasting and fungicides. A few biocontrol organisms are being considered for commercial application. The pathogen's sexual life cycle has been investigated in depth, and with its complete genome sequence known, the pathways and genes controlling the sexual development and ascospore release of F. graminearum are being explored. The 3-acetyldeoxynivalenol chemotype of F. graminearum has increased in prevalence in Canada with attendant risks of higher DON levels in cereal grain. Stringent limits on allowable levels of Fusarium mycotoxins in the food/feed chain have been enacted in Europe and the USA, but regulations for Canada are only at the discussion stage with the Canadian Food Inspection Agency. Efforts to develop FHB-resistant lines proceed apace, as these can be selected in most wheat populations despite the adverse effects of dwarfing genes on FHB severity. While more quantitative trait loci (QTLs) for disease resistance continue to be identified and mapped, new resistant cultivars remain disappointingly few. We present some encouraging early results from an alternative approach based on epigenetics.

Differences in sexual behavior of two distant populations of the funnel-web wolf spider Aglaoctenus lagotis

Generally, sexual repertoire within a species is conserved, but frequencies of occurrence of sexual behavioral acts often vary, and wide geographic distributions may favor these variations. Aglaoctenus lagotis is distributed along South America and belongs to Sosippinae, a subfamily of wolf spiders that builds funnel webs. Previous reports, based on different populations, suggested variations in sexual behavior and life cycle. Our objective was to describe and compare the sexual behavior of two populations of A. lagotis: ‘Southern Uruguay’ (SU) and ‘Central Argentina’ (CA). We carried out intrapopulation trials, in the laboratory, with 15 female–male pair matings. The most representative courtship acts in SU were web-stretching, striding-forward and forelegs-elevating, whereas in CA they were alternate-waving, web-stretching and leg-tapping. Juddering, forelegs-elevating and striding-forward were exclusive for SU, while alternate-waving and simultaneous-waving were exclusive for CA. We also found differences in copulatory characteristics such as frequencies of insertions and ejaculations. We documented body-shaking during copulation for the first time. Some sexual acts were exclusive of each population, while the shared ones differed in pattern and frequencies of occurrence. In addition to variations in sexual periods, these differences may favor divergence processes or an exceptional high level of flexibility in the sexual behavior of A. lagotis.

Reproductive effort of Mastocarpus papillatus (Rhodophyta) along the California coast.

Species with sexual and asexual life cycles may exhibit intraspecific differences in reproductive effort. The spatial separation of sexual and asexual lineages, called geographic parthenogenesis, is common in plants, animals and algae. Mastocarpus papillatus is a well-documented case of geographic parthenogenesis in which sexuals dominate southern populations, asexuals dominate northern populations, while mixed populations occur throughout central California. We quantified abundances and reproductive effort of sexual and asexual fronds and tetrasporophytes at eight sites in California to test the hypotheses that (1) reduced sexual reproduction at higher latitudes and tidal heights explains the observed geographic parthenogenesis and (2) reproductive effort (spore production per blade area) declines with increasing latitude. Abundances of all phases varied site-specifically. However, there was no geographic pattern of reproductive effort of fronds. Reproductive effort of fronds was greater in 2006 than in 2007 and correlated with sea surface temperatures. Sexual fronds exhibited greater reproductive effort than did asexual fronds and sexual reproductive effort was also inversely correlated with local upwelling index. Tetrasporophytes showed greater reproductive effort in northern sites, but total supply of tetraspores per m2 was greatest in the middle of the sampling range where crusts were more abundant. There was no decline of reproductive effort at higher latitudes. Geographic patterns of fecundity of life stages do not explain geographic parthenogenesis in M. papillatus. Site-specific differences in viability among spores or established thalli of different life cycles may explain their respective geographic distributions, as the sexual and asexual life cycles responded differently to environmental variations.

Extensive Divergence Between Mating-Type Chromosomes of the Anther-Smut Fungus

Genomic regions that determine mating compatibility are subject to distinct evolutionary forces that can lead to a cessation of meiotic recombination and the accumulation of structural changes between members of the homologous chromosome pair. The relatively recent discovery of dimorphic mating-type chromosomes in fungi can aid the understanding of sex chromosome evolution that is common to dioecious plants and animals. For the anther-smut fungus, Microbotryum lychnidis-dioicae (= M. violaceum isolated from Silene latifolia), the extent of recombination cessation on the dimorphic mating-type chromosomes has been conflictingly reported. Comparison of restriction digest optical maps for the two mating-type chromosomes shows that divergence extends over 90% of the chromosome lengths, flanked at either end by two pseudoautosomal regions. Evidence to support the expansion of recombination cessation in stages from the mating-type locus toward the pseudoautosomal regions was not found, but evidence of such expansion could be obscured by ongoing processes that affect genome structure. This study encourages the comparison of forces that may drive large-scale recombination suppression in fungi and other eukaryotes characterized by dimorphic chromosome pairs associated with sexual life cycles.

