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The paper reports a process of sexual reproduction in the Black Sea diatom Climaconeis scalaris (Brebisson) E.J. Cox, 1982, initiated in laboratory conditions. A crossing system of this species allows both homo- and heterothallic reproduction. The fertilization is allogamous. Diploid mother gametangial cells secreted mucilage, forming a mucilage track, while actively gliding relative to each other. Each gametangium in a pair produced two elongated, cylindrical round-ended haploid gametes, which were largely morphologically and behaviorally isogamous. The division of the protoplast of the gametangial cell occurred in the transapical plane without the rearrangement of gametes. Growing auxospores were located parallel to the parent frustules. The research produced data on changes in the cell size, number of chloroplasts, and the position of cardinal points in the life cycle of the examined species.

The sexual reproduction and life history of the marine pennate diatom Entomoneis cf. paludosa have been described for the first time. The sexual process has been found to involve two gametangia, each producing two gametes. This species is characterized by morphological and behavioral isogamy. Its mating system includes the heterothallic mode of reproduction, with no cases of homothallic reproduction recorded. The type of sexual process is categorized as IC in Geitler’s system. © 2021, Pleiades Publishing, Ltd.

Bryophytes are unique among land plants in that the gametophyte generation is photosynthetically dominant, with the sporophyte permanently attached to and partially parasitic upon the gametophyte. It is therefore convenient to consider the process of sexual reproduction as beginning with the development of gametangia upon the gametophyte and proceeding through gametangial maturation, fertilization, sporophyte development, and sporogenesis to the release of spores. There have been two main phases in studies of seasonal patterns of reproductive development. In early investigations a number of authors reported dates of fertilization and spore release in a wide range of European and North American mosses. The environmental factors controlling the different phases of development are likely to vary between species. However, common features sometimes may be detected among groups of species occupying particular habitats or showing similar patterns of geographical distribution. Reproductive phenology in several widely ranging species has been compared in temperate, boreal forest, and polar localities.

The reproductive adaptations of land plants have played a key role in their terrestrial colonization and radiation. This encompasses mechanisms used for the production, dispersal and union of gametes to support sexual reproduction. The production of small motile male gametes and larger immotile female gametes (oogamy) in specialized multicellular gametangia evolved in the charophyte algae, the closest extant relatives of land plants. Reliance on water and motile male gametes for sexual reproduction was retained by bryophytes and basal vascular plants, but was overcome in seed plants by the dispersal of pollen and the guided delivery of non-motile sperm to the female gametes. Here we discuss the evolutionary history of male gametogenesis in streptophytes (green plants) and the underlying developmental biology, including recent advances in bryophyte and angiosperm models. We conclude with a perspective on research trends that promise to deliver a deeper understanding of the evolutionary and developmental mechanisms of male gametogenesis in plants.

Summary In angiosperms, the phase transition from vegetative to reproductive growth involves the de-repression of the squamosa promoter-binding-protein-like (SPL) class of transcription factors, which is negatively regulated by the specific microRNAs (miRNAs/miRs) miR156/529 [ 1 ]. Non-vascular land plants also undergo growth-phase transition to the reproductive state, but knowledge regarding the controlling mechanisms is limited. Here, we investigate the reproductive transition in the liverwort Marchantia polymorpha, focusing on the roles of miR529c [ 2 , 3 , 4 ] and MpSPL2. First, we established mir529c-null mutants using CRISPR/Cas9. Even in the absence of far-red light-supplemented long-day condition, which is usually needed to induce reproductive development [ 5 , 6 ], the mutant thalli developed sexual reproductive organs (gametangia) and produced gametes. Transgenic plants expressing a miR529-resistant MpSPL2 transgene also showed a similar phenotype of reproductive transition in the absence of inductive far-red light signals. In these mutants and transgenic plants, the MpSPL2 mRNA abundance was elevated. Mpspl2ko mutant plants showed successful gamete development and fertilization, which suggests that MpSPL2 is involved in, but not essential for, sexual reproduction in M. polymorpha. Furthermore, analysis of Mpspl2ko mutant and its complemented lines suggests that MpSPL2 may have a role in promotion of reproductive transition. These findings support the notion that the transition to reproductive development in liverworts is controlled by a system similar to that in angiosperms, and the miR156/529-SPL module has common significance in the control of the vegetative-to-reproductive transition during development in many land plants, including liverworts.

