On the sexual reproduction ofDictyosiphon foeniculaceus (Phaeophyceae,Dictyosiphonales)

Dictyosiphon foeniculaceus from Sweden and Newfoundland was studied in laboratory culture. Zoids from unilocular sporangia developed into dioecious microscopic filamentous gametophytes which produced uniseriate plurilocular gametangia in low temperatures (0 to 8 °C). Zygotes and unfused isogametes gave rise to filamentous protonemata on which parenchymatous macroscopic sporophytes were formed. Isolates from Sweden and Newfoundland were interfertile. Although formed in culture, genetically unisexual sporophytes were not detected in nature. Female gametes ofD. foeniculaceus produced a sexual pheromone. It was identified as finavarrene, which is also known as the sperm attractant inAscophyllum nodosum.     

LIFE HISTORY OF COLPOMENIA SINUOSA (SYCTOSIPHONACEAE,PHAEOPHYCEAE) IN THE AZORES1

Colpomenia sinuosa (Mertens ex Roth) Derbès and Solier (Scytosiphonaceae, Phaeophyceae) is a common species on the rocky intertidal shores of the Azores, where reproductive gametophytes occur throughout the year. Life‐history studies of this species were carried out in culture, and both sexual and asexual reproduction were observed. Anisogamous gametes fused to form zygotes. The zygotes gave rise to a filamentous prostrate sporophyte generation bearing unilocular sporangia, under both short‐day and long‐day conditions at 15 and 22°C, and to both unilocular and plurilocular sporangia, under the lower temperature condition. Unispores developed into gametophytes, and plurispores gave rise to filamentous sporophytes. Asexual reproduction was carried out by unfused female gametes and asexual plurispores produced from the same gametophyte. Unfused gametes developed into filamentous prostrate sporophytes producing unilocular sporangia in both culture conditions, and unispores released from the sporangia gave rise to gametophytes. Asexual plurispores from field gametophytes, under both culture conditions, developed directly into new gametophytes. The species exhibited three types of life history: a heteromorphic, diplohaplontic; a heteromorphic, monophasic (both with alternation between the erect and filamentous prostrate thalli); and a monomorphic, monophasic.     

Myrionema strangulans (Chordariales, Phaeophyceae) epiphyte on Ulva spp. (Ulvophyceae) from Patagonian Atlantic coasts

Fronds of Ulva spp. from Patagonian Atlantic coasts exhibited brown spots produced by the presence of Myrionema strangulans (Chordariales, Phaeophyceae). The occurrence of M. strangulans on Ulva spp. is widely reported from several regions of the world, but there were no detailed studies about the subject. In the present study, we describe the morphology and interactions of M. strangulans with Ulva spp. as observed under light and electron microscopes, and we reconstruct all stages of its life cycle based upon in vitro experiments. The prevalence of infection by M. strangulans was 100%. In case of the strongest epiphytism, the host cuticle exhibited perforations, massive depigmentation, cellular disorganization, and cuticle rupture. It was possible to demonstrate a purely epiphytic life strategy of the organism by transmission electron microscopy. M. strangulans formed discoid thalli constituted by vegetative filaments and radiating from a central zone to a peripheral zone. Transversally, the discs were formed by two strata: a basal monostromatic and a filamentous erect stratum. From the monostromatic stratum, hyaline hairs and reproductive structures were produced. Both plurilocular and unilocular sporangia were present. Zoids from both plurilocular and unilocular sporangia were able to germinate in culture. M. strangulans exhibited a haploid–diploid, heteromorphic life cycle with thalli with three different morphologies. The haploid chromosome number was 12?±?2 chromosomes.     

Life history of Chnoospora implexa (Chnoosporaceae, Phaeophyceae) in culture

The life history of the brown alga Chnoospora implexa J. Agardh (Chnoosporaceae, Scytosiphonales) from Japan was studied in laboratory cultures. This species showed a heteromorphic and diphasic life history, alternating between erect gametophytes and discoid sporophytes. The gametophytes were dioecious and produced isogametes. The zygotes developed into sporophytes at 20°C under long‐day conditions, which formed plurilocular zoidangia. Zoids released from the plurilocular zoidangia developed again into sporophytes that always formed plurilocular zoidangia at 20°C and 25°C in long‐day conditions, and mainly unilocular zoidangia at 25°C in short‐day conditions. Zoids released from unilocular zoidangia developed into dioecious gametophytes. At 15°C zygotic erect thalli were formed and were revealed to be diploid by microspectrofluorometric measurements of nuclear DNA contents. The development and reproduction of unfused gametes were similar to those of zygotes. Some strains showed a direct‐type life history; gametophytic thalli were produced, but not via a sporophytic phase.     

