Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Effects of dietary lipid source on reproductive performance and tissue lipid levels of Nile tilapia Oreochromis niloticus (Linnaeus) broodstock

Nile tilapia were fed diets supplemented with one of the following lipid sources at 5% level: cod liver oil, corn oil, soybean oil, a coconut oil-based cooking oil or a combination of cod liver oil and corn oil (1 : 1). The control diet had no lipid supplement and tad fish meal as a sole protein source. A diet with soybean meal as a protein source was also tested. The number of females that spawned, spawning frequency, number of fry per spawning, and total fry production were increased at varying degrees by the supplemental lipid sources except for the cod liver oil. Fish fed the soybean oil diet tad the best overall reproductive performance over a 24-week period. Fish fed the cod liver oil diet had the highest weight gain but the poorest reproductive performance. The suplemental lipids significantly increased crude fat levels in the liver and ovaries. Both males and females Ld the cod liver oil diet had the highest levels of fat in the liver and muscle. The ratio of total n-6/n-3 fatty acid in the liver, ovaries and testes was influenced by the supplemental lipid sources. It was highest in fish fed either the soybean oil diet, the corn oil diet, or the soybean meal diet and lowest in fish fed the control diet or the cod liver oil diet.     

Behaviour of Candida utilis during growth in relation to Mg2+ and K+ concentration in sugar cane molasses

Magnesium and potassium ions are present in sugar cane molasses in a concentration of about 0.3% and 2.5%, respectively, which is high enough to support biomass production from Candida utilis. Culture broth with 40 g/l of total reducing substances supplemented by the addition of 1 ppm of Mg²⁺ leads to a higher yield (Y x/s) in batch fermentation experiments. The subsequent addition of Mg²⁺ up to 10 ppm decreases the yield coefficient from 0.53 to 0.42 without affecting the growth rate. Fermentation media supplemented with 1 to 10 ppm of K⁺ decreased both the yield coefficient and the specific growth rate. A Mg/K ratio of about 0.1 seems to be optimal for yeast biomass propagation.     

Study of β-1,3-glucanase activity during autolysis of Aspergillus nidulans by FPLC ion-exchange chromatography

The behaviour of β-1,3-glucanase activity during Aspergillus nidulans autolysis was studied in a basal medium and in the same medium supplemented with 0.5 g l^-1 of microcrystalline cellulose, laminarin, pectin, seedling of Lycopersicum esculentum extract, chitin and xylan respectively. In any case β-1,3-glucanase activity was detected in the culture fluid before the onset of the autolysis, but afterwards a progressive increase of β-1,3-glucanase activity took place with incubation time. In the media supplemented with pectin and seedling of Lycopersicum esculentum extract higher activity in the first days of autolysis was found. The activity at the end of the studied process by sample was 2.5, 2.1, 2.5, 1.9, 2.2, 2.3 and 2.3 U, and the specific activity 83, 53, 85, 55, 64, 90 and 53 mU mg^-1 of protein for each medium respectively. The β-1,3-glucanase activity in Aspergillus nidulans seems to be related to autolysis and not to the presence of different substances in the culture medium. The behaviour of β-1,3-glucanase activity during the degradative process was followed by FPLC ion-exchange chromatography. Three proteins (I, II, III) with β-1,3-glucanase activity were separated and quantified. These proteins have similar behaviour in all the media. Proteins I and II increase progressively with incubation time but protein III is only present at the first and last days of autolysis.     

A highly conserved nuclear gene for low-level phylogenetics: elongation factor-1 alpha recovers morphology-based tree for heliothine moths

Molecular systematists need increased access to nuclear genes. Highly conserved, low copy number protein-encoding nuclear genes have attractive features for phylogenetic inference but have heretofore been applied mostly to very ancient divergences. By virtue of their synonymous substitutions, such genes should contain a wealth of information about lower-level taxonomic relationships as well, with the advantage that amino acid conservatism makes both alignment and primer definition straightforward. We tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene in the noctuid moth subfamily Heliothinae, which has probably diversified since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing heliothine groupings strongly supported by previous morphological and allozyme studies. The single most parsimonious gene tree and the neighbor-joining tree for all nucleotides show almost complete concordance with the morphological tree. Homoplasy and pairwise divergence levels are low, transition/transversion ratios are high, and phylogenetic information is spread evenly across gene regions. The EF-1 alpha gene and presumably other highly conserved genes hold much promise for phylogenetics of Tertiary age eukaryote groups.      

Mesodern-inducing factors and mesodermal patterning

Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation.