Growth and development of immature life stages ofPropylaea 14-punctata L. andCoccinella 7-punctata L. [Col.: Coccinellidae] simulated by the metabolic pool model

The conversion of aphid prey tissue (Acyrthosiphon pisum Harris) into predator biomass (immature life stages ofPropylaea 14-punctata L. andCoccinella 7-punctata L.) is calculated by plotting weight gain against assimilation (i.e. consumption minus egestion). This concept is added to the metabolic pool model byGutierrez et al. (1981) that enables the simulation of growth and development of a predator on a physiological basis. Physiological time is expressed in daydegrees above lower development thresholds for both species. Visual examination of observed and calculated values showed that the model satisfactorily describes the growth patterns of the above predators.      

Microbial metabolism of chlorosalicylates: effect of prolonged subcultivation on constructed strains

The hybrid strain Pseudomonas sp. WR4016 was subcultivated with increasing concentrations of 5-chlorosalicylate (510 mM) as sole carbon source over a period of 9 months. At intervals of approximately 3 months derivative strains WR4017, WR4018 and WR4019 were isolated which exhibited higher growth rates and increased substrate tolerance. Comparative analysis of the turnover rates of the key enzymes in chlorosalicylate degradation showed that the adaptation process did not result from structural modifications of these proteins. Instead, balanced over-production of the salicylate hydroxylase and catechol 1,2-dioxygenase prevented the accumulation of toxic chlorocatechols and accounted for the reduction of the doubling times with 4- or 5-chlorosalicylate. A comparative analysis of a genetically engineered chlorosalicylate degrader PL300-1 showed similar regulatory patterns as the most advanced isolate WR4019 from the adaptation series.     

Models for age structured populations with distributed maturation rates

In the use of age structured population models for agricultural applications such as the modeling of crop-pest interactions it is often essential that the model take into account the distribution in maturation rates present in some or all of the populations. The traditional method for incorporating distributed maturation rates into crop and pest models has been the so-called distributed delay method. In this paper we review the application of the distributed delay formalism to the McKendrick equation of an age structured population. We discuss the mathematical properties of the system of ordinary differential equations arising out of the distributed delay formalism. We then discuss an alternative method involving modification of the Leslie matrix.     

Survival of the parasitic protozoan, Babesia bigemina, in blood cooled at widely different rates to -196 degrees C

Survival of the parasitic protozoan, Babesia bigemina, in blood cooled at widely different rates to ? 196°C. International Journal for Parasitology4: 169–172. The infectivity of Babesia bigemina in blood containing 2 m DMSO was tested in 99 cattle after the blood had been cooled to ? 196°C at eight rates ranging from 0·73–3070°C/min. Blood cooled at each rate was infective; 95 of the recipients became infected, the exceptions being four of the seven cattle inoculated with blood cooled at 3070° C/min. The infectivity of blood cooled at 39, 82 and 212°C/min was higher than that of blood cooled at slower or faster rates. Least depression of infectivity occurred at 82°C/min.     

DNA microenvironments and the molecular clock

Summary A few years ago we presented a stationary Markov model of gene evolution according to which only homologous genes from not too divergent species obeying the condition of being stationary may behave as reliable molecular clocks. A compartmentalized model of the nuclear genome in which the genes are distributed in compartments, the isochores, defined by their G+C content has been proposed recently. We have found that only homologous gene pairs that are stationary, and belong to the same isochore, can be used consistently for the determination of phylogeny and base substitution rate. In particular, for the rodent-human couple, only about half of the homologous gene pairs are stationary. Stationary genes evolve at the third silent codon position with the same velocity independent of the genes and base composition. By contrast, nonstationary genes display apparent rate values (pseudovelocities) that are significantly higher. Our results cast doubt upon recent claims of a large acceleration in the rate of molecular evolution in rodents.     

