THE REQUIREMENT FOR SILICON IN SYNURA PETERSENII (CHRYSOPHYCEAE)1,2

A silicon requirement for growth is demonstrated for an alga other than a diatom. Concentrations of less than 1 μM silicate greatly decreased the growth rate of Synura petersenii Korshikov and caused morphological changes. Half of maximum growth rate (μ_max= 1.12 divisions/day) appeared at a concentration of only 0.23 μM silicate. Germanium dioxide inhibited, growth considerably; the degree of inhibition varying from none to almost 100% depending upon both Si and Ge concentrations. The amount of silicon deposited in the external scales of S. petersenii is comparable per unit area to that of diatoms. S. petersenii is able to deplete the medium of silicate to very low levels. The feasibility of batch culture techniques for this kind of work is discussed briefly.     

彼得森黄群藻孢囊的形成及形态

利用光镜及扫描电镜对彼得森黄群藻的形态结构、孢囊形成进行详细观察和描述.结果显示,彼得森黄群藻分布广泛,营养体形态变化也大,可以分为不同的变种和变型,其孢囊形态也有多种形态.根据鳞片结构,鉴定出其中的2个变型,并对其所产生的孢囊形态进行了对应.     

MERCURY AND TEMPERATURE INTERACTIONS ON THE GROWTH RATES OF THREE SPECIES OF FRESHWATER PHYTOPLANKTON1,2

Cultures of freshwater algae, representing three algal divisions, Synura petersenii Korshikov; Chlamydomonas sp.: and Nitzschia sp., were subjected to four different mercury-temperature shock interactions to demonstrate synergistic effects between mercury and temperature. Algal growth, measured by temporal changes in vivo fluorescence of chlorophyll was used to ascertain the effects. Mercury addition and temperature shock had various inhibitory effects on algal growth. Prior environmental conditions influence the effect of subsequent treatments. Growth of S. petersenii was severely inhibited by mercury in all experiments. Control cultures would not grow at 30 C and died when shacked at this temperature. Chlamydomonas sp. cultures initially inhibited by mercury were able to recover under most conditions after a period of reduced growth. Nitzschia sp. was resistant to mercury except when simultaneously shocked with temperature. Mercury analyses showed that Nitzschia cells at 25 C and 30 C contained a high percentage of the mercury initially added to the cultures. There was a significant loss of mercury at the end of each experiment from all cultures, probably due to volatilization.     

Morphological delineation and distribution patterns of four newly described species within the Synura petersenii species complex (Chrysophyceae,Stramenopiles)

The Synura petersenii species complex represents a common, cosmopolitan and highly diverse taxon of autotrophic freshwater flagellates. In this paper, we describe and characterize four new species (S. borealis, S. heteropora, S. hibernica and S. laticarina) that have been identified during our extensive sampling of freshwater habitats in 15 European countries. Morphometric analyses of siliceous scales led to the significant phenotypic differentiation of all four newly described species, and their separation from other related species of the S. petersenii complex. Two of these newly described species (S. hibernica and S. borealis) can be clearly distinguished by characteristic large colonies consisting of elongated, lanceolate-shaped cells. Development of strongly elongated, narrow cells in S. hibernica could be explained by the adaptation of this species to oligotrophic conditions. Though morphologically distinct, S. borealis possesses an exceptionally high degree of genetic diversity, possibly indicating recent speciation and evolutionary diversification within this taxon. Three of the four newly described species exhibit restricted biogeographic distribution. The evolutionarily related S. borealis and S. laticarina occur only in Northern Europe, and seem to be adapted to colder areas. The most remarkable distribution pattern was observed for S. hibernica, which has a geographic distribution that is restricted to western Ireland.     