Some charophyte species reproduce sexually by oospores and vegetatively by bul- bils, and the proportion of branch whorls that contain reproductive organs can be used as quanti- tative measures of the degree of sexual reproduction. We examined inter-specific differences in the proportion of bulbils (PB) by total weight and the proportion of branch whorls containing gametangia (PG) or oospores (PO), as well as morphological and physiological differences among 3 charophyte species (Chara vulgaris Linnaeus, Chara braunii Gmelin, and Nitella gracilens Morioka) responding to variation in water depth (0.5, 1, 1.5, 2, and 3 m) in an outdoor experiment. A 2-way ANOVA contrasting species and water depth revealed that shoot elongation and the chlorophyll a to carotenoid (chl a/caro) ratio were primarily affected by water depth. However, variation among species contributed more than water depth to the differences in weight, sexual reproduction (PG and PO), and the chl a/chl b ratio. Additionally, variation among species con- tributed almost equally to the differences in PB that occurred among different water depths. Both Chara species extended their shoots and increased their PB in response to increasing water depth (from 0.5 to 1.5 m). However, deeper water (2 and 3 m) led to elongated shoots as well as decreased PB, PG, and PO. For N. gracilens, elongated shoots with increased water depth (from 0.5 to 3 m) occurred at the expense of both vegetative (decreased PB) and sexual reproduction (reduced PG and PO).

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...

Plagiospora gracilis, a mucilaginous crustose red alga growing on subtidal pebbles on\ud both coasts of the North Atlantic Ocean, forms distinctive tetrasporangia (red algal\ud meiotic structures that release haploid tetraspores) but gametophytes have never been\ud reported. In the absence of gametangia, the taxonomic position of this monotypic genus\ud has always been uncertain; it is currently placed provisionally in the Gloiosiphoniaceae\ud (Gigartinales) by comparison with sporophytes of Gloiosiphonia obtained in culture.\ud Dioecious gametophytic crusts of P. gracilis are now reported for the first time, forming\ud gametangia in inconspicuous superficial sori. There is no evidence that fertilization ever\ud occurs in the field although fertile males and female were collected together. In culture,\ud tetraspores grew into tetrasporophytes for three successive generations, by presumed\ud apomictic sporophyte recycling. The life history of P. gracilis may represent a late stage\ud in the loss of sexual reproduction leading to tetraspore-to-tetrasporophyte life histories\ud such as that in Hildenbrandia. Phylogenetic analysis of sequences of the rbcL, LSU\ud (28S) rDNA and coxI (COI-5P) genes for P. gracilis with other Gigartinales resolved P.\ud gracilis as a distinct lineage in a well-supported clade of the families Sphaerococcaceae,\ud Gloiosiphoniaceae, Endocladiaceae, Nizymeniaceae and Phacelocarpaceae. We here\ud propose the monotypic Plagiosporaceae fam. nov. to accommodate P. gracilis.

For decades, the diatom genus Haslea has been known to comprise both "colorless" species and one species containing a blue pigment, the latter being known as H. ostrearia. Recently, a new blue diatom named H. karadagensis has been isolated from the Black Sea. The mating compatibility of the two species has been tested, and their reproductive isolation confirmed. We provide a detailed description of the heterothallic sexual reproduction process in this new species. Cells from clones which are sexually compatible arrange gametangial pairs. Each gametangium in the pair produces two gametes, which to a large extent are morphologically and behaviorally isogamous. No mucilage or mucilage structures are observed. Zygotes and auxospores have no contact with parental frustules, and their orientation is rather irregular though they tend to lie parallel to each other. Evaluation of the position of cardinal points in the life cycle of the species, and the rate of cell size decrease in culture are presented. In the breeding system of this species both homo- and heterothallic ways of reproduction are realized. The latter is basic and predominant. Among the 36 clones investigated, 16 were sexually compatible with the other 20. Homothallic behavior was extremely rare; only one clone displayed a homothallic mode of reproduction.

Sexual behaviour, pattern of auxosporulation, and breeding system of the araphid diatom Tabularia fasciculata were studied using 64 clones derived from two natural populations from the Canadian Atlantic seashore and the Black Sea. Both inter- and intraclonal reproductions were observed. Heterothallic reproduction was morphologically and behaviourally heterogamous. The heterothallic nature of sexual reproduction in this species allowed the determination of sex ratio in the population, which was 1:1 male:female. A novel type of active movement of gametes designated as male was described and pathways traced and recorded. A few male clones could reproduce intraclonally, but this was not abundant compared to interclonal reproduction. The advantages and inferred significance of each mode of reproduction are discussed. In the semi-natural population of T. fasciculata, two size classes were detected among sexualized individuals, and they gave rise to two size groups of initial cells. Sexual compatibility of all derived clones was independent of cell size class. In cultures, the apical length of initial cells was also strongly correlated to the size of parental gametangia. Cell sizes corresponding to cardinal points in the life cycle were established. Interbreeding of clones derived from the Canadian Atlantic and the Black Sea suggests a pan-Atlantic reproductive compatibility of populations of diatoms conforming to current morphological delineation of T. fasciculata.

