Isomorphic Alternation Of Generations Research Articles

Grateloupia oligoclora (Halymeniaceae, Rhodophyta): a new species from China based on morphological observation, life history and rbcL gene sequence analysis

ABSTRACT A new species of Grateloupia from Wenzhou Nanji Island in Zhejiang province, China, was illustrated based on morphological observation, early development, life history and rbcL gene sequence analysis, and named Grateloupia oligoclora H.W.Wang & Y.Bian sp. nov. The morphological features of this new species can be summarized as upright thalli, solitary or cespitose, dark red in colour, cartilaginous and mucilaginous in texture. The margins of the thalli were smooth, without lateral branches, proliferations, or branched, dichotomously branched or with 3–5 irregular rod-shaped branches. The thalli were consisted of cortex cells (6–9 cell layers) and medulla. The cystocarps were spherical and appeared to be speckled from the surface of the thalli. The carpogonial branch ampullae and auxiliary cell branch were typical Grateloupia-type. During the cruciate dividing of tetrasporangia, some dyads showed asynchronous phenomenon. Type of spore development and life history were typical mediate discal type and isomorphic alternation of generations. Phylogenetic analysis based on rbcL sequence indicated that the new taxon formed an independent clade from other Grateloupia species, and this clade was sister to G. subpectinata Holmes with high interspecific divergence 12 bp (1%), supporting its specific status. Accordingly, G. oligoclora H.W.Wang & Y.Bian sp. nov is proposed as a new species of Grateloupia. This study provides new resource and species diversity of marine Rhodophyta in China.

Early development, life history and ecological habits of Grateloupia constricata Li et Ding

As the largest genus of Halymeniaceae, Grateloupia has been widely reported. Here, we observed the life history and early development of Grateloupia constricata Li et Ding and investigated the effects of temperature, irradiance, and photoperiod on the discoid crust and sporeling development of G. constricata under laboratory conditions. We observed that the type of carpospore development was “mediate discal type”. The life history included homotypic gametophyte (haploid), carposporophyte (diploid), and tetrasporophyte (diploid), with typical isomorphic alternation of generations. The results of double factorial analysis showed that both single factorial effects and interaction among temperature, photoperiod, and irradiance were obviously significant on the discoid crust and sporeling development. Furthermore, we found that the optimum combination of condition for the early growth and development of G. constricata was temperature 20°C, irradiance 80 µmol photons/(m2·s) and photoperiod 16L:8D. This study provides the theoretical basis and technical support for the conservation of the Grateloupia germplasm, artificial breeding, large-scale cultivation and sustainable development.

Early evolution of life cycles in embryophytes: A focus on the fossil evidence of gametophyte/sporophyte size and morphological complexity

Embryophytes (land plants) are distinguished from their green algal ancestors by diplobiontic life cycles, that is, alternation of multicellular gametophytic and sporophytic generations. The bryophyte sporophyte is small and matrotrophic on the dominant gametophyte; extant vascular plants have an independent, dominant sporophyte and a reduced gametophyte. The elaboration of the diplobiontic life cycle in embryophytes has been thoroughly discussed within the context of the Antithetic and the Homologous Theories. The Antithetic Theory proposes a green algal ancestor with a gametophyte-dominant haplobiontic life cycle. The Homologous Theory suggests a green algal ancestor with alternation of isomorphic generations. The shifts that led from haplobiontic to diplobiontic life cycles andfromgametophytictosporophyticdominancearemostprobablyrelatedwithterrestrialhabitats.Cladisticstudies strongly support the Antithetic Theory in repeatedly identifying charophycean green algae as the closest relatives of land plants. In recent years, exceptionally well-preserved axial gametophytes have been described from the Rhynie chert (Lower Devonian, 410 Ma), and the complete life cycle of several Rhynie chert plants has been reconstructed. All show an alternation of more or less isomorphic generations, which is currently accepted as the plesiomorphic condition among all early polysporangiophytes, including basal tracheophytes. Here we review the existing evidence for early embryophyte gametophytes. We also discuss some recently discovered plants preserved as compression fossils and interpreted as gametophytes. All the fossil evidence supports the Antithetic Theory and indicates that the gametophytic generation/sporophytic generation size and complexity ratios show a gradual decrease along the land

The Genus Martensia Hering (Delesseriaceae, Rhodophyta) with M. albida sp. nov. and M. flammifolia sp. nov. on Jeju Island, Korea