Comparing Morphological and Molecular Estimates of Species Diversity in the Freshwater Genus Synura (Stramenopiles): A Model for Understanding Diversity of Eukaryotic Microorganisms

We performed a comparison of molecular and morphological diversity in a freshwater colonial genus Synura (Chrysophyceae, Stramenopiles), using the island of Newfoundland (Canada) as a case study. We examined the morphological species diversity in collections from 79 localities, and compared these findings to diversity based on molecular characters for 150 strains isolated from the same sites. Of 27 species or species-level lineages identified, only one third was recorded by both molecular and morphological techniques, showing both approaches are complementary in estimating species diversity within this genus. Eight taxa, each representing young evolutionary lineages, were recovered only by sequencing of isolated colonies, whereas ten species were recovered only microscopically. Our complex investigation, involving both morphological and molecular examinations, indicates that our knowledge of Synura diversity is still poor, limited only to a few well-studied areas. We revealed considerable cryptic diversity within the core S. petersenii and S. leptorrhabda lineages. We further resolved the phylogenetic position of two previously described taxa, S. kristiansenii and S. petersenii f. praefracta, propose species-level status for S. petersenii f. praefracta, and describe three new species, S. vinlandica, S. fluviatilis, and S. cornuta. Our findings add to the growing body of literature detailing distribution patterns observed in the genus, ranging from cosmopolitan species, to highly restricted taxa, to species such as S. hibernica found along coastal regions on multiple continents. Finally, our study illustrates the usefulness of combining detailed morphological information with gene sequence data to examine species diversity within chrysophyte algae.     

HETEROTHALLIC SEXUALITY AND DENSITY DEPENDENT ENCYSTMENT IN THE CHRYSOPHYCEAN ALGA SYNURA PETERSENII KORSH.1

Sexual reproduction of the common planktonic chrysophyte Synura petersenii is described from observations made on clonal isolates grown in defined culture. Sexual fusion was isogamous and heterothallic, with cells of normal appearance from compatible clones serving as hologametes. No special culture conditions were required to induce sexual behavior; actively growing cell populations appeared to be continually receptive to mating when mixed with a sufficient number of cells from a compatible clone. A single, bipolar mating group was documented containing five of the seven clones tested. Zygotic statospores were found to be binucleate and to contain 4 chloroplasts at maturity. Production rates of zygospores were low for even the most highly compatible clones, with batch culture yields ranging from 1-20% of final cell density under the culture conditions utilized. Six of the clones tested were also capable of very low frequency (0.001-0.01%) homothallic statospore production but the reproductive significance of these cysts remains enigmatic. The dynamics of sexual encystment suggest that the process proceeds during periods of active population growth and is density dependent. Based on the characteristics of cyst induction and encystment dynamics, it is concluded that chrysophycean flagellates may have a perennation strategy quite different from that of the majority of planktonic diatoms, dinoflagellates, and green algae for which resting cyst production requires an exogenous trigger usually associated with physiological stress and periods of negative growth.     

A CHEMOTAXONOMIC STUDY OF LEMNACEAE

One hundred eighty-six clones of Lemnaceae, representing world-wide collections of 22 taxa, were grown in axenic cultures reproduced by clonal subcultures. Following morphological examinations under a range of culture conditions, a “key” clone was selected to represent each taxon. These key clones were completely representative of the qualitative flavonoid chemistry of the taxa as determined from a number of clones. With the exceptions of Spirodela polyrhiza and S. biperforala which produce identical flavonoids, the flavonoid associations of each species of Lemnaceae were unique in the family. Through paper chromatographic comparisons of purified compounds, plus visible and ultraviolet absorption spectroscopy of isolated individual flavonoids, a total of 47 different compounds was described. These substances included: glycosides of anthocyanidins (cyanidin and petunidin); glycosides of flavonols (kaempferol and quercetin); glycosides of flavones (apigenin and luteolin); and several glycoflavones (C-glycosyl-flavones). When grown under equivalent controlled conditions of culture, infraspecific variation in the qualitative production of these 47 flavonoids was detected in only one flavone glycoside of the species Lemna perpusilla. The reliability of the flavonoid patterns under various conditions of culture was investigated. Under 62 different regimes S. oligorhiza and S. polyrhiza showed only minor variations in their flavonoid glycosides. Studies of other taxa supported this generalization. Under controlled conditions, morphological intergradation obscured identification of many collections. Each could be conclusively identified by its flavonoid chemistry.     

