Absence Of Sexual Reproduction Research Articles

Mating type and microsatellite genotyping indicate that the Tunisian population of Phyllosticta citricarpa is clonal and thrives only asexually

Citrus black spot (CBS) caused by Phyllosticta citricarpa was reported for the first time in Tunisia in 2019. This was also the first reported occurrence of the disease in a Mediterranean climate. In Tunisia, CBS is mainly found in lemon (Citrus limon) orchards, and is seldom observed on sweet orange (Citrus × sinensis). This recent finding in North Africa raises questions about how the disease has been able to spread under Mediterranean climatic conditions. In this work, 216 Phyllosticta strains collected from lemon orchards in 2021, 2022 and 2023 throughout the country's main citrus-growing provinces were characterised by species morphological and molecular identification, mating type and Simple Sequence Repeats (SSR) microsatellite genotyping (MLG). P. citricarpa was the only species found to be associated with CBS in Tunisia. Although P. citricarpa is a heterothallic fungal species, potentially able to reproduce both sexually and asexually, a single mating type (MAT 1-1-1) idiomorph was found in the population. In addition, three MLGs were observed, across ten microsatellite loci, one of which was massively represented (93 %), indicating a clonal population. The clonality observed suggests a single recent introduction of the pathogen into the country. These findings support the idea that in Tunisia, P. citricarpa only reproduces asexually by pycniospores, with a relatively limited dispersal potential. This is consistent with the absence of pseudothecia on the leaf litter. These results show that CBS is able to thrive under Mediterranean conditions, even in the absence of sexual reproduction. This should be taken into consideration for CBS risk assessment and management.

Distinct responses in sexual reproduction onset and growth of Chara braunii Gmelin to light level and temperature: evidence from a greenhouse experiment

The importance of oospores in the ecology and life cycle of annual charophyte species is now widely recognized. To elucidate the primary factor that determines the timing (onset) of sexual reproduction, a controlled 3 × 2 factorial experiment with various light levels (100%, 50% and 10% of natural irradiance) and temperatures (25 °C and 20 °C) was conducted to assess their interactive effects on Chara braunii Gmelin under greenhouse conditions. Results revealed that when the light level decreased from 100% to 10% of natural irradiance, the occurrence of gametangia was postponed for 8 days and the proportions of branch whorls with gametangia (PG) and oospores (PO) significantly decreased under high-temperature conditions. Decreased temperature significantly delayed the emergence of gametangia (100% of light levels for 10 days, 50% of light level for 6 days) and decreased PG and PO. Under low-temperature conditions, no gametangia were found at the lowest light level (10/20). This indicated that the combination of low light and low temperature could result in the absence of sexual reproduction in C. braunii. Furthermore, the internode length, dry weight length ratio and pigment pattern of cultured C. braunii were also significantly altered in response to different light levels and temperature treatments. Two-way ANOVA analysis revealed that temperature contributed more to PG and PO than light levels, while light levels contributed more to morphology and pigment ratio than temperature. This might suggest distinct responses of sexual reproduction onset and growth of C. braunii to varied light level and temperature.

The evolutionary history of Cardamine bulbifera shows a successful rapid postglacial Eurasian range expansion in the absence of sexual reproduction.

