Lack Of Directional Selectivity Research Articles

Molecular basis of permethrin and DDT resistance in an Anopheles funestus population from Benin

BackgroundInsecticide resistance in Anopheles mosquitoes is threatening the success of malaria control programmes. In order to implement suitable insecticide resistance management strategies, it is necessary to understand the underlying mechanisms involved. To achieve this, the molecular basis of permethrin and DDT resistance in the principal malaria vector, Anopheles funestus from inland Benin (Kpome), was investigated.ResultsHere, using a microarray-based genome-wide transcription and qRT-PCR analysis, we showed that metabolic resistance mechanisms through over-expression of cytochrome P450 and glutathione S-transferase genes (GSTs) are a major contributor to DDT and permethrin resistance in Anopheles funestus from Kpome. The GSTe2 gene was the most upregulated detoxification gene in both DDT- [fold-change (FC: 16.0)] and permethrin-resistant (FC: 18.1) mosquitoes suggesting that upregulation of this gene could contribute to DDT resistance and cross-resistance to permethrin. CYP6P9a and CYP6P9b genes that have been previously associated with pyrethroid resistance were also significantly overexpressed with FC 5.4 and 4.8, respectively, in a permethrin resistant population. Noticeably, the GSTs, GSTd1-5 and GSTd3, were more upregulated in DDT-resistant than in permethrin-resistant Anopheles funestus suggesting these genes are more implicated in DDT resistance. The absence of the L1014F or L1014S kdr mutations in the voltage-gated sodium channel gene coupled with the lack of directional selection at the gene further supported that knockdown resistance plays little role in this resistance.ConclusionsThe major role played by metabolic resistance to pyrethroids in this An. funestus population in Benin suggests that using novel control tools combining the P450 synergist piperonyl butoxide (PBO), such as PBO-based bednets, could help manage the growing pyrethroid resistance in this malaria vector in Benin.

DUAL-TREE COMPLEX WAVELET TRANSFORM FOR ROBUST VISUAL TRACKING OF MULTIPLE OBJECTS IN VIDEO

We developed a robust multiscale visual tracker of multiple objects in video using the Dual-tree Complex Wavelet Transform (DT-CWT). Real-valued wavelet transforms were previously used for visual tracking, but most suffer from shift variance and lack of directional selectivity. Therefore, we used DT-CWT to avoid such shortcomings. In our tracker, a captured video frame was represented as different subbands using DT-CWT. Then we applied N independent particle filters to a small subset of these subbands, where the choice of these subbands changed adaptively with each captured frame.Finally, we fused the position tracks resulting from these particle filters to obtain final position tracks of multiple moving objects in the video. To demonstrate robustness of our visual tracker, we compared the performance of our multiscale tracker to a standard particle filter full resolution-based tracker and a single wavelet subband (LL)2 based tracker, our multiscale tracker demonstrates significantly better tracking performance.

Genome-Wide Transcription and Functional Analyses Reveal Heterogeneous Molecular Mechanisms Driving Pyrethroids Resistance in the Major Malaria Vector Anopheles funestus Across Africa.

Pyrethroid resistance in malaria vector, An. funestus is increasingly reported across Africa, threatening the sustainability of pyrethroid-based control interventions, including long lasting insecticidal nets (LLINs). Managing this problem requires understanding of the molecular basis of the resistance from different regions of the continent, to establish whether it is being driven by a single or independent selective events. Here, using a genome-wide transcription profiling of pyrethroid resistant populations from southern (Malawi), East (Uganda), and West Africa (Benin), we investigated the molecular basis of resistance, revealing strong differences between the different African regions. The duplicated cytochrome P450 genes (CYP6P9a and CYP6P9b) which were highly overexpressed in southern Africa are not the most upregulated in other regions, where other genes are more overexpressed, including GSTe2 in West (Benin) and CYP9K1 in East (Uganda). The lack of directional selection on both CYP6P9a and CYP6P9b in Uganda in contrast to southern Africa further supports the limited role of these genes outside southern Africa. However, other genes such as the P450 CYP9J11 are commonly overexpressed in all countries across Africa. Here, CYP9J11 is functionally characterized and shown to confer resistance to pyrethroids and moderate cross-resistance to carbamates (bendiocarb). The consistent overexpression of GSTe2 in Benin is coupled with a role of allelic variation at this gene as GAL4-UAS transgenic expression in Drosophila flies showed that the resistant 119F allele is highly efficient in conferring both DDT and permethrin resistance than the L119. The heterogeneity in the molecular basis of resistance and cross-resistance to insecticides in An. funestus populations throughout sub-Saharan African should be taken into account in designing resistance management strategies.

