2006

Title: Morphology, molecular phylogeny and taxonomy of two new species of Pleodorina (Volvoceae, Chlorophyceae)

Author(s): Nozaki H (Nozaki, Hisayoshi), Ott FD (Ott, Franklyn D.), Coleman AW (Coleman, Annette W.)

Source: JOURNAL OF PHYCOLOGY 42 (5): 1072-1080 OCT 2006

Abstract: The volvocacean genus Pleodorina has been morphologically characterized as having small somatic cells in spheroidal colonies and anisogamous sexual reproduction with sperm packets. In this study we examined two new species that can be assigned to the genus Pleodorina based on morphology: P. starrii H. Nozaki et al. sp. nov. and P. thompsonii F. D. Ott et al. sp. nov. P. starrii was collected from Japan and had 32- or 64-celled colonies with anterior somatic cells and spheroidal individual cellular sheaths that were weakly attached to each other within the colonial envelope. P. thompsonii from Texas (USA) exhibited four or 12 somatic cells in the anterior pole of 16- or 32-celled colonies, respectively, and had a single large pyrenoid in the chloroplast of mature reproductive cells. The chloroplast multigene phylogeny placed P. starrii and P. indica (Iyenger) H. Nozaki in a clade that was robustly separated from the type species P. californica Shaw and P. japonica H. Nozaki. Pleodorina thompsonii was resolved as a basal branch within a large monophyletic group (Eudorina group) composed of Eudorina, Pleodorina and Volvox (excluding section Volvox). Thus, Pleodorina was found among three separate lineages within the Eudorina group in which Eudorina and Volvox were also resolved as nonmonophyletic. The DNA sequences from additional species/strains as well as recognition of morphological attributes that characterize the monophyletic groups within the Eudorina group are needed to construct a natural generic classification within these members of the Volvocaceae.

Title: Morphogenesis in the family Volvocaceae: Different tactics for turning an embryo right-side out

Author(s): Hallmann A (Hallmann, Armin)

Source: PROTIST 157 (4): 445-461 OCT 2006

Abstract: Green algae of the family Volvocaceae provide an unrivalled opportunity to analyze an evolutionary pathway leading from unicellularity to multicellularity with division of labor. One key step required for achieving multicellularity in this group was the development of a process for turning an embryo inside out: a morphogenetic process that is now known as "inversion," and that is a diagnostic feature of the group. Inversion is essential because at the end of its embryonic cleavage divisions, each volvocacean embryo contains all of the cells that will be present in an adult, but the flagellar ends of all cells are pointed toward the interior, rather than toward the exterior where they will need to be to function in locomotion. Inversion has been studied in greatest detail in Volvox carteri, but although all other volvocacean species have to struggle with the same awkward situation of being wrong-side out at the end of cleavage, they do it in rather different ways. Here, the inversion processes of six different volvocacean species (Gonium pectorale, Pandorina morum, Eudorina unicocca, Volvox carteri, Volvox tertius, and Volvox globator) are compared, in order to illustrate the variation in inversion patterns that exists within this family. The simplest inversion process occurs in the plate-shaped alga Gonium pectorale, and the most complicated in the spherical alga Volvox globator Gonium pectorale goes only from a concave-bowl shape to a slightly convex plate. In Volvox globator, the posterior hemisphere inverts completely before the anterior pole opens and the anterior hemisphere slides over the already-inverted posterior hemisphere; during both halves of this inversion process, the regions of maximum cell-sheet curvature move progressively, as radially symmetrical waves, along the posterior-anterior axis.

2005

Title: A twelve-step program for evolving multicellularity and a division of labor

Author(s): Kirk DL

Source: BIOESSAYS 27 (3): 299-310 MAR 2005

Abstract: The volvocine algae provide an unrivalled opportunity to explore details of an evolutionary pathway leading from a unicellular ancestor to multicellular organisms with a division of labor between different cell types. Members of this monophyletic group of green flagellates range in complexity from unicellular Chlamydomonas through a series of extant organisms of intermediate size and complexity to Volvox, a genus of spherical organisms that have thousands of cells and a germ-soma division of labor. It is estimated that these organisms all shared a common ancestor about 50 +/- 20 MYA. Here we outline twelve important ways in which the developmental repertoire of an ancestral unicell similar to modern C. reinhardtii was modified to produce first a small colonial organism like Gonium that was capable of swimming directionally, then a sequence of larger organisms (such as Pandorina, Eudorina and Pleodorina) in which there was an increasing tendency to differentiate two cell types, and eventually Volvox carteri with its complete germ-soma division of labor.