Sexual reproduction is known to drive plant diversification and adaptation. Here we investigate the evolutionary history and spatiotemporal origin of a dodecaploid (2n = 12x = 96) Eurasian deciduous woodland species, Cardamine bulbifera, which reproduces and spreads via vegetative bulb-like structures only. The species has been among the most successful range-expanding understorey woodland plants in Europe, which raises the question of the genetic architecture of its gene pool, since its hexaploid (2n = 6x = 48) but putatively outcrossing closest relative, C. quinquefolia, displays a smaller distribution range in Eastern Europe towards the Caucasus region. Cardamine bulbifera belongs to a small monophyletic clade of four species comprising also C. abchasica (2n = 2x = 16) and C. bipinnata (unknown ploidy) from the Caucasus region. We sequenced the genomes of the two polyploids and their two putative ancestors using Illumina short-read sequencing technology (×7-8 coverage). Covering the entire distribution range, genomic data were generated for 67 samples of the two polyploids (51 samples of C. bulbifera, 16 samples of C. quinquefolia) and 6 samples of the putative diploid taxa (4 samples of C. abchasica, 2 samples of C. bipinnata) to unravel the evolutionary origin of the polyploid taxa using phylogenetic reconstructions of biparentally and maternally inherited genetic sequence data. Ploidy levels of C. bulbifera and C. quinquefolia were analysed by comparative chromosome painting. We used genetic assignment analysis (STRUCTURE) and approximate Bayesian computation (ABC) modelling to test whether C. bulbifera represents genetically differentiated lineages and addressed the hypothesis of its hybrid origin. Comparative ecological modelling was applied to unravel possible niche differentiation among the two polyploid species. Cardamine bulbifera was shown to be a non-hybridogenous, auto-dodecaploid taxon of early Pleistocene origin, but with a history of past gene flow with its hexaploid sister species C. quinquefolia, likely during the last glacial maximum in shared refuge areas in Eastern Europe towards Western Turkey and the Crimean Peninsula region. The diploid Caucasian endemic C. abchasica is considered an ancestral species, which also provides evidence for the origin of the species complex in the Caucasus region. Cardamine bulbifera successfully expanded its distribution range postglacially towards Central and Western Europe accompanied by a transition to exclusively vegetative propagation. A transition to vegetative propagation in C. bulbifera is hypothesized as the major innovation to rapidly expand its distribution range following postglacially progressing woodland vegetation throughout Europe. Preceding and introgressive gene flow from its sister species C. quinquefolia in the joint refuge area is documented. This transition and ecological differentiation may have been triggered by preceding introgressive gene flow from its sister species in the joint East European refuge areas.

Starvation-induced cell fusion and heterokaryosis frequently escape imperfect allorecognition systems in an asexual fungal pathogen

BackgroundAsexual fungi include important pathogens of plants and other organisms, and their effective management requires understanding of their evolutionary dynamics. Genetic recombination is critical for adaptability and could be achieved via heterokaryosis — the co-existence of genetically different nuclei in a cell resulting from fusion of non-self spores or hyphae — and the parasexual cycle in the absence of sexual reproduction. Fusion between different strains and establishment of viable heterokaryons are believed to be rare due to non-self recognition systems. Here, we investigate the extent and mechanisms of cell fusion and heterokaryosis in the important asexual plant pathogen Verticillium dahliae.ResultsWe used live-cell imaging and genetic complementation assays of tagged V. dahliae strains to analyze the extent of non-self vegetative fusion, heterokaryotic cell fate, and nuclear behavior. An efficient CRISPR/Cas9-mediated system was developed to investigate the involvement of autophagy in heterokaryosis. Under starvation, non-self fusion of germinating spores occurs frequently regardless of the previously assessed vegetative compatibility of the partners. Supposedly “incompatible” fusions often establish viable heterokaryotic cells and mosaic mycelia, where nuclei can engage in fusion or transfer of genetic material. The molecular machinery of autophagy has a protective function against the destruction of “incompatible” heterokaryons.ConclusionsWe demonstrate an imperfect function of somatic incompatibility systems in V. dahliae. These systems frequently tolerate the establishment of heterokaryons and potentially the initiation of the parasexual cycle even between strains that were previously regarded as “incompatible.”

Parasitoid pressure does not elicit defensive polyphenism in the green peach aphid

