Early Devonian fungi: a blastocladalean fungus with sexual reproduction

In this paper we describe a fossil fungus–Paleoblastocladia milleri gen. et sp. nov.–from the 400 million-year-old Early Devonian Rhynie chert that shares numerous features with modern zoosporic fungi placed in the order Blastocladiales. The fungus occurs in tufts that arise from stomata or between the cuticle and epidermis of Aglaophyton major axes. Thallus development begins from an irregular bipolar basal cell that produces a system of intramatrical rhizoids and clavate-shaped extramatrical, nonseptate hyphae. These hyphae develop into two types of mature thalli. Sporothalli are characterized by several orders of dichotomous branching and the production of terminal, globose zoosporangia, as well as thick-walled, pitted resting sporangia. On separate dichotomously branched thalli (gametothalli) are terminal chains of two or three gametangia, in which the terminal one is slightly larger. Despite the fact that all of the reproductive organs contain either zoospores or gametes, none show evidence of discharge papillae. The fossil fungus is compared with extant members of the Blastocladiales, and the presence of sexual reproduction is discussed.     

THE LIFE CYCLE OE SARGASSUM HORNERI (PHAEOPHYTA) IN LABORATORY CULTURE1

The life cycle of the large dioecious alga Sargassum horneri (Turner) C. Agardh was completed in unialgal culture by controlling photoperiod in relation to the phase of growth. Embryos isolated from a naturally grown female thallus gave rise to early germlings that rapidly formed blades under both short-day (9 h L) and long-day (15 h L) conditions at 20° C Shoot elongation, which followed early blade formation, occurred under the short-day conditions hut not under the long-day conditions. Functional female and male receptacles developed when thalli 8–14 cm long grown under the short-day conditions were transferred to the long-day conditions; gamete fusion occurred when male and female thalli were grown together. Fertilized oospores gave rise to normal thalli in a manner similar to that for in situ plants. Thus, the life cycle of S. horneri was completed in laboratory culture.     

Effect of the Nature of the Substratum on the Force Required to Detach a Common Littoral Alga

It has been shown that the force required to detach the holdfastsof Fucus vesiculosus depends upon the nature of the substratum;adhesion is less to barnacle shells. The loweradhesion appearsto be due to a partial dissolution of the shell by acidic material,probably exndates. Growth of germlings on various substrataindicates that thalli and primary rhizoids develop better oncalcareous substrata. Some ecological consequences of the phenomenaare examined.     

Induction of callus in the liverwort Marchantia palmata Nees

Abstract

In Marchantia palmata Nees, normal growth of thalli occurs on Nitsch's basal medium with 1% sucrose. With 4% sucrose, dark green callus is initiated by light intensities of 150–4,500 lux after 13–15 days of growth. In the dark only rhizoids develop from callus and at low light intensity (150 lux) rhizoids as well as knob-like green outgrowths differentiate. Increased light intensities induce differentiation of thalli and rhizoids from callus. The callus inducing effect of increased sucrose level can be replaced by higher concentrations of mannitol. Histological studies reveal that callus initially arises from the lower epidermis.     

Food quality triggers the reproductive mode in the cyclical parthenogen <Emphasis Type="Italic">Daphnia</Emphasis> (Cladocera)

Cyclic parthenogenesis (heterogony) is a widespread reproductive mode found in diverse taxa such as digenean trematodes, gall wasps, gall midges, aphids, cladocerans and rotifers. It is of particular interest as it combines the advantages of asexual reproduction (rapid population growth) and sexual reproduction (recombination). Usually sexual reproduction is initiated when, or slightly before, environmental conditions deteriorate, and often results in the production of resting stages. The optimal timing of diapause induction must thus be under strong natural selection. Using the cladoceran Daphnia as a model system, we show here for the first time that the switch from parthenogenetic to sexual reproduction in a cyclical parthenogenetic organism can be influenced by the chemical composition of food. Under crowding conditions Daphnia reproduced parthenogenetically with subitaneous eggs when fed the algal species Cryptomonas sp., but started the production of resting eggs when fed with the green algal species Scenedesmus obliquus. Supplementation experiments with lipids and especially proteins showed that the induction of resting egg production in two clones of different Daphnia species was due to a dietary deficiency in the green alga. Hence, the low food quality induced a switch in the reproductive mode that may contribute to optimal timing of the sexual reproduction of Daphnia in nature. Furthermore, our results have two other major implications: first, they suggest that protein compounds should be added to the list of diet constituents potentially limiting or influencing Daphnia reproduction. Second, we show that the role of food quality goes far beyond the up to now documented effects of food quality on somatic growth and trophic transfer efficiency of herbivores: due to its effects on sexual reproduction and the production of resting eggs, food quality might influence genetic diversity and long-term persistence of Daphnia in lakes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The life history of Porphyra endiviifolium from the South Shetland Islands, Antarctica