RELATION OF TEMPERATURE TO DEVELOPMENT OF THE MACROTHALLUS OF DESMOTRICHUM UNDULATUM1,2

Desmotrichum undulatum (J. Agardh) Reinke (Phaeophyta) was found in the winter months in the littoral zone of a tidal marsh in Virginia. When field collections were maintained in culture media at 21 C, most cells of the thallus developed into plurilocular sporangia. Released zoospores developed into microthalli from which clonal cultures were established. At 21 C microthalli produced sporangia which released zoospores, subsequently developing into more microthalli. However, microthalli at 6 C formed filaments which subsequently developed into thalloid plants. When the thalloid plants of Desmotrichum formed in culture were subjected to 21 C, plurilocular sporangia were formed. These results support the proposition that the seasonal periodicity of Desmotrichum is due to a temperature-regulated phenomenon in the development of macrothalli.     

CULTURE STUDIES ON REPRODUCTION OF SPERMATOCHNUS PARADOXUS (PHAEOPHYCEAE,CHORDARIALES)1

The life history of Spermatochnus paradoxus (Roth) Kütz. isolated from the Mediterranean Sea was studied in culture. Meiospores develop to a microscopic stage (microthallus) which at 20°C perpetuates asexually by plurilocular sporangia and formation of new microthalli. At 9°C microthalli act as homothallic gametophytes. Fusion of isogametes results in a diploid microthallus which, after differentiation of an apical cell, leads back to Spermatochnus plants. In addition, gametes develop without fusion to form haploid macrothalli, the further fate of which has not been determined. Chromosome numbers alternate between n = 20 ± 2 in the microthalli and 2n = 41 ± 4 in macrothalli.     

Morphology and life history of Scytosiphon canaliculatus comb. nov. (Scytosiphonales,Phaeophyceae) from Japan*

Morphology of field material and life history in culture were studied in Scytosiphon canaliculatus (Setchell et Gardner) comb. nov. from northern Japan. Erect gametophytes of S. canaliculatus are cylindrical, tubular, up to 7 mm wide and 40 cm long, and without regular constrictions. S. canaliculatus has pronounced anisogamy and ascocysts accompanied with plurilocular gametangia. The life history of S. canaliculatus showed an alternation between erect gametophytes and crustose prostrate sporophytes bearing unilocular sporangia. Since field sporophytes of S. canaliculatus were found to be identical with Hapterophycus canaliculatus Setchell et Gardner (Ralfsiaceae, Phaeophyceae), it is proposed to transfer H. canaliculatus to the genus Scytosiphon. In the field, gametophytes with plurilocular gametangia appeared in spring and disappeared in summer. Sporophytes with unilocular sporangia were collected in late autumn and winter. Unilocular sporangia were produced at 15°C in short-day culture conditions and unispores developed into erect gametophytes at 5–15°C. It is suggested that the seasonal Occurrence of gametophytes in the field is due to the seasonal formation of unilocular sporangia, which is regulated by temperature and photoperiod.     

The specific identity and the life history of JapaneseSyringoderma (Syringodermatales,phaeophyceae)

Observations on JapaneseSyringoderma from Rishiri Island, which had been previously identified asS. australe, were made based on newly collected fertile material. These results and comparisons with the type specimen ofSyringoderma abyssicola (=Chlanidophora abyssicola) revealed that the Rishiri Island plants should be identified asSyringoderma abyssicola. Syringoderma abyssicola from Rishiri Island formed unilocular sporangia among the paraphyses on the fan-shaped blades in winter. The first products (uni-spores) in the unilocular sporangia form flagella, and soon after form cell walls before release. Then these reduced gametophytes divide into tetrads and form swarmers, each of which contains a chloroplast with a stigma. These swarmers germinate into branched filaments, from which thicker erect filaments of apical growth tissue. At 5–10 C these erect filaments formed fan-shaped blades under long-day conditions, and unilocular sporangia under short-day conditions corresponding respectively to spring and winter at Rishiri Island. Accordingly, the seasonal growth pattern of the species is considered to be controlled by responses to photoregime and temperature. Dedicated to the memory of the late Professor Muneao Kurogi.     

