The effects of time,space and spectrum on auditory grouping in túngara frogs

Male túngara frogs (Physalaemus pustulosus) produce complex calls consisting of two components, a ~350 ms FM sweep called the “whine” followed by up to seven ~40 ms harmonic bursts called “chucks”. In order to choose and locate a calling male, females attending to choruses must group call components into auditory streams to correctly assign calls to their sources. Previously we showed that spatial cues play a limited role in grouping: calls with normal spectra and temporal structure are grouped over wide angular separations (≤135°). In this study we again use phonotaxis to first test whether an alternative cue, the sequence of call components, plays a role in auditory grouping and second, whether grouping is mediated by peripheral or central mechanisms. We found that while grouping is not limited to the natural call sequence, it does vary with the relative onset times of the two calls. To test whether overlapping stimulation in the periphery is required for grouping, the whine and chuck were filtered to restrict their spectra to the sensitivity ranges of the amphibian and basilar papillae, respectively. For these dichotic-like stimuli, grouping still occurred (albeit only to 45° separation), suggesting that stream formation is mediated by central mechanisms.     

Influence of near null magnetic field on in vitro growth of potato and wild Solanum species

The influence of near null magnetic field on in vitro growth of different cultures of potato and related Solanum species was investigated for various exposure times and dates. Potato (Solanum tuberosum L. cv. Désirée) in vitro cultures of shoot tips or nodal segments were used. Three different exposure periods revealed either stimulation or inhibition of root, stem, or leaf in vitro growth after 14 or 28 days of exposure. In one experiment the significant stimulation of leaf growth was also demonstrated at biochemical level, the quantity of chlorophyll a and b and carotenoids increasing more than two-fold. For the wild species Solanum chacoense, S. microdontum, and S. verrucosum, standardized in vitro cultures of nodal stem segments were used. Root and stem growth was either stimulated or slightly inhibited after 9 days exposure to near null magnetic field. Callus cultures obtained from potato dihaploid line 120/19 were maintained in near null magnetic field in 2 different months. For these experiments as well as for Solanum verrucosum, callus cultures recorded either slight inhibition or no effect on fresh weight. For all experiments significant growth variation was brought about only when geomagnetic activity (AP index) showed variations at the beginning of in vitro growth and when the explant had at least one meristematic tissue. Moreover longer maintenance in near null magnetic field, 28 days as compared to 14 days or the controls, can also make a difference in plant growth in response to geomagnetic field variations when static component was reduced to zero value. These results of in vitro plant growth stimulation by variable component of geomagnetic field also sustain the so-called seasonal "window" effect.     

Seasonal effect on tissue culture response and plant regeneration frequency from non-bombarded and bombarded immature scutella of barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis>) harvested from controlled environment

Scutella of immature embryos from two barley cultivars were used for cell culture and transformation. Explants were supplied by continuous growth of donor plants in a 2-week schedule under defined conditions at first plants were grown for 6–7 weeks in a growth chamber, followed by 10–13 weeks in a greenhouse with stringent control of temperature and light round the year. Strong seasonal variation in plant regeneration frequency was observed for both genotypes in non-bombarded (control) as well as bombarded and subsequent selected explants. Scutella from immature embryos of cv. Salome showed increased frequencies of plant regeneration from January to March, reaching highest values in March/April and followed by a continuous and strong decrease from May to December. This tendency was observed in all 3 years studied, although absolute numbers of plant regeneration varied between the years. The same seasonal effect was evident for plant regeneration from immature scutella of cv. Golden Promise. Frequency of embryogenic callus formation was also found to be influenced by season but this effect was not so pronounced as for plant regeneration.     

Diapause incidence in the two-spotted spider mite increases due to predator presence, not due to selective predation

We recently reported evidence for increased diapause incidence in the spider mite Tetranychus urticae in presence of the predatory mite Typhlodromus pyri. This effect may arise from (1) selective predation on non-diapause spider mites, (2) predator-induced diapause in spider mites, or (3) both. Using a different strain of T. urticae, we first recovered increased diapause incidence in association with predators. Then, we tested for selective feeding in two-choice experiments with equal numbers of non-diapause and diapause spider mites. We found that the predatory mite had a significant preference for the latter. This indicates that increased diapause incidence in association with predatory mites is not due to selective predation. Therefore, predator-mediated physiological induction of diapause seems a more likely explanation. The cues leading to induction appear to relate to the predators, not their effects, since predation simulated by spider-mite removal or puncturing did not significantly affect diapause incidence. Why spider mites benefit from this response, remains an open question.This revised version was published online in May 2005 with a corrected cover date.     