This paper describes the reproduction and life history of an intertidal species, Porphyra endiviifolium, from Antarctica. Field specimens were examined microscopically, prepared for electron microscopy and used to establish cultures. Wild populations comprised two kinds of leafy thalli, morphologically similar but distinguished by their mode of reproduction, either sexual or asexual. Carpospores from monoecious leafy gametophytes developed into conchocelis filaments in culture, and under “winter-spring” conditions these formed conchospores that germinated to produce leafy thalli. Monospores from asexual leafy thalli developed directly into two different forms of leafy thalli. Only one of the cultured morphotypes became fertile, reproducing asexually by monospores. We conclude that the phases of the life history of P. endiviifolium show different ecological strategies, the conchocelis phase reproducing in response to short days unlike the leafy thalli in which growth and reproduction respond primarily to irradiance. Received: 2 May 1997 / Accepted: 11 October 1997     

Parthenogenesis is rare in the reproduction of a sexual field population of the isogamous brown alga Scytosiphon (Scytosiphonaceae,Ectocarpales)

Parthenogenetic development of unfused gametes is commonly observed in laboratory cultures among various brown algal taxa. There is, however, little information on the contribution of parthenogenesis to the reproduction of field populations. In this study, we investigated whether parthenogenesis is present in a sexual population of the isogamous brown alga Scytosiphon with a 1:1 sex ratio. In culture, both female and male gametes showed higher mortality and slower development compared to zygotes. More than 90% of surviving partheno‐germlings formed parthenosporophytes irrespective of the culture conditions tested. Therefore, if parthenogenesis occurs in the field, most unfused gametes are expected to form parthenosporophytes. Contrary to this expectation, parthenosporophytes were rare in the field population. We collected 126 sporophytic thalli and isolated and cultured a unilocular sporangium from each of them. We confirmed that cultures of 120 unilocular sporangia produced both female and male gametophytes by the observation of zygotes or amplification of PCR‐based sex markers indicating that these sporangia originated from zygotic sporophytes. Only females were detected in cultures from two sporangia and only males from four sporangia suggesting that these sporangia originated from parthenosporophytes. In the Scytosiphon population, although parthenogenesis is observable in culture, our results demonstrate that the contribution of parthenogenesis to reproduction is small (≤4.8%) compared to sexual reproduction. Unfused gametes may not survive to form mature parthenosporophytes in significant numbers in the field partly due to their higher mortality and slower development compared from zygotes.     

The so locus is required for vegetative cell fusion and postfertilization events in Neurospora crassa

The process of cell fusion is a basic developmental feature found in most eukaryotic organisms. In filamentous fungi, cell fusion events play an important role during both vegetative growth and sexual reproduction. We employ the model organism Neurospora crassa to dissect the mechanisms of cell fusion and cell-cell communication involved in fusion processes. In this study, we characterized a mutant with a mutation in the gene so, which exhibits defects in cell fusion. The so mutant has a pleiotropic phenotype, including shortened aerial hyphae, an altered conidiation pattern, and female sterility. Using light microscopy and heterokaryon tests, the so mutant was shown to possess defects in germling and hyphal fusion. Although so produces conidial anastomosis tubes, so germlings did not home toward wild-type germlings nor were wild-type germlings attracted to so germlings. We employed a trichogyne attraction and fusion assay to determine whether the female sterility of the so mutant is caused by impaired communication or fusion failure between mating partners. so showed no defects in attraction or fusion between mating partners, indicating that so is specific for vegetative hyphal fusion and/or associated communication events. The so gene encodes a protein of unknown function, but which contains a WW domain; WW domains are predicted to be involved in protein-protein interactions. Database searches showed that so was conserved in the genomes of filamentous ascomycete fungi but was absent in ascomycete yeast and basidiomycete species.     

Obtaining plantlets from apical meristem of the red alga Gelidium sp.

For the first time, plantlets were obtained from fragments and cell aggregates (CA) of apical meristem of the red alga Gelidium sp. After two months of cultivation, an initial weight of 100 mg of fragments and CA from fresh meristem produced 3 g of plantlets without rhizoids. During the same period of cultivation, 100 mg of meristem fragments and CA isolated from thalli by the freezing-thawing procedure produced more than 20 g of plantlets with rhizoids. It is assumed that our methods for obtaining plantlets from fragments and CA of fresh and frozen-thawed meristem could be used to generate mass planting material for cultivation of algae (plantlets with rhizoids) in the sea and for tank-bubbling cultivation (plantlets without rhizoids). We speculate that meristem cells of frozen-thawed algae might be natural “seedstock” in the Arctic and Antarctic seas.     