Title: The occurrence of a bloom-forming green alga Pleodorina indica (Volvocales) in the downstream reach of the River Malse (Czech Republic)

Author(s): Znachor P, Jezberova J

Source: HYDROBIOLOGIA 541: 221-228 JUN 1 2005

Abstract: In mid-August 2003 a massive bloom of the green alga Pleodorina indica (Iyengar) Nozaki (Volvocales) occurred in the downstream reach of the River Malse in the Czech Republic. An exceptionally long period of the hot dry weather resulted in low flow conditions and warm water temperatures. These environmental conditions combined with high nutrient concentrations led to the macroscopic appearance of P. indica in the form of an extensive surface scum formation with diurnal changes. The alga soon dominated the river phytoplankton, attaining concentrations of 2000 colonies per millilitre. The bloom persisted in the river from the 10-17 August when it was eventually flushed out. P. indica is an indigenous species of tropical climatic regions and prior to this its massive occurrence has not been reported in the temperate region of Central Europe.

2003

Nozaki H

Origin and evolution of the genera Pleodorina and Volvox (Volvocales)
BIOLOGIA 58 (4): 425-431 JUL 2003

Abstract:
The previous molecular phylogenetic study using 6021 base pairs from five chloroplast genes suggested that two species of Pleodorina (P. californica, P. japonica) might have evolved from a Volvox-like alga by the decrease in colony cell number and size. However, number of species of the genus Volvox was very limited especially in the section Merrillosphaera.

In the present study, 6021 base pairs of the concatenated five chloroplast genes from 10 strains representing seven taxa of the genus Volvox were added to the previous data matrix. The sequence data resolved two anisogamous/oogamous clades within a large monophyletic group comprising five advanced genera of the Volvocaceae (Yamagishiella, Platydorina, Eudorina, Pleodorina and Volvox), one containing Volvox sect. Volvox and the anisogamous genus Platydorina (32-celled flattened colony), and the other (Eudorina group) composed of three other sections of Volvox, Pleodorina and Eudorina. The isogamous genus Yamagishiella (32-celled colony) was positioned basally to the Eudorina group. Therefore, evolution of anisogamy with sperm packets from isogamy might have occurred twice within the Volvocaceae. Based on the present molecular phylogenetic analysis, species of Volvox and Pleodorina within the Eudorina group represented three and two, respectively, separate lineages. One the three Volvox lineages [composed of V (sect. Merrillosphaera) carteri, V (sect. Merrillosphaera) obversus, V. (sect. Merrillosphaera) tertius, V. (sect. Merrillosphaera) africanus and V (sect. Copelandosphaera) dissipatrix] was sister to the monophyletic group consisting of one of the two Pleodorina lineages (P. californica and P. japonica) and V (sect. Janetosphaera) aureus. In addition, species of Eudorina were basal to the two lineages of Pleodorina and three Volvox lineages within the Eudorina group, representing the ancestral situation of Pleodorina/Volvox (excluding sect. Volvox). Thus, reverse evolution from a Volvox-like alga to Pleodorina suggested previously appears unlikely.

2002

Coleman AW

Comparison of Eudorina/Pleodorina ITS sequences of isolates from nature with those from experimental hybrids
AM J BOT 89 (9): 1523-1530 SEP 2002

Abstract:
Internal transcribed spacer (ITS) regions of nuclear ribosomal repeats were compared among 50 Eudorina and Pleodorina isolates and two Volvox species known to clade with Eudorina species. Of the six major subclades found, four containing Eudorina and Pleodorina illinoisensis isolates, one containing Eudorina and Pleodorina indica, and one containing Volvox gigas and V. powersii, the basal branching order remains uncertain, but the positioning of isolates known to mate was always as nearest neighbors on the terminal branches of the tree. Four hybrid clones from a cross of E. elegans with P. illinoisensis, known from chromosome counts to be products of the failure of meiosis at zygote germination, contain both parental ITS repeat regions, as expected. However, they have in addition both crossover and other variant ITS cistrons among their many repeats of ITS. Such variation is limited to terminal regions of helices, as recognized from knowledge of RNA transcript secondary structure. Proper alignment then utilizes all of the nucleotide positions; the hybrid variants appear in positions intermediate between their parents in the tree. In fact, such variants seem to be hallmarks of recent hybridization events, since they were not found in any of the other 50 isolates.

Nozaki H, Takahara M, Nakazawa A, et al.

Evolution of rbcL group IA introns and intron open reading frames within the colonial Volvocales (Chlorophyceae)
MOL PHYLOGENET EVOL 23 (3): 326-338 JUN 2002