Morphology and life history of Halopteris filicina (Sphacelariales, Phaeophyceae) from Korea

The vegetative morphology and life history of Halopteris filicina (Grateloup) Kutzing, collected from Korea, were examined in laboratory culture. Field plants attaining 3–5 cm in height were epilithic, tufted, yellowish-brown, and produced numerous erect axes with alternately distichous branches from compact basal discs. They were cultured under a 12:12 h LD photoperiod at 10°-C, 15°C and 20°C to observe the influence of temperature on reproduction. At 10°C plants grew only vegetatively, whereas at 15°C and 20°C they produced unilocular sporangia. Unispores released from sporangia developed into monoecious, anisogamous gametophytes that formed plurilocular female and male gametangia on the same lateral branches. The zygotes, by fusion of female macrogametes and male microgametes, developed into sporophytes bearing unilocular sporangia, whereas the unfused female gametes germinated parthenogenetically. This species was confirmed to have an isomorphic life history, basically similar to the other species of Sphacelariales.     

Sexuelle Fortpflanzung bei der braunen KrustenalgePseudolithoderma extensum

Reproduction was studied inPseudolithoderma extensum (Crouan et Crouan) Lund (Lithodermataceae, Phaeophyceae) from Helgoland. Both gametophytes and sporophytes are crustose. Fertile gametophytes were found in nature in January and February. They released motile isogametes from plurilocular gametangia, each gamete leaving its locule through a separate opening. Plasmogamy was observed directly under the microscope. In laboratory culture, zygotes developed to crustose thalli, whereas unfused gametes died soon after germination. Sporophytes were found in nature with fertile unilocular sporangia in March. In culture, zoospores released from these sporangia also developed to crusts. Kuckuck’s observation at the beginning of the century (1912a) thatP. extensum exhibits an alternation of isomorphic generations and isogamy is thus confirmed.

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Anschrift bis Ende 1989: Instituto de Botánica, Universidad Austral de Chile, Cas. 567, Valdivia, Chile     

MORPHOLOGY AND LIFE HISTORY OF SCYTOSIPHON LOMENTARIA (SCYTOSIPHONACEAE,PHAEOPHYCEAE) FROM THE AZORES1

Morphological and culture studies of Scytosiphon lomentaria (Lyngbye) Link and Microspongium gelatinosum Reinke (Scytosiphonaceae, Phaeophyceae) were undertaken on material collected on the Island of São Miguel, Azores, where both species were commonly found. Erect thalli of S. lomentaria collected in the field were up to 33 cm long and 2.3 mm wide, tubular, hollow, and commonly constricted at intervals. The plurilocular sporangia were positioned in continuous sori on the thallus surface. Ascocysts were present. In the field, M. gelatinosum formed crustose to slightly pulvinate plants, were spongy in texture, and dark brown to black in color, which were circular or irregularly spreading over several centimeters and firmly attached to the substratum. Sessile unilocular sporangia were located in sori on the crust surface. In culture S. lomentaria plurispores developed into Microspongium‐like crustose prostrate thalli that formed unilocular sporangia. Unispores developed into new erect thalli that formed plurilocular sporangia. Sexual reproduction was not observed. In culture, M. gelatinosum unispores developed into erect thalli identical with S. lomentaria. These results are similar to those reported for other areas and suggest the occurrence in the Azorean plants of a monophasic and heteromorphic life history, involving both entities studied.     

Growth and reproduction of Scytosiphon lomentaria (Fucophyceae) in relation to temperature in two populations from Denmark

Two strains of Scytosiphon lomentaria from Denmark have been grown under long-day conditions on a temperature-gradient plate. The material from north-west Jutland (strain No. 46) has a reduced prostrate system (a few-celled lump) whereas the other material from the Sound (strain No. S41) has a well-developed crust. This difference plays a significant role in growth and reproductive patterns. Strain No. 46 rapidly produces a great number of cylindrical macrothalli. Within a four-week experimental period, formation of swarmers from plurilocular sporangia on the macrothalli takes place and results in a maximum dry weight of 32.9 mg at 18.2°C.
Swarmers from the macrothalli of strain S41 always develop into knot-filamentous or crust-shaped thalli. The development of the macrothalli, therefore, takes a longer time than in strain 46 and the maximum dry weight is only 16.5 mg at 16°C even within an experimental period of six weeks. The reproductive pattern is more complex than in strain 46. The crusts produce unilocular sporangia at temperatures between 16°C and 23.8°C, and function, therefore, as the reproductive system during the summer as macrothalli disappear at temperatures above 18°C both in nature and in culture. Formation of plurilocular sporangia on macrothalli starts when they are from 6–9 weeks old at temperatures between 11°C and 18°C.
The temperature range for growth in the two strains also differs: Strain 46 grows from 7.3–24.4°C while strain S41 grows at least from 4–5.1°C to an upper limit of 27.1°C, but lower limit has not been determined precisely in the present experiment. These results indicate that temperature ecotypes exist, even within a limited geographic area.     