Growth characteristics of two bloom‐forming synurophytes (Mallomonas elongata and Synura petersenii) at different nitrate and phosphate concentrations

Two dominant planktonic bloom‐forming algal species in a small shallow eutrophic pond were identified as Mallomonas elongata and Synura petersenii by electron microscopy. Their growth requirements were investigated as uni‐algal cultures in a laboratory study. The maximum population growth and maximum growth rate of M. elongata occurred at concentrations of 24 μM nitrate (NO₃) and 5 μM phosphate (PO₄) at a temperature of 15°C and a pH of 6. Synura petersenii grew maximally and exhibited the highest growth rate at a NO₃ concentration of 24 μM and a PO₄ concentration of 2 μM. Mallomonas elongata and S. petersenii had similar nutrient requirements for optimum growth, suggesting that the biomass of these two species can be controlled by nutrient gradients.     

SILICEOUS SCALE PRODUCTION IN CHRYSOPHYTE AND SYNUROPHYTE ALGAE. I. EFFECTS OF SILICA-LIMITED GROWTH ON CELL SILICA CONTENT,SCALE MORPHOLOGY,AND THE CONSTRUCTION OF THE SCALE LAYER OF SYNURA PETERSENII1

The cells of synurophyte flagellates (algal class Synurophyceae, formerly included in the Chrysophyceae) are enclosed within a regularly imbricate layer of ornamented siliceous scales. Scale morphology is of critical taxonomic importance within this group of algae, and the scales are valuable indicator microfossils in paleolimnological studies. The data presented here demonstrate that scale morphology and the integrity of the scale layer can exhibit extreme variability in culture as a function of the cellular quota of silica under silica-limited growth. Silica-limited, steady-state populations of the colonial flagellate Synura petersenii Korsh. were maintained over a range of specific growth rates (μ= 0.11–0.69 days^?1) and silica cell quotas (Q_si= 0.13–2.40 pmoles Si · cell¹). Scale morphology and the organization of the scale layer became increasingly aberrant as silica stress increased. Under severe stress, scale deposition was completely suppressed so that cells appeared scale-free. This depression of scale deposition was reversible; populations of silica-starved, scale-free cells rapidly regenerated new scale layers when placed in batch culture and spiked with dissolved silica. During recovery from silica stress, cell division was repressed for 24 h while mean cell silica quota increased 25-fold. The first new scales appeared within 2 h after the silica addition, and development of the new scale layer proceeded in an approximately synchronous manner, residting in normal scale layers on virtually all cells after 48 h of recovery in Sirich medium. Silica content of silica-replete Synura cells is comparable to freshwater diatoms of siynilar size, but Synura has much greater potential quota variability than diatoms and no apparent threshold silica requirement. Silica-limited growth kinetics and competition between diatoms and Synura for silica are discussed. The results suggest that morphological variability of siliceous scales in natural populations of synurophyte flagellates may result from silica stress and that the experimental approach developed here has great potential value as a means for circumscribing ecotypic variation in scale morphology. Results also demonstrate that scale production can be uncoupled from cell division, suggesting that cell cycle regulation of silica biomineralization in the Synurophyceae may be fundamentally different from that of diatoms (algal class Bacillariophyceae). This experimental system has application in the future study of the intracellular membrane systems and the regulatory processes involved in silica biomineralization.     