Abstract:
Mobile group I introns sometimes contain an open reading frame (ORE) possibly encoding a site-specific DNA endonuclease. However, previous phylogenetic studies have not clearly deduced the evolutionary roles of the group I intron ORFs. In this paper, we examined the phylogeny of group IA2 introns inserted in the position identical to that of the chloroplast-encoded rbcL coding region (rbcL-462 introns) and their ORFs from 13 strains of five genera (Volvox, Pleodorina, Volvulina, Astrephomene, and Gonium) of the colonial Volvocales (Chlorophyceae) and a related unicellular green alga, Vitreochlamys. The rbcL-462 introns contained an intact or degenerate ORE of various sizes except for the Gonium multicoccum rbcL-462 intron. Partial amino acid sequences of some rbcL-462 intron ORFs exhibited possible homology to the endo/excinuclease amino acid terminal domain. The distribution of the rbcL-462 introns is sporadic in the phylogenetic trees of the colonial Volvocales based on the five chloroplast exon sequences (6021 bp). Phylogenetic analyses of the conserved intron sequences resolved that the G. multicoccum rbcL-462 intron had a phylogenetic position separate from those of other colonial volvocalean rbcL-462 introns, indicating the recent horizontal transmission of the intron in the G. multicoccum lineage. However, the combined data set from conserved intron sequences and ORFs from most of the rbcL-462 introns resolved robust phylogenetic relationships of the introns that were consistent with those of the host organisms. Therefore, most of the extant rbcL-462 introns may have been vertically inherited from the common ancestor of their host organisms, whereas such introns may have been lost in other lineages during evolution of the colonial Volvocales. In addition, apparently higher synonymous substitutions than nonsynonymous substitutions in the rbcL-462 intron ORFs indicated that the ORFs might evolve under functional constraint, which could result in homing of the rbcL-462 intron in cases of spontaneous intron loss. On the other hand, the presence of intact to largely degenerate ORFs of the rbcL-462 introns within the three isolates of Gonium viridistellatum and the rare occurrence of the ORF-lacking rbcL-462 intron suggested that the ORF's might degenerate to result in the spontaneous intron loss during a very short evolutionary time following the loss of the ORF function. Thus, the sporadic distribution of the rbcL-462 introns within the colonial Volvocales can be largely explained by an equilibrium between maintenance of the introns by the intron ORF and spontaneous loss of introns when the introns do not have a functional ORE. (C) 2002 Elsevier Science (USA). All rights reserved.

2001

Nozaki H, Krienitz L

Morphology and phylogeny of Eudorina minodii (Chodat) Nozaki et Krienitz, comb. nov (Volvocales, Chlorophyta) from Germany
EUR J PHYCOL 36 (1): 23-28 FEB 2001

Abstract:
Morphology, sexual reproduction and phylogeny of a colonial green alga collected from Germany were studied in culture. Light and electron microscopy of the gelatinous (extracellular) matrix of vegetative colonies, the absence of obligately somatic cells, and the anisogamous sexual reproduction with sperm packets in this alga indicated that if: is assignable to the genus Eudorina. This German alga was similar to E. elegans Ehrenberg in its multiple pyrenoids of nearly identical size and almost identical sized vegetative cells in the colony, but differed from it in having a prominent tubular structure (flagellar sheath) surrounding each flagellum in the gelatinous matrix of the vegetative colonies. Sexual reproduction was homothallic and dioecious. On the other hand, the vegetative morphology agreed well with that of Pandorina minodii Chodat with regard to multiple pyrenoids and the prominent flagellar sheaths. Thus, a new combination, Eudorina minodii (Chodat) Nozaki et Krienitz, is proposed. Molecular phylogenetic analyses of the rbcL-atpB gene sequences from the colonial Volvocales reserved that E. minodii and several heterothallic strains of E, elegans constituted a robust clade. Therefore, prominent flagellar sheaths and homothallic sexual reproduction in E. minodii may be derived characters that evolved recently within the clade.

2000

Nozaki H, Misawa K, Kajita T, et al.

Origin and evolution of the colonial Volvocales (Chlorophyceae) as inferred from multiple, chloroplast gene sequences
MOL PHYLOGENET EVOL 17 (2): 256-268 NOV 2000

Abstract:
A combined data set of DNA sequences (6021 bp) from five protein-coding genes of the chloroplast genome (rbcL, atpB, psaA, psaB, and psbC genes) were analyzed for 42 strains representing 30 species of the colonial Volvocales (Volvox and its relatives) and 5 related species of green algae to deduce robust phylogenetic relationships within the colonial green flagellates. The 4-celled family Tetrabaenaceae was robustly resolved as the most basal group within the colonial Volvocales. The sequence data also suggested that all five volvocacean genera with 32 or more cells in a vegetative colony (all four of the anisogamous/oogamous genera, Eudorina, Platydorina, Pleodorina, and Volvox, plus the isogamous genus Yamagishiella) constituted a large monophyletic group, in which 2 Pleodorina species were positioned distally to 3 species of Volvox. Therefore, most of the evolution of the colonial Volvocales appears to constitute a gradual progression in colonial complexity and in types of sexual reproduction, as in the traditional volvocine lineage hypothesis, although reverse evolution must be considered for the origin of certain species of Pleodorina. Data presented here also provide robust support for a monophyletic family Goniaceae consisting of two genera: Gonium and Astrephomene. (C) 2000 Academic Press.

