Lower Ordovician sponge bioherms in the Makkol Formation, Taebaeksan Basin, mideast Korea

Summary Isolated sponge bioherms are documented from the Lower Ordovician Makkol Formation of the Taebaek Group in the Taebaeksan Basin, mideast Korea. They are formed by an association of a lithistid spongeArchaeoscyphia, a receptaculidCalathium and stromatolitic algae, and share many features with the Lower Ordovician buildups known elsewhere. These bioherms were established in an incised bottom and reached up to about 1 m in height. As the bioherms grew upward, they were more severely affected by intense wave action and frequent storms, which eventually perished the bioherms. The occurrence ofArchaeoscyphia-Calathium association suggests a close biogeographic link between Korea and North China, supporting the paleogeographic model that the Taebaeksan Basin was connected through contiguous shallow waters to North China in the early Paleozoic.     

ENVIRONMENTAL CONDITIONS, GROWTH AND PRODUCTION OF ANADARA SENILIS (LINNAEUS, 1758) IN A SENEGAL LAGOON

Two populations of Anadara senilis were sampled periodicallyin a lagoon of Senegal. Spatfall occurs in summer during therainy season. Population density decreases from about 50, 000.m^–2,two months after spatfall, down to 6, 750 one year later and750 after 28 months. The average growth, measured on the surfaceof the shell, following the umbo rim axis is 0.8 mm per month.The main reduction in growth rate occurs in winter and endsby the deposition of a growth ring. A second growth reductiontakes place during the rainy season and sometimes ends by aweak growth ring. The microgrowth increments are conspicuousand widest during spring equinox. They are not directly relatedto the tidal cycle, but it was impossible to determine if theyhave a tidal or a daily periodicity. (Received 11 February 1990; accepted 16 July 1993)     

Dendroid morphology and growth patterns: 3-D computed tomographic reconstruction

This paper analyzes the growth patterns of dendrolite in the Zhangxia Formation (Middle Cambrian), Shandong Province, China, using the technique of 3-D computed tomographic reconstruction. Dendroids are classified into V-dendroids, columnar dendroids, and arborescent dendroids, based on morphological characteristics. The means of interconnection between dendroids are classified into trunks, nodules, shoots, and fingers. Stacking and tiering control the gross morphology and structural framework of dendrolite. Stacking is a process of vertical growth, in which V-dendroids create a staircase-like structure. Tiering occurs when a layer of dendroids is covered by sediment, and then partially eroded, allowing a new layer of dendroids to form.A comprehensive blueprint of the structural divisions of dendrolite is presented, according to scale, being divided into micro-, meso-, macro-, and megastructures. The mesostructure, which includes individual dendroids and their combined structures, is subsequently divided into primary (V-dendroid), secondary (columnar and arborescent dendroid), and tertiary (stair and tier) structures and a basic growth model is provided for V-dendroids. The stages of V-dendroid growth are: 1) trunk extension and base expansion, 2) divergence, 3) expansion and convergence, followed by repetition of stages 2 and 3, until 4) growth completion, followed by the subsequent emergence of a new dendroid by either stacking or tiering. This development of systematically ordered structures is suggestive of the reaction of microbial colonies to external environmental conditions.     

High-throughput genotyping assays for identification of glycophorin B deletion variants in population studies

Glycophorins are the most abundant sialoglycoproteins on the surface of human erythrocyte membranes. Genetic variation in glycophorin region of human chromosome 4 (containing GYPA, GYPB, and GYPE genes) is of interest because the gene products serve as receptors for pathogens of major public health interest, including Plasmodium sp., Babesia sp., Influenza virus, Vibrio cholerae El Tor Hemolysin, and Escherichia coli. A large structural rearrangement and hybrid glycophorin variant, known as Dantu, which was identified in East African populations, has been linked with a 40% reduction in risk for severe malaria. Apart from Dantu, other large structural variants exist, with the most common being deletion of the whole GYPB gene and its surrounding region, resulting in multiple different deletion forms. In West Africa particularly, these deletions are estimated to account for between 5 and 15% of the variation in different populations, mostly attributed to the forms known as DEL1 and DEL2. Due to the lack of specific variant assays, little is known of the distribution of these variants. Here, we report a modification of a previous GYPB DEL1 assay and the development of a novel GYPB DEL2 assay as high-throughput PCR-RFLP assays, as well as the identification of the crossover/breakpoint for GYPB DEL2. Using 393 samples from three study sites in Ghana as well as samples from HapMap and 1000 G projects for validation, we show that our assays are sensitive and reliable for genotyping GYPB DEL1 and DEL2. To the best of our knowledge, this is the first report of such high-throughput genotyping assays by PCR-RFLP for identifying specific GYPB deletion types in populations. These assays will enable better identification of GYPB deletions for large genetic association studies and functional experiments to understand the role of this gene cluster region in susceptibility to malaria and other diseases.