West: Life history of Rhodochorton membranaceum I I I

Botanica Marina Vol. XXII, PP' 111- 115,1979

The Life History of Rhadochorton membranaceum , an Endozoic Red Algal l .A. West

Department ofBotany , University ofCalif ornia, Berkeley, California 94720, USA

(Received April S, 1978)

Abstract Two clones of Rhodochorton membranaceum Magnus were isolated into unialgal culture from hydroids collected subtidally in Puget Sound , Washington (USA) during July and August, 1972 . Tetr asporangia were formed on the upright branches. The tetraspores produced 1- 4 germ tubes which gave rise to a basal system .When these basal filaments contacted chitin, they penetrated and grew between the layers, forming a distinctive basal system con­ sisting of compressed and lobed cells. No difference was observed between basal systems formed in insect chitin and hydroid chitin. The basal system of plants not grown in contact with chitin consisted of unoriented, narrow, elongate , irregularly branched filaments very different from those of the endozoic system. The plants derived from tet raspores produced tetrasporangia in all conditions tested . No evidence of was obt ained. Although repro­ duct ively similar to R . concrescens Drew and R . penicilliforme (KjeUman) Rosenvinge, R. memb ranaceum appears to be taxonomically distinct because of its endozoic basal system.

Introduction Ma terials and Methods

Rhodochorton membranaceum Magnus is a marine red Rhodochorton membranaceum was evident as fmc , red alga (Acrochaetiaceae, Nemaliales) occurring principally to pink patches on the axes of the hydroids Selaginopsis in hydroid s. It consists of an endozoic filamentous basal pinnata and Tubularia crocea obtained by dredging from system which ramifies between the layers of chitin in 12-18 meters depth at Partridge Bank, West of Whidbey the hydroid perisarc and gives rise to upright branched Island. Washington. 4 July 1972. It was also present on filaments which bear tetrasporangia. This species has a Selaginopsis mirabilis and Sertularia tricuspidata dredged broad distribution in the northern hemisphere. occur­ from 12-16 meters depth at Hein Bank , South of San ring primarily in the cooler waters on both sides of the Juan Island, Washington, 4 August 1972 . These plants North Atlantic (Woelkerling 1973) and in the Eastern were generally not reproductive . Two related Nort h Pacific (Drew 1928). It is also kno wn from occurred with Rhodochorton m em branaceum on these Mediterranean France (Ollivier 1929) . In the southern hydroids - Rhodochorton concrescens Drew, which hemisphere it is recorded from New Zealand (Chapman forms an epizoic discoid basal system and Acrochaetium 1969) and the Anta rctic Peninsula (Moe and DeLaca pectinatum (Kylin) Hamel, with an endozoic system 1976). Fossil deposits dated at 11,000 years from the similar to that of R . m em brana ceum. They also were Champlain Sea (Ottawa, Canada) contain hydroids with isolated into culture and appear similar morphologically pink endozo ic filament s resembling R . mem branaceum and reproductively to clones isolated and studied earlier (Illman et al. 1970). Despite its abundance no previous (West 1968, 1970). The cultured plants of R. membrana­ culture studies have been undertaken. It is reasonable ceum were isolated using tech niques described for to presume that certain of the tetrasporangiate, micro­ R . concrescens (We st 1972) . scopic, filamentous forms currently placed in the Acrochaetiaceae possibly represent alternate phases in To test the responses to a chitin substrate , insect chitin the life histories of other macroscopic or microscopic flakes (C grade, Calbiochem, La Jolla, California) and red algae. This study was undertaken to establish whether segments of Selaginopsis were autoclaved and placed in R. membranaceum is such a form . the culture vessel. Tetr asporanglate plants were placed on the chitin until sporelings were established and had 1 This paper was presented at the VIIIlntemational Seaweed Sym posium August, 1974. penetrated the chitin.

0006-8055/79 /00 22-0111502.00 © by Walter de Gruyter & Co. . Berlin · New York 112 West: Life history of Rhodochorton membranaceum