1. Aphids are capable of adapting to parasitoid pressure in the absence of sexual reproduction using epigenetically controlled polyphenism. Asexual lineages of aphids could thus become resistant to parasitoids over time and with repeated exposure, hampering biocontrol efforts that rely on parasitoid wasps.2. Prior to this study, wing polyphenism and reproductive polyphenism had been reported as parasitoid‐adaptive responses in asexual lineages of at least two species of aphids, but it remained unclear whether parasitoid exposure could induce other defensive polyphenisms. Using a rigorous, replicated experimental evolution design, we aimed to induce adaptive polyphenisms in the green peach aphid, Myzus persicae Sulzer, through serial exposures of single asexual lines to the parasitoid Aphidius colemani Viereck over four consecutive generations.3. We measured changes in parasitoid susceptibility, reproductive schedule, body size, and production of pink or alate offspring compared to aphid control lines not exposed to parasitoids. Despite this consistently strong selective parasitoid pressure, there was no evidence that asexual lineages of M. persicae adapt to parasitoid pressure using adaptive polyphenism.4. Our data indicate that pseudo‐crowding stress – where aphids disturbed by parasitoids or predators wander within a colony, increasing aphid‐to‐aphid contact and creating the illusion of a more crowded environment – may be necessary for M. persicae to produce defensive polyphenisms in response to parasitoid attack.

Mitotic Recombination and Rapid Genome Evolution in the Invasive Forest Pathogen Phytophthora ramorum.

Invasive alien species often have reduced genetic diversity and must adapt to new environments. Given the success of many invasions, this is sometimes called the genetic paradox of invasion. Phytophthora ramorum is invasive, limited to asexual reproduction within four lineages, and presumed clonal. It is responsible for sudden oak death in the United States, sudden larch death in Europe, and ramorum blight in North America and Europe. We sequenced the genomes of 107 isolates to determine how this pathogen can overcome the invasion paradox. Mitotic recombination (MR) associated with transposons and low gene density has generated runs of homozygosity (ROH) affecting 2,698 genes, resulting in novel genotypic diversity within the lineages. One ROH enriched in effectors was fixed in the NA1 lineage. An independent ROH affected the same scaffold in the EU1 lineage, suggesting an MR hot spot and a selection target. Differences in host infection between EU1 isolates with and without the ROH suggest that they may differ in aggressiveness. Non-core regions (not shared by all lineages) had signatures of accelerated evolution and were enriched in putative pathogenicity genes and transposons. There was a striking pattern of gene loss, including all effectors, in the non-core EU2 genome. Positive selection was observed in 8.0% of RxLR and 18.8% of Crinkler effector genes compared with 0.9% of the core eukaryotic gene set. We conclude that the P. ramorum lineages are diverging via a rapidly evolving non-core genome and that the invasive asexual lineages are not clonal, but display genotypic diversity caused by MR.IMPORTANCE Alien species are often successful invaders in new environments, despite the introduction of a few isolates with a reduced genetic pool. This is called the genetic paradox of invasion. We found two mechanisms by which the invasive forest pathogen causing sudden oak and sudden larch death can evolve. Extensive mitotic recombination producing runs of homozygosity generates genotypic diversity even in the absence of sexual reproduction, and rapid turnover of genes in the non-core, or nonessential portion of genome not shared by all isolates, allows pathogenicity genes to evolve rapidly or be eliminated while retaining essential genes. Mitotic recombination events occur in genomic hot spots, resulting in similar ROH patterns in different isolates or groups; one ROH, independently generated in two different groups, was enriched in pathogenicity genes and may be a target for selection. This provides important insights into the evolution of invasive alien pathogens and their potential for adaptation and future persistence.

Chloroplast DNA sequencing and detailed microsatellite genotyping of all remnant populations suggests that only a single genet survives of the critically endangered plant Rehmannia japonica.

Rehmannia japonica (Thunb.) Makino ex T. Yamaz. is an endangered perennial herb species in Japan. Although earlier the Japanese considered it a variety of R. glutinosa, recent Japanese taxonomists have consistently regarded it as an independent species. According to the historical literature, Rehmannia japonica seems to have been known in China and Japan in the past. However, Chinese taxonomists do not recognize R. japonica at present. In Japan, only two populations are known, and although these populations flower every year, seed reproduction has not been observed. In this study, we aimed to reveal the phylogenetic relationships and levels of genetic diversity of R. japonica. A haplotype network based on two chloroplast DNA regions (trnL-trnF and rps16) showed that the sequences of R. japonica were distinguishable by three or four sites of indels from the most closely related species, R. chingii, consistent with the separate species status of R. japonica. An analysis of genetic diversity using twelve microsatellite loci showed that all of the ramets of R. japonica collected from two geographically isolated populations had an identical multilocus genotype, including identical heterozygous genotypes at six loci. This result indicated asexual origin of all sampled ramets. This study also suggests that the absence of sexual reproduction of R. japonica is explained by self-incompatibility combined with only a single genet remaining in the R. japonica populations.

