Parnassia palustris: a genetically diverse species in Scandinavia

Patterns of variation at nine enzyme loci were examined in 528 plants representing diploid and tetraploid populations of Parnassia palustris s. l. in Europe to assess genetic variation patterns and migration history. Half of the plants showed a unique multilocus phenotype and 75% of all phenotypes occurred only in Scandinavia. Diploid populations showed similar levels of genetic diversity as other widespread outbreeding species with animal-mediated pollination and F -statistics indicated excessive heterozygosity and low rates of gene flow among them. In spite of dramatic population histories caused by the ice ages, diploid populations have maintained the same genetic diversity in Scandinavia as in central and southern Europe. Northern populations have apparently been established through the gradual advance of genetically variable populations and patterns of variation at individual loci indicate different migration routes, from the south-south-west and the east-north-east, respectively. The data strongly support a repeated autoploid origin of the tetraploid cytotype which has been much more successful than the diploid progenitors in colonizing new land since the last ice age. High genetic diversity in Scandinavia has apparently been obtained by a combination of immigration of plants from different source areas and recurrent formation of autotetraploids from diploid progenitors.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 347−372.     

Topographically generated fronts, very nearshore oceanography and the distribution and settlement of mussel larvae and barnacle cyprids

Flow patterns adjacent to shore may prevent or aid shorewardmigration of benthic invertebrate larvae. We hypothesized thata front at the mouth of Sunset Bay, Oregon, prevents shorewarddispersal of larvae, significantly altering settlement of mussellarvae and barnacle cyprids. Settlement was measured at threesets of moorings (three moorings per site) distributed acrossthe front at Sunset Bay. From 6 July to 4 September 2000, sampleswere collected roughly every other day. Concurrently, we madevertical zooplankton tows adjacent to each mooring site andcollected physical oceanographic data. During upwelling-favorablewinds, the front was always present at the bay mouth, separatingsignificantly cooler, saltier and denser offshore water fromthat within the bay. During downwelling winds, the front brokedown and we found no significant difference in the surface physicaloceanographic parameters across the bay mouth. During upwelling,the concentration of mussel larvae was higher seaward of thefront than landward, but there was no significant differencein concentration during downwelling, suggesting that the frontmay act as a barrier to the shoreward dispersal of mussels.Mussel settlement was too low and sporadic to allow statisticalanalysis. There was no difference in cyprid concentrations acrossthe bay mouth whether the front was present or not. Cyprid settlementwas, however, nearly an order of magnitude lower at mooringsseaward of the front than at those landward. A significant cross-correlationwas found between settlement at the offshore mooring and tidalrange (r = 0.464, lag = 0 days) and between settlement at themid and inner moorings and downwelling winds (r = 0.532 midbay, r = 0.532 inner bay, lag = 0 days). Seaward of the front,settlement varied with tidal range, while landward of the front,most settlement occurred as brief pulses during downwellingwinds, periods when the front was not present. We found largedifferences in the distribution of cyprids, and mussel larvaeand cyprid settlement relative to the front; larval distributionsand settlement varied with upwelling versus downwelling windsand was due to differences in the very nearshore (i.e. within100–1000 m of shore) coastal oceanography.     