The genus Martensia (Delesseriaceae, Rhodophyta) is characterized by thalli composed of one to several blades that consist of proximal membranous sections and distal latticework. Nerves or veins are absent in the membranous sections. The life cycle of Martensia is accomplished by isomorphic alternation of generations. The gametophytes of Martensia are dioecious, and the male and female gametangial plants are morphologically similar. The type species of Martensia is M. elegans Hering. In this study, nine species were confirmed to occur in the subtidal regions of Jeju Island, Korea: M. albida sp. nov., M. australis Harvey, M. bibarii Y. Lee, M. elegans Hering, M. flammifolia sp. nov, M. fragilis Harvey, M. jejuensis Y. Lee, M. palmata Y. Lee, and M. projecta Y. Lee. Three of these, M. australis, M. fragilis, and M. elegans, are new records in the flora of Korea. The results of molecular analyses of the internal transcribed spacer (ITS) 1 region in the nrDNA showed that M. elegans is identical to M. australis, and M. fragilis coincides with M. bibarii. It may be a less effective tool for the species discrimination in Martensia.

Reproductive patterns of Caloglossa species (Delesseriaceae, Rhodophyta) from Australia and New Zealand: multiple origins of asexuality in C. leprieurii. Literature review on apomixis, mixed-phase, bisexuality and sexual compatibility

SUMMARY Reproduction and life history patterns in culture of five Caloglossa speaes from Australia and New Zealand are compared. Caloglossa adhaerens King et Puttock and Caloglossa bengalensis (Martens) King et Puttock have a Polyslphonla-type sexual life history (P-type, isomorphic alternation of generations). Caloglossa monosticha Kamiya occurs only in Western Australia (WA) and is a P-type. Caloglossa ogasawaraensis Okamura occurs in WA, Northern Territory (NT), Queensland (QLD), New South Wales (NSW), Victoria (VIC) and South Australia (SA) and is for the most part a P-type in culture. A few isolates have bisexual gametophytes that are self-compatible, while most are unisexual. Caloglossa ogasawaraensis from Adelaide, SA and from Wilsons Promontory, VIC are new records for these States. In Australia, Caloglossa postiae (King et Puttock) Kamiya et King occurs in NSW, NT and QLD. All nine isolates are P-type. Isolates of Caloglossa leprieurii (Montagne) G. Martens from NSW, NT, QLD, Tasmania, VIC and New Zealand are P-type except for the freshwater isolates in which tetraspore germlings do not reproduce. In some isolates mixed-phase reproduction is seen with male gametophytes producing both viable spermatia and tetrasporangia and female gametophytes producing procarps and sori with non-dividing sporangia. All isolates of C. leprieurii irom Spencer Gulf and Gulf of St Vincent, SA and one isolate from QLD give rise to successive asexual generations of tetrasporophytes. Based on RuBisCO spacer DNA data an asexual life history has arisen several times in the C. leprieurii complex. The literature on apomixis, mixed-phase reproduction, bisexuality and sexual compatibility in red algae is surveyed.

Ecology and the Evolution of Biphasic Life Cycles.

Sexual eukaryotes undergo an alternation between haploid and diploid nuclear phases. In some organisms, both the haploid and diploid phases undergo somatic development and exist as independent entities. Despite recent attention, the mechanisms by which such biphasic life cycles evolve and persist remain obscure. One explanation that has received little theoretical attention is that haploid-diploid organisms may exploit their environments more efficiently through niche differentiation of the two ploidy phases. Even in isomorphic species, in which adults are morphologically similar, slight differences in the adult phase or among juveniles may play an important ecological role and help maintain haploid-diploidy. We develop a genetic model for the evolution of life cycles that incorporates density-dependent growth. We find that ecological differences between haploid and diploid phases can lead to the evolution and maintenance of biphasic life cycles under a broad range of conditions. Parameter estimates derived from demographic data on a population of Gracilaria gracilis, a haploid-diploid red alga with an isomorphic alternation of generations, are used to demonstrate that an ecological explanation for haploid-diploidy is plausible even when there are only slight morphological differences among adults.

Dudresnaya kuroshioensis sp. nov. (Dumontiaceae, Rhodophyta) from Japan

The marine red alga Dudresnaya kuroshioensis sp. nov. (Dumontiaceae, Rhodophyta) is described from southernmost Honshu, Japan. It is a deep-water species with the following characters: terete, radially branched and not villose thalli, hexagonal crystals in axial cells, hairs, distinct primary axes, cylindrical outer cortical cells, rhizoids up to 21 μm in diameter, carpogonia once obliquely or transversely divided, a distinctly cleft cystocarp and an isomorphic alternation of generations. It lacks annulations in young branches, indeterminate-axis primordia, rhizoids with cortical laterals, a mucilage coat around the carpogonial and auxiliary-cell filaments; gonimoblast initials mayor may not be recurved around their auxiliary-cell filaments.Dudresnaya kuroshioensis is compared to Japanese, Austral-Pacific and North American species that most resemble it anatomically but differ in at least one significant character. It is concluded that the Australian D. capricornica is probably the closest relative of the new species, differing mainly in overall size, rhizoid diameter and the anatomy of the mature cystocarp.