SCALED CHRYSOPHYTES (CHRYSOPHYCEAE AND SYNUROPHYCEAE) FROM ADIRONDACK DRAINAGE LAKES AND THEIR RELATIONSHIP TO ENVIRONMENTAL VARIABLES1

The relationships between 23 scaled chrysophyte taxa (Chrysophyceae and Synurophyceae) and measured limnological variables in 62 Adirondack, New York, drainage lakes were examined by canonical correspondence analysis (CCA). The major proportion of variation in chrysophyte species distributions was strongly related to total monomeric Al (Al_m) and Mg concentrations, and their close correlates pH, Na, Ca, and acid-neutralizing capacity (ANC). Total monomeric Al concentrations explain a greater proportion of species variation than pH, suggesting that Al_m concentrations may be more important in governing the distribution of chrysophyte taxa in these lakes. Gaussian logit (GL) and linear logit (LL) regressions of the relative percentages of individual chrysophyte taxa to lakewater pH and Al_m concentrations and the examination of pH–Al_m response surfaces show that many chrysophyte taxa exhibit unique responses to these environmental gradients; taxa can be characterized as alkaline, circumneutral, acidic, and pH indifferent. Within each of these groups, taxa can be characterized further based upon their optima and tolerances to Al_m concentrations. Chrysophyte indicator species (i.e. a taxon with a strong statistical relationship to the environmental variable of interest, a well-defined optimum, and a narrow tolerance to the variable of interest) for pH include Mallomonas hindonii, M. crassisquama, M. pseudocoronata, and Synura uvella; M. hindonii, M. crassisquama, M. pseudocoronata, S. petersenii, and S. spinosa are good indicators of Al_m concentrations. Highly significant predictive models were developed to infer lakewater pH and Al_m concentrations from the relative percentages of chrysophyte scales in the study lakes. Model evaluation was based on their correlation coefficients and the root-mean-squared error of prediction (RMSE) derived from bootstrapping. Weighted averaging regression and calibration with tolerance down-weighting (i.e. weighting taxa inversely to their variance) produced superior results when compared to the computationally and data-demanding maximum likelihood methods and to simple weighted averaging regression and calibration.     

DIFFERENCES IN NITROGEN REQUIREMENTS OF TWO CLONES OF CONVOLVULUS ARVENSIS IN VITRO

Various nitrogen sources were shown to alter the growth and modify nitrate reductase activities of stem callus tissue derived from two clones of Convolvulus arvensis L. (field bindweed). Callus from a Washington (S) clone grew better and had a higher level of nitrate reductase activity than callus from a New Mexico (R) clone when nitrate was the only source of nitrogen available in the culture medium. The addition of glycine to the culture medium decreased growth of the R clone and increased growth of the S clone, but glutamic acid repressed growth of both clones. An amide source of nitrogen such as glutamine or asparagine, or ammonium was required to produce maximum growth of both bindweed clones. Glutamine increased nitrate reductase activity in the two clones, and glycine increased nitrate reductase activity in the S clone but decreased it in the R clone. Glutamic acid decreased nitrate reductase activities in both the R and S tissues.     

Clonal genetic structure and diversity in populations of an aquatic plant with combined vs. separate sexes

Clonality is often implicated in models of the evolution of dioecy, but few studies have explicitly compared clonal structure between plant sexual systems, or between the sexes in dioecious populations. Here, we exploit the occurrence of monoecy and dioecy in clonal Sagittaria latifola (Alismataceae) to evaluate two main hypotheses: (i) clone sizes are smaller in monoecious than dioecious populations, because of constraints imposed on clone size by costs associated with geitonogamy; (ii) in dioecious populations, male clones are larger and flower more often than female clones because of sex‐differential reproductive costs. Differences in clone size and flowering could result in discordance between ramet‐ and genet‐based sex ratios. We used spatially explicit sampling to address these hypotheses in 10 monoecious and 11 dioecious populations of S. latifolia at the northern range limit in Eastern North America. In contrast to our predictions, monoecious clones were significantly larger than dioecious clones, probably due to their higher rates of vegetative growth and corm production, and in dioecious populations, there was no difference in clone size between females and males; ramet‐ and genet‐based sex ratios were therefore highly correlated. Genotypic diversity declined with latitude for both sexual systems, but monoecious populations exhibited lower genotypic richness. Differences in life history between the sexual systems of S. latifolia appear to be the most important determinants of clonal structure and diversity.     