1999

Coleman AW

Phylogenetic analysis of "Volvocacae" for comparative genetic studies
P NATL ACAD SCI USA 96 (24): 13892-13897 NOV 23 1999

Abstract:
Sequence analysis based on multiple isolates representing essentially all genera and species of the classic family Volvocaeae has clarified their phylogenetic relationships. Cloned internal transcribed spacer sequences (ITS-1. and ITS-2, flanking the 5.8S gene of the nuclear ribosomal gene cistrons) were aligned, guided by ITS transcript secondary structural features, and subjected to parsimony and neighbor joining distance analysis. Results confirm the notion of a single common ancestor, and Chlamydomonas reinharditii alone among all sequenced green unicells is most similar. interbreeding isolates were nearest neighbors on the evolutionary tree in all cases. Some taxa, at whatever level, prove to be clades by sequence comparisons, but others provide striking exceptions. The morphological species Pandorina morum, known to be widespread and diverse in mating pairs, was found to encompass all of the isolates of the four species of Volvulina. Platydorina appears to have originated early and not to fall within the genus Eudorina, with which it can sometimes be confused by morphology. The four species of Pleodorina appear variously associated with Eudorina examples. Although the species of Volvox are each clades, the genus Volvox is not The conclusions confirm and extend prior, more limited, studies on nuclear SSU and LSU rDNA genes and plastid-encoded rbcL and atpB. The phylogenetic tree suggests which classical taxonomic characters are most misleading and provides a framework for molecular studies of the cell cycle-related and other alterations that have engendered diversity in both vegetative and sexual colony patterns in this classical family.

Angeler DG, Schagerl M, Coleman AW

Phylogenetic relationships among isolates of Eudorina species (Volvocales, Chlorophyta) inferred from molecular and biochemical data
J PHYCOL 35 (4): 815-823 AUG 1999

Abstract:
Phylogenetic analyses of 19 strains representing five species of Eudorina, one strain of Pleodorina indica, and seven strains of Yamagishiella unicocca were carried out by sequencing the internal transcribed spacer region (ITS 1 and ITS 2) of the nuclear ribosomal DNA (rDNA) repeats. The sequence data resolved five phylogenetic groups, one consisting of Y. unicocca and the other four encompassing all the Eudorina species. Two isolates, Eudorina sp, (ASW 05157) and Pleodorina indica (ASW 05153), were of uncertain affiliation, Whereas one monophyletic group included strains of E. elegans only, the other strains of E. elegans appeared alongside E. cylindrica, E. illinoisensis, and E. unicocca var. unicocca in the other Eudorina clades. The distribution pattern of the carotenoid loroxanthin ([3R,3'R,6'R]beta,epsilon-carotene-3,19,3'-triol), a systematically useful biochemical marker within chlorophycean flagellates, was shown to match the evaluated molecular data. Whereas it was either totally absent or universally present in six of the deduced phylogenetic lines, it occurred randomly in the E. elegans clade containing only E, elegans isolates. The results substantiated the current hypothesis that the unique vegetative morphology of E. elegans has independently arisen at various times during evolution and that it is not a marker of a monophyletic group.

Nozaki H, Ohta N, Takano H, et al.

Reexamination of phylogenetic relationships within the colonial Volvocales (Chlorophyta): An analysis of atpB and rbcL gene sequences
J PHYCOL 35 (1): 104-112 FEB 1999

Abstract:
The chloroplast-encoded atpB gene was sequenced from 33 strains representing 28 species of the colonial Volvocales (the Volvocaceae and its relatives) to reexamine phylogenetic relationships as previously deduced by morphological data and rbcL gene sequence data.1128 base pairs in the coding regions of the atpB gene were analyzed by MP, NJ, and ML analyses, Although supported with relatively low bootstrap values (75% and 65% in the NJ and ML analyses, respectively), three anisogamous/oogamous volvocacean genera-Eudorina, Pleodorina, and Volvox, excluding the section Volvox(= Euvolvox, illegitimate name), constituted a large monophyletic group (Eudorina group), Outside the Eudorina group, a robust Lineage composed of three species of Volvox sect, Volvox was resolved as in the rbcL gene trees, rejecting the hypothesis of the previous cladistic analysis based on morphological data that the genus Volvox is monophyletic, In addition, the NJ and ML trees suggested that Eudorina is a non-monophyletic genus as inferred from the morphological data and rbcL gene sequences. Although phylogenetic status of the genus Gonium is ambiguous in the rbcL gene trees and the paraphyly of this genus is resolved in the cladistic analysis based on morphological data, the atpB gene sequence data suggest monophyly of Gonium with relatively low bootstrap values (56-61%) in the NJ and ML trees. On the basis of the combined sequence data (2256 base pairs) from atpB and rbcL genes, Gonium was resolved as a robust monophyletic genus in the NJ and ML trees (with 68-86% bootstrap values), and Eudorina elegans Ehrenberg represented a paraphyletic species positioned most basally within the Eudorina group, However, phylogenetic status and relationships of the families of the colonial Volvocales were still almost ambiguous even in the combined analysis.