The Punta Lara Natural Reserve is located on the riverside of the La Plata River in the province of Buenos Aires, Argentina. It is the Southernmost relict in the world of subtropical riparian forest. The epiphytic ferns studied in this work belong to the Polypodiaceae family: Microgramma mortoniana and Pleopeltis macrocarpa. Plant communities are subject to high levels of anthropization and introduction of exotic species. The goals of this work are to provide information on the morphogenesis of epiphytic gametophytes and to extend knowledge of their life cycles, contributing to their conservation. Sowing was carried out in Dyer medium. In both species the spores are monolete, ellipsoidal, yellowish and with verrucate sculpture. The equatorial diameter is 60-61 μm, the polar diameter is 39-42 μm. The germination is the Vittaria type; in M. mortoniana occurs at 20 days, while in P.macrocarpa occurs at six days. The filaments are uniseriate of 3-6 cells in length. The gametophyte development is Drynaria type. The cordated form is given after 40 days. In M. mortoniana, buds originated after 40 days. In P. macrocarpa, after 120 days, clathrate trichomes scale-like appear mainly on the margins of the gametophyte. The gametangia are typical of leptosporangiate ferns. The sporophyte of M. mortoniana emerged after 120 days and that of P. macrocarpa arose after 500 days, its blades are simple, spatulate and unicellular and multicellular branching hairs were observed. The germination pattern, gametophyte development, the presence of a lipid globule in the prothalic cell and the formation of unicellular capitated hairs are relevant characters that could be considered for systematic group. The delay in the formation of sporophytes through sexual reproduction, allows us to infer that the success of their establishment in situ would be given by the vegetative reproduction through creeping rhizomes and buds of gametophytes., Facultad de Ciencias Naturales y Museo

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...

Sexual reproduction is documented for the first time in field populations of the pennate diatoms Pseudo-nitzschia australis Freng. and P. pungens (Grunow ex Cleve) Hasle (var. cingulata Villac and hybrids between var. cingulata and var. pungens). A bloom dominated by these species began on June 26, 2006, along Kalaloch Beach, Washington, USA, coincident with a drop in the Si(OH)4:NO3 ratio to below two. Multimodal size distributions were detected for both species, and synchronous auxosporulation occurred within the smallest size class during a 3-week window. Auxospores and initial cells created a new class of large cells, and cells in the intermediate size classes increased in abundance during auxosporulation. Mating cells of both species were attached to colonies of surf-zone diatoms. Paired gametangia, gametes, zygotes, auxospores, and large initial cells were found. Auxosporulation began first for P. pungens (June 30), apparently once a critical, high cell concentration was reached, followed by P. australis (July 5), when the total Pseudo-nitzschia cell concentration reached 929,000 cells · L−1. Low frequencies of auxosporulation occurred throughout the bloom but increased 4-fold for P. australis and 3-fold for P. pungens when macronutrients were reduced to low levels on July 11. A 2-year life cycle was estimated for P. australis and 3 years for P. pungens, both with annual auxosporulation. Domoic acid (DA) in razor clams reached a maximum of 38 μg DA · g−1 on July 18. A significant relationship existed between the percent of cells within the new size range and DA concentrations in razor clams on the same beach.

Previous molecular genetic and life cycle studies have revealed the existence of a vigorously homothallic deme within the Sellaphora pupula species complex, which was given the provisional name of Sellaphora [pupula K-LB] Φ 'urban elliptical'. This is described here as S. bisexualis sp. nov., with a cox1 DNA-barcoded type from Scotland. A detailed description of frustule ultrastructure is given, the most complete for a Sellaphora species. The morphology of the terminal raphe fissure is variable, becoming vestigial in some small pre-auxospore valves, and the boundary between the raphe-sternum and striae is sometimes strongly, sometimes weakly marked by larger areolae and an external groove. The cingulum contains at least three plain bands. The pars interior of band 1 (the valvocopula), as well as being undulate with a pitch corresponding to the transapical ribs, bears a very fine fringe of short fimbriae. Sexual reproduction involves 'male' and 'female' gametangia, as in other allogamous species of Sellaphora, but in S. bisexualis cells of the same clone can differentiate into either sex, allowing homothallic reproduction and successive inbred generations. The proven distribution of the species includes sites in the UK and Australia.

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...

