Robert W. Hoshaw

PHYLOGENY OF THE CONJUGATING GREEN ALGAE (ZYGNEMOPHYCEAE) BASED ON rbc L SEQUENCES

Sequences of the gene encoding the large subunit of RUBISCO (rbcL) for 30 genera in the six currently recognized families of conjugating green algae (Desmidiaceae, Gonatozygaceae, Mesotaeniaceae, Peniaceae, and Zygnemataceae) were analyzed using maximum parsimony and maximum likelihood; bootstrap replications were performed as a measure of support for clades. Other Charophyceae sensu Mattox and Stewart and representative land plants were used as outgroups. All analyses supported the monophyly of the conjugating green algae. The Desmidiales, or placoderm desmids, constitute a monophyletic group, with moderate to strong support for the four component families of this assemblage (Closteriaceae, Desmidiaceae, Gonatozygaceae, and Peniaceae). The analyses showed that the two families of Zygnematales (Mesotaeniaceae, Zygnemataceae), which have plesiomorphic, unornamented and unsegmented cell walls, are not monophyletic. However, combined taxa of these two traditional families may constitute a monophyletic group. Partitioning the data by codon position revealed no significant differences across all positions or between partitions of positions one and two versus position three. The trees resulting from parsimony analyses using first plus second positions versus third position differed only in topology of branches with poor bootstrap support. The tree derived from third positions only was more resolved than the tree derived from first and second positions. The rbcL‐based phylogeny is largely congruent with published analyses of small subunit rDNA sequences for the Zygnematales. The molecular data do not support hypotheses of monophyly for groups of extant unicellular and filamentous or colonial desmid genera exhibiting a common cell shape. A trend is evident from simple omniradiate cell shapes to taxa with lobed cell and plastid shapes, which supports the hypothesis that chloroplast shape evolved generally from simple to complex. The data imply that multicellular placoderm desmids are monophyletic. Several anomalous placements of genera were found, including the saccoderm desmid Roya in the Gonatozygaceae and the zygnematacean Entransia in the Coleochaetales. The former is strongly supported, although the latter is not, and Entransias phylogenetic position warrants further study.

Ribosomal RNA gene sequences: Analysis and significance in the phytogeny and taxonomy of green algae

Abstract The morphologically diverse green algae (Chlorophyta) include distinct, ancient lineages for which phylogenetic inference from morphological, ultrastructural, and biochemical characters has led to conflicting hypotheses. Cladistic analysis of ribosomal RNA (rRNA) sequences has indicated that (1) some traditional genera are not monophyletic (natural) and taxonomic revisions are needed; (2) ultrastructural characters associated with mitosis and cytokinesis appear to be better indicators of phylogeny than flagellar characters for some taxa; (3) the unusual, subaerial Trentepohliales of incertae sedis appear to be most closely related to the marine siphonaceous green algae; and (4) ancient groups (e.g., Charophyceae and Dasycladales) are resolved. With polymerase chain reaction (PCR) amplification and sequencing of highly variable rDNA gene spacer regions, closely related taxa or populations of one species can be compared and biogeographic studies based on rRNA are feasible. Sequence comparisons for ...

USING rbcL SEQUENCES TO TEST HYPOTHESES OF CHLOROPLAST AND THALLUS EVOLUTION IN CONJUGATING GREEN ALGAE (ZYGNEMATALES, CHAROPHYCEAE)

Sequences for the Rubisco large subunit (rbcL) gene were used to test hypotheses about the evolution of chloroplast shape and thallus type in genera of two families of conjugating green algae (Zygnematales): the Mesotaeniaceae (saccoderm desmids, mostly unicellular) and the Zygnemataceae (strictly filamentous). Unicellular (u) and filamentous (f) genera exhibit a series of three similar chloroplast shapes: ribbonlike (e.g. Spirotaenia [u], Spirogyra [f], and Sirogonium [f], laminate (e.g. Mesotaenium [u] and Mougeotia [f]), and twin‐stellate (e.g. Cylindrocystis [u] and Zygnema [f]. Two conflicting phylogenetic hypotheses have been proposed: 1) families are polyphyletic constructs drawn from three lineages, each with unicellular and filamentous taxa characterized by a specific chloroplast shape; or 2) unicells form one monophyletic lineage (Mesotaeniaceae) and filaments form another (Zygnemataceae), with some chloroplast shapes independently derived. The rbcL data strongly refute hypothesis 2 (monophyly of the two traditional families) and support hypothesis 1 in part. Parsimony, maximum likelihood, and neighbor‐joining analyses of the rbcL data strongly support monophyly of a clade containing taxa with ribbonlike chloroplasts and, to a lesser extent, monophyly of a second clade of the four genera with the other two chloroplast shapes. Two saccoderm genera (Roya, curved laminate chloroplasts; Netrium, “cucumber”‐shaped chloroplasts) are not members of either of these clades, but they are included in a monophyletic Zygnematales.