Porphyra yezoensis bei Helgoland — eine entwicklungsgeschichtliche Studie

APorphyropsis-like epiphytic specimen found in the harbour of Helgoland was grown in culture and proved to be identical with the JapanesePorphyra yezoensis. Life history studies on this economically important alga resulted in some interesting and hitherto unknown details. The variability of the adult frond is fundamentally determined by the pattern of spore germination. Settled onChaetomorpha filaments, monospores elongate within 20 minutes; the epiphytic germlings are attached to the substrate by a typical basal cell and give rise exclusively to elongated fronds provided with a cuneate base. Unattached spores, however, germinate into buds with rhizoids; they develop into elongated elliptical to oval fronds provided with round or cordate bases. Only plants with male areas were observed in the cultures, butConchocelis was abundantly produced from cells of aged thalli. Grown in mussel-shells, the filamentous phase liberated conchospores for a long time.

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Herrn Paul-Heinz Sahling zum 75. Geburtstag gewidmet, mit Anerkennung und Dank für 50jährige Zusammenarbeit.     

Regeneration of Enteromorpha

Young plants of E. intestinalis have been grown in culture. Cutting off the thalli of attached plants just above the basal rhizoids leads to the regeneration of new branches. After a short time the point of wounding is indistinguishable. The process can be repeated many times; each regeneration resulting in a more branched thallus. Segments of unattached plants kept in culture may give rise to rhizoids from the basal cut ends and to papillae from the upper ends. They may also produce “bottle brush” forms similar to those found amongst ship-fouling algae. Such forms seem to arise when “swarmers” are retained in the parent cell and germinate in situ to give aggregations of juvenile plants. Their formation can be stimulated by a temperature shock.     

Cell wall formation in zoospores of Allomyces arbuscula

Carbohydrate composition was determined in isolated cell walls of meiospores of Allomyces arbuscula after incubation for 15 min (encysted meiospores: cysts), 150 min (germlings: cysts + rhizoids) and 24 h (cysts + rhizoids + hyphae). The principal constituent in all cell wall samples is chitin, accounting for about 75% of the recovered carbohydrates. In addition, cell walls of all stages examined contain polysaccharides which release galactose, glucose, mannose, arabinose, xylose, fucose, and rhamnose on acid hydrolysis. While different developmental stages show minor quantitative changes in chitin, the ratio of galactose to glucose decreases sharply during differentiation of ungerminated cysts into germlings with rhizoids and hyphae. The increase in glucose is accompanied by a decrease in the amount of xylose and/or fucose and of galactose.List of Abbreviation TFA trifluoroacetic acid     

Novel microsatellite markers suggest the mechanism of parthenogenesis in Extatosoma tiaratum is automixis with terminal fusion

Parthenogenetic reproduction is taxonomically widespread and occurs through various cytological mechanisms, which have different impact on the genetic variation of the offspring. Extatosoma tiaratum is a facultatively parthenogenetic Australian insect (Phasmatodea), in which females oviposit continuously throughout their adult lifespan irrespective of mating. Fertilized eggs produce sons and daughters through sexual reproduction and unfertilized eggs produce female offspring via parthenogenesis. Here, we developed novel microsatellite markers for E. tiaratum and characterized them by genotyping individuals from a natural population. We then used the microsatellite markers to infer the cytological mechanism of parthenogenesis in this species. We found evidence suggesting parthenogenesis in E. tiaratum occurs through automixis with terminal fusion, resulting in substantial loss of microsatellite heterozygosity in the offspring. Loss of microsatellite heterozygosity may be associated with loss of heterozygosity in fitness related loci. The mechanism of parthenogenetic reproduction can therefore affect fitness outcomes and needs to be considered when comparing costs and benefits of sex versus parthenogenesis.     

Development of adventive embryos in cauline leaves of Sargassum macrocarpum (Fucales, Phaeophyta)

Spontaneous formation and development of adventive embryos were observed in cauline leaves of Sargassum macrocarpum in laboratory culture. Semi-spherical swellings, which were 200–250 μm in diameter, arose from the surface of cauline leaves of thalli cultured for 4 months from zygotic embryos. Swellings became cylindrical protuberances and grew into ‘daughter’ thalli with one or two small cauline leaves. These thalli detached from ‘mother’ thalli and attached to the surface of culture vessels by rhizoids produced within 1 week after detachment. Each daughter thallus developed into an individual thallus exhibiting the same morphological processes as zygotic embryos.     