8 pages, 5 figures, 3 tables, Most pennate diatoms are allogamous, and various types of mating systems have been described. In Pseudo-nitzschia, reproductive stages have been identified in some species, and it is generally accepted that the genus is mainly heterothallic. Here we report homothallic auxosporulation of Pseudo-nitzschia brasiliana Lundholm, Hasle et G. A. Fryxell. To our knowledge, this is the first verified description of homothallic sexual reproduction in the genus. Auxospore formation was observed in all 16 subclones derived from three initial clonal cultures of P. brasiliana. Pairing was followed by production of two gametes per gametangium, which fused to give two zygotes. Each zygote (early auxospore) was initially spherical and adhered to one girdle band of the parental frustule. The two auxospores tended to expand parallel to each other and perpendicular to the parental frustule. Elongation was synchronous, slightly asynchronous, or totally asynchronous. The entire process of sexual reproduction, from gamete formation to the appearance of the initial vegetative cells, took 2–4 d. The occurrence of sex in a homothallic species seems an advantageous life strategy for this species in that any encounter between cells of the right size class is potentially sexual, This study was supported by the EC funded Research Project SEED (Life cycle transformations among HAB species, and the environmental and physiological factors that regulate them), GOCE-CT-2005-003875, and the CRA (Centre de Referencia en Aquicultura, CIRIT-Generalitat de Catalunya, Spain). E. Garcés work was supported by a Ramon y Cajal contract of the Spanish Ministry of Education and Science. S. Quijanós work was supported by a PROMEP grant (Mexico), Colima University

Dioicous bryophytes often exist in isolated populations with low rates of sexual reproduction. While most populations contain individuals of both sexes, some species have single-sex populations that depend solely on asexual reproduction for population expansion and persistence. Life history trade-offs can constrain population divergence and the relative investment in growth, asexual and sexual reproduction may differ in single-sex and both-sex populations. A common garden experiment and field observations were used to assess trait variation and determine genetic differences among single-sex and both-sex populations of Marchantia inflexa, a dioicous liverwort. Populations were significantly genetically differentiated, and plants from single-sex and both-sex populations differed in their life history strategies. Plants from single-sex populations invested more in growth than asexual production, and although they produced as many sexual structures, they produced fewer gametangia per gametophore than...

The morphology and sexual reproduction of the attached diatom Cocconeis scutellum Ehr. var. scutellum have been investigated using field and culture materials. The diatom grew well at 14–22° C and in a medium using enriched full strength seawater or 50% diluted seawater. One gamete was formed without cytokinesis in a gametangium and one auxospore arose from paired gametangia. The size of gametangia and initial cells were 17.8–29.9 μm and 43.3–59.5 μm, respectively. Valve width decreased linearly with decreasing valve length. The regression coefficient between them was invariable with the change of the environment. The transapical striation densities were 7–12 and 7.5–13.5 in 10 μm in araphid and raphid valves, respectively. The density showed a tendency to increase with decreasing valve length in both valves. The densities in both valves, except the small araphid valve, are invariable with the change of the environment. The relationships between valve length and width, and between valve length and striation density have been compared with those of taxa allied to C. scutellum var. scutellum. It is concluded that C. scutellum var. scutellum, as usually delimited, is a heterogenous taxon.

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 ...

Homothallic sexual reproduction and auxosporulation were studied in monoclonal cultures and seminatural populations of the freshwater epipelic diatom Navicula cryptocephala Kutz. Gametangia paired via the girdle, one gamete was formed per gametangium (and hence one zygote per pair of gametangia), and gamete fusion took place without the formation of any copulation envelope or copulation canal. Superfluous nuclei from meiosis survived unusually long, so that gametes and young zygotes were probably functionally polyploid; later, all but two haploid nuclei degenerated. Expanded auxospores had a swollen center, but during formation of the initial valves, the auxospore contracted away from the perizonium to produce linear-lanceolate valves. The pattern of reproductive behavior found in N. cryptocephala can be classified as type IIA2a auxosporulation in Geitler's system. The same type of zygote and auxospore formation seen in clonal cultures was observed in seminatural material from four lakes in Scotland and the Czech Republic. Variation in nuclear structure and auxosporulation in the N. cryptocephala species complex is discussed, as is the evolution of type II auxosporulation (one zygote per pair of gametangia) from type I auxosporulation (two zygotes per pair). The penalty of smaller numbers of zygote produced in type II may be outweighed by formation of larger auxospores (prolonging the vegetative phase) or more vigorous auxospores. The variation present among members of the N. cryptocephala complex indicates that biogeographical analyses based on use of the name N. cryptocephala, as performed recently to support the ubiquity hypothesis of protist distributions, are almost meaningless.

