Search

The planktonic diatom Fragilariopsis kerguelensis plays an important role in the biogeochemical cycles of the Southern Ocean, where remains of its frustules form the largest deposit of biogenic silica anywhere in the world. We assessed the genetic identity of 26 strains, from cells collected at various sites in the Southern Ocean, using three molecular markers, LSU and ITS rDNA and rbcL. The LSU sequences were identical among the tested strains, ITS sequences were highly similar, and only one base pair difference was detected among the rbcL sequences. These results, together with a large number of successful mating experiments demonstrated that the strains belong to a single biological species. We investigated the mating system and life cycle traits of F. kerguelensis. Cell size diminished gradually in clonal strains. Gamete formation only occurred when strains of opposite mating type – within a cell size range of 7–36 µm – were mixed together. Two binucleate gametes were formed in each gametangium and ga...

We give a detailed account of sexual reproduction and auxospore development in the diatom genus Diploneis, principally from clonal cultures of the marine benthic Diploneis papula. Sexual reproduction of D. papula was apparently homothallic. After pairing side to side, cells entered meiosis, and each gametangium produced two gametes. Fertilization was physiologically anisogamous, and both gametes of one gametangium were active and those of the other gametangium passive so that the two zygotes were formed within or close to the ‘passive’ gametangium. Each gamete contained a single chloroplast. The zygote became surrounded by delicate incunabula that contained circular or elliptical scales; this confirmed recent observations that scales (or apparently homologous strips or plates) are quite commonly formed by the zygotes of raphid diatoms. Subsequently, a robust transverse perizonium was built up as the auxospore expanded, and the perizonium was comprised of a closed primary band at the centre and open secondary bands towards each pole. The ends of the secondary bands, which met along one side of the auxospore to form a suture as in other pennate diatoms, were curved inwards towards the centre of the auxospore. Novel features were the extension of the transverse perizonium to cover the tips of the auxospores (in other diatoms it stopped short of the poles, leaving an apical dome covered only by the incunabula) and a differentiation of the ends of the transverse bands into truncated and prolonged variants, which alternated along the suture. The longitudinal perizonium possessed the same highly conserved configuration as in other pennate diatoms, with a wide bifacial central band flanked by two other bands, which here differed in shape and structure. All the perizonial bands were fimbriate. The possible homology of the longitudinal perizonium to the thecae of vegetative cells was discussed. During formation of the initial cell, the protoplast contracted away from the perizonium, but the latter nevertheless moulded the outline shape of the initial valves, which were more strongly constricted than preauxospore cells and gametangia. Other Diploneis species produced either one or two gametes per gametangium.

Paedogamy (fusion of gametes produced within the same gametangium following meiosis) has rarely been reported in diatoms, with fewer than 10 confirmed examples. One of these, reported by L. Geitler, was in a diatom from Illmitz, Lake Neusiedl (Austria), identified as ‘Nitzschia frustulum var. perpusilla'. We observed uniparental auxosporulation in two Nitzschia clones isolated from the lower Ebro River (Catalonia, Spain), morphologically similar to Geitler's material and belonging to the N. inconspicua species complex. We established that the auxospores were formed paedogamously by Feulgen staining of the nuclei and time-lapse microscopy of living cells. However, reinvestigation of Geitler's original cytological preparations revealed differences between the Illmitz and Ebro material with respect to the length of the initial cells, the structure of the perizonium, and the timing of degeneration of superfluous haploid nuclei during gametogenesis, indicating a genetic and possibly a taxonomic separation. Sca...

Documented fossil evidence of zygomyce- tous fungi is rare. A conspicuous fungal fossil, Jimwhitea circumtecta gen. et sp. nov., occurs in permineralized peat from the Middle Triassic of Antarctica. The fossil is interpreted as a mantled zygosporangium that buds from a macrogametan- gium subtended by a sac-like macrosuspensor. The macrogametangium is united at its tip with a microgametangium which is subtended by a micro- suspensor. This configuration is strikingly similar to the zygosporangium-gametangia complexes seen in certain modern Endogonaceae. Co-occurring with J. circumtecta are isolated propagules closely resembling the zygosporangium of J. circumtecta and a portion of a sporocarp containing zygosporangia embedded in a gleba. Several of the sporangia are borne on ovoid or elongate structures, which we interpret as gametan- gia. These fossils offer an exceptionally detailed view of the morphology and reproductive biology of early Mesozoic zygomycetes.

Miravalles A.B., Leonardi P.I. and Caceres E.J. 2011. Male gametogenesis ultrastructure of Codium fragile subsp. novae-zelandiae (Bryopsidophyceae, Chlorophyta). Phycologia 50: 370–378. DOI: 10.2216/10-25.1 Male gametogenesis was studied by light and electron microscopy in the dioecious siphonous green alga Codium fragile subsp. novae-zelandiae. Gametangia were formed on the sides of utricules. Initially, gametangia showed vegetative interphase nuclei and chloroplasts already with a mature structure with few thylakoid lamellae and a single starch granule. Then, mitotic divisions occurred, originating a proliferation of gametic nuclei. Features of the gametangial mitosis were similar to vegetative mitoses of other Bryopsidophyceae. The fusion of minute vesicles clearly delimited uninucleate portions of protoplasm with a large mitochondrion and chloroplasts. Ultimately, the gamete final shape was delimited, and the basal-flagellar apparatus developed. Mature gametes were liberated immersed in a muc...

