Genetic structure of Pseudo-nitzschia pungens (Bacillariophyceae) populations: Implications of a global diversification of the diatom

Pseudo-nitzschia pungens is a planktonic marine diatom known to be widespread in tropical and temperate coastal waters. We examined the population genetic structure of tropical Southeast Asian populations of P. pungens and compared it with those of northern and southern temperate populations. The secondary structures of the nuclear encoded internal transcribed spacer (ITS) region of 164 strains of P. pungens were modeled and analyzed. The tree revealed three ITS entities: clade I (comprised of P. pungens var. pungens) was distributed mainly in northern temperate waters; clade II (comprised of both P. pungens var. pungens and var. cingulata) was mainly from the NE Pacific; and clade III (comprised of both P. pungens var. pungens and var. aveirensis) was restricted to tropical and warm-temperate waters. Hybrids of both P. pungens var. pungens and var. cingulata co-occurred in clades I and II. Sixty haplotypes were revealed from the sequences of 164 strains. Haplotype diversity inferred from the median-joining network was in accordance with phylogenetic analysis, further supporting the grouping of the P. pungens haplogroups. Our results revealed limited gene flow between P. pungens from tropical and temperate waters, and significant population structure, as estimated by an analysis of molecular variance (AMOVA), with 75% of the total ITS variation found among populations (KST = 0.75). This study suggests that distinct environmental clines, such as ocean thermohaline circulation, have a potential for fragmenting and dispersing global populations of P. pungens. Formation of the Isthmus of Panama, in particular, is speculated to play a role in this allopatric differentiation in P. pungens populations worldwide

Pseudo-nitzschia kodamae sp. nov. (Bacillariophyceae), a toxigenic species from the Strait of Malacca, Malaysia

A recent field survey of Pseudo-nitzschia species from coastal waters of Malaysia demonstrated the presence of a novel morphotype, P. sp. Port Dickson, in the Strait of Malacca. In this study, we revisited the site and established five clonal cultures of this morphotype, assessed the strains’ morphology and genetics, and delineated it as a novel species. As observed by electron microscopy, these strains showed morphological features identical to those of the previous field specimens designated as P. sp. Port Dickson. The cells differ from other Pseudo-nitzschia species in the P. pseudodelicatissima complex sensu lato by their lower densities of fibulae, striae and band striae in 10 mm. Molecular data of the nuclear encoded large subunit ribosomal rRNA gene and the internal transcript spacer region (ITS) further supported the delineation of this novel lineage. Based on both morphological and molecular data, P. sp. Port Dickson is considered to represent a new species, for which we propose the name Pseudo-nitzschia kodamae sp. nov. Production of domoic acid (DA) in the strains was examined by FMOC–LC–FLD. Only strains of P. kodamae were observed with a peak corresponding to DA, giving a concentration of 1.2– 42.5 pg DA cell�1. Screening of Pseudo-nitzschia caciantha, Pseudo-nitzschia batesiana, Pseudo-nitzschia fukuyoi and Pseudo-nitzschia lundholmiae cultures from the same waters, however, showed no detectable DA. This is the first report of a potentially toxigenic Pseudo-nitzschia species from the region

A bloom of Karlodinium australe (Gymnodiniales, Dinophyceae) associated with mass mortality of cage-cultured fishes in West Johor Strait, Malaysia

A recent (February 2014) mass mortality of fishes was observed in the cage-farming region of the West Johor Strait of Malaysia, involving over four different species of cultured fishes, numbering ∼50,000 fish. A field investigation at six stations along the West Johor Strait collected water samples and examined for the presence of harmful species. Dead fishes were collected for necropsy. The phytoplankton composition was dominated by a species of Karlodinium, at a considerably high cell concentration (0.31–2.34 × 106 cells l−1), and constituting 68.8–98.6% of the phytoplankton relative abundance at all stations. Detailed morphological assessment by light and scanning electron microscopy revealed that the species was Karlodinium australe de Salas, Bolch and Hallegraeff. This was supported by molecular evidence of the nuclear encoded large subunit ribosomal gene (LSU rDNA) and the second internal transcribed spacer (ITS2) via single-cell PCR. The sequences of LSU rDNA yielded 3.6–4.0% divergence when compared to the sister taxon, K. armiger; and >6.5% when compared to other Karlodinium species. Fish necropsy showed symptoms similar to those affected by karlotoxin ichthyotoxins. This is the first report of a mass mortality of cage-cultured and wild fishes attributed to the unarmored dinoflagellate K. australe

Recent progress on univariate and multivariate polynomial and spline quasi-interpolants

Polynomial and spline quasi-interpolants (QIs) are practical and effective approximation operators. Among their remarkable properties, let us cite for example: good shape properties, easy computation and evaluation (no linear system to solve), uniform boundedness independently of the degree (polynomials) or of the partition (splines), good approximation order. We shall emphasize new results on various types of univariate and multivariate polynomial or spline QIs, depending on the nature of coefficient functionals, which can be differential, discrete or integral. We shall also present some applications of QIs to numerical methods