UNIQUE CHLOROPLAST GENOME IN SPIROGYRA MAXIMA (CHLOROPHYTA) REVEALED BY PHYSICAL AND GENE MAPPING1

The choroplast genome in Spirogyra maxima (Hassall) Kützing is 130 kb in size and locks large repeat units. The 16S and 23S rRNA genes are separated by approximately 44 kb, which makes co‐transcription of these genes unlikely. Spirogyra maxima is unusual among green algae in that its chloroplast genome apparently does not contain the tufA gene, the absence of which is characteristic of land plant chloroplast DNAs. Apart from three groups of genes, pasA‐psaB, psbC‐psbD, and atpA‐atpF/H, which are co‐transcribed in land plants and also map together in S. maxima chloroplast DNA, the S. maxima gene order overall is unlike that of any other chloroplast genome.

CHLAMYDOMONAS SMITHII SP. NOV.–A CHLAMYDOMONAD INTERFERTILE WITH CHLAMYDOMONAS REINHARDTIP

Chlamyclomonas smithii sp. nov. is described from two strains of Chlamyclomonas originally isolated by Dr. Gilbert M. Smith. The mating types are inter‐fertile with those of Chlamyclomonas reinhardtii (Culture No. 89 and 90) maintained in the Culture Collection of Algae at Indiana University. This species is distinguished from all others by the body shape and slit chromatophore.

DISTRIBUTION, MORPHOLOGICAL DIVERSITY AND EVIDENCE FOR POLYPLOIDY IN NORTH AMERICAN ZYGNEMATACEAE (CHLOROPHYTA)

Large‐scale collections of Zygnemataceae in the continental United States of America were made between March and August in 1982, 1983, and 1984. Collections were made on a 31000‐km transect through 35 states. Zygnemataceae were found at 318 sites was inspected. Temperature average 19°C and pH averaged 6.1 over all sites. Algal strains in collections were identified to genus, characterized for filament width, chloroplast number, and end wall type, then photographed and isolated into unialgal culture. Spirogyra was the most common genus collected(632 strains), followed in abundance by Zygnema (174 Strains) and Mougeotia (135 strains). These three genera contained 95% of the strains collected and were equally widely distributed. Strains of the three genera frequently occurred together; no genus displayed evidence of habitat specialization among the three habitat types: flowing water, permanent ponds or lakes, and temporary pools. In Spirogyra, strains with plane (flat) end walls were four times more abundant than those with replicate (interlocking) end walls. Spirogyra with plane end walls showed more variation in filament width than Zygnema, Mougeotia, or Spirogyra with replicate end walls. In Spirogyra with plane end walls, filament width was correlted with nuclear DNA content and number of strains found per collection site was twice that of other genera or Spirogyra, with replicate end walls. Spirogyra strains wider than 70 μm were more frequent on the northern part of the transect. It is proposed that polyploidy may be of widespread occurrence in Spirogyra with plane end walls and that associated morphological plasticity may account for the high apparent specied diversity and survival of the genus in a wider variety of microhabitats than occupied by other Zygnemataceae.

A polyploid species complex of Spirogyra communis (Chlorophyta) occurring in nature