High-frequency in vitro plant regeneration via callus induction in a rare sexual plant of Cenchrus ciliaris L.

Cenchrus ciliaris L. is an important perennial forage grass that grows throughout the semi-arid tropics. It reproduces predominantly by apomixis, which provides a means of clonal propagation through seeds. The absence of sexual reproduction in C. ciliaris limits the possibilities of genetic improvement by hybridization. A rare obligate sexual plant of C. ciliaris (IGFRI-CcSx-08/1) that is self-incompatible in nature requires vegetative propagation to maintain its genotype. In vitro culture is one of the possible ways for clonal multiplication and a prerequisite for genetic manipulation. Here, we report high frequency in vitro plant regeneration via callus induction from immature inflorescences of this obligate sexual plant. Embryogenic calli were induced on Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (3.5 mg L−1), and shoot organogenesis was obtained on MS medium supplemented with kinetin (2.0 mg L−1). Rooting from the regenerated shoots was achieved on MS medium containing indolebutyric acid (2.0 mg L−1) and activated charcoal (2.0 g L−1). The survival rate of the plants under ex vitro conditions was 70%. Molecular analysis of the tissue cultured plants using sequence characterized amplified region (SCAR) markers and by embryo sac analysis revealed obligate sexual reproduction in all the regenerated plants. The tissue cultured plants were true to the mother plant type. The high frequency of in vitro plant regeneration achieved by this protocol would be very useful for clonal multiplication and genetic manipulation of this rare genotype of C. ciliaris.

Parasitic success without sex – the nematode experience.

Asexual reproduction is usually considered as an evolutionary dead end, and difficulties for asexual lineages to adapt to a fluctuating environment are anticipated due to the lack of sufficient genetic plasticity. Yet, unlike their sexual congeners, mitotic parthenogenetic root-knot nematode species, Meloidogyne spp., are remarkably widespread and polyphagous, with the ability to parasitize most flowering plants. Although this may reflect in part the short-term stability of agricultural environments, the extreme parasitic success of these clonal species points them as an outstanding evolutionary paradox regarding current theories on the benefits of sex. The discovery that most of the genome of the clonal species M. incognita is composed of pairs of homologous but divergent segments that have presumably been evolving independently in the absence of sexual recombination has shed new light on this evolutionary paradox. Together with recent studies on other biological systems, including the closely related sexual species M. hapla and the ancient asexual bdelloid rotifers, this observation suggests that functional innovation could emerge from such a peculiar genome architecture, which may in turn account for the extreme adaptive capacities of these asexual parasites. Additionally, the higher proportion of transposable elements in M. incognita compared to M. hapla and other nematodes may also be responsible in part for genome plasticity in the absence of sexual reproduction. We foresee that ongoing sequencing efforts should lead soon to a genomic framework involving genetically diverse Meloidogyne species with various different reproductive modes. This will undoubtedly promote the entire genus as a unique and valuable model system to help deciphering the evolution of asexual reproduction in eukaryotes.

Unseen sex in ancient virgin fungi

Unseen sex in ancient virgin fungi

Modeling loss and recovery of Zostera marina beds in the Chesapeake Bay: The role of seedlings and seed-bank viability