ALTERNATION OF GENERATIONS IN LAND PLANTS: NEW PHYLOGENETIC AND PALAEOBOTANICAL EVIDENCE

SummaryCurrent ideas on the evolution of alternation of generations in land plants are reviewed in the context of important recent advances in plant systematics and the discovery of remarkable new palaeobotanical evidence on early embryophyte life cycles. An overview of relationships in major groups of green plants is presented together with a brief review of the early fossil record as a prelude to discussing hypotheses of life cycle evolution. Recent discoveries of life cycles in the early fossil record are described and assessed. The newly discovered gametophyte and sporophyte associations are based on exceptionally well‐preserved material from the Rhynie Chert, Scotland (Middle Devonian: 380–408 Myr) and compression fossils from other Devonian localities. These data document diplobiontic life cycles in plants at the ‘protracheophyte’ and early tracheophyte level of organization. Furthermore, the early fossils have a more or less isomorphic alternation of generations, a striking departure from life cycles in extant embryophytes. This unexpected similarity between gametophyte and sporophyte calls for a cautious approach in identifying ploidy level in early groups. Viewed in a systematic context, the neontological and palaeontological data contribute towards the formulation of a coherent hypothesis of life cycle evolution in major, early embryophyte groups. Evidence from extant groups strongly supports a single direct origin of the diplobiontic life cycles of land plants from haploid, haplobiontic life cycles in ancestral ‘charophycean algae’. The interest of the new palaeobotanical data lies in its relevance to life cycle evolution at the restricted level of vascular plants rather than at the more general level of embryophytes (vascular plants plus ‘bryophytes’). The occurrence of morphologically complex, axial gametophytes in early vascular plants is consistent with the moss sister‐group proposed in some cladistic analyses. Similarities of moss gametophytes to fossils in the vascular plant stem‐group are discussed, and it is argued that the late appearance of mosses in the macrofossil record may be due to the problem of recognizing stem‐group taxa. The new palaeobotanical evidence conflicts with previous hypotheses based on extant groups that interpret morphological simplicity as the plesiomorphic condition in the gametophytes of vascular plants. These new data indicate that a significant elaboration of both gametophyte and sporophyte occurred early in the tracheophyte lineage, and that the gametophytes of extant ‘pteridophytes’ are highly reduced compared to those of some of the earliest ‘protracheophytes’. Vestiges of this early morphological complexity may remain in the gametophytes of some extant groups such as Lycopodiaceae.

Dudresnaya okiensis sp. nov. (Dumontiaceae, Rhodophyta) from the Sea of Japan

The marine red alga Dudresnaya okiensis sp. nov. (Dumontiaceae, Rhodophyta) is described from the Sea of Japan. It is a deep-water species with the following characters: terete, radially branched thallus, with annulations in young branches, hexagonal crystals in axial cells, hairs, distinct primary axes, cylindrical outer cortical cells, rhizoids up to 36 μm in diameter and bearing cortical laterals, carpogonia once or twice obliquely divided, and an isomorphic alternation of generations; lacking indeterminate-axis primordia, a mucilage coat around the carpogonial and auxiliary-cell filaments, and distinctly cleft cystocarps; and with gonimoblast initials that may or may not be recurved around their auxiliary-cell filament.

Water-Conducting Cells in Early Fossil Land Plants: Implications for the Early Evolution of Tracheophytes

Wall structure in the water-conducting cells of Rhynia gwynne-vaughanii and Asteroxylon mackiei from the Lower Devonian Rhynie Chert was examined and compared using thin sections and scanning electron microscopy of etched sections. Although the internal thickenings of these cells are superficially similar in both plants, there are significant differences in other aspects of wall structure. The tracheids of A. mackiei are shown to be of a basic type (G-type) that is common in some early land plant fossils such as zosterophylls and lycopods, and they are comparable to protoxylem elements in some extant `pteridophytes'. The "tracheids" of R. gwynne-vaughanii are more similar to another kind of water-conducting cell (S-type) that combines certain features of tracheids and moss hydroids. The S-type cell is known from two other Lower Devonian sporophytes, Stockmansella langii and Huvenia kleui, supporting recent suggestions that these three taxa form a natural group. S-type cells are also found in the gametophyte Sciadophyton sp. as well as two taxa, Sennicaulis hippocrepiformis and Taeniocrada dubia, for which reproductive structures are unknown. The water-conducting tissues of other early land plants are briefly reviewed and detailed reconstructions of the S-type and G-type cell are provided. A preliminary cladistic analysis focusing on the Rhyniophytina of Banks results in the recognition of a `protracheophyte' grade, as well as a small clade, the Rhyniaceae, comprising Rhynia, Stockmansella, and Huvenia. If the tracheid-like features of S-type and G-type cells are regarded as homologous, then the Rhyniaceae are resolved as the basal clade that forms the sister group to all other tracheophytes. The occurrence of a more or less isomorphic alternation of generations in some Devonian `protracheophytes' and the Rhyniaceae implies that the gametophytes of all extant `pteridophytes' are phylogenetically reduced.