The zinc finger protein Zfr1p is localized specifically to conjugation junction and required for sexual development in Tetrahymena thermophila.

Conjugation in Tetrahymena thermophila involves a developmental program consisting of three prezygotic nuclear divisions, pronuclear exchange and fusion, and postzygotic and exconjugant stages. The conjugation junction structure appears during the initiation of conjugation development, and disappears during the exconjugant stage. Many structural and functional proteins are involved in the establishment and maintenance of the junction structure in T. thermophila. In the present study, a zinc finger protein-encoding gene ZFR1 was found to be expressed specifically during conjugation and to localize specifically to the conjugation junction region. Truncated Zfr1p localized at the plasma membrane in ordered arrays and decorated Golgi apparatus located adjacent to basal body. The N-terminal zinc finger and C-terminal hydrophobic domains of Zfr1p were found to be required for its specific conjugation junction localization. Conjugation development of ZFR1 somatic knockout cells was aborted at the pronuclear exchange and fusion conjugation stages. Furthermore, Zfr1p was found to be important for conjugation junction stability during the prezygotic nuclear division stage. Taken together, our data reveal that Zfr1p is required for the stability and integrity of the conjugation junction structure and essential for the sexual life cycle of the Tetrahymena cell.

Development and application of a two-tier multiple-choice diagnostic test for high school students’ understanding of cell division and reproduction

This study involved the development and application of a two-tier diagnostic test for measuring students’ understanding of cell division and reproduction. The instrument development procedure had three general steps: defining the content boundaries of the test, collecting information on students’ misconceptions, and instrument development. Misconception data were collected from interviews and multiple-choice questions with open response. The data were used to develop fourteen two-tier multiple-choice items. The conceptual knowledge examined was preliminary functions of cell division, basic processes in cell division, mitotic cell cycle and asexual reproduction, the role of meiosis in sexual life cycles, as well as cell types and cell division. The diagnostic instrument was administered to 403 high-school students. The reliability coefficient of the test was 0.81. Difficulty indices ranged from 0.31 to 0.72, and discrimination indices ranged from 0.23 to 0.61. Results of the cell division and reproduction diagnostic test suggested that students did not acquire a satisfactory understanding of cell division and reproduction concepts. The obtained misconceptions and the reasons for them were discussed in the analysis of the items which could inform biology instruction and resource.

Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant

Fungal diseases of plants represent one of the most eminent threats to agriculture. Given the food needs of a growing world population and that more and more crops are devoted to fuel production, the necessity to develop crops with better resistance to disease is increasing. To accomplish this, the mechanisms that plant pathogenic fungi use to colonize plants need to be elucidated. As of now, there are only few examples/models in which this can be done on a functional, genome-wide level, taking into account both the pathogen and its host plant [1]. The fungus Ustilago maydis (U. maydis) is one of these examples. It is a member of the smut fungi: a large group of parasites infecting mostly grasses, including several important crop plants such as maize (Figure 1B), wheat, barley, and sugar cane. Smut fungi are biotrophs, i.e., parasites that need the living host plant to complete their sexual life cycle [2], [3]. They do not establish prominent feeding structures like the related, haustoria-forming rust fungi. During penetration, the host plasma membrane invaginates and completely encases the intracellular hyphae (Figure 1A), establishing an extended interaction zone [4] mediating the exchange of molecules between fungus and host. In contrast to most smut fungi that cause a systemic infection, remaining symptomless until the plant flowers, U. maydis can infect all above-ground parts of the maize plant but fails to spread systemically. U. maydis induces local tumors in which spores develop (Figure 1B) – a unique feature that allows detection of symptoms in corn seedlings less than a week after syringe infection with high levels of inoculum. This, together with the toolbox developed for reverse genetics, cell biology, and functional studies, has contributed to its status as a model for biotrophic basidiomycete fungi [5]. Here the current level of our understanding of the elaborate molecular crosstalk between U. maydis and its host plant will be discussed. Figure 1 Disease symptoms and schematic presentation of effector cocktail use in different maize organs and tissues infected by U. maydis.

