Distribution and breeding biology of offshore cichlids in Lake Malawi/ Niassa

Synopsis Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km², and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. bigeye, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the large Rhamphochromis group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices.     

Is vegetation in equilibrium with climate? How to interpret late-Quaternary pollen data

Current methods for estimating past climatic patterns from pollen data require that the vegetation be in dynamic equilibrium with the climate. Because climate varies continuously on all time scales, judgement about equilibrium conditions must be made separately for each frequency band (i.e. time scale) of climatic change. For equilibrium conditions to exist between vegetation and climatic changes at a particular time scale, the climatic response time of the vegetation must be small compared to the time scale of climatic variation to which it is responding. The time required for vegetation to respond completely to climatic forcing at a time scale of 10⁴ yr is still unknown, but records of the vegetational response to climatic events of 500-to 1000-yr duration provide evidence for relatively short response times. Independent estimates for the possible patterns and timing of late-Quaternary climate changes suggest that much of the vegetational evidence previously interpreted as resulting from disequilibrium conditions can instead be interpreted as resulting from the individualistic response of plant taxa to the different regional patterns of temperature and precipitation change. The differences among taxa in their response to climate can lead a) to rates and direction of plant-population movements that differ among taxa and b) to fossil assemblages that differ from any modern assemblage. An example of late-Holocene vegetational change in southern Quebec illustrates how separate changes in summer and winter climates may explain the simultaneous expansion of spruce (Picea) populations southward and beech (Fagus) populations northward.     

Modification of an algal culture medium for sustained growth of a saxitoxin-producing isolate of Alexandrium minutum

In order to study saxitoxin (STX) production bymicro-algae in the laboratory, a defined algal culture medium which supports optimum growth over a longtime-period is a requirement. In the development of such a medium, a number of modifications were made to a standard algal culture medium (GP) and growth of a STX-producing isolate of Alexandrium minutum in the different formulations was assessed by measuring maximum cell densities and mean generation times (MGT). All experiments were carried out under controlled conditions in an aerobic atmosphere with increased CO₂. Whilst maximum cell densities in the different modifications were similar, the MGT was significantly shortened by the addition of Tris buffer and the trace metals strontium, selenium and molybdenum. Replacement of natural with artificial seawater and removal of soil extract did not adversely affect algal growth. Five of the six media formulations supported the growth of A. minutumover a 9-month period. This revised version was published online in August 2006 with corrections to the Cover Date.     

A centralized model for creating shared,standardized, microsatellite data that simplifies inter-laboratory collaboration

We demonstrate an efficient model for standardizing microsatellite DNA data among laboratories studying Oncorhynchus mykiss. Eight laboratories standardized 13 microsatellite loci following allele nomenclature of a central laboratory (average inter-laboratory genotyping concordance >98%). Following this central model, we have currently standardized 298 alleles from throughout the species native range. Although we focus here on O. mykiss, our experiences and recommendation apply equally to other broadly distributed species that may benefit from multi-laboratory collaborative data collection.     

A proteomics approach to cloning fenestrin from the nuclear exchange junction of tetrahymena

ABSTRACT. We set out to find the " fenestrin " gene, a gene whose protein is associated with numerous cellular apertures, including the nuclear exchange junction in mating Tetrahymena thermophila . First we developed protocols for imaging and isolating intact nuclear exchange junctions from conjugating cells. Proteins from these junctions were purified using SDS-PAGE, subjected to limited proteolysis, and precise molecular weights were determined by mass spectrometry. Using Protein Prospector^® software and the published Tetrahymena Genome Database, genes for 15 of the most abundant proteins found in our extracts were identified. The most promising candidate was cloned by PCR, fused to yellow fluorescent protein (YFP), and placed under the control of an inducible metallothionein promoter. YFP-localization within live Tetrahymena transformants strongly suggested that one of these genes encoded the fenestrin protein, a result that was subsequently confirmed by Western blotting.     

Interannual fluctuations in copepod abundance and contribution of small forms in the Drake Passage during austral summer

The relative importance of small forms of copepods has been historically underestimated by the traditional use of 200?C300-??m mesh nets. This work quantified the distribution and abundance of copepods, considering two size fractions (<300???m and >300???m), in superficial waters (9?m deep) of the Drake Passage and contributed to the knowledge of their interannual fluctuations among three summers. Four types of nauplii and eleven species of copepods at copepodite and adult stages were identified, with abundance values of up to 13 ind L^?1 and 28,300???g C m^?3. The <300-??m fraction, composed of Oithona similis, small cyclopoids and nauplii, dominated the copepod communities in the 3?years; it accounted for more than 77% of the total number and for between 40 and 63% of the total biomass. Changes in density and biomass values among the three cruises differed according to copepod size fraction and water mass; the >300-??m fraction showed no changes among the 3?years, both in Antarctic (density and biomass) and in Subantarctic waters (density), whereas the <300-??m fraction showed higher (density and biomass) values in 2001 both in Subantarctic and in Antarctic waters. Sea surface temperature and its anomaly accounted for the largest proportion of variability in copepod density and biomass, particularly for the <300-??m fraction.     

Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 1. Leaf position and phenology determine acclimation response

We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO₂ concentration, and ample and limiting N supplies, within a field experiment using free-air CO₂ enrichment (FACE). To understand how leaf age and developmental stage affected any acclimation response, measurements were made on a vertical profile of leaves every week from tillering until maturity. The response of assimilation (A) to internal CO₂ concentration (C_i) was used to estimate the in vivo carboxylation capacity (Vc_max) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (A _sat). The total activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and leaf content of Rubisco and the Light Harvesting Chlorophyll a/b protein associated with Photosystem II (LHC II), were determined. Elevated CO₂ did not alter Vc_max in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vc_max and A _sat was observed, and was found to correlate with reduced Rubisco activity and content. The dependency of acclimation on N supply was different at each developmental stage. With adequate N supply, acclimation to elevated CO₂ was also accompanied by an increased LHC II/Rubisco ratio. At low N supply, contents of Rubisco and LHC II were reduced in all leaves, although an increased LHC II/Rubisco ratio under elevated CO₂ was still observed. These results underscore the importance of leaf position, leaf age and crop developmental stage in understanding the acclimation of photosynthesis to elevated CO₂ and nutrient stress. This revised version was published online in June 2006 with corrections to the Cover Date.