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

Fine structure of the diatoms Thalassiosira and Coscinodiscus (Bacillariophyceae) : Light and electron microscopy observation

A study was carried out to examine the morphology of diatom species in Sarawak, Malaysia. Plankton sampling was conducted using 20 μm mesh-size plankton net at two estuaries in Kuching, Sarawak, Malaysia; Santubong and Samariang Batu. Plankton samples were brought back to the laboratory and treated with acid wash before detailed observation under the light and electron microscopes. All samples were identified to species level based on the transmission and scanning electron microscope (TEM and SEM)

Identification of Alexandrium Halim (Dinophyceae) using EPI-fluorescence microscopy

Alexandriumspecies is a group of dinoflagellates comprise of more than 20 different toxic and non toxic species More than half of them are capable in producing a type of neurotoxins called saxitoxins which act as a sodium channel blocker in mammalian nerve system. The occurrences of toxic Alexandrium blooms have increased tremendously over the past decade throughout the world. Lack of distinctive characteristic such as horn, spine or heavy ornamentation of the thecal plates caused the difficulty in identification of this ..

Morphological variation of two Alexandrium species responsible for paralytic shellfish poisoning in Southeast Asia

We examined in clonal cultures the morphological variation of two toxic dinoflagellates, Alexandrium tamiyavanichii and A. minutum, responsible for paralytic shellfish poisoning events in Southeast Asia. The Malaysian strain of A. tamiyavanichii had either a straight or oblique posterior margin on the first apical plate, and a triangular, square to trapezoid-shaped precingular part of the anterior sulcal plate. Morphological variability was also detected in the shape of the first apical plate, its connection to the apical pore, and the position of the ventral pore. In A. minutum, the Malaysian strains showed variation in the sixth precingular plate and the anterior sulcal plate. The length: width ratio of the sixth precingular plate varied from one to two. An anterior sulcal plate with a long left extension also occurred in both of the Malaysian strains. Several characters that have been extensively used in the identification of Alexandrium species have been proven quite variabl

Growth and toxin production of tropical Alexandrium minutum Halim (Dinophyceae) under various nitrogen to phosphorus ratios

Effects of nitrogen to phosphorous (N/P) ratios of two nitrogen sources (nitrate and ammonium) on growth and toxin production of a tropical estuarine dinoflagellate, Alexandrium minutum Halim, were examined using a strain isolated from a bloom at Tumpat Estuary, Malaysia in September 2001. Experiments were carried out in batch cultures, using either nitrate (N-NO3) or ammonium (NNH4) as the nitrogen source at a constant amount, and with initial N/P ratios ranging from 5 to 500. Cell density, residual N and P in the medium, cellular toxin quota (Qt), and toxin composition were analyzed throughout the growths. Our results showed that cell densities and growth rates of A. minutum were severely suppressed under high N/P ratios (>100) in both N-NO3 and N-NH4 treatments. Cells tended to be larger at lower growth rate and P-limited cultures. Toxin profile was relatively constant throughout the experiments, with GTX4/GTX1 as the dominant toxin congeners. Cellular toxin quota (Qt) increased with elevated N/P ratios in both N-NO3 and N-NH4 treatments. Toxin production rate, Rtox, however was enhanced in N-NH4- grown cultures when P was limited, but showed no difference between N-NO3- and N-NH4-grown cultures when P was replete. Our results clearly showed that N/P ratios as well as the nitrogen compounds not only affected the growth of A. minutum, but also the cellular toxin quota and its toxin production rate

First report of Alexandrium taylori and Alexandrium peruvianum (Dinophyceae) in Malaysia waters

The occurrence of Alexandrium taylori and Alexandrium peruvianum is reported for the first time in Malaysia waters. The Malaysian A. taylori isolates were pyriform in shape with a transdiameter range of 36–40 mm and a cell length range of 33– 37 mm. The first apical plate (10) was pentagonal with two distinctive anterior margins. No direct connection between 10 and the apical pore complex was observed. The posterior sulcal plate (S.p.) was large, elongated and oblique to the right with anterior projections. The ventral pore (vp) was relatively large and situated at a confluence point of 10, the second apical (20) and the fourth apical (40) plates. Cells of A. peruvianum were slightly anteriorly and posteriorly compressed. S.p. had an irregular pentagonal shape, with the anterior margin divided into 2 portions. 10 was boomerang-shaped with a large and truncated ventral pore in the middle right margin. The anterior right margin of 10 was straight. The sixth precingular plate (600) was wider than long. The anterior sulcal plate (S.a.) was triangular and lacked a left portion extension. In laboratory cultures, both A. taylori and A. peruvianum produced paralytic shellfish toxins, with GTX4 and GTX6 as the predominant toxin, respectively. This is the first report of PSP toxins production for both species as well as the occurrences in Malaysia waters