Reproduction of Daphnia pulex in a Northern Italy pond

This paper reports on the occurrence of Daphnia pulex in a small fishless water body of Northern Italy (Bodrio del pastore III) and describes its population dynamics. Bodrio is a typical water body originated by erosion from the old Po river-bed surface. During a three year study (2011-2013), D. pulex population showed an increase in density from spring to early summer, it declined in July-August and did not recover, presumably from ephippia, until the following spring. The seasonal dynamics was related to the species thermal tolerance and to invertebrate predation by Chaoborus that resulted in juvenile high mortality and in adaptive predator-avoidance cyclomorphosis. Seasonal variation was observed in the frequency of individuals, most juveniles, showing neckteeth. D. pulex population reproduces by cyclical parthenogenesis and showed a very early investment in sexual reproduction, independent of population density. Males and ephippial females appeared at the beginning of growth season before the density peak according to a typical feature of Daphnia populations from temporary habitats. This suggests a lower influence of the environmental factors on sex determination compared to populations inhabiting more permanent habitats. Lineages that produce males and ephippial females early in the season had lower growth rate than parthenogenetic ones but may preserve from selection pressure by predators a significant percentage of genetic variation linked to sex allocation so that evolution proceeds toward earlier and increased sexual reproduction. Our results suggest further investigation to verify whether the current population is the last remnant of a once much larger metapopulation eventually reduced by anthropogenic disturbances or if it represents the invasion of North American strains

Spatial segregation of Darwinula stevensoni (Crustacea: Ostracoda) genotypes in lentic and lotic habitats of Northern Italy

The clonal structure of apomictic populations of Darwinula stevensoni from Northern Italy lacustrine and riverine habitats has been analysed by allozyme electrophoresis. Thirty two sites were sampled and a total of 748 individuals were analysed. Only one polymorphic locus, Gpi, turned out to have enough variation to be informative. Two thirds of all individuals were homozygous for the most frequent allele but the frequency of this genotype was significantly lower in rivers (16%) than in lakes (92%). As a consequence homozygous clonal females are dominant in lacustrine habitats while heterozygous clonal females are dominant in riverine ones. Differences in genetic structure between habitats were observed even at distances of a few meters. Allele and genotype frequencies are significantly different between Lake Montorfano and its outflow (River Seveso) and between Mantova lakes and their two tributaries, the River Mincio and Corniano Channel. The former is also the outflow of Lake Garda. By laboratory experiments, we previously reported difference between genotypes: homozygous females from Mantova lakes show significantly lower starvation tolerance than heterozygous females from River Mincio. We discuss the hypothesis that habitat segregation is related to this difference. Riverine females should be better adapted to low productivity ecosystems than lacustrine ones

phenology of daphnia in a northern italy pond during the weather anomalous 2014

This note reports a comparison between Daphnia phenology in the weather anomalous 2014 and a previous three years period (2011-2013), in a shallow water body of Northern Italy (Bodrio del pastore III) where we recorded D. pulex. In 2011-2013, Daphnia population showed 1-2 density peaks from mid spring to early summer, it declined in July-August and did not recover, from ephippia, until the following spring. The seasonal dynamics was probably related to the species thermal tolerance. Males and ephippial females appeared at the beginning of growth season according to a typical feature of Daphnia populations from temporary habitats. The presence of the Chaoborus larvae resulted in juvenile adaptive predator-avoidance cyclomorphosis. In 2014, in the study area, mean winter air temperature was much warmer than average recorded during the past three years while it was much colder than average in July and August. This reflected the relatively rainy and cloudy summer months: the winter and summer precipitations total was above the previous three years average. In 2014, Daphnia was found all over the year and showed a maximum peak of density in November. The general increase of Daphnia was related to a shift in D. pulex population phenology, seasonal growth started earlier and lasted longer, and to the occurrence of D. longispina. Both species were identified by genetic markers and phylogenetic analyses of ND5 sequences placed isolates from the Bodrio del pastore III into the European D. pulex group. Both populations reproduced by cyclical parthenogenesis and showed cyclomorphosis. However, D. pulex produced more males and ephippial females than D. longispina. Their seasonal dynamics were quite different: D. longispina dominated in late summer while D. pulex showed the highest density in November. The presence of D. pulex in the Bodrio is important in the framework of conservation ecology especially because we have showed that it is native European strain instead of the invasive North American clone that replaced native D. pulex throughout Africa and was already recorded in Italy. We provide some indications and discuss how Daphnia phenology of shallow lakes of temperate areas may be susceptible to inter-annual variability in weather conditions.</p

Ostracoda of the Italian ricefields thirty years on: new synthesis and hypothesis

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On the origine of the Boson peak

We show that the phonon-saddle transition in the ensemble of generalized inherent structures (minima and saddles) happens at the same point as the dynamical phase transition in glasses, that has been studied in the framework of the mode coupling approximation. The Boson peak observed in glasses at low temperature is a remanent of this transition.Comment: Proceeding of the Pisa conference September 2002, 13 pages+ 4 figures, To be publiched by Journal of Physic

Monte Carlo in radiotherapy: experience in a distributed computational environment

New technologies in cancer radiotherapy need a more accurate computation of the dose delivered in the radiotherapeutical treatment plan, and it is important to integrate sophisticated mathematical models and advanced computing knowledge into the treatment planning (TP) process. We present some results about using Monte Carlo (MC) codes in dose calculation for treatment planning. A distributed computing resource located in the Technologies and Health Department of the Italian National Institute of Health (ISS) along with other computer facilities (CASPUR - Inter-University Consortium for the Application of Super-Computing for Universities and Research) has been used to perform a fully complete MC simulation to compute dose distribution on phantoms irradiated with a radiotherapy accelerator. Using BEAMnrc and GEANT4 MC based codes we calculated dose distributions on a plain water phantom and air/water phantom. Experimental and calculated dose values below ±2% (for depth between 5 mm and 130 mm) were in agreement both in PDD (Percentage Depth Dose) and transversal sections of the phantom. We consider these results a first step towards a system suitable for medical physics departments to simulate a complete treatment plan using remote computing facilities for MC simulations

Osmotic fragility associated with sucrose vacuolation

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