Loss and recovery processes following a documented large scale decline in Zostera marina beds in the York River, Virginia in 2005 were modeled by coupling production and sexual reproduction models. The reproduction model included formulations for reproductive shoot production, seed production, seed-bank density, seed viability, and seed germination. After the model was calibrated and validated using in situ water quality and plant performance measurements from two different sites, model scenarios were run for three years (1 year pre-decline, 2 years post-decline) to quantify the effects of (1) the presence or absence of sexual reproduction, (2) increases in water temperatures from ambient to ambient +5°C in 1°C increments, and (3) the potential interactive effects of light and temperature conditions on bed maintenance and re-establishment. Model projections of Z. marina production following the decline corresponded to in situ measurements of recovery only when sexual reproduction was added. However, a 1°C increase in temperature resulted in a complete loss of biomass after two consecutive years of temperature stress following the depletion of the viable sediment seed bank. Interactions between light and temperature stress resulted in overall lower production and resilience to declines under lower light conditions due to corresponding decreases in photosynthetic rates and increases in respiration. Model results highlight (1) the need to incorporate sexual reproduction into Z. marina ecosystem models, (2) the projected sensitivity of established beds to consecutive years of stress, and (3) the negative effects of multiple stressors on Z. marina resilience and recovery.

The double allopolyploid Sphagnum ×falcatulum (Sphagnaceae) in Tierra del Fuego, a Holantarctic perspective

A Holantarctic species, the inter-subgeneric allopolyploid Sphagnum ×falcatulum s.l. is a cryptic species complex composed of allodiploid and allotriploid cytotypes. The allotriploid plants are double allopolyploids (one of just two reported for bryophytes), with the allodiploid cytotype being one parent. Using a combination of microsatellites, nucleotide sequences, and morphological characters, allotriploid S. ×falcatulum is shown to be the most widespread Sphagnum species in the Holantarctic, with genetically documented populations in South America (Tierra del Fuego), New Zealand (South Island), and Australia (Macquarie Island, Tasmania). It is further concluded that six Sphagnum species described from the Tierra del Fuego Archipelago (TDF) of South America and a seventh described from South Island, New Zealand are synonymous with the allotriploid cytotype of S. ×falcatulum. The synonymized species include five named by Heikki Roivainen in 1937, S. ×ehyalinum, and S. subditivum. Allotriploid S. ×falcatulum is the predominant, perhaps the only, subgenus Cuspidata species present in TDF and immediate vicinity. The combination of low genetic diversity and an apparent absence of sexual reproduction indicate that the TDF population of the dioicous allotriploid S. ×falcatulum was likely founded by one or a limited number of individuals. The same is apparently the case for Macquarie I. and Tasmanian populations of allotriploid S. ×falcatulum. Several lines of evidence, including high genetic diversity, frequent sporophyte production, and the occurrence of the allodiploid parent, suggest that allotriploid S. ×falcatulum likely evolved in New Zealand.

The Production of Monokaryotic Hyphae by Cryptococcus neoformans Can Be Induced by High Temperature Arrest of the Cell Cycle and Is Independent of Same-Sex Mating

Cryptococcus neoformans is a heterothallic fungal pathogen of humans and animals. Although the fungus grows primarily as a yeast, hyphae are produced during the sexual phase and during a process called monokaryotic fruiting, which is also believed to involve sexual reproduction, but between cells of the same mating type. Here we report a novel monokaryotic fruiting mechanism that is dependent on the cell cycle and occurs in haploid cells in the absence of sexual reproduction. Cells grown at 37°C were found to rapidly produce hyphae (∼4 hrs) and at high frequency (∼40% of the population) after inoculation onto hyphae-inducing agar. Microscopic examination of the 37°C seed culture revealed a mixture of normal-sized and enlarged cells. Micromanipulation of single cells demonstrated that only enlarged cells were able to produce hyphae and genetic analysis confirmed that hyphae did not arise from α-α mating or endoduplication. Cell cycle analysis revealed that cells grown at 37°C had an increased population of cells in G2 arrest, with the proportion correlated with the frequency of monokaryotic fruiting. Cell sorting experiments demonstrated that enlarged cells were only found in the G2-arrested population and only this population contained cells able to produce hyphae. Treatment of cells at low temperature with the G2 cell cycle arrest agent, nocodazole, induced hyphal growth, confirming the role of the cell cycle in this process. Taken together, these results reveal a mating-independent mechanism for monokaryotic fruiting, which is dependent on the cell cycle for induction of hyphal competency.