Regionally selective alterations in enzymatic activities and metabolic fluxes during thiamin deficiency

To further elucidate the molecular basis of the selective damage to various brain regions by thiamin deficiency, changes in enzymatic activities were compared to carbohydrate flux through various pathways from vulnerable (mammillary bodies and inferior colliculi) and nonvulnerable (cochlear nuclei) regions after 11 or 14 days of pyrithiamin-induced thiamin deficiency. After 11 days,large decreases (–43 to –59%) in transketolase (TK) occurred in all 3 regions; 2-ketoglutarate dehydrogenase (KGDHC) declined (–45%), but only in mammillary bodies; pyruvate dehydrogenase (PDHC) was unaffected. By day 14, TK remained reduced by 58%–66%; KGDHC was now reduced in all regions (–48 to –55%); PDHC was also reduced (–32%), but only in the mammillary bodies. Thus, the enzyme changes did not parallel the pathological vulnerability of these regions to thiamin deficiency.¹⁴CO₂ production from¹⁴C-glucose labeled in various positions was utilized to assess metabolic flux. After 14 days, CO₂ production in the vulnerable regions declined severely (–46 to 70%) and approximately twice as much as those in the cochlear nucleus. Also by day 14, the ratio of enzymatic activity to metabolic flux increased as much as 56% in the vulnerable regions, but decreased 18 to 30% in the cochlear nuclei. These differences reflect a greater decrease in flux than enzyme activities in the two vulnerable regions. Thus, selective cellular responses to thiamin deficiency can be demonstrated ex vivo, and these changes can be directly related to alterations in metabolic flux. Since they cannot be related to enzymatic alterations in the three regions, factors other than decreases in the activity of these TPP-dependent enzymes must underlie selective vulnerability in this model of thiamin deficiency.Abbreviations KGDHC 2-ketoglutarate dehydrogenase complex EC 1.2.4.2., EC 2.3.1.61, EC 1.6.4.3. - PDHC pyruvate dehydrogenase complex EC 1.2.4.2., EC 2.3.1.12, EC 1.6.4.3 - TK transketolase (EC 2.2.1.1) - TPP thiamin pyrophosphate     

Predicting variability in catch-per-effort in Atlantic cod, Gadus morhua, trap and gillnet fisheries

The relationships between catch rates and fish abundance, hydrographic conditions and fishing effort, for Atlantic cod caught by trapnets (fixed gear) and gillnets (non-fixed gear) in the northern Gulf of St Lawrence have been quantified. Daily changes in trap catch rates were accounted for by changes in salinity, currents and mean local cod densities in 1985 ( R ²= 0.78), and predicted 1986 trap catch rate changes (by 1985 model) were correlated significantly with those observed ( r = 0.60, P < 0.05). In contrast, the daily changes in 1985 gillnet catch rates were determined by currents, maximum (not mean) local cod densities, and fishing effort (negative) ( R ²= 0.68), while predicted 1986 gillnet catch rates (by 1985 model) were significantly correlated with those observed ( r = 0.35, P < 0.05). Seasonal catchability coefficients of the traps were similar in 1985 and 1986, but for gillnets this index was an order of magnitude higher in 1986 than in 1985.     

Why fly? The possible benefits for lower mortality

In adult endotherms—birds and mammals—mortality rates are lower in flying than non-flying species. Rates vary with size, but allowing for this they are higher in penguins than flying birds, and in rodents than bats. These observations are most simply explained in terms of predation since flight, allowing movement in three dimensions, increases the chances of escape.
There are various problems in obtaining and comparing data on rates of mortality and this partly explains a wide scattering of points. Nevertheless the main results are statistically significant, mostly at P<0.001. Amongst birds, there are several other significant differences. Mortality rates are lower at lower latitudes, and in aquatic compared to terrestrial species, with cliff-nesters having lower rates than other aquatic birds and co-operative breeders than other terrestrial ones. No latitudinal effect was detected in mammals. The exceptionally low rates of mortality in bats and swifts are attributed to their being particularly hard to catch.