The Dumontieae, a resurrected tribe of red algae (Dumontiaceae, Rhodophyta)

Abstract Several monophyletic groups of taxa were produced by a cladistic analysis of all species belonging to the red algal family Dumontiaceae (Gigartinales). One of these groups is recognized here as the tribe Dumontieae. It consists of the species of Dumontia, Crypto siphonia, Hyalosiphonia, Masudaphycus gen. nov., Neodilsea, and Dilsea, all found in the North Pacific with some spillover into the North Atlantic. Dasyphloea insignis, the only species of an endemic, southern Australian genus, is included in the Dumontieae with reservation. An explicit hypothesis of phylogenetic relationships, based mostly on morphological features, is presented for all species of the Dumontieae. The primitive condition in the tribe is hypothesized to be a relatively short carpogonial branch (no more than 11 cells long), an anticlinal–periclinal pattern of division of periaxial branches, an alternation of isomorphic generations, a lateral trichogyne, the carpogonium not always dividing after fertilization, relatively lar...

Observations on marine Chaetophoraceae (Chlorophyta)

Abstract Three species of the genus Entocladia Reinke, E. viridis Reinke, E. wittroekii Wille, and E. eodicola Setchell et Gardner, and the type species of the genus Epicladia Reinke, E. flustrae Reinke, are described in nature and culture from material collected on the Atlantic and Pacific coasts of North America. A sexual life history involving an alternation of isomorphic generations is demonstrated for E. viridis and E. codicola. Sequential cleavage of sporangial and gametangial mother cell contents occurs in all four species. Setae appear in allisolates of Entocladia and Epicladia examined, but some isolates produce them rarely or unpredictably. The circumscription of the genus Entocladia is reviewed on the basis of these and other recent findings. The genera Ectoehaete (Huber) Wille and Epicladia are considered synonymous with Entocladia, which is in turn considered distinct from Phaeophila Hauck and Aeroeheate Pringsheim.

Observations on the life history of Membranoptera multiramosa Gardner (Rhodophyceae, Ceramiales) in culture

Abstract Membranoptera multiramosa Gardner was maintained in unialgal culture and was observed to have a life history involving alternation of isomorphic generations typical of the higher Florideophycidae. Although existing reports state that members of the Delesseriaceae are always dioecious, this cultured material was found to be monoecious.

LIFE HISTORY STUDIES OF THE PACIFIC COAST MARINE ALGA, COLLINSIELLA TUBERCULATA SETCHELL AND GARDNER

Culture studies of a marine green alga, described from the Pacific Coast of North America as Collinsiella tuberculata Setchell and Gardner, have shown it to be a stage in the life history of a form of Enteromorpha intestinalis (L.) Link. The Collinsiella-stage is thought to be the sexual phase, or a basal remnant of the Enteromorpha-stage, and produces biflagellate gametes. The typical tubular thallus of Enteromorpha has been grown in culture from zygotes of the Collinsiella-stage and zoospores of the Enteromorpha-stage. Parthenogenetic development of gametes is also indicated. Some of the tubular plants produce biflagellate gametes which cannot be distinguished from those of the Collinsiella-stage. Others produce quadriflagellate zoospores, which may be meiospores or mitospores. An accessory method of reproduction by quadriflagellate mitospores (neutral spores) occurs and this asexual cycle has been carried through three successive generations in culture without an intervening sexual phase. Tubular thalli of Enteromorpha inteslinalis (L.) Link producing biflagellate gametes during the spring and early summer and quadriflagellate zoospores during the late summer are found in nature in the same area from which the Collinsiella-stage was obtained. These are believed to represent in nature the normal sexual life cycle of this plant, which has been reported to have an alternation of isomorphic generations. The possible relationships between the stages obtained in culture and those observed in nature are discussed. A number of hypothetical conclusions have been drawn with respect to the systematic position of the genus Enteromorpha and related genera. These studies are being continued to clarify several unknown aspects brought out by this preliminary study. A cytological study is being undertaken to substantiate the conclusions drawn from the morphological data.