A closer look at the spatial architecture of aphid clones

Nearly 25 years ago, Ellstrand & Roose (1987) reviewed what was known at the time of the genetic structure of clonal plant species. What is the relationship between space and clonal fitness, they asked. What is the best way for a clone to grow within its ecological neighbourhood? The pot had been stirred 10 years previously by Janzen (1977) , who pointed out how little we know about the population biology of clonal organisms like dandelions and aphids. He wondered whether, like good curries, outward appearances masked common ingredients. Because in no small part of the advent of molecular ecology, we know more about clonal life histories today, particularly in plants ( van Dijk 2003 ; Vallejo‐Marín et al. 2010 ). Surprisingly, studies of the spatial architecture of aphid clones have been comparably rare. In this issue of Molecular Ecology, Vantaux et al. characterize the fine‐scale distribution of the black bean aphid (Aphis fabae) and in so doing, help to fill that gap. They describe a moderate degree of intermingling between aphid clones over a growing season—A. fabae clones are ‘sticky’, but only a bit. By mixing, clones directly compete with each other as well. The results of Vantaux et al. (2011) will help to integrate evolutionary patterns in aphids with the appropriate ecological scales out of which those patterns emerge.     

Short-term changes in biomass partitioning of two full-sib clones of Pinus taeda L. under differing fertilizer regimes over 4?months

Clonal forestry is a reality in the southeastern United States due to improvements in somatic embryogenesis of Pinus taeda L. Differences in below-ground carbon (C) allocation between individual genotypes could alter C sequestration and cycling in these clonal plantations. Biomass partitioning may vary between clones and in response to management practices, like fertilization. Our objective was to quantify differences in biomass partitioning due to fertilization in contrasting clones of P. taeda produced from the same full-sib cross. A two (clone)-by-two (fertilizer)-by-four (sequential harvest) factorial randomized complete block design was replicated eight times in a greenhouse for 4 months. Trees were destructively harvested monthly following fertilizer application, so changes in biomass partitioning could be determined. Both clones responded to fertilizer with a short-term reduction in root:shoot ratio and increase in foliar biomass. These changes were ephemeral, returning to control levels within 4 months. Fertilizer responses in below-ground partitioning were due to allometric differences in one clone, but were only attributable to altered rates of development in the other. Ephemeral changes in biomass partitioning in response to fertilizer application were consistent with a theory of short-term physiological response to increased nutrient availability fueling long-term fertilizer growth responses.     

Trade-offs among growth, clonal, and sexual reproduction in an invasive plant Spartina alterniflora responding to inundation and clonal integration

The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass, and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother, daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration.     

PLASTICITY OF OXYLIPIN METABOLISM AMONG CLONES OF THE MARINE DIATOM SKELETONEMA MARINOI (BACILLARIOPHYCEAE)1

Diatom oxylipins have been observed to deleteriously impact copepod reproductive success. However, field studies have revealed very variable and case‐dependent results. Therefore, the plasticity of diatom oxylipin metabolism was studied among four clones of the marine diatom Skeletonema marinoi Sarno et Zingone. Diatom oxylipin metabolism was studied by two lipoxygenase (LOX) activity assays carried out at different pH values and by oxylipin quantification. The four clones showed no major metabolic differences in terms of protein content or growth rate. However, two of the clones produced significantly higher levels of oxylipins than the other two. LOX activity measurements also indicated clonal variability in fatty acid oxidative metabolism. The presence of clone‐specific differences in oxylipin metabolism may play a role in shaping diatom population dynamics by conferring selective advantages to certain clones.     

Will variation among genetic individuals influence species responses to global climate change?