1998

Schagerl M, Angeler DG

The distribution of the xanthophyll loroxanthin and its systematic significance in the colonial Volvocales (Chlorophyta)
PHYCOLOGIA 37 (2): 79-83 MAR 1998

Abstract:
The distribution of the xanthophyll loroxanthin [(3R,3'R,6'R)- beta,epsilon-carotene-3,19,3'-triol] within colonial volvocalean families was analyzed by reversed-phase high pressure Liquid chromatography (rP-HPLC). The results demonstrate that loroxanthin is a physiological marker delineating the families Tetrabaenaceae Nozaki et Itoh and Goniaceae (Pascher) Pascher. Thus loroxanthin may be considered to be of systematic significance within the Volvocales, and its use as a marker supports recent ideas on phylogenetic relationships. Within the Volvocaceae Ehrenberg, its infraspecific disjunct distribution indicates that it is not useful systematically in this family and that it varies even within a morphologically defined species. The pattern of loroxanthin distribution was compared with molecular data and traditional characters.

Nozaki H, Ohta N, Yamada T, et al.

Characterization of rbcL group IA introns from two colonial volvocalean species (Chlorophyceae)
PLANT MOL BIOL 37 (1): 77-85 MAY 1998

Abstract:
Group I introns were reported for the first time in the large subunit of Rubisco (rbcL) genes, using two colonial green algae, Pleodorina californica and Gonium multicoccum (Volvocales). The rbcL gene of P. californica contained an intron (PlC intron) of 1320 bp harboring an open reading frame (ORF). The G. multicoccum rbcL gene had two ORF-lacking introns of 549 (GM1 intron) and 295 (GM2 intron) base pairs. Based on the conserved nucleotide sequences of the secondary structure, the PlC and GM1 introns were assigned to group IA2 whereas the GM2 intron belonged to group IA1. Southern hybridization analyses of nuclear and chloroplast DNAs indicated that such intron-containing rbcL genes are located in the chloroplast genome. Sequencing RNAs from the two algae revealed that these introns are spliced out during mRNA maturation. In addition, the PlC and GM1 introns were inserted in the same position of the rbcL exons, and phylogenetic analysis of group IA introns indicated a close phylogenetic relationship between the PlC and GM1 introns within the lineage of bacteriophage group IA2 introns. However, P. californica and G. multicoccum occupy distinct clades in the phylogenetic trees of the colonial Volvocales, and the majority of other colonial volvocalean species do not have such introns in the rbcL genes. Therefore, these introns might have been recently inserted in the rbcL genes independently by horizontal transmission by viruses or bacteriophage.

1997

Nozaki H, Ito M, Uchida H, et al.

Phylogenetic analysis of Eudorina species (Valvocaceae, Chlorophyta) based on rbcL gene sequences
J PHYCOL 33 (5): 859-863 OCT 1997

Abstract:
Species and varieties in the genus Eudorina Ehrenberg (Volvocaceae, Chlorophyta) were evaluated on the basis of phylogenetic analyses of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene sequence from 14 strains of four Eudorina species, as well as from nine species of Pleodorina and Volvox. The sequence data suggested that 10 of the 14 Eudorina strains form three separate and robust monophyletic groups within the nonmonophyletic genus Eudorina. The first group comprises ail three strains off. unicocca G. M. Smith; the second group consists of one of the E, elegans Ehrenberg var elegans strains, the E. cylindrica Korshikov strain, and both E. illinoisensis (Kofoid) Pascher strains; and the third group consists of two monoecious varieties off, elegans [two strains of E. elegans var synoica Goldstein and one strain of E. elegans var. carteri (G. hi. Smith) Goldstein]. In addition, E. illinoisensis represents a poly- or paraphyletic species within the second group. The remaining four strains, all of which are assigned to E. elegans var. elegans, are nonmonophyletic. Although their position in the phylogenetic trees is more or less ambiguous, they are ancestral to other taxa ill the large anisogamous/oogamous monophyletic group including Eudorina, Pleodorina, and Volvox (except for sect. Volvox). Thus, the four Eudorina groups resolved in the present molecular phylogeny do not correspond with the species concepts of Eudorina based on vegetative morphology, but they do reflect the results Of the previous intercrossing experiments and modes of monoecious and dioecious sexual reproduction.

Nozaki H, Ito M, Sano R, et al.

