Life history and cytological studies in Bryopsis flanaganii (Bryopsidales, Chlorophyceae) from the Natal Coast I.S. Harper and R.N. Pienaar Department of Botany, University of Natal, Pietermaritzburg Bryopsis flanaganii Barton from the Natal coast appears to Introduction possess a monophasic life history in culture. Gametangia are Members of the siphonaceous green algae (Bryopsidales, formed from lateral branches and release anisogametes. according to Silva 1982) are characterized by a multinucleate Zygotes germinate immediately and develop into erect siphons similar to those of the parent thalli. These germlings coenocytic thallus. Development of the septa occurs only at do not, however, produce lateral branches under laboratory the base of gametangia or sporangia during the reproductive conditions. Nuclear divisions occurring during the formation phase, or in response to wounding. Septa may also occa­ of the gametes are mitotic and the chromosome number of sionally be laid down in older parts of the thallus. Early texts B. flanaganii is 11 . The chromosomes form an equatorial (Fritsch 1935; Smith 1955; Chapman 1964) reported that the plate at metaphase and separate at anaphase leaving behind life history of these algae was gametic with a single diploid a persistent interzonal spindle. The nucleus of the zygote is characteristically large and persistent. gametophyte phase. Cytological evidence in support of such S. A fr. J. Bot. 1985, 51: 401 - 407 gametic life histories has, however, only been provided for Codium (Williams 1925; Schussnig 1950) and Derbesia Bryopsis flanaganii Barton van die Natalse kus het (Neumann 1969a; Rietema 1972), while the evidence for waarskynlik 'n enkelfase-lewensiklus onder kultuurtoestande. Caulerpa (Schussnig 1939) has been questioned (Goldstein & Gametangia word op sytakke gevorm en stel anisogamete Morrall 1970). Furthermore the reports of gametic meiosis vry. Sigote ontkiem dadelik en ontwikkel tot regopstaande sifone soortgelyk aan die van die moedertalli. Hierdie in Bryopsis (Neumann 1969b) and Caulerpa (Price 1972) kiemlinge vorm egter nie sytakke onder laboratorium­ remain questionable as they were presented without adequate toestande nie. Kerndelings wat tot gameetvorming lei, is substantiation of the results (Tanner 1982). mitoties en die chromosoomgetal van B. flanaganii is 11 . Die Following the discovery of an alternation of generations chromosome vorm 'n ekwatoriale plaat tydens metafase, skei between Bryopsis halymeniae Berthold and Derbesia neglecta tydens anatase en vorm 'n stabiele intersonale spoel. Die Berthold (Hustede 1964), numerous reports have been kern van die sigoot is kenmerkend groot en blywend. published describing the life history of various species of S.-Afr. Tydskr. P/antk. 1985, 51: 401-407 Bryopsis. At present four types of life history are known for Keywords: Bryopsis flanaganii, green alga, life history, different species of Bryopsis in culture. mitosis (i) A heteromorphic, biphasic (diplobiontic) life history, where a gamete-producing Bryopsis phase (B. halymeniae) alternates with a stephanokont wid­ producing Derbesia phase (D. neglecta) (Hustede 1964). (ii) A heteromorphic, biphasic life history, where an erect gametophyte (recognizable as Bryopsis) alternates with a prostrate, microthallic sporophyte. This type of life history is known for some populations of B. plumosa (Huds.) Ag. (Rietema 1969, 1970; Tatewaki 1973; Commemorating the 75th Anniversary Richardson 1982), B. hypnoides Lamouroux (Rietema of the University of Natal 1971b; Diaz-Piferrer & Burrows 1974), B. monoica Funk (Rietema 1971a), B. maxima Okam. (Tatewaki 1973), B. ryukyuensis Yamada (Tatewaki 1977) and B. lyngbyei I.S. Harper* Homemann (Kommann & Sahling 1976). In these species Present address: Institute for Electron Microscopy, M.R.C., the microthallic phase releases stephanokont zoids P.O. Box 70, Tygerberg, 7505 Republic of South Africa (stephanospores) which germinate to re-establish the R.N. Pienaar** gametophyte generation. Department of Botany, University of Natal, P.O. Box 375, (iii) A monophasic (haplobiontic) life history similar to the Pietermaritzburg, 3200 Republic of South Africa above life history involves the formation of a microthallic *To whom correspondence should be addressed phase from the released gametes. These microthalli, how­ **Reprints ever, develop directly into the Bryopsis phase with the apparent absence of stephanospores. Populations of Accepted 27 June 1985 B. plumosa (Neumann 1969b; Rietema 1969, 1970) and 402 S.