Mann D.G. and PoulIckova A. 2010. Mating system, auxosporulation, species taxonomy and evidence for homoploid evolution in Amphora (Bacillariophyta). Phycologia 49: 183–201. DOI: 10.2216/09-08.1 Cytological characteristics of the mitotic cycle, sexual reproduction and auxospore formation are described for three members of the type group of Amphora: A. ovalis, A. copulata and A. minutissima. All have a single lobed ventral chloroplast, nuclei with granular heterochromatin and a single nucleolus (unusually large in A. ovalis). Amphora copulata is heterothallic, with two mating types that do not differ in gamete behaviour. All three species reproduce allogamously via fusion of two rearranged gametes per gametangium to produce elongate zygotes enclosed within the volume delimited by the gametangial thecae. Pairing is strictly via the ventral sides of the cells, with tight apposition of the cells, and expansion of the auxospores is strictly perpendicular to the gametangium long axes. Comparisons are m...

Twelve clonal cultures of the marine pennate diatom Haslea ostrearia (Gaillon) Simonsen were used to study sexual reproduction and auxosporulation. After crossing, compatible gametangia paired girdle to girdle, with no visible surrounding mucilage. Two gametes were formed per gametangium; these were not attached to the thecae of the parental frustule and gametes from one gametangium fused with the gametes from the other gametangium. Sexual reproduction was isogamous, resulting in the production of two zygotes per paired gametangia. The pattern of reproduction in H. ostrearia can be classified as type IB2a according to Geitler's system. The expansion of auxospores, which was bipolar, was accompanied by the formation of a transverse perizonium. Superfluous nuclei resulting from meiosis were not visible. The upper limit of the cell size range suitable for sexualization was c. 68 µm, i.e. about half the maximum species-specific size of about 140 µm. Sexual reproduction has been shown by previous authors to oc...

The cytology and life cycle of Pinnularia cf. gibba was examined in nine clones from three Scottish localities. This freshwater epipelic diatom is heterothallic and produces two isogametes per gametangium in type IC auxosporulation (Geitler's classification [1973]). The zygote undergoes a highly unusual metamorphosis before beginning expansion, becoming shortly linear-lanceolate; this is accompanied by formation of a complete covering of thin, oxidation-resistant strips and scale-like structures (at the poles), which are quite separate from the perizonium formed during auxospore expansion. Observations of similar incunabular structures in P. acidojaponica show that these elements are siliceous. The P. cf. gibba perizonium also has unusual features, including a remarkably wide primary band. Trikaryotic and haploid auxospores are sometimes formed and haploid 'zygotes' mature and expand like diploids, but do not develop into mature initial cells. Several phases of mucilage secretion take place, from the gametangia, zygotes and auxospores. Triplets of gametangia and polyspermy occurred with high frequency; this and the systematic significance of variation in auxospore, incunabula and perizonium structure, are discussed. Aspects of the taxonomy of the P. gibba group are treated in supplementary material provided on the European Journal of Phycology website.

Clones identified as Eunotia bilunaris were isolated from two freshwater habitats in New Zealand and one in Tasmania. Experimental studies of sexual reproduction showed that the mating system was strictly heterothallic. All clones were morphologically similar and, in mixtures of compatible clones, were able to produce a viable F1, regardless of geographical origin. There was nevertheless some geographically related variation in ITS rDNA sequences, suggesting that dispersal and concerted evolution are unable to prevent allopatric divergence. Isolates from two of the three localities also showed significant ITS polymorphisms. Auxosporulation followed a similar pattern to that in other Eunotia species, being isogamous with a single functional gamete per gametangium; plasmogamy was effected via two fusing papillae. Details of auxospore structure, initial cell size, and vegetative valve metrics (width, striation densities) show that conspecificity with a recently studied European E. bilunaris is doubtful. The ...

Two new species of Volvocalean green snow algae are described from Upstate New York, Chloromonas chenangoensis and Chloromonas tughillensis. According to rbcL sequence analysis, these species belong to a subclade of five snow species of Chloromonas that includes Cr. brevispina, Cr. nivalis and Cr. pichinchae. These species have zoosporangia/gametangia (cell packs) that are propelled by flagella. The life cycles of Cr. chenangoensis and Cr. tughillensis include a change in cell shape from oblong to spherical before the loss of the cell wall. Using 8-h laboratory experiments, a peak in the change of cell shape occurred at 4 h for Cr. chenangoensis and between 2 and 4 h for Cr. tughillensis after the onset of light, and this was followed by a decline in change of cell shape for both species. Spherical cells peaked between 6 and 8 h for Cr. chenangoensis and at 8 h for Cr. tughillensis. Maximum total matings occurred at 4 h for Cr. chenangoensis and 6 h for Cr. tughillensis, which was followed by a p...

A small prostrate filamentous brown alga, isolated from the warm temperate Pacific coast of Japan, was cultured to investigate its life history, morphology, ultrastructure and molecular phylogenetic position. The isolate had an isomorphic, diphasic life history with anisogamous sexual reproduction. Gametogenesis was regulated by temperature and occurred only at temperatures ≤14°C. At higher temperatures, gametophytes reproduced by means of asexual zoids. All swarmers from plurilocular and unilocular zoidangia lacked an eyespot. Both sporophytes and gametophytes had oligostichous filamentous axes, lateral hairs with a basal sheath and no erect thalli. Three to eight oblong chloroplasts, each with a protruding pyrenoid, aggregated to form a stellate chloroplast configuration. All these morphological features suggested that this alga belongs to the genus Asterocladon. Plurilocular gametangia produced in an intercalary or terminal position and zoids lacking eyespots, are, however, unlike those of Asterocladon...