Phylogenetic analysis of Yamagishiella and Platydorina (Volvocaceae, Chlorophyta) based on rbcL gene sequences
J PHYCOL 33 (2): 272-278 APR 1997

Abstract:
Yamagishiella, based on Pandorina unicocca Rayburn et Starr is distinguished from Eudorina by its isogamous sexual reproduction, whereas Platydorina exhibits anisogamous sexual reproduction. In the present study, rue sequenced the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) genes from five Japanese and North American strains of Y. unicocca (Rayburn et Stair) Nozaki, true Platydorina caudata Kofoid strains, and two strains of Eudorina unicocca G. M. Smith, as well as eight related colonial and unicellular species. Phylogenetic trees were constructed based on these sequence data and on previously published rbcL gene sequences from 23 volvocalean species in order to deduce phylogenetic relationships within the colonial Volvocales, with particular regard to the phylogenetic positions and status of the genera Yamagishiella and Platydorina. Two robust monophyletic groups of the anisogamous/oogamous volvocacean species were resolved in the maximum-parsimony tree as well as in the neighbor-joining distance tree. One of the two groups comprises three species of Volvox section Volvox, whereas the other is composed of other sections of Volvox as well as of all the species of Eudorina and Pleodorina. Platydorina, however, was positioned outside these two monophyletic groups. Therefore, derivation of the Platydorina lineage may be earlier than that of such anisogamous/oogamous groups, or origin of ''anisogamy with sperm, packets'' in Platydorina may De independent of sperm packet evolution in Eudorina, Pleodorina, and Volvox. It was also resolved with high bootstrap values that all of the Y. unicocca strains form a monophyletic group positioned outside the large monophyletic group including Eudorina and Pleodorina. These reject the possibility of the reverse evolution of isogamy from anisogamy to give rise to Yamagishiella within the lineage of Eudorina.

Liss M, Kirk DL, Beyser K, et al.

Intron sequences provide a tool for high-resolution phylogenetic analysis of volvocine algae
CURR GENET 31 (3): 214-227 MAR 1997

Abstract:
Three nuclear spliceosomal introns in conserved locations were amplified and sequenced from 28 strains representing 14 species and 4 genera of volvocalean green algae. Data derived from the three different introns yielded congruent results in nearly all cases. In pairwise comparisons, a spectrum of taxon-specific sequence differences ranging from complete identity to no significant similarity was observed, with the most distantly related organisms lacking any conserved elements apart from exon-intron boundaries and a pyrimidine-rich stretch near the 3' splice site. A metric (SI50), providing a measure of the degree of similarity of any pair of intron sequences, was defined and used to calculate phylogenetic distances between organisms whose introns displayed statistically significant similarities. The rate of sequences divergence in the introns was great enough to provide useful information about relationships among different geographical isolates of a single species, but in most cases was too great to provide reliable guides to relationships above the species level. A substitution rate of approximately 3 x 10(-8) per intron position per year was estimated, which is about 150-fold higher than in nuclear genes encoding rRNA and about 10-fold higher than the synonymous substitution rate in protein-coding regions. Thus, these homologous introns not only provide useful information about intraspecific phylogenetic relationships, but also illustrate the concept that different parts of a gene may be subject to extremely different intensities of selection. The intron data generated here (1) reliably resolve for the first;time the relationships among the five most extensively studied strains of Volvox, (2) reveal that two other Volvox species may be more closely related than had previously been suspected, (3) confirm prior evidence that particular isolates of Eudorina elegans and Pleodorina illinoisensis appear to be sibling taxa, and (4) contribute to the resolution of several hitherto unsettled issues in Chlamydomonas taxonomy.

1996

Nozaki H

Morphology and evolution of sexual reproduction in the Volvocaceae (Chlorophyta)
J PLANT RES 109 (1095): 353-361 SEP 1996

Abstract:
Morphological features of sexual reproduction in the Volvocaceae are reviewed, focusing particularly on gametic union and zygote germination. Both of the two conjugating gametes of the isogamous genera Pandorina, Volvulina and Yamagishiella bear a tubular mating structure (mating papilla), and plasmogamy is initiated by union of the papillae tips. On zygote germination, a single biflagellate gone cell is released from the zygote wall. Although all the anisogamous and oogamous genera of the Volvocaceae produce ''sperm packets'' during gametogenesis and a single gone cell at zygote germination, some difference can be recognized in the male gametes. The male gametes of Eudorina bear a tubular cytoplasmic protuberance (putative mating papilla) near the base of the flagella, whereas such a structure recognized at the light microscopic level is not evident in Pleodorina and Volvox, Evolution of the sexual reproduction characteristics of volvocacean algae is discussed on the basis of recent cladistic analysis of morphological data as well as of the ribosomal (r) RNA phylogeny and large subunit of the ribulose-1,5-biphosphate carboxylase/oxygenase(rbcL) gene trees.

1994

HOOPS HJ, LONG JJ, HILE ES

FLAGELLAR APPARATUS STRUCTURE IS SIMILAR BUT NOT IDENTICAL IN VOLVULINA-STEINII, EUDORINA-ELEGANS, AND PLEODORINA-ILLINOISENSIS (CHLOROPHYTA) - IMPLICATIONS FOR THE VOLVOCINE EVOLUTIONARY LINEAGE
J PHYCOL 30 (4): 679-689 AUG 1994