Priority effects vary with species identity and origin in an experiment varying the timing of seed arrival

Exotic species are sometimes phenologically distinct from native species in the invaded community, allowing them to be active when there may be reduced competition for resources. In southern California, annual species are particularly problematic invaders, and prior work has shown that these species germinate earlier in the growing season, giving them a competitive advantage over later‐germinating native species. This result begs the question, if being active earlier is advantageous, why have not native species adapted earlier cues for germination? We hypothesized native species would benefit less from earlier germination than exotic species (potentially due to slower growth following germination), thus negating potential selection for early germination. Here we manipulated planting time for common native and exotic species, growing them in all possible species pairs, to evaluate how competitive outcomes were altered by the time of arrival and the origin of competing species. In contrast to our hypotheses, the exotic species often had lower biomass when planted first, potentially due to disturbance when the second species was planted. In contrast, three out of our four native species benefited from earlier planting (a priority effect). Unlike the potential benefit of arriving early, we found no evidence that being planted one week later resulted in a competitive disadvantage, when compared to being planted simultaneously with a competitor. Further, we found that the magnitude and even direction of priority effects varied depending on the identity of the interacting species. Together these results suggest that a lack of directional selection may prevent adaptation towards earlier germination times of native species. Although this experiment was conducted with a limited suite of species, the results show that the role of seasonal priority effects varies among species, and that native species could benefit from seasonal priority effects in restoration efforts even when in competition with fast‐growing exotic annual species.

Dual tree complex wavelet transform based denoising of optical microscopy images

Photon shot noise is the main noise source of optical microscopy images and can be modeled by a Poisson process. Several discrete wavelet transform based methods have been proposed in the literature for denoising images corrupted by Poisson noise. However, the discrete wavelet transform (DWT) has disadvantages such as shift variance, aliasing, and lack of directional selectivity. To overcome these problems, a dual tree complex wavelet transform is used in our proposed denoising algorithm. Our denoising algorithm is based on the assumption that for the Poisson noise case threshold values for wavelet coefficients can be estimated from the approximation coefficients. Our proposed method was compared with one of the state of the art denoising algorithms. Better results were obtained by using the proposed algorithm in terms of image quality metrics. Furthermore, the contrast enhancement effect of the proposed method on collagen fıber images is examined. Our method allows fast and efficient enhancement of images obtained under low light intensity conditions.

Environmental and genetic influences on queen and worker body size in the social wasp Vespula maculifrons

Many social insects exhibit morphologically distinct worker and queen castes that perform different functions. These functional differences may generate unique selection regimes operating on body size. For example, queens may be under directional selection for large body size, whereas directional selection on worker body size may be limited. Such contrasting selection pressures may differentially affect levels of genetic variation associated with size variation in the two castes. This study sought to determine if genetic effects underlying phenotypic differences varied between the worker and queen castes of the social wasp Vespula maculifrons. We predicted that directional selection would remove genetic variation associated with size differences in the queen caste, whereas a lack of directional selection would tend to maintain genetic variation associated with size differences in the worker caste. We thus (1) calculated broad and narrow sense heritabilities for several morphological traits, (2) examined whether some paternal genotypes produced more morphologically diverse offspring than others, and (3) determined whether trait size variation was associated with genetic variation within colonies. We found that few morphological traits were significantly heritable, indicating that little genetic variance for those traits existed within our study population. We also found that some patrilines produced more morphologically variable offspring than others, suggesting a role of genotype in phenotypic plasticity. And finally, no significant correlations between genetic diversity arising from multiple mating by queens within colonies and trait variation in either caste were found. Overall, our findings indicate a weak effect of genotype on both worker and queen body size variation and are suggestive of a large environmental influence on morphological trait size. Moreover, our results do not indicate that levels of genetic variation underlying size variation differ substantially between castes in this species.

Lack of directional selectivity of cassaine in excitation of the medullary emetic chemoreceptor trigger zone from blood and cerebrospinal fluid in cats.

SummaryCassaine sulfate produced emesis in cats when given by intracerebroventricular (0.02 mg in 0.20 ml) and intravenous (0.5 mg/kg) injection with an average latency of 6 min in either case. The emesis elicited through both routes of administration was eliminated after chronic ablation of the chemoreceptor trigger zone in the area post-rema of the medulla oblongata. The emetic response to intravenous cassaine was blocked by pretreatment with intraventricular cassaine. Intravenous deslanoside only partially blocked the emetic activity of intraventricular cassaine. These results indicate that the emetic receptors of the chemoreceptor trigger zone are accessible to cassaine from the blood as well as from the cerebrospinal fluid, and that identical receptor elements are stimulated by the drug through both routes of administration. This lack of directional selectivity of cassaine stands in contrast to the known selectivity of the cardiac glycosides.