Does pigeon homing depend on stimuli perceived during displacement?

Summary In order to test whether stimuli perceived during passive displacement are important for the subsequent homing, pigeons were transported in an apparatus designed to prevent them from receiving relevant information: The experimental birds were continuously rotated quite rapidly (1.5 cps, radial acceleration about 4 g); in addition, they were exposed to an artificial magnetic field and supplied with bottled air. Control birds were transported in open-air cages on top of the van with free view to all sides.Five pairs of releases from equal distances in opposite directions were conducted. Experienced birds were released at distances of about 15, 90, and 300 km from the loft, inexperienced birds at distances of about 180km. In each pair of releases both groups of pigeons were significantly homeward oriented. Neither in initial orientation nor in homing performance nor in the distribution of recoveries were the experimental birds inferior to the controls or in any perceptable way different from them.It is concluded that homing of passively displaced pigeons is not primarily based on information gathered during the outward journey.Abbreviations EP experimental pigeon(s) - CP control pigeon(s) The possibility to maintain our pigeon loft in a building that belongs to the Zoological Institute (Prof. M. Lindauer) of the University of Würzburg is gratefully acknowledged.     

Impacts of enemy-mediated effects and the additivity of interactions in an insect trophic system

In this study, we used data from both experiments and mathematical simulations to analyze the consequences of the interacting effects of intraguild predation (IGP), cannibalism and parasitism occurring in isolation and simultaneously in trophic interactions involving two blowfly species under shared parasitism. We conducted experiments to determine the short-term response of two blowfly species to these interactions with respect to their persistence. A mathematical model was employed to extend the results obtained from these experiments to the long-term consequences of these interactions for the persistence of the blowfly species. Our experimental results revealed that IGP attenuated the strength of the effects of cannibalism and parasitism between blowfly host species, increasing the probability of persistence of both populations. The simulations obtained from the mathematical model indicated that IGP is a key interaction for the long-term dynamics of this system. The presence of different species interacting in a tri-trophic system relaxed the severity of the effects of a particular interaction between two species, changing species abundances and promoting persistence through time. This pattern was related to indirect interactions with a third species, the parasitoid species included in this study.     

The Use of Artificial Benthic Collectors for Assessment of Spatial Patterns of Settlement of Megalopae of Carcinus maenas (L.) (Brachyura: Portunidae) in the Lower Mira Estuary, Portugal

Artificial benthic collectors have been widely used for the assessment of settlement rates of decapod crustaceans. However, to date no consistent works have addressed spatial patterns of settlement in different estuarine habitats, and no specific studies targeted the interaction of artificial surfaces with the surrounding natural substrate. It may be expected that the artificial surface may produce a different thigmotactic response when compared to the natural substrate, which may limit the use of this technique for assessment of natural settlement rates. In this study the settlement rates of megalopae of the estuarine crab Carcinus maenas were addressed, specifically deploying artificial benthic collectors in different habitats both intertidal and subtidal in the lower Mira estuary. A number of experiments were performed concerning stratification and temporal fluctuations of settlement. Further, the interaction of collector surface with the surrounding substrate was investigated, by comparing settlement rates in natural and artificial substrates in different habitats. Results have shown significant differences in settlement between different estuarine habitats, both in spatially replicated experiments and in a high-resolution temporal experiment. However, comparison between settlement rates in artificial and natural substrates has shown that there is a strong interference between collectors and surrounding substrate, limiting interpretation of results concerning settlement rates in artificial substrate alone.     

Tolerance of Bradyrhizobium japonicum E109 to Osmotic Stress and the Stability of Liquid Inoculants Depend on Growth Phase

Salinity and drought induce osmotic stress in plants and nodulating bacteria. The introduction of soybean in areas with higher soil salt contents or periods of drought pose a challenge for the rhizobial inoculants used to improve nodulation and enhance nitrogen fixation. Bradyrhizobium japonicum is a slow-growing rhizobium used for soybean inoculation that was previously regarded as salt-sensitive. We tested the survival ability of cultures of B. japonicum E109 at the exponential and stationary phases of growth in liquid culture medium against different concentrations of NaCl. We found that stationary-phase cells could tolerate higher levels of salt than exponential-phase cells. This result suggested that the physiological manipulation of the cultures could improve the salt tolerance of this strain. Nonetheless, we also found that exponential-phase cells adapted significantly better to two key situations that a commercial product must face, survival in liquid formulations and survival in soil microcosms resembling conditions of drought. These results suggest that the use of actively growing cells could be an improvement in the production of inoculants. However, it is not cost-effective, because bacteria should be harvested at a time when cell density is lower than that of early stationary-phase cultures, which are normally used in the industry. To overcome this drawback we proved that a fed-batch system can produce exponential-phase cultures with higher cell densities and able to produce liquid inoculants with acceptable survival rates.     

Primaquine can mediate hydroxyl radical generation by Trypanosoma cruzi extracts

Primaquine increases the NAD(P)H dependent oxygen consumption and hydroxyl radical generation by extracts of Trypanosoma cruzi, the causative agent of Chagas' disease. Spin-trapping studies show that hydroxyl radical yield is completely inhibited by catalase and slightly increased by SOD, indicating that radical generation is dependent on the pair primaquine-NAD(P)H and their interaction product, H2O2. Primaquine effects upon Trypanosoma cruzi extracts are compared with those obtained with nifurtimox, a compound effective in the treatment of Chagas' disease. The observed similarity suggests that hydroxyl radical may be involved in the antiprotozoan activity of primaquine.     

Hemoglobin-mediated oxidation of the carcinogen 1,2-dimethylhydrazine to methyl radicals

Oxidation of 1,2-dimethylhydrazine (SDMH) catalyzed by hemoglobin is investigated by oxygen consumption studies, ESR spin-trapping experiments, and gas chromatography. Kinetic analysis and the study of the effects of superoxide dismutase, catalase, and azide on reaction rates indicate that SDMH oxidation is primarily dependent on ferric hemoglobin and autoxidatively formed H2O2. SDMH oxidation generates both methyl and hydroxyl radicals as ascertained by spin-trapping experiments with alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone, 5,5-dimethyl-1-pyrroline-N-oxide, and tert-nitrosobutane. Quantitative estimates indicate that the yield of the methyl radical trapped by alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone is about 8% of the consumed oxygen. Analysis of the gaseous products by gas chromatography shows methane formation at a yield 10 times lower than that obtained for the spin-trap methyl adduct. These results are discussed within the context of the spin-trapping technique. The relative efficiencies of oxyhemoglobin in catalyzing SDMH, 2-phenylethylhydrazine, and phenylhydrazine oxidation, defined as Vmax/KM, are estimated as 1, 13, and 386, respectively. The higher efficiency obtained for the monosubstituted derivatives leads us to suggest that hemoglobin-catalyzed oxidation could be a detoxification route for these compounds. By contrast, SDMH oxidation requires a peroxidase-like activity, a fact that may be related to the efficacy and specificity of this carcinogen.     

A rapid diagnostic test for schistosomiasis mansoni

This article presents an improvement to the Kato-Katz (KK) method, making it faster and more efficient for the visualisation of fertile eggs in stool samples. This modified KK method uses sodium acetate formalin as a fixative and reveals the intensity of infection in less than 1 h, reducing the diagnostic time without increasing the cost. This modified method may contribute to future epidemiological studies in both hospitals and the field due to its rapid and precise diagnostic, which allow for immediate treatment.