Abstract:
The colonial and multicellular members of the Volvocales can be arranged in order of increasing size and complexity as the ''volvocine series.'' This series is often assumed to reflect an evolutionary progression. The flagellar apparatuses of previously examined algae are not consistent with a simple lineage. The flagellar apparatuses of Astrephomene gubernaculifera Pocock, Gonium pectorale Muller, Platydorina caudata Kofoid, Volvox rousseletii G. S. West, and V. carteri f. weismannia (Powers) Iyengar differ from one another, and there is no apparent progression in flagellar apparatus features from the simple to complex colonial forms. We examined the flagellar apparatuses of Volvulina steinii Playfair, Eudorina elegans Ehr., and Pleodorina illinoisensis Kofoid and found then to be similar to one another. The basal bodies ave connected by a distal fiber that is offset to the anti side of the cell. Two microtubular rootlets originate on the inside of the basal bodies and extend toward the syn side. The other two rootlets are oriented perpendicular to the first two and are anti-parallel to each other. A coarsely striated component underlies the four-membered rootlets and extends to the basal bodies. A proximal fiber complex connects the two basal bodies. This complex consists of a branched striated component on the cis side of each basal body. One part extends toward the anti side of the cell, while the other extends into a fibrous component that runs between basal bodies. An additional structure extends in the anti direction from the trans side of each basal body. A fibrous component extends past one basal body in all four species. This component goes past the trans basal body in Volvulina steinii and the cis basal body in E. elegans and P. illinoisensis. The flagellar apparatuses of these organisms are similar to those of G. pectorale and Volvox carteri but different from the other colonial volvocalean algae examined. The algae examined in this study plus G. pectorale and V. carteri probably share a common evolutionary history that postdates the transition from the unicellular to colonial habit. Such a shared evolutionary history is a requirement of the volvocine hypothesis. However, we have not observed progressive changes in the flagellar apparatus correlated with increasing cell number, differentiation, and sexual specialization. Thus, it is possible, but not certain, that G. pectorale, Volvulina steinii, E. elegans, P. illinoisensis, and Volvox carteri may form part of a volvocine lineage.

NOZAKI H, AIZAWA K, WATANABE MM

A TAXONOMIC STUDY OF 4 SPECIES OF CARTERIA (VOLVOCALES, CHLOROPHYTA) WITH CRUCIATE ANTERIOR PAPILLAE, BASED ON CULTURED MATERIAL
PHYCOLOGIA 33 (4): 239-247 JUL 1994

Abstract:
The taxonomy of four species of Carteria with cruciate anterior papilla (Volvocales, Chlorophyta) was studied in two strains isolated recently from Japan, four UTEX and five Japanese NIES strains. Light and scanning electron microscopy demonstrated that the papillae of all strains were pentagonal in side view and exhibited four ridges twisting counterclockwise in top view. The strains were clearly delineated into four species, C. crucifera Korshikov ex Pascher, C. eugametos Mitra, C. inversa (Korshikov) Bourrelly and C. cerasiformis Nozaki, Aizawa et M.M. Watanabe sp. nov., based on differences in cell shape, position of the nucleus, form of the stigma, structure of the anterior papilla and pyrenoid, as well as the mode of cell division during asexual reproduction. The taxonomic conclusion of Fott (1968) who synonymized C. eugametos with C. lunzensis Pascher et Jahoda, is rejected after re-examination of the type strain of C. eugametos.

NOZAKI H, ITOH M

PHYLOGENETIC-RELATIONSHIPS WITHIN THE COLONIAL VOLVOCALES (CHLOROPHYTA) INFERRED FROM CLADISTIC-ANALYSIS BASED ON MORPHOLOGICAL DATA
J PHYCOL 30 (2): 353-365 APR 1994

Abstract:
A cladistic analysis was used to deduce the phylogenetic relationships within the colonial Volvocales. Forty-one pairs of characters related to gross morphology and ultrastructure of vegetative colonies as well as asexual and sexual reproduction were analyzed based on parsimony, using the PAUP 3.0 computer program, for 25 species belonging to nine volvocacean and goniacean genera of the colonial Volvocales. Chlamydomonas reinhardtii Dangeard was the outgroup. The strict consensus tree indicated the presence of two monophyletic groups, one composed of all the volvocacean species analyzed in this study and the other containing the goniacean species except for the four-celled species Gonium sociale (Dujardin) Warming. In addition, these two groups constitute a large monophyletic group, to which G. sociale is a sister group. A new combination Tetrabaena socialis (Dujardin) Nozaki et Itoh and a new family Tetrabaenaceae Nozaki et Itoh are thus proposed for G. sociale. In addition, the analysis suggests that the volvocacean genera Eudorina and Pleodorina are paraphyletic groups, respectively, and that the monotypic genus Yamagishiella has no autapomorphic characters and represents primitive features of the anisogamous and oogamous genera of the Volvocaceae. Phylogenetic relationships within the Volvocaceae and the Goniaceae, as well as the various modes of sexual reproduction exhibited by these organisms, are discussed on the basis of the analysis.