D.G. MANN AND V.A. CHEPURNOV. 2005. Auxosporulation, mating system, and reproductive isolation in Neidium (Bacillariophyta). Phycologia 44: 335‐350. Three allogamous Neidium demes, referrable to N. ampliatum sensu lato,coexist without intergradation in Blackford Pond, Edinburgh, and some other lakes. A slight change in valve shape has occurred in one deme during the last 20 years. Morphological deme traits persist in healthy clonal cultures, but with time or during senescence, aberrant morphologies and sizes of cell can be produced that have no parallel in nature. Simplification of valve outline occurs as cells get smaller, but the initial cells also have a simplified morphology. The rostrate apices of some N. ampliatum demes develop rapidly after auxosporulation, during the first divisions of the initial cells. The ‘major’ and ‘minor’ demes of N. ampliatum are heterothallic, although some inbreeding occurs. Very rarely, mixed pairs of ‘major’ 3 ‘minor’ are formed, but hybrid auxospores are apparently never produced, so the demes are reproductively isolated. The ‘maternal’ gametangium has a nongenetic influence on initial cell size; however, the effect is slight and control of initial cell size is very well buffered to variation in gametangium size, so the concept of ‘cardinal points’ is valid for this species complex. The characteristics of sexual reproduction in clones and seminatural populations (including the effective, though incomplete, suppression of triplets and larger groups during copulation) prompt hypotheses about pairing mechanisms, in particular that a chemoattractant is involved. Preferential polyandry in Sellaphora and theoretical considerations indicate that the chemoattractant is produced by only one mating type. Size selection of mates in the ‘minor’ deme probably reflects progressively easier and more rapid sexualization as cells become smaller.

A seasonal study of the blade phase of Porphyra dioica at its type locality, Sidmouth, Devon, UK, undertaken between June 1999 and May 2000 revealed that individuals were present in the middle and lower littoral zones all year. Field-collected specimens were vegetative (8%), or possessed male (40%) or female (47%) reproductive structures, or had both on the same blade (6%) but totally segregated by a distinct line. Mean wet mass of individuals was greatest in June and least in February. There were no significant differences between the wet mass of individuals with male or female gametangia. Mean frond length was greatest in June and least in February. Mean frond width was greatest in May and least in February. Reproductive sori were marginal and pale straw-yellow for male gametangia, cream to pale green in unfertilized female gametangia, and bright red to dark red-brown once fertilization had taken place. Male gametangia were found in packets of 64 [2 X 4 in surface view (SV)]. Individuals with f...

The reproduction of Pohlia nutans (Hedw.) Lindb. and Pleurozium schreberi (Brid.) Mitt. were compared in the surroundings of copper smelters at Harjavalta, Finland. Samples of both species were collected from 16 sample plots, which were situated on a 12-km transect at intervals of half a kilometre from the smelters. As a result of pollution the production of gametangia decreased in P. schreberi, and near the smelters most of the shoots were sterile. The biomass of shoots seems to have an effect on the production of perichaetia; reproducing females were always the largest ones in the colonies. The reproductive strategy of Pohlia nutans also varied. While, in moderately clean areas, colonies reproduced sexually and formed sporophytes, in the vicinity of the smelters caducous shoot apices were produced. The numbers of sporophytes in colonies were highest in moderately polluted areas and decreased further away from the smelters. The numbers of spores per capsule in P. nutans decreased at polluted site...

While examining specimens of Fissidens Hedw. collected from the Nile Valley, I came across one unusual collection. This voucher, namely IV-B(8), was collected by Refai in 1986 and labelled as Fissi...

Eighteen collections of red-coloured Audouinella from Central Mexico and southeastern Brazil detected three species. The most common species, A. eugenea, is characterized by macroscopic thalli, the erect system consisting of filaments with cylindrical cells, undifferentiated into proximal and distal parts, and relatively large monosporangia (≥12.0 µm long). Spermatangia and possible propagules were observed in some Mexican populations. This is the third Audouinella species observed to have gametangia and the first member of the Acrochaetiales with putative propagules. The second species, from Central Mexico, was characterized by the following features : macroscopic thalli, the erect system differentiated into proximal parts with cylindrical cells, unbranched or rarely branched, and distal parts with barrel-shaped cells, abundantly branched to form dense fascicles, with alternate or dichotomous branching, some at right-angles to the axis, and relatively large monosporangia (≥12.0 µm long). The morphologica...

Sematophyllum subpinnatum (Brid.) E.Britton is an autoicous species of moss with a pantropical distribution. Two populations of S. subpinnatum from a Tropical Lowland Forest remnant were sampled monthly over a period of 2 years. The results were similar in the two populations. The average number of antheridia produced per perigonium ranged from eight to 20, and of archegonia per perichaetium from three to 26. Antheridial and archegonial initiation, maturation and fertilized archegonia occur throughout the year, but increased in frequency during the rainy season. The initial stages of sporophyte development were most common between the months of June and September, indicating that, although S. subpinnatum produces gametangia all year round, the rainy season is the most favourable period for fertilization.