Reproductive patterns of Caloglossa species (Delesseriaceae, Rhodophyta) from Australia and New Zealand: multiple origins of asexuality in C. leprieurii. Literature review on apomixis, mixed-phase, bisexuality and sexual compatibility

Reproduction and life history patterns in culture of five Caloglossa speaes from Australia and New Zealand are compared. Caloglossa adhaerens King et Puttock and Caloglossa bengalensis (Martens) King et Puttock have a Polyslphonla‐type sexual life history (P‐type, isomorphic alternation of generations). Caloglossa monosticha Kamiya occurs only in Western Australia (WA) and is a P‐type. Caloglossa ogasawaraensis Okamura occurs in WA, Northern Territory (NT), Queensland (QLD), New South Wales (NSW), Victoria (VIC) and South Australia (SA) and is for the most part a P‐type in culture. A few isolates have bisexual gametophytes that are self‐compatible, while most are unisexual. Caloglossa ogasawaraensis from Adelaide, SA and from Wilsons Promontory, VIC are new records for these States. In Australia, Caloglossa postiae (King et Puttock) Kamiya et King occurs in NSW, NT and QLD. All nine isolates are P‐type. Isolates of Caloglossa leprieurii (Montagne) G. Martens from NSW, NT, QLD, Tasmania, VIC and New Zealand are P‐type except for the freshwater isolates in which tetraspore germlings do not reproduce. In some isolates mixed‐phase reproduction is seen with male gametophytes producing both viable spermatia and tetrasporangia and female gametophytes producing procarps and sori with non‐dividing sporangia. All isolates of C. leprieurii irom Spencer Gulf and Gulf of St Vincent, SA and one isolate from QLD give rise to successive asexual generations of tetrasporophytes. Based on RuBisCO spacer DNA data an asexual life history has arisen several times in the C. leprieurii complex. The literature on apomixis, mixed‐phase reproduction, bisexuality and sexual compatibility in red algae is surveyed.     

Evidence of fusion and artificially initialized parthenogenesis in isogametes of Endarachne binghamiae (Scytosiphonaceae, Phaeophyta) from Taiwan

Approximately 120–140 minutes after Endarachne binghamiae isogametes are released and kept in an incubator (50 μmol photonm^-2s^-1, 18 ^°C, 10/14 h L/D), the isogametes from single or mixed cultures undergo isogamete fusion to mate sexually. It can therefore be inferred that E. binghamiae is monoecious. However, when these newly released isogametes are keptin similar conditions, but treated with low dosages of various kinds of solution (0.012% (v/v) formaldehyde,0.105% w/v EDTA, 0.198% w/v EGTA, in filtered seawater) that can paralyze flagellar movement to initiate parthenogenesis, the isogametes in one of these, 0.012% formaldehyde, develop parthenogenetically into filament, precrustose (early, middle and late stage), crustose and finally erect thalli. SEM and TEM show that the mastigoneme of the anterior flagellum in this group is broken, which results in the isogametes being non-motile. In comparison, the development of the isogametes in the other two groups stops somewhere before the stage where they grow into erect thalli. In other words parthenogenetic reproduction occurs under our culture conditions and we have identified clearly the morphology and parthenogenetic development of E. binghamiae. It is suggested tha the findings of this study could be applied to increase the biomass of E. binghamiae, an edible species of very high economic value in north-east Asia. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evidence for an even sex allocation in haplodiploid cyclical parthenogens

Recent theoretical work has shown that haplodiploid cyclical parthenogens, such as rotifers, are expected to have an equal frequency of male‐producing and resting‐egg producing females during their sexual phase. We tested this prediction by following sexual reproduction dynamics in two laboratory populations and one field population of the rotifer Brachionus plicatilis through two growing seasons. We recorded population density, proportion of sexual females, and sex allocation (the proportion of male‐producing sexual females as a fraction of total sexual females). We found this sex allocation ratio to vary from 0.3 to 1.0 in single sampling events. However, when we computed sex allocation by using the integrated densities of both male‐producing sexual females and resting‐egg producing sexual females over time, the two laboratory populations and one of the two field growing seasons showed sex allocation ratios that did not significantly differ from the expected value of 0.5.     

Taxonomic study of the genusMyagropsis (Cystoseiraceae,Phaeophyta)

The generic names of the brown algaeMyagropsis, Cystoseira andCystophyllum have been used in Japan, Korea and China for a small group of seaweeds whose limits have not been clearly understood. Studies on the development of the eggs and subsequent germlings show that substantial differences occur betweenCystoseira andMyagropsis. Myagropsis Kützing is distinguished fromCystoseira C. Agardh by the following characteristics: (1) the tongue cell is undivided during development of the conceptacle; (2) paraphyses are projected from the conceptacle ostiole and become entangled; (3) during development, oospore germlings are mixed among paraphyses projecting from the ostiole; (4) oospores are large, with eight nuclei at maturity; (5) thirty-two primary rhizoids are produced on the germlings; and (6) the thallus is bilateral in organization. The shape and size of vesicles, their formation, and the presence of cryptostomata have been used as specific characters, but their use cannot be continued. It is concluded that the genusMyagropsis is monotypic, with a single species,M. myagroides (Turner) Fensholt. The status of this species is also discussed.