Stock cultures were maintained at wOe, 16:8" daily into successive layers of the chitin (Fig. 5, 8). Whe n cells photoregirne. 200- 500 lux. cool white tluorescent of adjacent endozoic branches make contact, they lighting, in 1/2 or full strength Provasoli's enriched adhere together (Fig. 6,9) although they do not exhibit seawater medium adjusted to 30%0 salinity. Exper­ cytoplasmic fusion as do cells of R hodochorton con· imental cultures were grown in similar conditions ex­ crescens and R . penicilliforme (Rosenvinge 1923- 24, cept for increased light intensity (1000- 1500 lux). West 1970). In R. membranaceum the adhesion results in a complex network of basal filaments. Adhesion does not occur between cells of the nonendozoic basal Observations system. No morphological difference was observed gem ination between the basal systems formed in insect and hydroid chitin. The e-ndozoic system often becomes extensive The tetraspores are spherical, 9.5-12 ~m in diameter and non-amoeboid, immediately following discharge and compact before erect filaments emerge (Fig. 6). At (Fig. 4). The germinating spore does not usually divide; other times erect filaments develop quickly (Fig. 9). In instead, it enlarges up to twice its initial diameter, devel­ culture an endozoic system often develops secondarily ops a wall and sends out one or two germ tubes (Fig. 4). when free basal filaments penetrate the chitin. Occasionally up to five germ tubes develop successively (Fig. 3) or the original spore divides once or more Erect system (Fig. I , 2). The germ tubes generally form narrow rhiz­ In field-collected specimens the erect branches are oidal filaments 4.5-6/lm in diameter (Fig. I). Larger generally determinate, short, and unbranched except for diameter germ tubes are also produced and these appear lateral sporangia. In culture these axes tend to be longer similar to the erect branches (Fig. 2). In culture the (up to 2 mm) and indeterminate. As with field-collected percentage of germination is quite low-less than 5 %. specimens, cultured specimens have erect axes with short Many liberated appear to be lysed by bacteria. sporangial branches. These may revert to vegetative branches when low light intensity repressessporangial Basal sy stem formation . When the sporeling is not in contact with a chitin substrate the rhizoidal filaments generally are narrow, Tetrasporangia elongate, irregularly branched, unoriented and limited Even though the developmental pathway of the basal in growth (Fig. 3). Branches are formed which differ­ system is strongly influenced by substrate, the repro­ entiate into erect filaments 6- 7.5 urn in diameter and ductive cycle is not. Tetrasporangia form in both free form tetrasporangia (Fig. 3). At times the basal system living and endozoic plants. When plants are grown in consists of a tight knot of cells from which erect fll­ association with a chitin substrate , tetrasporangia are aments are derived (Fig. 2). borne only on the emergent upright filaments. The When the basal filaments contact chitin, they penetrate emergent filaments are short (1- 2 cells) or longer (up the substrate and undergo a marked change in morphol­ to 20 cells) with tetra sporangia pedicellate or sessile and ogy (Fig. 4). As the filaments grow between the layers lateral or terminal on the main axis. Internal and lateral of chitin the cells become compressed (Fig. 5), up to proliferation occurs, usually no more than three times 12/lffi wide and 4-5 urn thick, with length being quite at the same locus. Frequently new vegetative axes grow variable and each cell developingelaborate lateral and out through the empty sporangia. The tetrasporangia terminal digitate processes (Fig. 7, 8). These cells are are ovoid or globose, somewhat variable in size 13- 16 quite different from the cylindrical cells of non-endozoic (18) 11m X 19-24 (29) /lm and decussately or cruciately basal filaments. The filaments penetrate and expand divided (Fig. 10, II). Although tetr asporangia are quite

Fo r F ig. 1,2, 4,9,10 use magn ificat ion scale in Fig. I. For Fig. 7 and 8 use magnification scale in Fig. 7. I. Sporeling with two germ tu bes from 3-ceUed spore. 2. Sporeling wit h cell mass derived from spore producing several germ tubes. One germ tube differentiating into erect axes with terminal tetrasporangium . 3. Mature free-living sporeli ng bearing numerous tetrasporangia, Original spore with four germ tubes. Note the disorg anized nature of the basal system. 4. Sporeling developing on insect chit in. Undivided spore with two germ tubes, one of which has penetrated chitin to form endozoic basal system. Note th e smaller recently released spore(s). 5. Cross sectio n of insect chitin flake with two successive endozoic layers (A and B). 6. Surface view of anastomosing filam entous reticulum of the endozoic system . 7. Actively growing cells of endozo ic system are extensively lobed. 8. Otder sector of endozoic ~ stem with filaments growing in two layers (A and B). Note conspicuous nucleus in each cell. 9. Young end ozo ic plant der ived from spore(s). Erect filaments developing at upper surface of chitin. 10. Erect axes bearing lateral tetrasporangia. II . Tetrasporangia and vegeta tive cells with numerous chloroplasts in each cell.