Recent field-based studies in the Bryopsidales have provided a wealth of reproductive information for several ecologically dominant genera, yet inconspicuous members of the order often remain poorly described. Here we report reproductive events for aquarium-grown populations of Rhipidosiphon javensis and provide statistical size ranges for vegetative and reproductive features for the first time. Hawaiian representatives of the genus develop gametangia over a three-day period, and follow the typical reproductive pattern found in other members of the suborder Halimedineae, being holocarpic and releasing gametes in predawn hours.

The allogamous raphid diatom Achnanthes longipes C. A. Agardh possesses a complex breeding system involving interactions between three types of clone: monoecious, unisexual and bisexual. Previous studies showed that these three types can be crossed with each other, with a tendency for sexual characteristics to be inherited: inbred monoecious lineages gave rise to monoecious or, very rarely, to bisexual clones, while inbred unisexual lineages yielded unisexual and bisexual clones. The current paper reports on the progeny of crosses between monoecious and unisexual clones and their inbred offspring. All three types of clone appeared in the F1 and F2, although unisexual clones of opposite sex to the parental clone were not found. Inbreeding depression was observed and also a tendency for ‘normal’ auxosporulation (producing two auxospores per pair of gametangia) to be replaced by ‘reduced’ or ‘intermediate’ auxosporulation (producing one auxospore per pair). In addition, patterns of incompatibility were obser...

Gametangial distribution patterns on gametophores of Physcomitrella (Aphanoregma) patens were studied. Plants were grown axenically under controlled laboratory conditions. Some gametophores produced clusters of archegonia at their apices or in the axils of their uppermost leaves. Of these gametophores, some possessed a few antheridia located at the periphery of the archegonial clusters. Other gametophores produced apical and axillary antheridial clusters unadulterated by archegonia. Thus, this P. patens isolate, ‘maintained in culture since 1962, is paroicous or autoicous depending upon which gametophores are considered. Typically, filiform paraphyses were associated with archegonial clusters and clavate paraphyses with antheridial clusters. Archegonia, solitary or in clusters, also developed from internodal surface cells of the gametophores. Such ectopic archegonia had no associated paraphyses. Many immature sporophytic stages were noticed within archegonia but their development into mature sporo...

Sexual reproduction in the domoic acid–producing pennate diatom Pseudo-nitzschia multiseries (Hasle) Hasle is dioecious and involves pairing of two morphologically isogamous parent cells (gametangia) and the production of two gametes per gametangium. Gamete fusion leads to the formation of zygotes, which elongate into auxospores. Within each auxospore, a long initial cell is formed, thereby restoring the longer cell sizes in the population. Mating experiments were performed by mixing active “male” and passive “female” cells from pairs of clones and growing them under different light : dark (L : D) cycle regimes. Two pairs of clones were studied: one pair was ontogenetically older and therefore shorter than the other. After mating, the relative abundance of gametes, zygotes, auxospores, and initial cells was determined for a minimum of four consecutive days. Cell size, which reflects population age, influences sexualization. The short-celled clones had a lower maximum proportion of gametes per vegetative cell (4%) than the long-celled clones (49%), suggesting that the former were nearing the minimal cell length capable of sexualization. The size range within which P. multiseries is able to reproduce sexually is 23–70% of the maximum cell length. A positive correlation was found between hours of light exposure per 24 h at approximately 100 μmol photons m⁻² s⁻¹ and sexual cell production of the ontogenetically younger clones. Greatest production of initial cells per female gamete (26%) occurred in 10 h of light. Results from this study indicate that the most biologically successful light regimen in culture corresponds in nature to the day length of the fall bloom from which these clones were isolated.

Two combinations of features exist in species of the Pseudobryopsis/Trichosolen complex (Bryopsidales, Chlorophyta): (1) gametangia are separated from the supporting branch by a plug and are emptie...

This paper continues a series of studies of the allogamous raphid diatom Achnanthes longipes, which has a complex reproductive system combining unisexual, bisexual and monoecious behaviour. Following earlier work on the effects of inbreeding in the progeny of crosses between two unisexual clones, we studied the progeny of clones that are capable of a high degree of selfing in monoclonal culture (‘monoecious clones’). Three generations of selfed progeny were examined. In addition, we investigated the F1 generation obtained after crossing two different monoecious clones. Monoecious clones produced monoecious or, more rarely, bisexual progeny, but did not give rise to unisexual progeny. As in inbred lineages made by crossing closely related unisexual clones, inbreeding in monoecious lineages leads to a reduction in the number of gametes formed by the gametangia, from two to one. Inbred clones exhibit marked inbreeding depression and only three inbred generations were possible in monoecious lineages. In the t...

Microspectrophotometry with the DNA-localizing fluorochrome 4′,6-diamidino-2-phenylindole (DAPI) was used to estimate nuclear genome sizes in 12 species representing two families of the Dasycladales. Estimated 2C DNA contents in these taxa range from 0.7–1.4 pg in the family Dasycladaceae and from 0.9–2.4 pg in the family Acetabulariaceae. In both families, species exhibiting characteristics considered to be primitive appear to have 2C DNA contents that approximate 50% of values found in species exhibiting characteristics considered to be more advanced. Results suggest that polyploidy events have accompanied evolution in the order but apparently have been infrequent and conservatively preserved, leading to a narrow range of relatively small genome sizes. Limitations on genome size increase are discussed in terms of constraints imposed by a prolonged uninucleate stage. Interspecific comparisons of genome size and gametangium volume suggest an inverse relationship. Gametangium volume appears to hav...