Pseudo-nitzschia delicatissima (Cleve) Heiden is a very common pennate planktonic diatom found in temperate marine waters, where it is often responsible for blooms. Recently, three distinct internal transcribed spacer types have been recorded during a P. delicatissima bloom in the Gulf of Naples (Mediterranean Sea, Italy), which suggests the existence of cryptic diversity. We carried out mating experiments with clonal strains belonging to the most abundant internal transcribed spacer type. Pseudo-nitzschia delicatissima is heterothallic and produces two functional anisogametes per gametangium. The elongated auxospore possesses a transverse and a longitudinal perizonium. The sexual phase was observed to occur over aw ide size spectrum, spanning 19–80l ma nd corresponding to almost the whole range of cell length observed for P. delicatissima .W e also investigated cell morphology, valve ultrastructure and morphometry of parental, F1-generation strains, and the progeny of crosses between parental and F1 strains. Although ultrastructural features match those described for P. delicatissima, variability in cell shape was recorded in the largest cells of the F1 generation as well as in valves with an abnormal arrangement of poroids. As many other diatoms, P. delicatissima undergoes size reduction over its life cycle, and cells of different size showed differences in growth rates and the amount of size reduction per cell cycle. Cells between 60 and 30l mi n length showed the fastest growth and the slowest rates of size reduction per generation. In culture, P. delicatissima cells can decrease to 8lm in length; however, such small cells ( � 30lm) are not recorded in the sea, and this raises interesting questions about the factors that control their survival in the natural environment.

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.

SUMMARY The auxosporulation of Licmophora communis is allogamous and dioecious. Pairing between sessile, shortstalked cells of compatible clones is followed by meiosis and gametogenesis, to form two gametes in each gametangium. The behavior of the gametes differs between the gametangia. In the male gametangium, the gametes detach from the frustule, round up, and migrate out of the gametangium after its dehiscence at the broader, unattached pole. In the female gametangium, both gametes remain attached to the adjacent theca over almost their whole length and do not move. Plasmogamy therefore occurs within the female gametangium and this is where the zygotes are formed and remain. After fertilization, the zygotes detach from the thecae of the female gametangia, contract, and become ellipsoidal, before expanding parallel to the apical axis of the gametangium. We review the types of auxosporulation in other pennate diatoms and the systems used for classifying these. Dioecy and cis-type anisogamy (in which one gametangium produces active gametes and the other produces passive gametes), as in L. communis, are probably primitive within the pennate group (although there is no information on the AsterionellopsisRhaphoneis clade). However, size can also be restored in various araphid pennates by allogamous sexual reproduction involving the formation of only one gamete per gametangium, or in rare cases by automixis or (apparently) vegetative enlargement.

The diatom genus Eunotia is unusual among raphid diatoms in having a raphe system consisting of two short slits that are not integrated into the primary pattern center. This and other characteristics, particularly the presence of rimoportulae, are consistent with the hypothesis that Eunotia is a basal lineage within the raphid group. We studied auxosporulation in E. bilunaris (Ehrenberg) Mills and E. tropica Hustedt for comparison with other raphid pennate diatoms and with araphid pennates; E. bilunaris was studied in parental and F1 generations. Like araphid pennates, E. bilunaris and E. tropica are heterothallic. Clones of the same mating type did not interact sexually, and intraclonal sexual reproduction was absent or very rare. Clones retained the same sex throughout the life cycle, as shown by experiments using abrupt size reduction to produce clones of similar age but different size and using subclones derived from a single initial cell within six mitotic generations. Unlike in araphid pennate diatoms, in the Eunotia species the gametes are not visibly or behaviorally differentiated. Gametogenesis is merogenous, because the gametangium formed a supernumerary cell as well as a single gametic cell, both undergoing meiosis II to form a surviving functional nucleus and a nucleus that quickly degenerated. Plasmogamy is via papillae that grew out toward each other from the ends of the gametangia to create a copulation canal. After plasmogamy, the gametes moves bodily into the copulation canal, producing an elongate zygote, which expands to form a curved sausage-like auxospore.