The use ofXenopus oocytes and embryos as a route towards cell replacement

When nuclei of somatic cells are transplanted to enucleated eggs ofXenopus, a complete reprogramming of nuclear function can take place. To identify mechanisms of nuclear reprogramming, somatic nuclei can be transplanted to growing meiotic oocytes ofXenopus, and stem cell genes activated without DNA replication. The combination of somatic cell nuclear transfer with morphogen signalling and the community effect may lead towards the possibility of cell replacement therapy. When mechanisms of nuclear reprogramming are understood, it may eventually be possible to directly reprogramme human somatic cell nuclei without the use of eggs.     

Shock wave treatment in medicine

Extracorporeal shock wave therapy in orthopedics and traumatology is still a young therapy method. Since the last few years the development of shock wave therapy has progressed rapidly. Shock waves have changed the treatment of urolithiasis substantially. Today shock waves are the first choice to treat kidney and urethral stones. Urology has long been the only medical field for shock waves in medicine. Meanwhile shock waves have been used in orthopedics and traumatology to treat insertion tendinitis, avascular necrosis of the head of femur and other necrotic bone alterations. Another field of shock wave application is the treatment of tendons, ligaments and bones on horses in veterinary medicine. In the present paper we discuss the basic theory and application of shock waves and its history in medicine. The idea behind using shock wave therapy for orthopedic diseases is the stimulation of healing in tendons, surrounding tissue and bones. This is a completely different approach compared to urology where shock waves are used for disintegration     

A model for radiation-induced bystander effects, with allowance for spatial position and the effects of cell turnover

Bystander effects, whereby cells that are not directly exposed to ionizing radiation exhibit adverse biological effects, have been observed in a number of experimental systems. A novel stochastic model of the radiation-induced bystander effect is developed that takes account of spatial location, cell killing and repopulation. The ionizing radiation dose- and time-responses of this model are explored, and it is shown to exhibit pronounced downward curvature in the high dose-rate region, similar to that observed in many experimental systems, reviewed in the paper. It is also shown to predict the augmentation of effect after fractionated delivery of dose that has been observed in certain experimental systems. It is shown that the generally intractable solution of the full stochastic system can be considerably simplified by assumption of pairwise conditional dependence that varies exponentially over time.     

The impact of mortality on predator population size and stability in systems with stage-structured prey

The relationships between a predator population's mortality rate and its population size and stability are investigated for several simple predator-prey models with stage-structured prey populations. Several alternative models are considered; these differ in their assumptions about the nature of density dependence in the prey's population growth; the nature of stage-transitions; and the stage-selectivity of the predator. Instability occurs at high, rather than low predator mortality rates in most models with highly stage-selective predation; this is the opposite of the effect of mortality on stability in models with homogeneous prey populations. Stage-selective predation also increases the range of parameters that lead to a stable equilibrium. The results suggest that it may be common for a stable predator population to increase in abundance as its own mortality rate increases in stable systems, provided that the predator has a saturating functional response. Sufficiently strong density dependence in the prey generally reverses this outcome, and results in a decrease in predator population size with increasing predator mortality rate. Stability is decreased when the juvenile stage has a fixed duration, but population increases with increasing mortality are still observed in large areas of stable parameter space. This raises two coupled questions which are as yet unanswered; (1) do such increases in population size with higher mortality actually occur in nature; and (2) if not, what prevents them from occurring? Stage-structured prey and stage-related predation can also reverse the 'paradox of enrichment', leading to stability rather than instability when prey growth is increased.     

The stability of predator-prey systems subject to the Allee effects

In recent years, many theoreticians and experimentalists have concentrated on the processes that affect the stability of predator-prey systems. But few papers have addressed the Allee effect with focus on the their stability. In this paper, we select two classical models describing predator-prey systems and introduce the Allee effects into the dynamics of both the predator and prey populations in these models, respectively. By combining mathematical analysis with numerical simulation, we have shown that the Allee effect may be a destabilizing force in predator-prey systems: the equilibrium point of the system could be changed from stable to unstable or otherwise, the system, even when it is stable, will take much longer time to reach the stable state. We also conclude that the equilibrium of the prey population will be enlarged due to the Allee effect of the predator, but the Allee effects of the prey may decrease the equilibrium value of the predator, or that of both the predator and prey. It should also be pointed out that the impact of the Allee effects of predator and prey due to different mechanisms on different predator-prey systems could also vary.