Abundance and diversity of planktonic rotifers in the Po River

Zooplankton samples from the middle reach of the Po River were collected daily from 27 July to 24 August 1988 from a station located near Viadana. Changes in the biocoenosis structure were analyzed in relation to variations in flow rate. Rotifers accounted for more than 99% of the total zooplankton (protozoans excluded) in every sample. The dominant species were Brachionus calyciflorus, Brachionus bennini, Brachionus budapestinensis and Epiphanes macrourus. Under scanty flow conditions, the taxocoenosis showed marked stability. An increase in flow rate acts as a disturbance factor leading to a significant decrease in both total density and dominance.     

Evidence for the lateral intraparietal area as the parietal eye field.

It has long been appreciated that the posterior parietal cortex plays a role in the processing of saccadic eye movements. Only recently has it been discovered that a small cortical area, the lateral intraparietal area, within this much larger area appears to be specialized for saccadic eye movements. Unlike other cortical areas in the posterior parietal cortex, the lateral intraparietal area has strong anatomical connections to other saccade centers, and its cells have saccade-related responses that begin before the saccades. The lateral intraparietal area appears to be neither a strictly visual nor strictly motor structure; rather it performs visuomotor integration functions including determining the spatial location of saccade targets and forming plans to make eye movements.     

Amiloride-sensitive Na+ pathways in capillary endothelial cell swelling during hemorrhagic shock.

We recently discovered that the endothelium of skeletal muscle capillaries swells in the low-flow ischemia induced by hemorrhagic shock. The present study was undertaken to determine the Na+ transmembrane pathways involved in this swelling, since hypoxic cell swelling is attributed to an influx of Na+ and water. In an initial series of experiments, amiloride (5 mg/kg body wt), which blocks multiple Na+ pathways, was infused intravenously into anesthetized rabbits 30 min prior to shock (40% single-withdrawal hemorrhage). Intravital microscopy of treated capillaries in the rabbit tenuissimus muscle showed that after a 1-h shock period, there was no endothelial cell swelling, as evidenced by no measurable change in the width of red blood cells traversing the capillary. In contrast, the swollen endothelium of untreated capillaries reduced the luminal diameter by 20-25% with a preserved stationary abluminal membrane. The specific effects of amiloride on Na+ transport were investigated with amiloride analogues. Animal pretreatment with 5-(N,N-hexamethylene)amiloride, a selective inhibitor of Na(+)-H+ activity, in a dose of 0.5 mg/kg did not significantly mitigate shock-induced swelling; however, a dose of 1 mg/kg completely prevented it. Phenamil, a selective inhibitor of Na+ channel conductance, even at a potent dosage of 0.5 mg/kg, did not affect swelling. These results suggest a primary role for Na(+)-H+ exchange in endothelial cell swelling during hemorrhagic shock, possibly as a means to regulate cellular pH, which may become acidic during ischemia. Narrowed capillaries with elevated hydraulic resistances could delay and diminish resumption of microcirculatory flow on shock resuscitation.     

Flora of the Isle su Cardulinu (Southern Sardinia)

Abstract

The results of two years of collection in a small isle in the southern Sardinia are reported, consisting in a floristic list of 116 entities distributed in 96 genera and 41 families. The biological spectrum of this flora puts in evidence a typical Mediterranean environment, characterized by a marked summer dryness. The ratio: number of entities/surface of the studied site has been compared with that of other small southern Sardinian islands, resulting the highest value. This floristic aspect, as well as differences in the biological spectrum, is interpreted as the result of the presence in the area under study of a desultory link with the mainland, in form of a sandy isthmus. This seems important in breaking the biological balance of the small island.     

Testing the short-term effects of a fish invader on the trophic ecology of a closely related species

The effects of invaders on native species are usually tested using species mean trait values over long time scales. However, considering individual variation over short timescales can help us better understand the interaction between invaders and native species. We compared trophic traits of the non-native guppy (Poecilia reticulata) and the native Brazilian poeciliid Phalloceros harpagos using experiments simulating the early stages of an invasive process. We used short-term mesocosms to simulate an early invasion scenario, where the two species were placed together, and a pre-invasion scenario, where species were kept separated, and analyzed interspecific and intraspecific trophic variability. We also compared the foraging efficiency of species in laboratory experiments. We found no differences on the mean diet of both species between pre and early invasion treatments. At the individual level, in the early invasion scenario, individuals of both species reduced their trophic niche as a probable effect of the presence of the heterospecific. Phalloceros harpagos had higher consumption rates than guppies indicating greater efficiency in feeding on invertebrates. Our results suggest that non-native species were not intrinsically better consumers of high-quality resources. Instead, intraspecific variation might be playing an overlooked role in shaping interactions between species during the early stages of invasion.