Two new species of the diatom genusChaetoceros (Bacillariophyta)

Two new planktonic diatom species of the genusChaetoceros are described herein:Ch. octagonus andCh. rectus, from material of Baja California coasts and the Gulf of California, respectively;Ch. rectus was also found in a sample from Australian waters.Ch. octagonus is a robust species, with a characteristic pyramidal valve shape, heavily silicified valves and setae, and one central rimoportula on every valve in the chain; it is compared with related species, which show a similar morphology, especially by electron microscopy. It belongs into subg.Chaetoceros, sect.Borealia. Ch. rectus is placed in subg.Hyalochaete, and provisionally within sect.Anastomosantia. Its major characters are: chains, cells, and setae are delicate and fragile, cells are joined in the chain by a bridge which connects sibling intercalary setae, valves and setae are weakly silicified, and one rimoportula is present on terminal valves only. Comparison is made with another species of the same section.Ch. rectus shows a different manner of chain-forming within the genus than previously described in the literature.     

Genome size variation in Chenopodium quinoa (Chenopodiaceae)

The extent and significance of intraspecific genome size variation were analysed in quinoa (Chenopodium quinoa Willd.), a pseudocereal important for human consumption in the Andean region of South America. Flow cytometry, with propidium iodide as the DNA stain, was used to estimate the genome size of 20 quinoa accessions from Ecuador, Peru, Bolivia, Argentina, Chile and the USA. Limited genome size variation was found among the analysed accessions. The differences between the accessions were statistically significant but the maximum inter-accession difference between the populations with the largest and the smallest genome reached only 5.9%. The largest genome was found in population C4 from Chile (mean 3.077 pg/2C) and the smallest in the Peruvian population P2 (mean 2.905 pg/2C). The variation was not correlated with collection site; however, the quinoa accessions analysed in this study belonged to three distinct geographical groups: northern highland, southern highland and lowland.     

Silicification of auxospores in the araphid diatom Tabularia fasciculata (Bacillariophyta)

We report on auxospore wall structure and development in the araphid pennate diatom Tabularia fasciculata. Similar to most other pennates, these auxospores showed a typical bidirectional elongation, but unexpectedly bore no transverse perizonium, and with no detectable silicon during much of their expansion. Energy dispersive X-ray spectroscopy (EDS) analyses segregated auxospores into two types: (1) those containing no detectable silicon and (2) those with measureable amounts. Both types were of similar size. Silica precipitation began throughout the auxospore at or near maximal length, but initially was detectable in isolated regions throughout the structure. Following this initial condition, silicon was consistently detectable throughout auxospores of comparable size and corresponded to deposition of longitudinal perizonium (visible through the thin organic outer layer of the wall in some auxospores), followed by the deposition of the initial valves. Our results raise the question as to how the tubular shape of bidirectionally expanding auxospores up to ∼90 μm long is maintained in the absence of transverse siliceous elements restricting isodiametric expansion of the cell, which are present in all other known pennate auxospores and all but one other diatom. Our study is the first to systematically examine mineral elements of the auxospore wall analytically.     

A probabilistic model of cell size reduction in Pseudo-nitzschia delicatissima (Bacillariophyta)

The pennate planktonic diatom Pseudo-nitzschia delicatissima is very common in temperate marine waters and often responsible for blooms. Due to its surrounding rigid silicate frustrule the diatom undergoes successive size reduction as its vegetative reproduction cycle proceeds. Since a long time the life cycle of diatoms has raised scientific interest and some years ago extensive samples of Pseudo-nitzschia have been taken from coastal waters. Mating and cell size reduction experiments were carried out and served us as a data basis for a probabilistic model of cell size reduction.We applied a homogenous non-stationary continuous-time Markov chain to model the development of individual diatoms from an initial size of about until cell death which occurred when the size reached its low at about . In contrast to conventional curve fitting models we are capable of calculating confidence intervals for estimates of the population ages as well as integrate the process of auxospore formation into the model. We thus propose a unique way to describe the stationary size distribution in a diatom population in terms of cell division and auxospore formation probabilities of its individuals.     

