Nozaki H, Itoh M, Sano R, et al.
Phylogenetic relationships within the colonial volvocales (Chlorophyta) inferred
from rbcL gene sequence data
J PHYCOL 31 (6): 970-979 DEC 1995
Abstract:
The chloroplast-encoded large subunit of the ribulose-1, 5-bisphosphate carboxylase/oxygenase (rbcL) gene
was sequenced from 20 species of the colonial Volvocales
(the Volvacaceae, Goniaceae,
and Tetrabaenaceae) in order to elucidate phylogenetic relationships within the colonial Volvocales. Eleven hundred twenty-eight base pairs In the coding regions of the (rbcL)
gene were analyzed by the neighbor-joining (NJ) method using three kinds of
distance estimations, as well as by the maximum parsimony (MP) method. A large
group comprising all the anisogamous and oogamous volvocacean species was
resolved in the MP tree as well as in the NJ trees based on overall and
synonymous substitutions. In all the trees constructed, Basichlamys
and Tetrabaena (Tetrabaenaceae)
constituted a very robust phylogenetic group.
Although not supported by high bootstrap values, the MP tree and the NJ tree
based on nonsynonymous substitutions indicated that
the Tetrabaenaceae is the sister group to the large
group comprising the Volvocaceae and the Goniaceae. In addition, the present analysis strongly
suggested that Pandorina and Astrephomene
are monophyletic genera whereas Eudorina is nonmonophyletic. These results are essentially consistent
with the results of the recent cladistic analyses of
morphological data. However, the monophyly of the Volvocaceae previously supported by four morphological synapomorphies is found only in the NJ tree based on nonsynonymous substitutions (with very low bootstrap values).
The genus Volvox was clearly resolved as a
polyphyletic group with V. rousseletii Pocock separated from other species of volvox
in the rbcL gene comparisons, although this genus
represents a monophyletic group in the previous morphological analyses. Furthermore,
none of the rbcL gene trees supported the monophyly of the Goniaceae; Astrephomene was placed in various phylogenetic
positions.
DEMOTT WR
THE INFLUENCE
OF PREY HARDNESS ON DAPHNIAS SELECTIVITY FOR LARGE PREY
HYDROBIOLOGIA 307 (1-3): 127-138
Abstract:
Two comparable methods were used to study the feeding of four species of
Daphnia on large spherical particles which differed in size and hardness. The
first method used gut analysis to estimate the selectivities
of daphnids feeding in a broad size range of a single
particle type, including polystyrene beads (4-60 mu m
diameter) in the laboratory and Eudorina
colonies (10-90 mu m) in the field. In the second
method, Daphnia of different sizes fed in a mixture of 6.5 mu
m Chlamydomonas and one of eight test particles.
Smaller daphnids were less effective in feeding on
large test particles. Nonlinear regression was therefore used to estimate the
Daphnia body size at which the clearance rate on a test particle was reduced to
50% of that for Chlamydomonas. The results of both
methods show that prey size and hardness are both very important in determining
daphnid feeding selectivity. For a given particle
size, 'soft' algae(naked and gelatinous flagellates)
are more readily ingested than 'hard' algae (diatoms and dinoflagellates),
and 'hard' algae are more readily ingested than polystyrene beads. Daphnia can
feed effectively on algae that are 2-5 times larger than the largest ingestible
bead.
DALDORPH PWG, THOMAS JD
FACTORS
INFLUENCING THE STABILITY OF NUTRIENT-ENRICHED FRESH-WATER MACROPHYTE COMMUNITIES
- THE ROLE OF STICKLEBACKS PUNGITIUS-PUNGITIUS AND FRESH-WATER SNAILS
FRESHWATER BIOL 33 (2): 271-289 APR 1995
Abstract:
1. Enclosures, with the following characteristics, were used to investigate the
effects of increased nutrient (nitrate and phosphate) loading on freshwater
communities: (a) controls with normal densities of invertebrates, and including
macrophytes, molluscs and
fish (sticklebacks), and communities similar to the controls but with (b) much
reduced snail densities and (c) increased fish densities.
2. The addition of nutrients resulted in increases in the biomass of phytoplankton and epiphyton, as well as zooplankton counts, in all the experimental enclosures.
3. A reduction in the snail population density resulted in a significant decrease in phytoplankton density and an increase, compared to controls, in the density of epiphytic algae growing on the leaves of the submerged macrophytes, Potamogeton crispus and Groenlandia densa. It also resulted in a significant increase (3.5 times that in the controls) in chlorophyll-a values of epilithic algae growing on glass slides, an increase in senescent tissue in macrophytes and a decline in the mass of Groenlandia densa by the end of the experiment
4. An increase in the fish population resulted in a significant decline, compared to the controls, in the densities of zooplankton (including Chydorus sphaericus and copepods), Lymnaea peregra (from May to mid-June), Asellus meridianus, Crangonyx pseudogracilis, Culex (P.) molestus and Physa fontinalis. It also resulted in a change in the composition of the phytoplankton, with an increase in the large colonial Eudorina elegans and a decline in smaller planktonic algae, including Ankistrodesmus and Cryptomonas spp.
5. The possible mechanisms responsible for the effects are evaluated and their relevance to conservation and management of freshwater macrophyte communities are discussed.