Shoots of Dicranum majus were collected monthly during the snow-free period from permanent plots to study the reproductive phenology in a boreal spruce forest in central Norway. Numbers of sporophytes (current and previous years), gametangia and dwarf males on each shoot and the reproductive stage of gametangia and sporophytes were registered. Gametangia are formed either in late autumn or in early spring, fertilization occurs in June and July and spores are dispersed during August to October in the following year.Mature archegonia were present only during a restricted period (June-July) while mature antheridia were found throughout the summer and autumn.Dwarf males were found only in a region about one cm below the apex. There was no trace of old male gametophores below, indicating that gametophores are annual. However, from this study it is not possible to conclude whether the gametophyte is annual or new males are formed through, for instance, perennial protonema.Fertilization frequency in the ...

Examination of type material, comparative studies on vegetative characters and data from published accounts of sporangia, gametangia and spermatozoids are used here to further develop and strengthen generic and species concepts in Zonaria and Homoeostrichus. Zonaria is characterized by octosporangia which lack a stalk cell and occur among whitish paraphyses, by the presence of cortical cells in indusiate sporangial and oogonial sori, and by slightly elongate sterile cells bordering the antheridial sori. Other characters (mucilage in sporangial and oogonial sori, biflagellate sperm with a row of many tall spines along the anterior flagellum) may also be diagnostic of Zonaria but have not been demonstrated in the generitype. Eight species are retained in Zonaria. Generic placement of Zonaria stipitata, described on vegetative characters, requires confirmation. Homoeostrichus, as typified by Homoeostrichus sinclairii, is defined by the presence of brown paraphyses in nonindusiate sporangial and oogonial sori...

Monoecious, bisexual and unisexual clones of Achnanthes longipes were isolated from the Black Sea and studied in laboratory culture. Clones differed in their growth characteristics : in monoecious clones the cells formed tufted aggregations while in other clones they were more dispersed. Bisexual and unisexual clones exhibited intraclonal (monoecious) reproduction, but only at a very low frequency and usually within a more restricted size range than in monoecious clones. Interclonal crosses were made in all possible pairwise combinations. Abundant auxosporulation took place in all crosses, except where unisexual clones of the same sex were incubated together. Auxosporulation was more vigorous and occurred over a wider size range in interclonal crosses than during monoecious reproduction. Sexual reproduction is isogamous. In the commonest pattern of auxosporulation, two paired gametangia each produce two gametes, which fuse to give two auxospores. More rarely (9% of pairs), the gametangia produce only one ...

A comparative study of fertile sporophytes has been carried out on seven dictyotalean species from Australia. Patterns of sporangial distribution and development are similar in Zonaria angustata, Zonaria diesingiana, Zonaria spiralis, Zonaria turneriana and Lobophora variegata but they differ in Homoeostrichus olsenii and Homoeostrichus sinclairii. In Zonaria and Lobophora, sporangia occur in indusiate sori, are embedded in a mucilaginous matrix and, in Z. diesingiana, Z. spiralis and Z. turneriana, are surrounded by whitish paraphyses. In contrast to Zonaria, the indusiate sporangial sori of H. olsenii form adjacent to concentric rows of brown paraphyses but they lack both mucilage and paraphyses. Sporangia of H. sinclairii occur among dense brown paraphyses which cover the terminal thallus segments. Sporogenesis in species of Zonaria and Lobophora differs conspicuously from other Dictyotalean genera in that nuclear divisions occur when the developing sporangium is quite small, a sporangial stalk cell is...

Zygorhizidium planktonicum (Chytridiales) an obligate, epibiotic parasite of freshwater diatoms was recently isolated from Lake Lanier, Georgia. Host specificity and ultrastructural morphology of clones infecting Synedra acus were investigated to further evaluate the life history and taxonomic significance of host-specific strains. Host range studies revealed that germination and sporangium development were con- fined to Synedra sp., S. acus, and S. ulna. On occasion, zoospores loosely adhered to Asterionellaformosa; how? ever, subsequent growth did not ensue despite efforts to induce parasitism in mixed cultures and altered environmental conditions. Ultrastructural studies of conjugating gametangia demonstrated the fusion of thalli by means of a narrow, smooth-walled tube and the apparent migration of the nucleus and other or- ganelles from the donor gametangium to the larger, recipient thallus. The resulting resting spore possessed a thick multilayered wall, either one or two nuclei, and electron opaque bodies of unknown composition. Zoospores contained discrete morphological features including a rumposome-associated fibrillar vesicle, dis- persed ribosomes, and a dense particulate body. Our findings regarding this disjunct population confirm the occurrence of host-specific variants in Z. plankton? icum. Host selection indicates a conserved ontogeny which further suggests that host-selective strains have coevolved with their respective diatom hosts.

Sexual reproduction and protoplast structure are used to check the classification of the naviculoid genus Placoneis Mereschkowsky (Bacillariophyta). The gametangia are closely associated within a robust mucilage capsule throughout auxosporulation, and pairing is ± random with respect to asymmetries of the frustule and protoplast. Two gametes are produced per gametangium, which are morphologically identical but differentiated into active and passive (physiological anisogamy). The supernumerary nuclei from meiosis II begin to degenerate soon after telophase II, but can still be detected in the initial cells. The gametes become rearranged within the gametangia after meiosis II and plasmogamy takes place via a single, simple aperture. The auxospores expand parallel to the apical axes of the gametangia. The classification of Placoneis in the Cymbellales, as the sister group to the cymbelloid and gomphonemoid diatoms, is supported by valve and protoplast structure, the method ofchloroplast division, an...