Cell division, the mating system, and auxosporulation were studied in the marine epipelic diatom Seminavis cf. robusta Danielidis & D. G. Mann. The interphase protoplast contains two girdle-appressed chloroplasts, each with an elongate bar-like pyrenoid, and also a central nucleus, located in a bridge between two vacuoles. Before cell division, the chloroplasts divide transversely and translocate onto the valves. The nucleus relocates to the ventral side for mitosis. After cytokinesis and valve formation, the chloroplasts move back to the girdle, showing a constant clockwise movement relative to the epitheca of the daughter cell. Seminavis cf. robusta is dioecious, and sexual reproduction is possible once cells are less than 50 μm. In crosses of compatible clones, gametangia pair laterally, without the formation of a copulation envelope, and produce two gametes apiece. The intensity of sexualization increases as cells reduce further in size below the 50-μm threshold. At plasmogamy, the gametangia dehisce fully and the gametes, which were morphologically and behaviorally isogamous, fuse in the space between the gametangial thecae. The auxospore forms a transverse and longitudinal perizonium. After expansion is complete, there is an unequal contraction of the protoplast within the perizonium, creating the asymmetrical shape of the vegetative cell. Apart from this last feature, almost all characteristics exhibited by the live cell and auxospores of Seminavis agree with what is found in Navicula sensu stricto, supporting the classification of both in the Naviculaceae. Haploid parthenogenesis and polyploid auxospores were found, lending support to the view that change in ploidy may be a significant mechanism in diatom evolution.

The reproductive biology of three sympatric species of Dicranoloma Ren. was investigated: D. billardierei (Brid. ex anon) Paris, D. menziesii (Taylor) Renauld, and D. platycaulon Dixon. The developmental stages of gametangia and sporophytes were identified for each species and a maturity index value assigned. Although archegonia were initiated after antheridia, archegonia matured within two months while antheridia took five to six months to reach maturity. Antheridia were initiated during winter and archegonia in spring in D. menziesii and D. platycaulon. In contrast, antheridia were initiated during late spring-summer and archegonia in autumn in D. billardierei. Fertilization occurred in late summer in D. menziesii, mid autumn in D. platycaulon, and early winter in D. billardierei. An overlap in sporophyte generations occurred in D. billardierei and D. platycaulon. Maturation of the sporophyte took 18–24 months in these species, whereas sporophytes of D. menziesii matured within 12 months.

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...

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.

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...

Male and female gametes were formed within the same gametangiurn on reproductive plants of Codium fragile (Sur.) Hariot ssp. tomentosoides (Van Goor) Silva growing off Appledore Island in the Gulf of Maine, USA. The female gametes were approximately twice the diameter of male gametes and outnumbered male gametes in the same gametangium by approximately six times. Fusion appears to require gametes from different gametangia if not different plants.

The morphology of gametangia was examined in 43 pairs of isolates (mating types A1‹A2; 11 A1 and 24 A2 isolates; five isozyme}electrophoretic types) of Phytophthora cinnamomi. An amphigynous antheridium always formed with each oogonium. However, in 41 of the crosses a proportion (39 had 0‐2‐10% and two had " 30%) of oogonia also consistently had single or multiple paragynous antheridia. Single or multiple paragynous antheridia formed concurrently with amphigynous ones during the period of gametangial production in paired colonies. Where there were multiple paragynous antheridia associated with an oogonium, sometimes additional antheridia formed after fertilization or even after oospores were visible. Developmental studies showed that when meiosis in amphigynous and paragynous antheridia was simultaneous, fertilization tubes developed synchronously from both. However, cytological examination indicated that either a nucleus from an amphigynous or a paragynous antheridium fertilized the oosphere. Observations of paragynous and amphigynous, and amphigynous-only associations suggested that fertilization from either type of antheridium only occurred when meiosis in the oogonium was nearly synchronous with that of the antheridium. Asynchronous meiosis between oogonia and antheridia may contribute to failed fertilization and aborted oospore development. This appears to be the first description of paragynous antheridia in P. cinnamomi and the second observation of oogonia with both paragynous and amphigynous antheridia in a heterothallic Phytophthora species. Moreover, the development of both paragynous and amphigynous antheridia with an oogonium is rare in Phytophthora, as is the development of multiple antheridia. Antheridial variation is a characteristic to be taken into account in isolate identification. Nuclei from paragynous antheridia appear able to fertilize oospheres and therefore, have a role in sexual reproduction.