Increased anthropogenic CO₂ emissions in the last two centuries have lead to rising sea surface temperature and falling ocean pH, and it is predicted that current global trends will worsen over the next few decades. There is limited understanding of how genetic variation among individuals will influence the responses of populations and species to these changes. A microcosm system was set up to study the effects of predicted temperature and CO₂ levels on the bryozoan Celleporella hyalina. In this marine species, colonies grow by the addition of male, female and feeding modular individuals (zooids) and can be physically subdivided to produce a clone of genetically identical colonies. We studied colony growth rate (the addition of zooids), reproductive investment (the ratio of sexual to feeding zooids) and sex ratio (male to female zooids) in four genetically distinct clonal lines. There was a significant effect of clone on growth rate, reproductive investment and sex ratio, with clones showing contrasting responses to the various temperature and pH combinations. Overall, decreasing pH and increasing temperature caused reduction of growth, and eventual cessation of growth was often observed at the highest temperature, especially during the latter half of the 15‐day trials. Reproductive investment increased with increasing temperature and decreasing pH, varying more widely with temperature at the lowest pH. The increased production of males, a general stress response of the bryozoan, was seen upon exposure to reduced pH, but was not expressed at the highest temperature tested, presumably due to the frequent cessation of growth. Further to the significant effect of pH on the measured whole‐colony parameters, observation by scanning electron microscopy revealed surface pitting of the calcified exoskeleton in colonies that were exposed to increased acidity. Studying ecologically relevant processes of growth and reproduction, we demonstrate the existence of relevant levels of variation among genetic individuals which may enable future adaptation via non‐mutational natural selection to falling pH and rising temperature.     

Scale Biogenesis in Synurophycean Protists: Phylogenetic Implications

The Synurophyceae is a class of golden-brown, freshwater, photosynthetic flagellates with a world-wide distribution. A well-developed taxonomy exists where genera and species are distinguished by colony or cell morphology or by the siliceous scales that cover the cells. However, phylogenetic relationships within the class are poorly understood, and incongruous taxonomic concepts occur. This study reviews scale morphology from field-collected samples and controlled culturing experiments as well as from studies of scale biogenesis. The information is used to identify homologous silicification surfaces among taxa and to document the diversity of the resulting scale structures. Thirty-two character states are coded into 11 characters in a cladistic analysis of 13 pivotal taxa. Colonial species are emphasized. One most-parsimonious phylogenetic tree is found (HI = 0, CI = 1). Synura lapponica is shown to be most closely related to Tessellaria volvocina. S. sphagnicola emerges at the base of the tree. Mallomonas caudata and the S. petersenii clade emerge from within Sectio Synura. Chrysodidymus synuroideus appears as an ancestral taxon in the Synura spinosa-like clade (i.e., Series Spinosae). The poorly understood developmental bases for some characters, especially secondary scale structures, are identified and may help focus future research.     

CHARACTERISTICS OF SEXUAL AND ASEXUAL RESTING CYST (STATOSPORE) FORMATION IN DINOBRYON CYLINDRICUM IMHOF (CHRYSOPHYTA)1

The reproductive significance of siliceous cysts (statospores) produced by the common vernal chrysophyte Dinobryon cylindricum Imhof has been investigated under defined culture conditions. Three types of statospores have thus far been induced in culture: 1) uninucleate, asexual; 2) binucleate, asexual (potentially autogamic); 3) binucleate, sexual (zygotic). The production of each type of cyst responds differently to an array of nutrient deficiencies (P, N, vitamins, micrometals). An individual clone may be capable of participating in the production of all or only a subset of these types of resting cysts. All D. cylindricum statospores are morphologically identical regardless of their reproductive significance. Sexual reproduction leading to zygotic statospore formation is anisogamous, heterothallic, and involves a gametogenic hormone (erogen) that is apparently continuously released from female clones. Only a single bipolar mating group is documented here and clonal compatibility varies considerably within the mating group. The dynamics of encystment for each type of statospore has been determined relative to the growth of the vegetative cell population. Statospores may be produced either during the exponential phase (intrinsic encystment) or stationary phase (extrinsic encystment) of culture growth depending on the clones involved. The effect of both asexual and sexual resting cyst production on the net growth rate and dynamics of natural chrysophyte populations is discussed. Statospores appear to represent a more flexible reproductive strategy than the resistant zygospores produced by the other common groups of planktonic microalgae.