The genus Dickieia is re-established for Navicula ulvacea, N. subinflata and N. expecta. Dickieia cells contain one complex chloroplast per cell; this consists of two ‘K’-shaped halves, linked by an isthmus containing the single discoid pyrenoid. The pyrenoid lies near one side of the girdle at the centre, while the nucleus lies opposite. Neither the nucleus nor the chloroplast move significantly within the cell during the cell cycle. The valves contain round poroids with hymenate occlusions. The raphe-sternum lacks accessory ribs and the central internal raphe endings are simple and straight. The epitheca contains several narrow, porous girdle bands. Auxosporulation is unusually variable in D. ulvacea and can be allogamous (with isogamy) or automictic, though the gametangia are always paired. Plasmogamy is brought about principally through expansion of the gametes until they meet and fuse. The orientation of the auxospores bears no fixed relation to the gametangia. Haploid parthenogenesis and the formati...

Sexual reproduction and auxospore formation of Achnanlhes javanica f. subconstricta have been observed in laboratory culture. This monoraphid diatom showed cis-type behavioural anisogamy and produced two auxospores in one of the paired gametangia. This diatom is unique in that the gametes become re-arranged only in the gametangium producing the stationary gametes, not in that producing the active gametes. Its position is thus obscure in the present classifications of sexual reproduction and auxospore formation. Some modification of these classifications is necessary.

The gametangia of the green seaweed Halimeda tuna are spherical bodies of diameter up to 250–300 μm. They are clustered in groups of 8–10 on hundreds of threads sprouting from all pale white segments of the fertile individuals. In addition to gametes, starch-containing chloroplasts, naked starch grains and two types of spherical bodies different in size and ultrastructure are the main corpuscular components. A layer of amorphous material of irregular thickness underlies the walls which are finely and evenly rough, structureless, electron translucent and 1–1.5 μm thick. Gametangia with superficial wall warts were found also.

An undescribed red alga was found in two streams of the Coastal Range and Cascades from Oregon, USA. This alga is characterized by barrel-shaped axial cells with a distinctly larger diameter (17.3–30.1 μm) than that of lateral branch cells (4.3–8.5 μm). The chromosome number of branch cells is n = c. 7. Unique spermatangial stalks produce two types of spermatangia at their tips. The carpogonium is typically acrochaetialean, with a swollen, cylindrical base and thin trichogyne, but carpospores germinate into a batrachospermalean-like chantransia phase. The gametophyte develops directly from this phase. DAPI relative fluorescence values are approximately twice as high for gonimoblast cells, carposporangia and chantransia cells as for the gametophyte vegetative cells and gametangia. Pit plugs have two cap layers, the outer typically domed. Nuclei in early mitotic prophase have one layer of perinuclear ER, a single-layered polar ring and chromatin associated with the nucleolus. Since the alga has cha...

The mature gametangia, gametes, gamete fusion, young motile zygotes and development of the settled zygotes into unicellular sporophytes (Codiolum stages) are described in Ulothrix flacca (Dillwyn) Thuret var. roscoffensis Berger-Perrot (Ulvophyceae, Chlorophyta) using light and electron microscopy. Flagella of gametes narrow to a hair-like point. Gamete fusion takes place near two lateral thickenings of the plasma membrane, which are considered to be poorly differentiated mating structures. The dilated perinuclear space contains an unidentified electron-dense substance. Karyogamy generally takes place 8–24 h after gamete fusion and chloroplasts have fused 12 h after gamete fusion. Flagella are shed approximately 8 h after fertilization. Twelve hours after, abundant osmiophilic droplets are secreted on the plasma membrane of the zygotes prior to formation of the cell wall. Forty-eight hours later, the quiescent zygotes become stalked sporophytes after striking cytological changes. These features a...

Sexual reproduction and auxospore development are described for a marine species of Bacillariaceae related to Nitzschia reversa. Oogamy, recently claimed to occur in N. pungens f. multiseries, was not found. No copulation envelope is produced and reproduction is isogamous. The orientations of the auxospores and gametangia bear no fixed relation to each other. A similar mode of auxosporulation occurs in some other species of Bacillariaceae, such as N.fonticola, N. angustata and apparently also N. subcurvata. Certain features are also shared by N. longissima, which shares a similar cell shape, with long rostrate apices. Two of the four plastids present in the zygotes and auxospores are often contracted and apparently degenerate. Oogamy is unlikely to occur in any members of the Bacillariaceae, though some slight doubt lingers; an old report (by Pascher), of the formation of four protoplasts (gametes?) within frustules of Nitzschia cf. hantzschiana, requires reinvestigation. The nature of the caps that cover...

To facilitate genetic selections of Acetabularia acetabulum (Linnaeus) P.C. Silva (Dasycladales, Chlorophyta), two culture techniques which reduce the labour in handling large cell populations and the life-cycle duration of this giant alga are described and quantified. Firstly, cell populations were easier to handle if they grew attached to a solid substratum. Zygotes preferentially attached to single, orange, cotton threads, and completed development while attached to these threads. The number of cells attached to a thread was controlled by varying the number of gametangia inoculated. Secondly, the density of the cell population dramatically affected rates of development. Although zygotes and young siphonous cells cultured at high densities (104 cells ml−1) initially grew faster than cells cultured at low densities (10 cells ml−1), they were unable to complete development at the higher densities. Older, siphonous cells required large volumes of media (1 cell/70 ml) to complete development. Regul...