Life history of Japanese Stypocaulon durum (Sphacelariales, Phaeophyceae)

Phenology, morphology, life history and responses to different temperature and photoperiod conditions were studied in Japanese Stypocaulon durum (Ruprecht) Okamura. Erect thalli of the species were collected year-round, but the mature thalli forming either uniloc-ular sporangia or two different types of plurilocular structures (evidently gametangia) on separate thalli were found only in winter. ln culture, an isomorphic life history is suggested for the species, alternating between a sporophyte forming unilocular sporangia and gam-etophytes forming plurilocular macro- (female) and micro- (male) gametangia. Contents of unilocular sporangia were not released, but germinated in situ, developing into erect thalli forming plurilocular gametangia. Macrogametangia released aplanogametes (oospores), but male gametangia appeared to be non-functional, although flagellated cells were once formed in the loc-uli. This is the first report of plurilocular gametangia in the species. Although the species grew well and matured under considerably lower temperature conditions than European Stypocaulon scoparium (L.) Sauvageau, its temperature requirements showed similarity to northwestern Atlantic Stypocaulon species. This supports the notion that northwestern Atlantic Stypocaulon is conspecific with S. durum.     

Life histories of Colpomenia sinuosa and Hydroclathrus clathratus (Scytosiphonaceae, Phaeophyceae) in culture

Life-history studies in culture were carried out on Colpomenia sinuosa (Mertens ex Roth) Derbès et Solier and Hydroclathrus clathratus (C. Agardh) Howe (Scytosiphonales, Phaeophyceae) from Japan. These species showed a heteromorphic life-history pattern with an alternation between erect thalli bearing plurilocular zoidangia and prostrate thalli bearing ectocarpoid plurilocular and unilocular zoidangia. Plurizoids released from erect and prostrate thalli developed into prostrate thalli. Unizoids, however, developed into erect thalli. Prostrate thalli produced plurilocular zoidangia in long-day conditions and unilocular zoidangia in short-day conditions at 10-20°C. Prostrate thalli of C. sinuosa formed ascocysts. Germlings of both species did not grow at 5°C.     

First record of Asteronema rhodochortonoides (Phaeophyceae) for the Pacific Ocean

Morphological observations of a minute, filamentous, branched brown alga epiphytic on Sargassum thun‐bergii (Mertens ex Roth) Kuntze were made on material collected at Tsuyazaki (33°48′N, 130°27′E), Fukuoka Prefecture, southern Japan. This alga was assignable to Asteronema rhodochortonoides (Børgesen) Möller et Parodi in having stellately arranged chloroplasts with several pyrenoids grouped in the center, predominantly apical growth, narrow filaments, and elliptical or broadly elliptical plurilocular zoidangia that are apically or laterally formed on upright filaments. A comparison of partial nuclear small subunit rDNA sequences between the Japanese material and A. rhodochortonoides from the Canary Islands showed only two or three nucleotide differences. This supports our assignment of the Japanese material to this species as a first report for the Pacific Ocean. In laboratory cultures, zoids released from plurilocular zoidangia developed into plants with morphology similar to the field‐collected plants. This cycle repeated without production of unilocular zoidangia in our cultures.     

The ship-fouling algaEctocarpus

Summary The unilocular reproductive stages of the brown algaEctocarpus have been examined with the electron microscope. One observation in particular, which is believed to have been made for the first time in Phaeophycean studies, is that the zoospore derived from unilocular sporangia possesses a microanatomy considerably different from that of spores formed by plurilocular sporangia. It is suggested that this difference may have an evolutionary significance and may lead to a better understanding of the life cycle ofEctocarpus.     