The reproductive strategy of a marine alga with a heteromorphic biphasic life cycle was studied by analyzing various sexual reproductive characters in light of the evolution of anisogamy. Gametophytes of Monostroma angicava were dioecious and their gametes were slightly anisogamous. Volume of gametangium, density of gametangia and area of mature gametangial parts on each gametophyte did not differ from male to female. Therefore, the reproductive biomass investment for gamete production was considered to be the same for each sex. Anisogamy in this alga appeared to be derived from the difference in the number of cell divisions during gametogenesis, because the majority of male gametangia each produced 64 (26) gametes and the female produced 32 (25) gametes. This corresponded with measurements of cell size in male and female gametes. Further, the sex ratio was 1:1 for sexually mature plants sampled at Charatsunai. Therefore, it was suggested that in the field twice as many male gametes are released as female gametes. Liberated gametes of both sexes showed positive phototaxis. The swimming velocity of freshly liberated male gametes was a little higher than that of female gametes. Male gametes had the potential to swim for ca. 72 h and female gametes for ca. 84 h. The difference in gamete motility between the two sexes seemed to be related to cell size. Planozygotes were negatively phototactic and swam more rapidly than gametes of either sex.

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 ...

We present the first experimental results on salinity tolerance and regulation mechanisms in the genus Tolypella. The two species investigated, T. nidifica and T. glomerata, regulate turgor pressure with almost complete effectiveness by adjustment of K + and Cl - concentrations. Sucrose is also involved. The mechanism is basically identical to the mechanism of turgor pressure regulation previously identified in representatives of the genera Chara and Lamprothamnium. Since Chara and Lamprothamnium on the one hand and Tolypella on the other belong to different phylogenetic branches that separated early in the geological history of the Characeae, the K + regulation mechanism can be assumed to represent an ancient pattern derived from a salt-tolerant common ancestor. Furthermore, our experiments provide evidence that salinity is a limiting factor for fertility in both T. nidifica and T. glomerata. Although the onset of gametangia covers the whole range of salinities tested here (0-29 psu), 12 psu was the inhibitory level for the formation of mature oospores. Fertilization is probably disturbed by an increase in salinity. An inability to reproduce sexually under euryhaline conditions could explain why the distribution of the two species is restricted to oligo- and mesohaline environments, despite the wide range of salinity tolerance of their vegetative apparatus.

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...

Sexuality is most often preserved in Sphagnum while asexual reproduction remains responsible for the perennity and multiplication of the species. Sexual reproduction success was assessed for two diecious species and four monecious – polyecious species, using fertilization rates, reproduction rates, and success of the reproduction. The effects of different crossing processes on the preceding parameters were emphasized. Accordingly, gynoecium numbers, archegone numbers per gynoecium, and sporogonia occurrences were assessed in more than 3500 capitula. Variable distribution of gametangia within capitula in different species determines the success of sexual reproduction. An evolutionary interpretation of this variation in the distribution of gametangia is proposed. Key words: Sphagnum, crossing processes, polyecious, sexualization rates, reproduction success. [Journal translation]

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.

Publisher Summary This chapter studies the genus Magnusiomyces. In the determination of the asexual reproduction, it is seen that colonies are white, farinose or hairy, usually dry, and consist of true hyphae that branch at acute angles with acuminate apices and disarticulate into arthroconidia. Additional sympodial and annellidic conidiogenesis may be present. Septa have micropores. In sexual reproduction it is found that gametangia form on opposite sides of hyphal septa, become broadly ellipsoidal, soon fuse entirely, and are transformed to an ascus. Asci are hyaline, subspherical to broadly ellipsoidal, and contain four ascospores. Ascospores are ellipsoidal to broadly ellipsoidal, hyaline, and have smooth walls surrounded by regular slime sheaths. The chapter also discusses physiology/biochemistry and phylogenetic placement of the genus. The type species taken is Magnusiomyces magnusii. The key characters of species assigned to the genus Magnusiomyces are presented. In the systematic discussion of the species, anamorph, synonyms, growth on 4% malt extract/0.5% yeast extract agar, growth radius on glucose-peptone-yeast extract agar, formation of ascospores, gene sequence accession numbers, type strain, cell carbohydrates, origin of the strains studied, complementary mating types, and systematics are determined.