A critical study of the crustose marine red alga Sporolithon episoredion (Adey, Townsend et Boykins) comb. nov. (Sporolithoideae, Corallinales) from the Spermonde Archipelago, southwestern Sulawesi, Indonesia, has been carried out. Gametangia and carposporangia are described in detail for the first time. Spermatangia are of the dendroid type, and occur on the floor and roof of the conceptacle. Short gonimoblast filaments arise from the dorsal side of the fusion cell. These new data have been used for a more complete characterization of Sporolithon episoredion.

Sexual reproduction in Splachnidium rugosum is anisogamous. Sporophytes produce unilocular sporangia in conceptacles. In culture, zoospores developed into filamentous gametophytes which remained sterile but occasionally gave rise to sporophytes directly. Wild gametophytes become fertile during spring and summer. They are dioecious and bear conical plurilocular gametangia. Male gametangia are distinguished from females by their orange colour and smaller loculi. Male gametes are smaller than female gametes and possess a smaller chloroplast with a more conspicuous eyespot. Plasmogamy occurs rapidly after female gametes have settled and withdrawn their flagella. Female gametes are capable of parthenogenesis and develop into more female gametophytes. Male gametes germinate but fail to develop beyond a few cells. Chromosome counts gave 20–24 for wild sporophytes and eight-10 for wild gametophytes, and it is inferred that meiosis occurs in unilocular sporangia. During sporogenesis, the characteristic stellate ch...

The reproductive biology of permanently submerged Baltic Fucus vesiculosus L. (Phaeophyceae) has been investigated at two sites (exposed and sheltered) in S. W. Finland. Phenological observations included the time of receptacle initiation, the periods of receptacle growth, oogonial maturation and receptacle abscission. The earliest stages of receptacle initiation were detected in the second week of October, when plants had been exposed to short-day ( < 12 h) stimulus for only 1-2 weeks. These receptacle initials were only a few mm in length and sexually immature. They remained dormant over winter until the April ice melt, when rapid increase in length occurred at water temperatures below 5°C. By early June, receptacles had reached maximum length but dry weight increased as gametangia (oogo-nia) matured. Spent receptacles were shed at the end of July. The effect of photoperiod on receptacle initiation was studied and initiation was found to occur under short-day conditions. The populations did not...

The spermatozoids of Zonaria angustata (Kutzing) Papenfuss (Phaeophyta) are biflagellate, and not uniflagellate as reported in other species of the Dictyotales. The anterior flagellum is 20–27 μm long and, in addition to mastigonemes and a terminal acronema, has a row of 23–33 spines distributed along its length. The posterior flagellum is very short, 1–1.5 μm long. Gametangial walls are not contiguous and sterile cortical cells occur between oogonia. The outer tier of the antheridia consists of sterile cells containing numerous physodes. It is argued that these characteristics of Z. angustata indicate that the order Dictyotales is more closely related to other brown algae than was previously thought, and the possibility of a phylogenetic relationship between the orders Dictyotales and Cutleriales is discussed.

Gametogenesis in Dictyota diemensis Kutzing commences the day after full moon and results in gamete release 10 d later. The gametophytes are dioecious. Mature antheridial sori appear as white blister-like patches on both surfaces of the thallus and are bounded by 3–5 layers of sterile cells. The antheridia are divided into many locules, each containing one spermatozoid. Mature oogonial sori appear as dark brown spots on both surfaces of the thallus. Oogonia each contain one egg and are arranged in rows within the sorus. The sterile cells bounding both oogonial and antheridial sori contain iridescent bodies. Light stimulates gamete release from mature gametangia, which commences approximately 30 min after the onset of the light period. Eggs are usually spherical but sometimes oval in shape, 50–78 μm in diameter, with two plate-like aggregations of chloroplasts around the nucleus. Spermatozoids are uniflagellate, the flagellum bearing mastigonemes with three terminal filaments, a row of spines and ...

The morphology, life histories and crossability in culture are described for the marine red algae Chondrus ocellatus Holmes forma ocellatus from Japan, China and Korea and C. ocellatus f. crispoides Mikami (Gigartinaceae, Rhodophyta) from Japan. In culture, all isolates of both formae showed a Polysiphonia-type life history typical of the family Gigartinaceae. Plants of C. ocellatus f. ocellatus from Korea and China and some strains from Japan formed gametangia under long-day conditions (LD) at 15-degrees-C; however, two other Japanese strains required short-day conditions (SD) at 15-degrees-C for gametogenesis, indicating a photoperiodic response. Plants of C. ocellatus f. crispoides did not require SD for gamete formation. In all strains, tetrasporophytes of both formae produced tetrasporangia under LD. Isolates of C. ocellatus f. ocellatus from Japan, China and Korea were found to be completely sexually compatible regardless of photoperiodic characteristics, and the responses to daylength shown by progeny of LD and SD strains suggested Mendelian inheritance of a daylength factor. Chondrus ocellatus f. ocellatus was sexually incompatible with C. nipponicus Yendo, a morphologically similar species from Japan, but C. ocellatus f. crispoides was partially interfertile with both C. ocellatus f. ocellatus and C. nipponicus, indicating that the three entities are closely related. In view of the apparently higher breeding compatibility between C. nipponicus and C. ocellatus f. crispoides, and the fact that these two entities are more similar morphologically and reproductively, it is proposed, provisionally, to refer C. ocellatus forma crispoides to C. nipponicus.

