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.