Use of C-banding for identifying radiation induced micronuclei

Differentiation of micronuclei (MN) caused by ionizing radiation from those caused by chemicals is a crucial step for managing treatment of individuals exposed to radiation. MN in binucleated lymphocytes in peripheral blood are widely used as biomarkers for estimating dose of radiation, but they are not specific for ionizing radiation. MN induced by ionizing radiation originate predominantly as a result of chromosome breaks (clastogenic action), whereas MN caused by chemical agents are derived from the loss of entire chromosomes (aneugenic action). C-banding highlights centromeres, which might make it possible to distinguish radiation induced MN, i.e., as a byproduct of acentric fragments, from those caused by the loss of entire chromosomes. To test the use of C-banding for identifying radiation induced MN, a blood sample from a healthy donor was irradiated with 3 Gy of Co-60 gamma rays and cultured. Cells were harvested and dropped onto slides, divided into a group stained directly with Giemsa and another processed for C banding, then stained with Giemsa. The frequency of MN in 500 binucleated cells was scored for each method. In preparations stained with Giemsa directly, the MN appeared as uniformly stained structures, whereas after C banding, some MN exhibited darker regions corresponding to centromeres that indicated that they were not derived from acentric fragments. The C-banding technique enables differentiation of MN from acentric chromosomal material. This distinction is useful for improving the specificity of the MN assay as a biomarker for ionizing radiation.     

Any way the wind blows - frequent wind dispersal drives species sorting in ephemeral aquatic communities

Despite an upsurge of interest in spatial interactions between communities and in the impact of dispersal on ecological and evolutionary processes, dispersal patterns and dynamics in natural metacommunities remain poorly understood. Although passive aerial dispersal of freshwater invertebrates is generally accepted, the frequency and relative importance of wind as a vector is still subject of considerable debate. We assessed the importance of wind dispersal in an invertebrate metacommunity in a cluster of 36 temporary rock pools on an isolated mountaintop in South Africa. Wind dispersal was quantified every four days using nine windsocks (about 1.5 m above rock base), placed in the field during one month. Distance to the nearest pool varied from 2 up to 16 m. Wind direction and speed were monitored for the entire period. About 850 propagules (mostly resting eggs) of 17 taxa were captured. The presence of water in the pools (level of exposure of the dormant propagule bank) and the dominant wind direction were the key factors affecting the yield. Wind speed was much less important.
Our results suggest that wind dispersal of propagules from temporary aquatic systems is more frequent than previously thought. This may stabilise the metacommunity by mediating gene flow among populations and facilitating rapid (re)colonisation of patches. On the other hand, wind erosion of the dormant propagule bank may lead to egg bank depletion and local extinction.
The measured frequent wind dispersal most likely fuels strong species sorting processes ultimately shaping the structure of the local communities as observed in an earlier study. To elucidate the link between local dispersal rates and their contribution to long range dispersal is a major challenge for future research on aerial dispersal of aquatic invertebrates.     

Biased competition through variations in amplitude of <Emphasis Type="Italic">γ</Emphasis>-oscillations

Experiments in visual cortex have shown that the firing rate of a neuron in response to the simultaneous presentation of a preferred and non-preferred stimulus within the receptive field is intermediate between that for the two stimuli alone (stimulus competition). Attention directed to one of the stimuli drives the response towards the response induced by the attended stimulus alone (selective attention). This study shows that a simple feedforward model with fixed synaptic conductance values can reproduce these two phenomena using synchronization in the gamma-frequency range to increase the effective synaptic gain for the responses to the attended stimulus. The performance of the model is robust to changes in the parameter values. The model predicts that the phase locking between presynaptic input and output spikes increases with attention.     

The effect of drought stress on heterozygosity–fitness correlations in pedunculate oak (Quercus robur)

Background and Aims

The interaction between forest fragmentation and predicted climate change may pose a serious threat to tree populations. In small and spatially isolated forest fragments, increased homozygosity may directly affect individual tree fitness through the expression of deleterious alleles. Climate change-induced drought stress may exacerbate these detrimental genetic consequences of forest fragmentation, as the fitness response to low levels of individual heterozygosity is generally thought to be stronger under environmental stress than under optimal conditions.

Methods

To test this hypothesis, a greenhouse experiment was performed in which various transpiration and growth traits of 6-month-old seedlings of Quercus robur differing in multilocus heterozygosity (MLH) were recorded for 3 months under a well-watered and a drought stress treatment. Heterozygosity–fitness correlations (HFC) were examined by correlating the recorded traits of individual seedlings to their MLH and by studying their response to drought stress.

Key Results

Weak, but significant, effects of MLH on several fitness traits were obtained, which were stronger for transpiration variables than for the recorded growth traits. High atmospheric stress (measured as vapour pressure deficit) influenced the strength of the HFCs of the transpiration variables, whereas only a limited effect of the irrigation treatment on the HFCs was observed.

Conclusions

Under ongoing climate change, increased atmospheric stress in the future may strengthen the negative fitness responses of trees to low MLH. This indicates the necessity to maximize individual multilocus heterozygosity in forest tree breeding programmes.     

Is sexual organ reciprocity related to legitimate pollen deposition in distylous Pulmonaria (Boraginaceae)?

Heterostyly, i.e. the reciprocal positioning of anthers and stigmas, is a floral polymorphism that is thought to promote disassortative (i.e. between‐morph) pollination and to maintain genetic diversity within populations. Recent research, however, has shown several cases of heterostylous plant species in which the reciprocal positioning of the sexual organs varies, which may affect the likelihood of ‘legitimate’ pollination between compatible morphs, and hence morph fitness and ultimately the stability of this floral polymorphism. In this study, we investigated floral morphology and stigmatic pollen deposition patterns in nine Pulmonaria species (Boraginaceae) across Europe to test the hypothesis that sexual organ reciprocity is related to legitimate pollen deposition. We used a recently developed adaptive accuracy concept to assess the level of reciprocity and to relate inaccuracies in positioning of sexual organs to legitimate pollen deposition measured on stigmas in the field. The nine investigated Pulmonaria species showed substantial deviations from perfect reciprocity, with total inaccuracies varying between 2.9 and 20.3% relative to the squared mean of all anther and stigma heights in the population. In almost all cases, most of the inaccuracy was generated by the high‐level organs. Total pollen deposition was always higher on stigmas of long‐styled individuals, but stigmas of short‐styled individuals received significantly more legitimate pollen than stigmas of long‐styled individuals (71.23% and 38.75% respectively). We also found a weak but significant relationship between measures of inaccuracy and the level of disassortative pollination. Under these conditions of pollen flow, the distylous mating system is predicted to persist in only eleven (27%) of all sampled populations. Overall, these results indicate that deviations from perfect reciprocal herkogamy are common in Pulmonaria and have an impact on legitimate pollen deposition.