Incorporation of Label from Acetate and Laurate into the Mannan of Leishmania donovani via the Glyoxylate Cycle

Leishmania donovani promastigotes in late-stationary phase incorporated label from [2-¹⁴C]acetate and [1-¹⁴C]laurate into the mannose residues of mannan, thus confirming the presence of a functional glyoxylate bypass in these parasitic protozoa. Isolated, washed calls also incorporated label from [2-¹⁴C]acetate and [1-¹⁴C]laurate into mannan during a 1-hr incubation in buffer. Glucose had no effect on label incorporation into mannan, but glutamate caused over a four-fold increase in incorporation from [2-¹⁴C]acetate and a 2.4-fold increase from [1-¹⁴C]laurate. Staurosporine, a protein kinase inhibitor that inhibits glutamate and alanine oxidation, did not inhibit label incorporation from [2-¹⁴C]acetate into mannan. Hyperosmolality caused about a 33% inhibition of label incorporation into mannan. These results show the glyoxylate cycle and/or the subsequent biosynthetic pathway from fructose-6-phosphate to mannan are subject to regulation.     

The role of refuge areas in the phenology of Rhopalosiphum padi in low rainfall cropping areas of South Australia

Extensive surveys of possible aphid habitats in South Australia indicated that irrigated perennial grass pastures in the Mount Lofty Ranges and Lower Murray Valley were summer refuges for Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Large numbers of aphids build up in these pastures each year during autumn (April and May) with numbers peaking in May. The size of the May peak was related to the number of aphids surviving the summer. The proportions of alates were highest in May and August/September. Both peaks coincided with a photoperiod of between 11.2 and 11.5 h, and partial correlations suggested that aphid density, photoperiod and temperature were all significant determinants of alate production.     

Energetic demands during brood rearing in the Wheatear Oenanthe oenanthe

Daily energy expenditure of Wheatears Oenanthe oenanthe during the brood rearing period was measured using the doubly-labelled water technique. The average daily metabolic rate (ADMR) (± 1 s.d.) for 24 individuals was 6.24 ± 1.17 cm³ CO₂/g/h, which corresponds to 95.3 ± 17.0 kJ/day (RQ = 0.75) for a bird of average mass (24.3 g).
There were no significant differences in daily energy expenditure between the sexes, nor between first-year and older birds. Individual males with longer tarsi had lower ADMR but raised larger broods. The ADMR increased at lower ambient temperatures, but this effect disappeared when the positive correlation with rainfall was taken into account. There was no relationship between the natural brood-size and parental daily energy expenditure. A positive correlation between ADMR and the time spent hopping and pecking suggests that foraging activity may account for some of the variability between individuals. The daily change in body-mass was not related to either the individual's age or its sex, and overall was not correlated with the level of daily energy expenditure. For birds examined on the same day, individuals with a higher ADMR had a greater loss of body-mass, which appears to be a high risk strategy. However, Wheatears also exhibited an ability to increase body-mass in conjunction with a drop in their daily energy expenditure.     

Experimental investigations of diel vertical movements by lotic mayflies over substrate surfaces

SUMMARY. 1. The vertical distribution within the substrate of three lotic mayflies (Rhithrogena sp., Paraleptophlebia sp. and Baetis tricaudalus Dodds) was examined in laboratory streams to determine if diel patterns of vertical movement across substrate surfaces existed and whether light intensity, temperature, substrate composition or food availability influenced the observed movement patterns.
2. Rhithrogena sp. and B. tricaudatus exhibited significant diel movement from lower substrate surfaces during the day to upper surfaces at night, although >64% of B. tricaudalus occupied the upper surfaces throughout the 24 h period. In contrast, Parakplophlebia sp. larvae did not change their vertical distribution over the 24 h period.
3. The proportion of mayflies occupying substrate surfaces was influenced by the amount of upper and lower surface area available in the substrate and, possibly, crevice sizes associated with lower surfaces.
4. The movement of Rhiihrogena sp. from lower surfaces during the day to the upper surfaces during the night was influenced by changes in light intensity, but not by changes in food availability or water temperature.
5. The diel patterns of vertical movement exhibited by lotic mayflies in this investigation raise the possibility that at least some biotic interactions may vary over a diel cycle. These could include competitive interactions or temporal cycling of prey availability to predators.     

Reconciling landscape and local views of aquatic communities: lessons from Michigan trout streams

1. Rapidly advancing geographical information systems (GIS) technologies are forcing a careful evaluation of the roles and biases of landscape and traditional site-based perspectives on assessments of aquatic communities. Viewing the world at very different scales can lead to seeming contradictions about the nature of specific ecological systems. In the case of Michigan trout streams, landscape analyses suggest a predictable community shaped by large-scale patterns in hydrology and geology. Most site-based studies, however, suggest these communities are highly variable in structure over time, and are strongly shaped by site-specific physical and biological dynamics. As the real world is comprised of processes operating both at local and landscape scales, an analytical framework for integrating these paradigms is desirable.
2. Decomposition of variances by factorial ANOVA into time, space and time–space interaction terms can provide a conceptual and analytical model for integrating processes operating at landscape and local scales. Using this approach, long-term data sets were examined for three insects and two fishes common in Michigan trout streams. Each taxon had a unique variance structure, and the observed variance structure was highly dependent upon sample size.
3. Both spatially extensive designs with little sampling over time (typical of many GIS studies) and temporally extensive designs with little or no spatial sampling (typical of population and community studies), are biased in terms of their view of the relative importance of local and landscape factors. The necessary, but in many cases costly, solution is to develop and analyse data sets that are both spatially and temporally extensive.     

Genetic differentiation in Daphnia obtusa: a continental perspective

1. The restricted scale of most prior studies of genetic diversity in daphniid populations provides limited information on the geographical patterning of gene frequencies. The present study addresses this gap by examining allozymic divergence in populations of the most broadly distributed daphniid in the warm temperate regions of North America, Daphnia obtusa, across its range.
2. Local populations of this species show the gene frequency differentiation typical of other daphniids. In contrast to other daphniids with broad distributions, however, further divergence is apparent at a larger geographical scale, with North American D. obtusa fragmented into three lineages showing largely allopatric distributions. The three lineages are based primarily on allele frequency shifts at three polymorphic loci and are represented by eastern, central and south-western groupings.
3. Because of this pattern of differentiation, there is no simple monotonic relationship between geographical distance and genetic divergence. Instead, local metapopulations belonging to a specific lineage show little genetic divergence over several thousand km, while marked shifts in gene frequency occur over a few hundred km in regions where different lineages are in contact.