1992

NOZAKI H, KUROIWA T

ULTRASTRUCTURE OF THE EXTRACELLULAR-MATRIX AND TAXONOMY OF EUDORINA, PLEODORINA AND YAMAGISHIELLA GEN-NOV (VOLVOCACEAE, CHLOROPHYTA)
PHYCOLOGIA 31 (6): 529-541 NOV 1992

Abstract:
Vegetative colonies of Pandorina unicocca Rayburn et Starr, four taxa of Eudorina [E. elegans Ehrenberg (type species), E. illinoisensis (Kofoid) Pascher, E. unicocca G.M. Smith var. unicocca and E. unicocca var. peripheralis Goldstein] and two species of Pleodorina [P. californica Shaw (type species) and P. indica (Iyengar) Nozaki] were examined with electron microscopy in order to characterize the structure of the extracellular matrix. Each cell of the colonies of all the taxa examined was tightly enclosed by a dense fibrillar zone of the extracellular matrix (cellular envelope) with sparse fibrillar material filling the space outside the cellular envelopes within the tripartite colonial boundary of the matrix. This arrangement is essentially different from that of Pandorina morum (O.F. Muller) Bory (type species) and P. colemaniae Nozaki. As Eudorina and Pleodorina both have anisogamous sexual reproduction with sperm packets (bundles of male gametes), a new genus, Yamagishiella Nozaki, is proposed for encompassing the isogamous species Yamagishiella unicocca (Rayburn et Starr) Nozaki comb. nov. [Pandorina unicocca].

LARSON A, KIRK MM, KIRK DL

MOLECULAR PHYLOGENY OF THE VOLVOCINE FLAGELLATES
MOL BIOL EVOL 9 (1): 85-105 JAN 1992

Abstract:
Phylogenetic studies of approximately 2,000 bases of sequence from the large and small nuclear-encoded ribosomal RNAs are used to investigate the origins of the genus Volvox. The colonial and multicellular genera currently placed in the family Volvocaceae form a monophyletic group that is significantly closer phylogenetically to Chlamydomonas reinhardtii than it is to the other unicellular green flagellates that were tested, including Chlamydomonas eugametos, Chlorella pyrenoidosa, and Haematococcus lacustris. Statistical analysis of 251 phylogenetically informative nucleotide positions rejects the "volvocine lineage" hypothesis, which postulates a monophyletic evolutionary progression from unicellular organisms (such as Chlamydomonas), through colonial organisms (e.g., Gonium, Pandorina, Eudorina, and Pleodorina) demonstrating increasing size, cell number, and tendency toward cellular differentiation, to multicellular organisms having fully differentiated somatic and reproductive cells (in the genus Volvox). The genus Volvox appears not to be monophyletic. Volvox capensis falls outside a lineage containing other representatives of Volvox(V. aureus, V. carteri, and V. obversus), and both of these Volvox lineages are more closely related to certain colonial genera than they are to each other. This implies either a diphyletic origin of Volvox from different colonial volvocacean ancestors, a phylogenetic derivation of some of the colonial genera from a multicellular (i.e., Volvox) ancestor, or both. Considered together with previously published observations, these results suggest that the different levels of organizational and developmental complexity found in the Volvocaceae represent alternative stable states, among which evolutionary transitions have occurred several times during the phylogenetic history of this group.

1991

HABERYAN KA, MHONE OK

ALGAL COMMUNITIES NEAR CAPE MACLEAR, SOUTHERN LAKE MALAWI, AFRICA
HYDROBIOLOGIA 215 (3): 175-188 JUN 21 1991

Abstract:
Algal communities were compared among benthic and net plankton samples from Cape Maclear, Lake Malawi. In the cool mixing season (from May to August), rocks were overgrown by Cladophora or Calothrix, accompanied by the diatoms Rhopalodia, Cymbella, and Navicula. These diatoms, together with Epithemia and Cocconeis, were epiphytic on Cladophora and macrophytes. In sandy areas, the common diatoms were Rhopalodia, Fragilaria, Epithemia, Navicula, Surirella, and Melosira.

In all phytoplankton samples, taken with a 10-mu-m mesh net, cyanophyte cells were the most common (70 to 80%), especially those of Oscillatoria. Biomass, however, was dominated by Peridinium from November to April and by Anabaena and Oscillatoria from September to April when the mixolimnion was stratified. Among the chlorophytes, Oedogonium was the most common, especially from May into December when Pleodorina became more common.

Diatoms dominated the biomass in the mixing season (May to September): Stephanodiscus in May, followed by Melosira nyassensis and lanceolate Nitzschia species from mid-June through August. For the rest of the year the epilimnion was stratified and these Nitzschia species were virtually the only diatoms present.

Benthic and planktonic communities share few taxa: benthic taxa never made up more than 2% of cells in offshore tows. This conclusion contrasts with previous reports, especially regarding Surirella. Consequently, an abundance of benthic taxa in sediment cores may be interpreted as lower lake level if sediment redistribution can be excluded. The seasonality of the planktonic diatoms is compatible with current ecological hypotheses, and therefore increases their value as paleolimnological indicators.