Spatial genetic structure of aquatic bryophytes in a connected lake system

Using genetic markers, we investigated the genetic structure of three clonal aquatic moss species, Calliergon megalophyllum Mikut., Fontinalis antipyretica Hedw. and F.hypnoides Hartm. on two scales: among populations in a connected lake system (large-scale spatial genetic structure) and among individuals within populations (fine-scale spatial genetic structure). Mean genetic diversities per population were 0.138, 0.247 and 0.271, respectively, and total diversities equalled 0.223, 0.385 and 0.421, respectively. Relative differentiation levels (FST values of 0.173, 0.280 and 0.142, respectively) were significant but showed that there is a moderate amount of gene flow taking place within the lake system connected with narrow streams. Bayesian STRUCTURE analysis provided some indication that the direction of water flow influences population genetic structuring in the studied aquatic mosses. We propose that dispersal leading to gene flow in C.megalophyllum, F.antipyretica and F.hypnoides takes place both along water via connecting streams and by animal vectors, such as waterfowl. Nevertheless, the slight genetic structuring pattern along the direction of water flow suggests that dispersal of shoots or their fragments along water is a means of dispersal in these mosses. The absence of sexual reproduction and spores may have caused the observed spatial genetic structure within populations, including aggregations of similar genotypes (clones or closely related genotypes) at short distances in populations otherwise showing an isolation by distance effect. Regardless of the results pointing to the dominance of vegetative propagation, it is impossible to completely rule out the potential role of rare long-distance spore dispersal from areas where the species are fertile.

Asexual reproduction induces a rapid and permanent loss of sexual reproduction capacity in the rice fungal pathogen Magnaporthe oryzae: results of in vitroexperimental evolution assays

BackgroundSexual reproduction is common in eukaryotic microorganisms, with few species reproducing exclusively asexually. However, in some organisms, such as fungi, asexual reproduction alternates with episodic sexual reproduction events. Fungi are thus appropriate organisms for studies of the reasons for the selection of sexuality or clonality and of the mechanisms underlying this selection. Magnaporthe oryzae, an Ascomycete causing blast disease on rice, reproduces mostly asexually in natura. Sexual reproduction is possible in vitro and requires (i) two strains of opposite mating types including (ii) at least one female-fertile strain (i.e. a strain able to produce perithecia, the female organs in which meiosis occurs). Female-fertile strains are found only in limited areas of Asia, in which evidence for contemporary recombination has recently been obtained. We induced the forced evolution of four Chinese female-fertile strains in vitro by the weekly transfer of asexual spores (conidia) between Petri dishes. We aimed to determine whether female fertility was rapidly lost in the absence of sexual reproduction and whether this loss was controlled genetically or epigenetically.ResultsAll the strains became female-sterile after 10 to 19 rounds of selection under asexual conditions. As no single-spore isolation was carried out, the observed decrease in the production of perithecia reflected the emergence and the invasion of female-sterile mutants. The female-sterile phenotype segregated in the offspring of crosses between female-sterile evolved strains and female-fertile wild-type strains. This segregation was maintained in the second generation in backcrosses. Female-sterile evolved strains were subjected to several stresses, but none induced the restoration of female fertility. This loss of fertility was therefore probably due to genetic rather than epigenetic mechanisms. In competition experiments, female-sterile mutants produced similar numbers of viable conidia to wild-type strains, but released them more efficiently. This advantage may account for the invasion of our populations by female-sterile mutants.ConclusionsWe show for the first time that, in the absence of sexual reproduction, female-sterile mutants of M. oryzae rice strains can arise and increase in abundance in asexual generations. This change in phenotype was frequent and probably caused by mutation. These results suggest that female fertility may have been lost rapidly during the dispersion of the fungus from Asia to the rest of the world.