Plastid inheritance in the planktonic raphid pennate diatom Pseudo-nitzschia delicatissima (Bacillariophyceae)

Plastid inheritance was followed during sexual reproduction in the raphid pennate diatom Pseudo-nitzschia delicatissima, using rbcL haplotypes as plastid identification tools. Pseudo-nitzschia species are dioecious and show functional anisogamy with 'male' mating type+(PNd(+)) cells and 'female' PNd(-) cells. Vegetative cells possess two plastids. In P. delicatissima, meiosis results in two gametes that both contribute two plastids to the zygote. The latter initially contains four plastids, but during auxospore development two of these four seem to disappear, and the initial cell emerging from the auxospore appears to contain only two. Here we assessed if the plastids are inherited strictly unipaternally, strictly biparentally, or randomly. We traced the source of the plastids in the F(1) generation by using PNd(+) and PNd(-) parental strains with different rbcL genotypes, here denoted AA (homoplastidial, with two plastids of rbcL haplotype A) and BB (homoplastidial; two plastids of haplotype B). Results showed that 16 out of 96 strains raised each from single F(1) cells had retained two paternal (PNd(+)) plastids, 20 had two maternal (PNd(-)) plastids and the remaining 60 had one maternal and one paternal plastid. This pattern is in accordance with the hypothesis that either two of the four plastids are eliminated during auxospore formation, or that all plastids are retained in the auxospore and segregate in pairs joining at random during the first mitotic division of the initial cell. Heteroplastidic F(1)-strains retained the AB genotype throughout the vegetative phase of their life cycle. The finding that 60 out of 96 F(1) strains were heteroplastidial contrasts with an absence of such genotypes in our strains raised from single cells sampled in the Gulf of Naples.     

Influence of the diadinoxanthin pool size on photoprotection in the marine planktonic diatom Phaeodactylum tricornutum

The pool size of the xanthophyll cycle pigment diadinoxanthin (DD) in the diatom Phaeodactylum tricornutum depends on illumination conditions during culture. Intermittent light caused a doubling of the DD pool without significant change in other pigment contents and photosynthetic parameters, including the photosystem II (PSII) antenna size. On exposure to high-light intensity, extensive de-epoxidation of DD to diatoxanthin (DT) rapidly caused a very strong quenching of the maximum chlorophyll fluorescence yield (F(m), PSII reaction centers closed), which was fully reversed in the dark. The non-photochemical quenching of the minimum fluorescence yield (F(o), PSII centers open) decreased the quantum efficiency of PSII proportionally. For both F(m) and F(o), the non-photochemical quenching expressed as F/F' - 1 (with F' the quenched level) was proportional to the DT concentration. However, the quenching of F(o) relative to that of F(m) was much stronger than random quenching in a homogeneous antenna could explain, showing that the rate of photochemical excitation trapping was limited by energy transfer to the reaction center rather than by charge separation. The cells can increase not only the amount of DT they can produce, but also its efficiency in competing with the PSII reaction center for excitation. The combined effect allowed intermittent light grown cells to down-regulate PSII by 90% and virtually eliminated photoinhibition by saturating light. The unusually rapid and effective photoprotection by the xanthophyll cycle in diatoms may help to explain their dominance in turbulent waters.     

Genome size evolution at the speciation level: The cryptic species complex Brachionus plicatilis (Rotifera)

Background  

Studies on genome size variation in animals are rarely done at lower taxonomic levels, e.g., slightly above/below the species level. Yet, such variation might provide important clues on the tempo and mode of genome size evolution. In this study we used the flow-cytometry method to study the evolution of genome size in the rotifer Brachionus plicatilis, a cryptic species complex consisting of at least 14 closely related species.     

Seascape analysis reveals regional gene flow patterns among populations of a marine planktonic diatom

We investigated the gene flow of the common marine diatom, Skeletonema marinoi, in Scandinavian waters and tested the null hypothesis of panmixia. Sediment samples were collected from the Danish Straits, Kattegat and Skagerrak. Individual strains were established from germinated resting stages. A total of 350 individuals were genotyped by eight microsatellite markers. Conventional F-statistics showed significant differentiation between the samples. We therefore investigated whether the genetic structure could be explained using genetic models based on isolation by distance (IBD) or by oceanographic connectivity. Patterns of oceanographic circulation are seasonally dependent and therefore we estimated how well local oceanographic connectivity explains gene flow month by month. We found no significant relationship between genetic differentiation and geographical distance. Instead, the genetic structure of this dominant marine primary producer is best explained by local oceanographic connectivity promoting gene flow in a primarily south to north direction throughout the year. Oceanographic data were consistent with the significant F_ST values between several pairs of samples. Because even a small amount of genetic exchange prevents the accumulation of genetic differences in F-statistics, we hypothesize that local retention at each sample site, possibly as resting stages, is an important component in explaining the observed genetic structure.     