Morphology and life history of Coelocladia arctica (Dictyosiphonales,Phaeophyceae), new to Japan*

The occurrence of Coelocladia arctica Rosenvinge (Dictyosiphonales, Phaeophyceae) is reported for the first time in the Pacific Ocean, from Oshoro, Hokkaido, Japan. The field material was approximately 30 mm in height, up to 300 M-μn in diameter, 2-3 times irregularly branched and provided with phaeophycean hairs and plurilocular sporangia. The thallus was composed of several (usually four) large, hyaline, rounded, isodiametric inner cells, with smaller sub-cortical and pigmented cortical cells. The plurilocular sporangia were 3-4 celled, often branched, and protruded from the cortical cells, arranged in a crown-shaped complex. In culture, the plurispores germinated unipolarly leaving an emptied original spore wall, and developed into a branched protonema. Cells of the protonema as well as the erect thallus contained several disc-shaped chloroplasts with pyrenoids. Uniseriate erect filaments arose from the protonema, then became polystichous and formed branches. Unilocular sporangia were never observed in the field or in cultured material. Erect thalli were formed under culture conditions of 5-15°C, and developed a thick parenchyma at 5-10°C, irrespective of the day length.     

REPRODUCTION AND LIFE HISTORY OF THE RED ALGA GALAXAURA OBLONGATA (NEMALIALES,GALAXAURACEAE)1

Culture and morphological studies showed that Galaxaura oblongata (Ellis et Solander) Lamouroux has a triphasic life history with conspicuous gametophytes and small filamentous tetrasporophytes. Development of male and female reproductive structures is very similar and both begin with the enlargement of a terminal cell of a filament branch occupying a normal vegetative position within the apical pit of a thallus branch. In male thalli this modified branch forms a conceptacle in which spermatangia are produced. In female thalli, this modified branch forms a three-celled carpogonial branch consisting of a carpogonium, hypogynous cell and basal cell. Filament branches from the basal cell form a pericarp and the gonimoblast develops directly from the carpogonium. Carposporangia are produced in conceptacles which resemble the male conceptacles. About the time the first carposporangia are produced, the carpogonium, hypogynous cell and basal cell form a large fusion cell. Released carpospores germinate in a unipolar or bipolar manner and form small filamentous thalli. Under short day conditions, cruciate tetrasporangia are produced in small clusters. Tetraspores germinate similarly to carpospores and also form small filamentous thalli. Under low nutrient conditions, small cylindrical thalli develop on the filaments and these appear similar to gametophytes collected in nature.     

Experimental evidence against sexual fusions of spores from unilocular sporangia of Ectocarpus siliculosus (Phaeophyta)

Evidence that sexual fusion does not occur in zoids from unilocular sporangia of Ectocarpus siliculosus is presented as follows: (1) Zoids from various types of unilocular sporangia do not interact with genuine gametes; (2) Aggregates of two zoids, previously claimed to be zygotes, were frequently seen in cultured material but could be demonstrated to be the result of incomplete cell separation during sporogenesis; (3) Culture studies showed that there is no fusion of male and female nuclei in such aggregates.     

Epi-endophytic symbiosis between Laminariocolax aecidioides (Ectocarpales, Phaeophyceae) and Undaria pinnatifida (Laminariales, Phaeophyceae) growing on Argentinian coasts

The present is the first study on epi-endophytic algae on thalli of Undaria pinnatifida growing along Argentinian coasts. The main goal is to describe the nature and the morphology of this symbiosis. Individuals of Laminariocolax aecidioides were detected in both June and December 2004, growing on U. pinnatifida sporophytes. In nature, the epi-endophyte were macroscopically observed as dark zones that partially covered the hosts’ fronds. L. aecidioides vegetative thalli were irregularly branched uniseriate filaments. The life cycle is described from laboratory cultures started from Patagonian populations. Caryology revealed that the sporophytic diploid phase presented 16 chromosomes whereas the gametophytic haploid phase presented 8 chromosomes. Isolates made from thalli growing in the interior of infected hosts developed into filamentous, branched sporophytes that reproduced by both unispores and plurispores that were produced in unilocular and plurilocular sporangia, respectively. The results of this paper also allowed us to conclude that L. aecidioides uses the thalli of U. pinnatifida as a proper substrate. The penetration of endophitic filaments among the host′s cortical cells produced a lateral compression and, finally, their thalli development generated perforations in the host tissues. The effects of the epi-endophytic infection of L. aecidioides on U. pinnatifida are neither severe nor deleterious.