Reproduction and dispersal in an ant‐associated root aphid community

Clonal organisms with occasional sex are important for our general understanding of the costs and benefits that maintain sexual reproduction. Cyclically parthenogenetic aphids are highly variable in their frequency of sexual reproduction. However, studies have mostly focused on free-living aphids above ground, whereas dispersal constraints and dependence on ant-tending may differentially affect the costs and benefits of sex in subterranean aphids. Here, we studied reproductive mode and dispersal in a community of root aphids that are obligately associated with the ant Lasius flavus. We assessed the genetic population structure of four species (Geoica utricularia, Tetraneura ulmi, Forda marginata and Forda formicaria) in a Dutch population and found that all species reproduce predominantly if not exclusively asexually, so that populations consist of multiple clonal lineages. We show that population viscosity is high and winged aphids rare, consistent with infrequent horizontal transmission between ant host colonies. The absence of the primary host shrub (Pistacia) may explain the absence of sex in three of the studied species, but elm trees (Ulmus) that are primary hosts of the fourth species (T.ulmi) occurred within a few km of the study population. We discuss the extent to which obligate ant-tending and absence of primary hosts may have affected selection for permanent parthenogenesis, and we highlight the need for further study of these aphids in Southern Europe where primary hosts may occur close to L.flavus populations, so that all four root aphid species would have realistic opportunities for completing their sexual life cycle.

CURRENT KNOWLEDGE OF THE LIFE CYCLES OF PHAEOCYSTIS GLOBOSA AND PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE)(1).

Despite continuous efforts since the 1950s and more recent advances in culturing flagellates and nonflagellate cells of the prymnesiophyte Phaeocystis, a number of different life-cycle models exist today that appear to apply for P. globosa Scherff. and P. antarctica G. Karst., both spherical colony formers. In one such model, this life cycle consists of three different flagellates and one nonmotile cell stage that is embedded in carbohydrate matrix-forming colonies of different sizes and forms. Recently, noncolonial aggregates of diploid nonmotile cells attached to surfaces of diatoms were put forward as a new stage in the sexual life cycle of P. antarctica. However, it can be discussed that these "attached aggregates" (AAs) are an intermediate between motile diploid flagellates, with their well-known tendency to adhere to surfaces, and the young spherical colony with its diploid nonmotile cells, which in nature is commonly found attached to diatoms. A life-cycle model pertaining to both P. globosa and P. antarctica is presented.

Extensive Genetic Diversity, Unique Population Structure and Evidence of Genetic Exchange in the Sexually Transmitted Parasite Trichomonas vaginalis

Background Trichomonas vaginalis is the causative agent of human trichomoniasis, the most common non-viral sexually transmitted infection world-wide. Despite its prevalence, little is known about the genetic diversity and population structure of this haploid parasite due to the lack of appropriate tools. The development of a panel of microsatellite makers and SNPs from mining the parasite's genome sequence has paved the way to a global analysis of the genetic structure of the pathogen and association with clinical phenotypes.Methodology/Principal FindingsHere we utilize a panel of T. vaginalis-specific genetic markers to genotype 235 isolates from Mexico, Chile, India, Australia, Papua New Guinea, Italy, Africa and the United States, including 19 clinical isolates recently collected from 270 women attending New York City sexually transmitted disease clinics. Using population genetic analysis, we show that T. vaginalis is a genetically diverse parasite with a unique population structure consisting of two types present in equal proportions world-wide. Parasites belonging to the two types (type 1 and type 2) differ significantly in the rate at which they harbor the T. vaginalis virus, a dsRNA virus implicated in parasite pathogenesis, and in their sensitivity to the widely-used drug, metronidazole. We also uncover evidence of genetic exchange, indicating a sexual life-cycle of the parasite despite an absence of morphologically-distinct sexual stages.Conclusions/SignificanceOur study represents the first robust and comprehensive evaluation of global T. vaginalis genetic diversity and population structure. Our identification of a unique two-type structure, and the clinically relevant phenotypes associated with them, provides a new dimension for understanding T. vaginalis pathogenesis. In addition, our demonstration of the possibility of genetic exchange in the parasite has important implications for genetic research and control of the disease.