Investigations were conducted to determine whether ploidal changes found in laboratory cultures of Spirogyra also occur in nature. In an earlier study filament types identifiable as three different species (Spirogyra singu‐laris Nordstedt, S. communis (Hassall)Kütz., S. fragilis Jao) arose from an original clonal culture through vegetative growth and sexual reproduction. These three “species” or filament groups differed in filament width, chloroplast number, zygospore size, and chromosome number. The differences in chromosome number represented a polyploid series of diploid (S. communis), triploid (S. fragilis), and tetraploid (S. singularis) forms in which width increased with ploidal level. The three width groups constituted a “species complex.” Five years after isolation of the original strain in this species complex, filaments corresponding to two of the width groups (S. singularis and S. communis) were found at the original collection site in the Santa Catalina Mountains in southern Arizona. The two field‐collected groups were indistinguishable from the laboratory species complex in morphology and chromosome number. Homothallic conjugation within the two field width groups yielded progeny similar to those from homothallic conjugation of groups in the laboratory species complex. Filament widths of progeny were generally within the width limits of respective parental groups. The four possible intergroup crosses between the two laboratory and two field width groups yielded progeny similar to the wider parent (S. singularis) or the parent of intermediate width (S. fragilis). Progeny characteristics were determined by the width groups of parents, regardless of whether parents came from the laboratory or field. The similarities in morphology, chromosome numbers, and reproductive behavior of laboratory and field width groups imply that the laboratory species complex of S. communis has a natural counterpart in the field.

ASEXUAL DEVELOPMENTAL PATTERNS OF THE DIATOM STAURONEIS ANCEPS IN CULTURE123

During several months under controlled growth conditions, cell division in the diatom Stauroneis anceps resulted in a gradual decrease in length as predicted by the Macdonald‐Pfitzer hypothesis. Cells of a clone decreased in average length from 35 to 17 μ. The smallest cell observed measured 12 μ. Cells longer than 26 μ typically had capitate ends. As the cells became shorter, there was a gradual decrease in this capitate configuration with the smallest cells being oval in outline. The estimated increment of size reduction due to cell division in the clone was 0.1 μ per division. This value is dependent on the assumption of random division. Populations with cells less than 28 μ in length showed an increase in valve aberrations, but these cells continued to reproduce. A cell 13 μ long and similar to the smallest specimen of the clone was observed from a core sample with fossil specimens of S. anceps.

A polyploid species complex in Spirogyra maxima (Chlorophyta, Zygnemataceae), a species with large chromosomes

A species complex in Spirogyra consists of the series of filament morphotypes of various ploidal levels arising from an original morphotype within a clonal culture or in nature. A clonal culture of filaments identified as Spirogyra maxima (Hassall) Kützing produced several morphotypes, i.e. filament types of distinctly different widths and ploidal levels. Banding patterns and satellites were visible on chromosomes stained at mitotic prophase and metaphase. The original culture of S. maxima contained filaments averaging 127 μ wide. Vegetative cells of the original culture contained six large chromosomes (>4 μ long), identifiable as three distinct pairs based on banding patterns and presence of satellites: (1) one pair of short chromosomes (ca. 5.0 μ); (2) one pair of long chromosomes (ca. 8.0 μm); and (3) a second pair of long chromosomes (ca. 9.0 μm) including a nucleolar organizing region and satellite. A larger morphotype averaging 175 μm in width contained 12 chromosomes, with two pairs of short chromosomes and four pairs of long chromosomes (satellites were usually indistinct). Aneuploid chromosome numbers ranging from 5 to 13 were observed in a few cells. Binucleate and trinucleate cells were also observed. A twobanded chromosome fragment was observed in a few cells with 6 chromosomes and a few cells with 12 chromosomes. The variety of morphotypes derived in this study could be identified as four different species of Spirogyra by conventional taxonomic criteria. The banding patterns and satellites on chromosomes suggest that three pairs of homologous chromosomes are present in filaments of the original clonal culture and that these filaments are themselves autopolyploid (diploid) descendants of ancestral form with a base chromosome number of x = 3.

Cell width as a taxonomic character with special reference to Zygnema circumcarinatum Czurda

Cell width is a much used taxonomic character in the algae. Yet no data are available on its genetic transmission and inheritance. To obtain evidence on the genetic stability of this character, cell-width inheritance in Zygnema circumcarinatum Czurda was investigated. Measurements of cell width were made on 63 F1 clones produced by germinating zygospores of a known mating. The cell widths of 60 of these clones were distributed around the parental mean width of 23 µm in an interval between 21 and 28 µm. Three clones had significantly greater cell widths and were placed in two groups (30–31 µm and 33–34 µm). Since the culturing environment was identical for all clones, the clustering of all cell-width measurements around parental values is attributed to the influence of polygenic factors. It is proposed from the results of this investigation that cell width is not a valid taxonomic character for Z. circumcarinatum. Further, it is suggested that cell width should be questioned as a valid taxonomic character ...