-Afr. Tydskr. Plantk. , 1985 , 51 (6) Figures 1-9 (I) General habit of Bryopsis f/anaganii. (2) Detail of the determinate lateral branches showing their characteristic distichous and overlapping arrangement. (3) Lateral branch in the vegetative stage with cytoplasm continuous between branch and main axis. (4) Septum formation at the base of the lateral branches (arrows). (5) Mature basal septum. Note the presence of vacuolar material (arrows) from which the septum is formed. (6) Initial stages in cytoplasmic cleavage, showing small clear regions (arrows) in the gametangia! cytoplasm. (7) Later stages in cleavage illustrating the characteristic fenestrate patterning within the gametangia. (8) Completed cleavage and the formation of motile gametes in dark green female gametangia. (9) Orange-brown male gametangia on a separate plant. Note the cup-shaped scars (arrows) remaining after the gametangia have become detached. S. Afr. J. Bot. , 1985, 51(6) 403 B. hypnoides (Rietema 1971b) exhibit this type of life were consistently obtained with several populations isolated history. over a period of two years from two collection sites. (iv) A heteromorphic, monophasic life history has been Bryopsisflanaganii grows in tufts (Figure 1) with erect axes reported for a population of B. hypnoides by Bartlett arising from a common basal area consisting of an interwoven & South (1973) . In this case the microthallic phase is mass of rhizoids. The determinate lateral branches arise from initially able to reproduce itself via the release of the terminal region of the main axis and commonly have a anisogametes but this later develops directly into the curved and overlapping appearance (Figure 2). During Bryopsis phase. vegetative growth the cytoplasm of the lateral branches is continuous with that of the main axis (Figure 3), but at the There is evidence that the particular type of life history may onset of the reproductive phase a septum is laid down at the be related to the habitat in which the plants grow. Biphasic base of those lateral branches which develop into gametangia life histories are associated with tropical to subtropical regions, (Figure 4) . Occasionally some lateral branches remain and the monophasic life history appears to be restricted to vegetative between the gametangia. The gametangia usually temperate latitudes in the northern hemisphere. To date no undergo synchronous reproductive differentiation. Electron information is available on the life history of any species of and light microscope observations of sectioned material reveal Bryopsis from the southern hemisphere. The aim of this article that the septa are laid down from vacuolar material which is to report on the life history and cytology of Bryopsis is proteinaceous and phospholipoid and can be seen in the flanaganii Barton from the subtropical waters of the Natal living thalli (Figure 5) (Harper 1983). south coast. Following septum formation the gametangia become darker in colour (Figure 6) as a result of chloroplast and nuclear Materials and Methods division (Harper 1983). Small clear regions develop in the Bryopsis flanaganii, identified from the type description by cytoplasm representing the initial stages of cleavage of the Barton (1895), was collected at monthly intervals from Widen­ cytoplasm into gametes. Further cleavage results in the ham (30°52' E, 30° 12' S) and Rocky Bay (30°47' E, 30°21' S) formation of a distinctly fenestrated pattern (Figure 7) and on the Natal south coast, from May 1982 to June 1983. Epi­ at this stage the gametes are visible as compact spheres. This phytes and molluscs were removed from the material, which stage is indicative of 8- 10 h before the release of gametes. was then divided into small tufts and placed into 10-15-1 Cleavage of the gametes is completed 2-4 h before gamete aquaria or into 2-1 Erlenmeyer flasks containing half strength release which occurs at the onset of the light period. The Provasoli enriched seawater (P.E.S.). Cultures were con­ cleaved gametes fill the entire gametangium resulting in the tinuously aerated. Those grown in Erlenmeyer flasks were gametangia being a darker colour than the vegetative lateral placed in a Conviron environmental chamber and subjected branches. Female gametangia have a dark green colour (Figure to an alternating 10L: 14D cycle, 20 and illuminated with oc 8) and the male gametangia, which are borne on separate cool white fluorescent tubes (25- 50 !-!Em - 2s- 1), conditions plants, are orange-brown (Figure 9). similar to those experienced by the algae in their natural Shortly before the onset of the light period the gametes habitat. The aquaria were placed near a north-east facing become actively motile and their shape changes from distinctly window in a laboratory with an ambient temperature at 20 spherical to elliptical. The initiation of motility is not always ± 3 oc. The growth medium was changed at fortnightly synchronous and often proceeds from the distal to the intervals. proximal region