Fungal development of the plant pathogenUstilago maydis

The maize pathogen Ustilago maydis has to undergo various morphological transitions for the completion of its sexual life cycle. For example, haploid cells respond to pheromone by forming conjugation tubes that fuse at their tips. The resulting dikaryon grows filamentously, expanding rapidly at the apex and inserting retraction septa at the basal pole. In this review, we present progress on the underlying mechanisms regulating such defined developmental programmes. The key findings of the postgenomic era are as follows: (1) endosomes function not only during receptor recycling, but also as multifunctional transport platforms; (2) a new transcriptional master regulator for pathogenicity is part of an intricate transcriptional network; (3) determinants for uniparental mitochondrial inheritance are encoded at the a2 mating-type locus; (4) microtubule-dependent mRNA transport is important in determining the axis of polarity; and (5) a battery of fungal effectors encoded in gene clusters is crucial for plant infection. Importantly, most processes are tightly controlled at the transcriptional, post-transcriptional and post-translational levels, resulting in a complex regulatory network. This intricate system is crucial for the timing of the correct order of developmental phases. Thus, new insights from all layers of regulation have substantially advanced our understanding of fungal development.

From Local Adaptation to Speciation: Specialization and Reinforcement

Local adaptation is the first step in the process of ecological speciation. It is, however, an unstable and dynamic situation. It can be strengthened by the occurrence of alleles more specialized to the different habitats or vanish if generalist alleles arise by mutations and increase in frequency. This process can have complicated dynamics as specialist alleles may be much more common and may maintain local adaptation for a long time. Thus, even in the absence of an absolute fitness tradeoff between habitats, local adaptation may persist a long time before vanishing. Furthermore, several feedback loops can help to maintain it (the reinforcement, demographic, and recombination loops). This reinforcement can occur by modifying one of the three fundamental steps in a sexual life cycle (dispersal, syngamy, meiosis), which promotes genetic clustering by causing specific genetic associations. Distinguishing these mechanisms complements the one- versus two-allele classification. Overall, the relative rates of the two processes (specialization and reinforcement) dictate whether ecological speciation will occur.

Double peaks reveal rare diplomonad sex

Diplomonads, single-celled eukaryotes, are unusual in having two nuclei. Each nucleus contains two copies of the genome and is transcriptionally active. It has long been assumed that diplomonads in general and Giardia intestinalis in particular are asexual. Genomic and population genetic data now challenge that assumption and extensive allelic sequence heterogeneity has been reported in some but not all examined diplomonad lineages. Here it is argued, in contrast to common assumptions, that allelic differences indicate recent sexual events, and isolates that have divided asexually for many generations have lost their allelic variation owing to within-cell recombination. Consequently, directed studies of the allelic sequence heterogeneity in diverse diplomonad lineages are likely to reveal details about the enigmatic diplomonad sexual life cycle.

Genetic Structure of Two Protist Species (Myxogastria, Amoebozoa) Suggests Asexual Reproduction in Sexual Amoebae

Plasmodial slime molds (Myxogastria or Myxomycetes) are common and widespread unicellular organisms that are commonly assumed to have a sexual life cycle culminating with the formation of often macroscopic fruiting bodies that efficiently disseminate spores. However, laboratory studies based on mating compatibility revealed the coexistence of asexual as well as sexual strains. To test this hypothesis in natural populations, we investigated the genetic variability of two species of the genus Lamproderma. Detailed ecological relevés were carried out in 2007 and 2009 in several deep ravines in the Elbsandsteingebirge (Saxony, south-eastern Germany). Morphological characters of 93 specimens of Lamproderma were recorded and genetic analyses, based on the small subunit ribosomal gene, the internal transcribed spacer 1 and partial elongation factor 1α sequences were carried out for 52 specimens. Genetic analyses showed the existence of two major clades, each composed of several discrete lineages. Most of these lineages were composed of several identical sequences (SSU, ITS 1 and EF-1α) which is explained best by an asexual mode of reproduction. Detrended Correspondence Analysis of morphological characters revealed two morphospecies that corresponded to the two major clades, except for one genotype (Lc6), thus challenging the morphospecies concept. Genetic patterns were not related to the geographical distribution: specimens belonging to the same genotype were found in distinct ravines, suggesting effective long-distance dispersal via spores, except for the Lc6 genotype which was found only in one ravine. Implications for the morphological and biological species concept are discussed.