The composition and structure of the benthic diatom taxocene (Bacillariophyta) near Cape Fiolent (the Crimea,the Black Sea)

For the first time in the waters of the Cape Fiolent Reserve, a high species richness of benthic diatoms was revealed on natural substrates, 290 species and infraspecific taxa (IT), belonging to 281 species, 68 genera, 32 families, 19 orders, and 3 classes. A total of 68 species and 3 genera were previously registered as new for the flora of the Black Sea; 3 species and 1 taxonomic combination were previously described as new to science, as well as 4 species that did not occur in the Black sea in the past 50 and 100 years of research. Navicula (41 species and IT), Amphora (30), Nitzschia (29), Fallacia (20), Cocconeis (17) and Diploneis (16) were the most represented genera. Only one representative was identified in each of the orders Anaulales, Ardissoneales, Thalassionematales, Rhaphoneidales, and Rhopalodiales. The diversity assessment that was carried out using taxonomic distinctness indices, TaxDI, revealed that the structure of the phylogenetic diatom tree was formed by branches with various species saturation levels and different hierarchical subordination, but with the predominance of polyspecific taxa up to at genera level. The TaxDI values (Δ⁺ = 76.71; Λ⁺ = 361.52) indicate the low evenness and high variability of the structure of the benthic diatom taxocene near Cape Fiolent.     

A low-latitude bloom of the surf-zone diatom, Anaulus australis (Centrales, Bacillariophyta) on the coast of Southern Queensland (Australia)

A novel bloom of the surf diatom Anaulus australis Drebes etSchultz was observed in subtropical waters off Surfers' Paradise,Queensland, Australia (27°55'S; 153°23'E) in early May2000. This is the lowest latitude in which an Anaulus australissurf diatom bloom has been reported. Nitrogen stable isotopeanalysis of surf diatoms may indicate anthropogenic nutrientinputs in this environment.     

Seasonal incidence of two co-occurring adult parasitoids of Acalymma vittatum in New York State: Centistes (Syrrhizus) diabroticae and Celatoria setosa

We report the incidence of striped cucumber beetle (Acalymma vittatum [Fabricius]) (Coleoptera: Chrysomelidae) parasitism in bi-weekly samples from diverse farm locations in central New York State over the course of two growing seasons. Two parasitoid species not previously verified in this geographic region were found: Celatoria setosa (Coquillett) (Diptera: Tachinidae) and Centistes (Syrrhizus) diabroticae (Gahan) (Hymenoptera: Braconidae). Parasitism by C. setosa, up to 43%, [mean 8.67%] was comparable to previously published rates. Contrary to the expectations of earlier authors, however, C. diabroticae was found to be ubiquitous and maximum rates of parasitism (~54%) were >threefold greater than the only other published report for this species [C. diabroticae mean 14.36%]. In laboratory assays, we investigated C. diabroticae larval development. We also tested the effects of wasp clone and host beetle sex on C. diabroticae larval development. This is the first documentation of life cycle information for this braconid.     

Phylogeography of island canary (Serinus canaria) populations

Island canaries (Serinus canaria) are characterised as a species living exclusively on North Atlantic islands, mainly on the Azores, Madeira and Canary Islands. Although they are very common in their habitats, their behaviour and breeding system has only recently been studied systematically. To advance the understanding of their ecology and to see if the rather isolated archipelagos are already promoting a genetic differentiation, we investigated their phylogeographic relationship as revealed by mtDNA sequences of the cytochrome b gene and investigated whether this measure corresponds to morphological characteristics within the islands. Genetic distances were very low throughout the distribution range of the species. Although the variation of genetic distances within the population of Pico (Azores) was larger than that on Madeira and Canary Islands, the genetic distances between island populations were very low throughout which prevented a clear phylogeographic differentiation. Moreover, morphological measurements did not reveal a consistent pattern to reliably separate the populations, although the measures of beak length and body weight revealed a clear island-specific differentiation. These data lead to the assumption that the colonisation of the Atlantic islands by the canaries occurred very recently, while there is no persisting gene flow between the populations.     

A comparison of reproduction in co-occurring chthamalid barnacles, Chthamalus stellatus (Poli) and Chthamalus montagui Southward

Reproduction in Chthamalus montagui Southward and Chthamalus stellatus (Poli) has been compared along gradients of wave exposure and tidal height. The proportion of barnacles carrying egg masses was greatest at low shore levels in both species, although the difference between levels was more pronounced in C. stellatus. Both species were found to breed between the beginning of May and the end of September. The mean number of broods released per season in both species ranged from 1.0 to 2.1 at high shore levels, from 2.2 to 3.2 at mid shore levels, and from 2.6 to 4.4 at low shore levels. C. stellatus predominated low on the shore at an intermediately exposed site and on the mid and low shore at the most exposed site. At these places it produced more broods per year than C. montagui. Development of the embryos of the two species was complete after 3 wk in vivo at 15°C. Eggs containing embryos of C. stellatus were larger than those of C. montagui, and within each species, larger barnacles produced larger eggs. Egg masses of C. stellanus included more eggs than those of C. montagui. Brood size in both species was greatest in shelter and least in exposure. Egg production was, however, similar in the two species when adjusted for differences in body mass. Egg production per unit body mass was greatest at an intermediately exposed site.     