Botanica Marina / Vol. XXII / 1979/ Fasc. 2 West: Life history of Rhodochorton membranaceum 113

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Botanica Marina / Vol. XXII / 1979 / Fasc. 2 114 West: Life history of Rhodochorton membranaceum

uncommon on my field-collected mat eria l, the y arc In 1<. membranaceum it is endozoic and lacks cell fusion pro duced profusely on endozoic and free -living plants where as that of R . concrescens and R . penicillif orme is in cult ure. endozoic and exhibits cell fusion. Furthermore , the The monosporangia reported by Chapman (1960) were penultimate cell of the R. concrescens erect axes divides no t observed in eithe r field-collected or cult ured spec­ transversely on ce (West 1970) whereas it does not divide imens discussed here no r have they been repor ted by transversely in R . membranaceum. ot her authors (Kucku ck 1897, Rosenvinge 1923- 24, According to Dixon and Irvine (1977 ) R . concrescens Woelkerling 1973).1 saw only once a cluster of 3-4 and R. spetsbergensis (KjeUman) Kjellman are very JllTI sperrnatan gia-like structures wh ich had discharged similar. Woelkerling (1973) has maintained these as their conten ts. These cells were borne on a plant which separate species, R . concrescens being transferred to also had produce d tet rasporangia. No carpogon ia were Colaconema because it app arently lacks sexual repro­ seen during the six years these plants have been cultured . duction , and R. penicil/iforme is recognized as a synonym of R . spetsbergense (Kjellman) Kjellrnan and placed in Cytology the sexually reproducing genus A udo uinella. The only Each vegetative cell of th e erect filaments contains a basis for recognition of sexual reprod uction is the single single axial nucleus, 2- 2.5 J.L m in diameter , enclosed by report of spermatangia by Rosenvinge (1923- 24). How­ a layer of starch granules, and about 5- 8 peri pheral ever , this is not suffi cient evidence to warrant the chloro plasts which lack a py renoid and tend 10 be transfer. Rarely have I observed spermatangia-like variable in shape alth ou gh generally they are elongate structures on tetrasporangiate plants of R hodo chorton and flat . Basal filament cells have smaller nuclei and membranaceum but sexual reproduction definitely does fewer chloroplasts, evidently because of their smaller not occur in culture. overall size . The tetrasporangial mother cells have a Among red algae sexual reproduction generally appears larger nucleus (5 JllTI in diameter) and pe rhaps 12 or to be an obligate process, i.e., there are few with speci­ more chloroplasts. alized accessory asexual reproductive structures (ex­ cluding the process of perennation of vegetative basal Life history structures which serves as an important means of survival The complete developmental cycle from spore to spore and regeneration among many red algae). The Aero­ requires one to two mon ths in bright light (1000 lux). chaetiaceae appear exceptional in this respect because Tet rasporangia are less abundant and develop more the vast majori ty of "s pecies" appear to be completely slowly in lower light intensity (less than 500 lux) but asexual, reproducing exclusively by m itotic mono­ as with A crochaetium proskaueri and R hodochorton sporangia , bisporangia or tetrasporangia. At present too concrescens (West 1970 , 1972) there is no influence of little is known to evaluate thi s on a genetic basis but it daylength on sporulation . would seem that asexual reproduction has provided a satisfactory foundation for substantial " speciat ion" in Discussion this ub iquitous group . It appears that a greater number of species in the Woelkerling transferred Rhodochorton membranaceum Acrochaetiaceae reproduce sexually in tropical localities to the genus Colaconema which he earli er ( 197 1) than in temperate and colder waters. Perhap s a greater redeflned> as lacking sexual reprodu ction in cont rast environmental uniformity in the tropics has resulted in with Audouinella in which he includes all species a greater propensity for sexual reproduction and genetic capable of sexual reproduction . Although it is no w variation . apparent that Rhodochorton membranaceum (at least within the clones I have studied) lacks sexual repr oduct­ ion, I choose for the pre sent to retain the binom ial Acknowledgeme nts R hodochorto n mem branaceum becau se of basic cytolog­ ical similarity of this species to other species o f Rhodo­ The specimens used for this invest igatio n were obtained chorton which have tet rasporangia and numerous and isolated during the Summer of 1972 at the University pyrenoidless chloroplasts, More recently Dixon and Irvine of Washington's Friday Harbor Labor at ories. I wish to (J 977) have placed all species of the com plex into the thank the Director, Professor R. L. Fernald for the use genus A udouinella. of these faciliti es. Drs . J . R. Waaland, Tom Mumford and Philip Lebed nik pro vided assistance and advice . Despite certain similarities in thei r life histories, the Dr. William Cooke identified the hydroids in which cytology and morphology of th e basal system clearly Rhodochorton was endozoic. Financial support for this separates R . membranaceum from R . concrescens resear ch was provided partially through NSF grants Drew and R . penicilliforme (Kjellrn an) Rosen vinge. GB-8 192 and GB-40550 and University ofCaIifornia • For a complete d iscussion of Colaconema as originally defined Comm itt ee on Research. Professor G. R. Papenfuss read refer to Papenfus s (194 5). the manuscript and suggested valuable changes.

Botanica Marina / Vol. XXlI / 1979 / Fase . 2 West : Life history of Rh odochorton me m branaceum 115

References

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