Observations on the distribution of meroplankton during an upwelling event

The distribution of the larvae of benthic invertebrates wasinvestigated relative to hydrographic structures as a test ofthe hypothesis that larvae behave as if they are passive particles.Observations of larval and oceanographic distributions weremade off Duck, North Carolina, USA in August 1994. Conditionswere characterized by wind-driven coastal upwelling; flow wasgenerally offshore near the surface and onshore below the pycnocline.Within 5 km of the shore the pycnocline was bent upward by theupwelling and it intersected the surface along most of the transects.In zooplankton samples, 20 taxa of larvae were counted (10 bivalveveligers, nine gastropod veligers and one polychaete larvae).Using cluster analysis, larvae were separated into groups withsimilar patterns of distribution and similar affinities to waterproperties. The larvae in Cluster 3 did not display a consistentdistribution pattern beyond that they tended to be found inwarmer surface waters. An earlier paper described the distributionof larvae in the same location during a downwelling event [A.Shanks et al. (2002) J. Plankton Res., 24, 391–416]. Twoof the clusters identified during this previous study were quitesimilar in composition to Clusters 1 and 2 in this study. Inboth studies, Cluster 1 larvae were found below the pycnocline,but during the upwelling event they were transported shorewardwith the advection of the subpycnocline waters by the upwellingcirculation. Within 5 km of the shore, Cluster 1 larvae werefound at depths shallower than the base of the pycnocline andwere often found in patches of high larval concentration. Thepatches were located where the waters were upwelling. Cluster2 larvae were found within 5 km of the shore in both studiesand tended to be highly concentrated in convergences or divergences.Larvae in Cluster 1 generally appeared to be dispersing as passiveparticles, except within the zone of upwelling where they mayhave been swimming against the upwelling flow leading to higherlarval concentrations. Cluster 2 larvae appeared to be consistentlyconcentrated in areas of vertical currents, suggesting thatthey may be attempting to maintain a preferred depth in theface of the vertical flow which would lead to high larval concentrationand nearshore larval distributions despite extensive cross-shelfmovement of water. Despite their slow swimming speeds, the larvaein Clusters 1 and 2 were not swept offshore by the upwellingevent.     

Previous agonistic experience determines both foraging behavior and territoriality in the limpet Lottia gigantea (Sowerby)

Lottia gigantea, the owl limpet, is an algal gardener. Territorial individuals actively defend gardens, which consist of clearedareas in the intertidal zone upon which a thick algal filmdevelops and upon which the territory holder feeds. Smaller,nonterritory holders raid these gardens and graze the algalfilm. Territorial individuals must obtain an adequate ration without compromising the productivity of the garden. In contrast,a nonterritory holder grazing on another limpet's territorymust obtain an adequate ration before it contacts the territoryholder and is driven off. In the laboratory, replicate setsof 10 limpets were trained to behave territorially and nonterritorially.Training mimicked natural encounters between territorial andnonterritorial L. gigantea. Limpets given territorial trainingleft significantly (t = -4.92, df = 9, p =.00041) more algalcover behind when grazing (on average 71%) than did limpetstrained to be nonterritorial (on average 50%). Territorial limpets seldom grazed over the same area more than once (4% of the grazedarea). In contrast, nonterritorial limpets frequently foragedover an area more than once; of the area grazed, 20% had beenvisited more than once. Previous agonistic experience determinesboth territorial behavior and foraging strategies, two of thecritical behaviors necessary for successful gardening behavior.Nonterritorial limpets maximize consumption per unit area, whereas territorial limpets appear to forage prudently, leaving a significantly greater proportion of the plant biomass behind.     

Development and validation of a cytochrome c-coupled assay for pteridine reductase 1 and dihydrofolate reductase

Activity of the pterin- and folate-salvaging enzymes pteridine reductase 1 (PTR1) and dihydrofolate reductase-thymidylate synthetase (DHFR-TS) is commonly measured as a decrease in absorbance at 340 nm, corresponding to oxidation of nicotinamide adenine dinucleotide phosphate (NADPH). Although this assay has been adequate to study the biology of these enzymes, it is not amenable to support any degree of routine inhibitor assessment because its restricted linearity is incompatible with enhanced throughput microtiter plate screening. In this article, we report the development and validation of a nonenzymatically coupled screening assay in which the product of the enzymatic reaction reduces cytochrome c, causing an increase in absorbance at 550 nm. We demonstrate this assay to be robust and accurate, and we describe its utility in supporting a structure-based design, small-molecule inhibitor campaign against Trypanosoma brucei PTR1 and DHFR-TS.     

Tertiary educational assessment with mean individual level knowledge.

It is proposed that Tertiary Educational Assessment should be made using a Curve-Unifying Paradigm with its Scientific And Ultra-Conservative Experiment Ratio. Central Ranking Evaluation And Marking was used to process examination results, generating the Mean Individual Level Knowledge for the group. The concept of MILK grew from the need to encourage the average examination candidate and with it came the need for a Judgmental Understanding Goal. The results of some candidates required further handling by the addition of Student''s Universal Grade Averaging Regimen.