Meiotic genes in the arbuscular mycorrhizal fungi

The arbuscular mycorrhizal fungi (AMF) are important symbionts of land plants, which are known for their tremendous positive effects on terrestrial ecosystems, their peculiar cellular features, and their very old evolutionary history. To date, no sexual stage or apparatus have ever been observed in these organisms; a remarkable absence for a eukaryotic lineage. For this reason, AMF have long been considered an evolutionary oddity, having evolved for over 500 millions of years in the absence of sexual reproduction and meiosis. Here, we discuss the recent identification across a number of AMF genomes, of many genes that are known to be involved in the process of meiosis in several eukaryotic model species. The presence of these genes in AMF is a previously unsuspected and highly intriguing finding, which suggests the presence of a “hidden” sexual (or parasexual) reproduction that awaits formal observation in these poorly studied fungi.

Sequence and Simple-Sequence Repeat Analyses of the Fungal PathogenSeiridium cardinaleIndicate California Is the Most Likely Source of the Cypress Canker Epidemic for the Mediterranean Region

Seiridium cardinale is the pathogenic fungus of unknown origin responsible for a world pandemic known as cypress canker affecting several species of Cupressaceae in both the Northern and Southern Hemisphere. In this study, a comparative genetic analysis of worldwide populations was performed using sequence analysis of a portion of the ?-tubulin locus and seven polymorphic simple-sequence repeat (SSR) loci on 96 isolates. Sequence analysis identified two distinct ?-tubulin alleles, both present in California. Only one of the two alleles was detected in the Mediterranean basin, while two isolates from the Southern Hemisphere were characterized by the presence of the allele absent from the Mediterranean. SSRs identified a total of 46 multilocus genotypes (MGs): genotypic diversity was always higher in the California population, and calculations of the index of association (I(A)) determined the presence of linkage disequilibrium associated with the absence of sexual reproduction only in the Mediterranean population but not in California. In 50 instances, the same MG was found at great geographic distances, implying a role played by humans in spreading the disease. Network analysis performed on SSR data identified three clusters of MGs: California, Morocco, and the rest of the Mediterranean. Both the Morocco and the Mediterranean clusters were linked to the California cluster. Coalescent analysis identified insignificant migration between California and Italy, as expected in the presence of a single introduction event, and very high migration from Italy into Greece, as expected of an outbreak still in exponential growth phase and starting from an Italian source.

ChemInform Abstract: Cyanobacteria: An Emerging Source for Drug Discovery

AbstractReview: 84 refs.

Cyanobacteria: an emerging source for drug discovery

The c group of Gram-negative gliding bacteria, has a long history of cosmopolitan occurrence. It has great biodiversity despite the absence of sexual reproduction. This wide biodiversity may be reflected in the wide spectrum of its secondary metabolites. These cyanobacterial secondary metabolites are biosynthesized by a variety of routes, notably by non-ribosomal peptide synthetase or polyketide synthetase systems, and show a wide range of biological activities including anticancer, antibacterial, antiviral and protease inhibition activities. This high degree of chemical diversity in cyanobacterial secondary metabolites may thus constitute a prolific source of new entities leading to the development of new pharmaceuticals.

The free-living Hormosira banksii in Botany Bay, Australia: twenty years on.

Hormosira Banksii is the most common fucoid alga on rocky shores in temperate Australasia. It is the only fucoid alga in the region which also exists in free-living populations, and in this is it comparable with the unattached saltmarsh fucoids occurring in the northern hemisphere. The unattached populations of Hormosira are most often associated with mangroves, and the characteristics of such plants have been described from New Zealand (moore 1950, Bergquist 1959) and south eastern Australia (Clarke and Womersley 1981, King 1981). The population that grows amongst the pneumatophores in the Avicennia mangrove communities of southern Botany Bay, Australia, has been described by King (1981). It appears to have been derived from adjacent populations on rocky shores. The characteristics that distinguish the thalli from those of rocky shore populations include the lack of holdfasts, the absence of sexual reproduction, and the compact and highly branched thallus form. Other features regarded as characteristic of unattached fucoids include dwarfed and twisted thalli often with yellowish tips (Norton and Mathieson 1983). King (1981) noted that small thalli were common in the free-living Hormosira but also noted that someplants were about four times larger than those found on rocky shores.