Plankton dynamics along a 180 km reach of the Saint Lawrence River from its headwaters in Lake Ontario

We test the hypothesis that phytoplankton biomass decrease upon entry into the St. Lawrence River from headwaters in Lake Ontario is attributable to a range of causal factors including, decreased photosynthetic fitness due to turbulence, cell loss due to increased flocculation and subsequent sedimentation, decreases in nutrients, and loss due to grazing. In order to test this, changes in phytoplankton and crustacean zooplankton concentrations were examined during four transects along the river, from 8 km offshore in Lake Ontario to the hydroelectric power dam 180 km downstream. Both phytoplankton biomass, measured as chlorophyll-a, and zooplankton decreased markedly upon entry of lake water into the river. Phytoplankton community composition and size changed little over the river reach and tended to reflect that in Lake Ontario. Total phosphorus increased with transit of river water downstream despite low tributary inputs of water into this reach of river. Light availability was high, photosynthetic efficiency suggested that phytoplankton were not physiologically stressed during transit in turbulent waters, and there was no direct evidence of flocculation causing sedimentation of phytoplankton. Grazing by the benthic community (filtering insect larvae and dreissenid mussels) is inferred to be a dominant biological factor as is the geomorphology in this reach of the river, which includes large littoral areas, shoals, and reaches of high water velocity that can increase particle contact in the water column with benthic grazers. The findings of this study have a bearing on understanding how changing water levels in a regulated river might alter areas of benthic grazing.     

Replicated high-density genetic maps of two great tit populations reveal fine-scale genomic departures from sex-equal recombination rates

Linking variation in quantitative traits to variation in the genome is an important, but challenging task in the study of life-history evolution. Linkage maps provide a valuable tool for the unravelling of such trait−gene associations. Moreover, they give insight into recombination landscapes and between-species karyotype evolution. Here we used genotype data, generated from a 10k single-nucleotide polymorphism (SNP) chip, of over 2000 individuals to produce high-density linkage maps of the great tit (Parus major), a passerine bird that serves as a model species for ecological and evolutionary questions. We created independent maps from two distinct populations: a captive F2-cross from The Netherlands (NL) and a wild population from the United Kingdom (UK). The two maps contained 6554 SNPs in 32 linkage groups, spanning 2010 cM and 1917 cM for the NL and UK populations, respectively, and were similar in size and marker order. Subtle levels of heterochiasmy within and between chromosomes were remarkably consistent between the populations, suggesting that the local departures from sex-equal recombination rates have evolved. This key and surprising result would have been impossible to detect if only one population was mapped. A comparison with zebra finch Taeniopygia guttata, chicken Gallus gallus and the green anole lizard Anolis carolinensis genomes provided further insight into the evolution of avian karyotypes.     

Inhibition of oleic acid incorporation into a non-lipid fraction by chloroacetamide herbicides

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction in Scenedesmus acutus. This incorporation is extremely sensitive to the chloroacetamide herbicide, metazachlor (I₅₀= ca 20 nM). Therefore, factors influencing the incorporation of radioactivity from oleic acid into this non-lipid fraction were investigated. S. acutus cells were cultivated under various conditions with or without inhibitors and [¹⁴C]-oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fraction monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethenamid and mefenacet (an oxyacetamide). In contrast, it could not be found with diuron, oryzalin, nor could it be observed with a non-herbicidal metazachlor derivative or iodoacetamide. Incorporation of oleic acid into that fraction required meta-bolically active cells and was stimulated by light. Other fatty acids (16:0, 18:2, and 18:3) were also incorporated into the non-lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contains proteins. However, a possible specific effect of chloroacetamides on the binding of oleic acid to proteins or on the in vitro activity of lipid transfer proteins could not be detected. Not much is known yet about mechanism and chemistry of oleic acid incorporation but this finding opens a new path for investigations towards the primary target of these herbicides.     

Susceptibility and signs associated with mouse adenovirus type 1 infection of adult outbred Swiss mice.

Adult Swiss outbred mice from two sources had a nearly 6,000-fold difference in susceptibility to mouse adenovirus type 1-induced disease. This difference was not attributable to differential organ tropism. Signs associated with mouse adenovirus type 1 infection that have not been previously reported are described at the clinical, gross pathological, and histological levels.     

Pelodera (syn. Rhabditis) strongyloides as a cause of dermatitis – a report of 11 dogs from Finland

Background  

Pelodera (Rhabditis) strongyloides is a small saprophytic nematode that lives in decaying organic matter. On rare occasions, it can invade the mammalian skin, causing a pruritic, erythematous, alopecic and crusting dermatitis on skin sites that come into contact with the ground. Diagnosis of the disease is based on case history (a dog living outdoors on damp straw bedding) with characteristic skin lesions and on the demonstration of typical larvae in skin scrapings or biopsy. Pelodera (rhabditic) dermatitis cases have been reported mainly from Central European countries and the United States.     

Bases and spaces: resources on the web for accessing the draft human genome - II - After publication of the draft

The volume of human genome sequence and the variety of web-based tools to access it continue to grow at an impressive rate, but a working knowledge of certain key resources can be sufficient to get the most from your genome. This article provides an update to Genome Biology 2000, 1(4):reviews2001.1-2001.5.