Genome properties of the diatom Phaeodactylum tricornutum

Diatoms are a ubiquitous class of microalgae of extreme importance for global primary productivity and for the biogeochemical cycling of minerals such as silica. However, very little is known about diatom cell biology or about their genome structure. For diatom researchers to take advantage of genomics and post-genomics technologies, it is necessary to establish a model diatom species. Phaeodactylum tricornutum is an obvious candidate because of its ease of culture and because it can be genetically transformed. Therefore, we have examined its genome composition by the generation of approximately 1,000 expressed sequence tags. Although more than 60% of the sequences could not be unequivocally identified by similarity to sequences in the databases, approximately 20% had high similarity with a range of genes defined functionally at the protein level. It is interesting that many of these sequences are more similar to animal rather than plant counterparts. Base composition at each codon position and GC content of the genome were compared with Arabidopsis, maize (Zea mays), and Chlamydomonas reinhardtii. It was found that distribution of GC within the coding sequences is as homogeneous in P. tricornutum as in Arabidopsis, but with a slightly higher GC content. Furthermore, we present evidence that the P. tricornutum genome is likely to be small (less than 20 Mb). Therefore, this combined information supports the development of this species as a model system for molecular-based studies of diatom biology. The nucleotide sequence data reported has been deposited in GenBank Nucleotide Sequence Database (dbEST section) under accession nos. BI306757 through BI307753.     

A displaced neritic diatom (Delphineis karstenii) in pelagic sediments of the southeast Atlantic

This paper documents the occurrence ofDelphineis karstenii, a neritic diatom, in pelagic sediments of the northern Cape and southern Angola Basins (southeast Atlantic Ocean). Maximum abundances are found in the southern Angola Basin, although the source area appears to be the diatomaceous sediments which blanket much of the Namibian continental shelf. The observed pattern implies large-scale displacement ofD. karstenii valves first northward along the continental margin, and then westward into deep waters. Transport evidently occurs in the surface waters of the Benguela Current, which flow northward along the Namibian coast and then turn westward, away from the coast of Angola and out into the Angola Basin. These observations suggest thatDelphineis valves, and perhaps other shallow-water diatom valves, may be displaced downslope on other continental margins. Failure to recognize such displacement could lead to incorrect ecological and paleoecological interpretations.     

Distribution of mitochondrial haplotypes (cytb) in Polish populations of Emys orbicularis (L., 1758)

The European pond turtle, Emys orbicularis, inhabits a wide distribution area in the western Palaearctic. Polish populations of pond turtle represent the nominotypical subspecies Emys orbicularis orbicularis. The mitochondrial DNA haplotype (cytb gene) variation among 131 turtles from 26 locations in five regions of Poland was investigated. Five haplotypes belonging to three distinct lineages were identified. Two clades (I and II) were represented by two haplotypes each, while the other clade (IV) was represented by one haplotype. Three haplotypes were reported for the first time in E. orbicularis. The eastern part of Poland is inhabited exclusively by turtles bearing haplotype Ia. The remaining four sequence variants were recorded in western Poland where only the IIb haplotype is considered endemic. The distribution of the other haplotypes in western Poland could thus reflect past introductions or accidental releases. The authors regarded the two locations (Drzeczkowo and Karpicko) that were first included in the western Poland populations as autochthonous catchment areas of haplotype Ia.     

Seasonal changes on planktonic diatom communities along an inshore-offshore gradient in the Gulf of Gabes (Tunisia)

We investigated the composition, biomass and cell size dynamics of the marine planktonic diatom species along a coastal-open sea gradient in relation to the hydrological characteristics, during four oceanographic cruises in July 2005, May–June 2006, September 2006 and March 2007 in the Gulf of Gabes. The study of the marine planktonic diatoms throughout the sampling period showed the presence of 40 different species belonging to 22 pennate and 18 centric diatom species. Centric diatoms were more abundant than the pennate ones; 56% and 44% of total diatom abundance, respectively. Diatoms were very abundant, representing about 60% of the total phytoplankton abundance, with an exception in July 2005 (19%) during which Dictyochophyceae were the most dominant group (41% of the total phytoplankton abundance). Diatoms, which were dominant in the coastal samples, mainly proliferate in the semi-mixing conditions (May–June 2006), whereas they declined in the offshore area, most likely due to silicate shortage. In this period, in spite of the high abundance of diatom planktonic cells, only diatom biomass was correlated with silica amount, proving that biomass was a better ecological bio-indicator than abundance. The results suggest that the marine planktonic diatoms taxa were generally adapted to specific hydrological structure. In fact, the dominance index of diatoms showed that the biodiversity of diatoms increased gradually along the coastal-open sea gradient except in May–June 2006 during which a slight decrease along the inshore towards offshore areas was observed. This index increase depended on a coastal-open sea distance during thermal stratification (July 2005 and September 2006) and mixing periods (March 2007).