Peyssonnelia immersa sp. nov. is described from the British Isles and France. The species has been found intertidally on bedrock and stones and on mobile substrata in the sublittoral. It differs from all previously described species by possessing a unique combination of vegetative and reproductive characters; of particular note is the development of reproductive organs in extensive immersed sori. Terminal cruciate tetrasporangia, occasionally borne on thickened filaments, are surrounded by a complex stratified wall. Carpogonial branches, auxiliary cell branches and spermatangia are accessory in origin and develop among pigmented sterile filaments in the same sori. One or more gonimoblasts arise from the connecting filament after fusion with a series of auxiliary cells and the mature carposporophyte consists of simple or branched chains of 2–5 large carposporangia. In laboratory culture, tetraspores obtained from field material of P. immersa gave rise to crusts similar to field plants. Gametangia and immat...

Sexual reproduction in N. protracta is isogamous, although one gametangium often dehisces, releasing its gametes, before the other gametangium has completed meiosis. Sexualized cells produce an envelope of mucilage, into which the gametes are released and within which the zygotes begin their development. Two gametes are produced per gametangium and the supernumerary nuclei begin to degenerate very quickly after meiosis II. The young auxospores lie between the empty gametangia and are ellipsoidal. Expansion of the auxospores takes place in directions bearing no fixed relation to the orientation of the gametangia. The initial epivalve lacks pseudosepta, while the rostrate poles of the vegetative cells must develop during size reduction, being absent from the initial cell. Comparisons with Navicula sensu stricto show no significant similarities in sexual reproduction or frustule structure. Thus, in spite of their superficially similar protoplast structure, N. protracta is probably not closely related to Navi...

Scytothamnus australis and S. fasciculatus have a southern circumpolar distribution. Wild macrothalli are diploid sporophytes bearing unilocular meiosporangia. Meiospores develop into filamentous microscopic gametophytes which, grown under short-day conditions, form plurilocular gametangia. The gametophytes are dioecious and produce isogametes. Zygotes and unfused gametes develop into diploid and haploid sporophytes, respectively. In all culture conditions haploid sporophytes also grow directly from gametophytes. The erect sporophytes are initiated on the gametophytic filaments in close association with phaeophycean hairs. Chromosome counts gave 24–28 for the diploid phase and 8–14 for the haploid phase. One wild tetraploid population was found. Ultrastructural details of meiosporogenesis and gametogenesis are described. During meiosporogenesis the chloroplast temporarily loses its stellate form and the central pyrenoid occupies a lateral position. The resemblance between the life history of Scytothamnus ...

Pyronema domesticum was cultured with daily cycles ranging from constant light to constant dark in combination with light intensities ranging from 150 to 0.15 fc. Light is required to initiate gametangial formation. A cyclical exposure to 150 fc for 6 h to 75 fc in constant light will allow the full expansion of most ascogonia. Production of poorly expanded or morphologically abnormal ascogonia increases with decreasing exposure to light. Under unfavorable conditions, juvenile gametangia or malformed small ascogonia predominate. Development of the ascogenous hyphae, asci, ascospores, and maturation of ascospores were generally favored by exposure to the higher light intensities for longer cyclical periods. Maximum production of apothecia with ascospores was found in those cultures exposed to constant light at 150 fc. The highest proportion of apothecia with matured ascospores occurred after exposure to 6-h light cycles at 150 fc with only 12.5% of the agar surface exposed to the light. Development of the sterile components (excipular hairs, paraphyses, and globular cells in the medullary excipulum) was favored by the shorter light cycles (4-6 h daily) and moderate light intensities. Inhibition of the sterile components was especially evident in cultures fully exposed to constant light at 150 fc. Maximum apothecial expansion was obtained with 6 h light daily with exposure to 75 or 150 fc. Sclerotia or sclerotial initials were formed when the cultures were grown in the dark or with low light intensities.

Trichosolen retrorsa sp. nov. was collected on calcareous cobbles at a depth of 15 m below Chart Datum off the coast of Ghana (tropical West Africa). This species is distinct from all others in the genus in that the gametangia arise laterally near the base of the ramelli, are directed back towards the central axis, and develop one or two distinct terminal papillae. Trichosolen has priority over Pseudobryopsis with which it is congeneric. The following new combinations are therefore necessary: T. blomquistii, T. gracilis, T. longipedicellata, T. planktonica and T. solomonensis.

One male and one female gametophyte of Ectocarpus siliculosus have been detected in a sample of 19 plants taken from the Isle of Man. Fertilization takes place between gametes formed in plurilocular gametangia. Clear cross-fertility exists with Mediterranean strains. This result confirms the notion that the concept of the gametic character of meiospores in Ectocarpus should be abandoned.

The life history of Myriotrichia clavaeformis from western Ireland was studied in culture. Zoids from unilocular sporangia of field sporophytes developed to microthalli. In long days, these functioned as dioecious gametophytes which produced isogametes in plurilocular gametangia. In short days, the microthalli formed morphologically identical asexual zoids. Both asexual zoids and unfused gametes could germinate and develop to gametophytes. Zygotes, in contrast, immediately gave rise to sporophytic macrothalli, starting with the formation of an upright filament terminated by a hair. Large zoids from plurilocular sporangia on the sporophyte reproduced this generation directly. Sporophytes in culture also formed unilocular sporangia, releasing meiospores which re-established the gametophyte generation. Chromosome numbers are n = 12 and 2n = 24. The culture results are used to model the phenology of M. clavaeformis.