Publisher Summary This chapter studies the genus Dipodascus. In the determination of asexual reproduction, colonies are white or cream-colored, farinose or hairy, usually dry, and consist of true hyphae that branch at broad or right angles, have rounded apices, and mostly disarticulate into arthroconidia. Some additional sympodial conidiogenesis from undifferentiated cells may be present. Budding is absent. Chlamydospores may be formed. Septa have micropores. The anamorph genus is Geotrichum. In sexual reproduction it is seen that clavate gametangia form on opposite sides of hyphal septa, fuse at the apex, and form an ascus. Asci are hyaline, broadly cylindrical to tubular, or acicular and contain 8 to more than 100 ascospores. Ascospores are broadly ellipsoidal or cylindrical, hyaline, and smooth-walled and have an even, thick, gelatinous coat. Ascospores are liberated through the apex by rupture of the firm ascus wall. In physiology and biochemistry it is seen that fermentation is mostly absent. Xylose is assimilated. Nitrate is not assimilated. Extracellular starch is not produced, and urease activity is absent. The diazonium blue B reaction is negative. Small subunit rRNA gene sequences are without deletions. The chapter further examines the phylogenetic placement where Dipodascus and its anamorph state Geotrichum are sister genera to the genus Magnusiomyces and its anamorph Saprochaete. The type of species mentioned is Dipodascus albidus. The species accepted are Dipodascus aggregatus, Dipodascus albidus, Dipodascus armillariae, Dipodascus australiensis, Dipodascus geniculatus, and Dipodascus macrosporus. The systematic discussion of the species includes synonyms, growth in malt extract, growth on 4% extract/0.5% yeast extract agar, growth radius on glucose-yeast extract-peptone agar, fermentation, formation of ascospores, CoQ, Mol% G + C, gene sequence accession numbers, type strain, cell carbohydrates, origin of the strains studied, systematics, ecology, biotechnology, agriculture and food, and clinical importance.

Sexual reproduction takes many forms within the diatoms. The variation has been classified by several authors, but in most cases the distinctions between their main categories have depended on the number of gametes produced per gametangium (and thus on how many zygotes per pair of copulating cells), and upon whether fusion is oogamous, anisogamous or isogamous. These classifications are not themselves an adequate basis for taxonomic comparison, which should be based on individual characteristics of the sexual process. Diatoms seem to be primitively oogamous. In araphid pennate diatoms and some raphid diatoms the gametes and gametangia are morphologically alike but physiologically distinct; one gametangium produces active gametes and the other passive ones. This may be the primitive condition in pennate diatoms, providing a link to the oogamy of centrics via the morphological anisogamy of Rhabdonema Kutz.

The marine red alga Helminthora stackhousei (Clemente) Cremades et Perez-Cirera [ = H. divaricata (C. Agardh) J. Agardh] from the west coast of Ireland has a heteromorphic life history in culture. Tetrasporangia are formed on uniseriate, filamentous tetrasporophytes, mainly under short-day conditions, at (7-)9-17-degrees-C. Although photoperiodic induction occurs, night-breaks of 1 h in the middle of a 16-h night are ineffective in suppressing this response. Tetraspores form further uniseriate filaments which produce multiaxial gametophytic thalli, mainly under long-day conditions at (7-)9-17-degrees-C. The critical daylength is not constant over this temperature range. Night-breaks promote the initiation of multiaxial thalli, and nine photoinductive long-day cycles induce a 50% response. At 16-degrees-C, equivalent photon exposures at two irradiance levels promote development of multiaxial thalli in long-day regimes but continue to inhibit induction in short days. Tetrasporophytes and uniseriate gametophytes reproduce asexually by fragmentation and monospores under all conditions. Multiaxial gametophytic thalli form monosporangia, gametangia, and develop carposporophytes regardless of photoperiod. Photoperiod and temperature as factors controlling the developmental life history sequence are used to formulate models to explain the phenology of H. stackhousei. These factors are also considered in relation to the biogeography of the species in the eastern North Atlantic and Mediterranean.

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...

We have improved zygote recovery 11–1,000 fold by optimizing the physiology of gamete release and mating inAcetabularia acetabulum. Gamete release was affected by agar purity, concentration, and volume/gametangial pair. Cold pre-treatment of gametangia (14–30 d at 10°C in the dark) synchronized subsequent gamete release at 21°C in the light. Cold pre-treatment was nearly twice as effective in synchronizing subsequent gamete release when intact, gametangia-bearing caps rather than isolated gametangia were pretreated. Synchronizing gamete release doubled mating efficiency. In a wild-type laboratory strain ofA. acetabulum, there were 1,561±207 gametes/gametangium which had half-lives of 14.5 d in 0.1% seawater-agar. We recovered 48–93% of the expected numbers of zygotes from a mass mating of 8 to 1,226 gametangia and 11–128% of the expected numbers of zygotes from mating single gametangial pairs: the large range in the calculated mating efficiency may be attributable to the variation in the numbers of gametes made per gametangium. Zygote recovery from single gametangial pairs was highly dependent on the volume of mating matrix. In addition, most zygotes recovered were unattached to any other zygotes in the subsequent generation (> 95% single cells from matings of 1–500 gametangial pairs). Our improvements in mating conditions and zygote recovery (1) have facilitated cell manipulation and culture ofA. acetabulum in the laboratory; and (2) have made controlled crosses for selection and genetic analysis of mutants feasible. These advances have removed a major barrier to genetic analysis of development inAcetabularia.

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 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.