Sexual dimorphism in amphipods: the role of male posterior gnathopods revealed in Gammarus pulex

In the mate-guarding amphipod, Gammarus pulex, the enlarged male posterior gnathopods have been variously suggested to function to grasp and subdue the female, to be used as weapons in fights between males, to signal to the female the male presence and stimulate moult accelaration, egg development or egg extrusion. These hypotheses were tested in a series of experiments, the results of which reveal an unexpected function. Ablation of the posterior gnathopods of males showed that they were neither necessary for, nor advantageous in, establishment and/ or maintenance of precopula mate guarding, with or without competition with intact males. Furthermore, these appendages do not function to advance female moult, or stimulate egg development or extrusion. However, only males with intact posterior gnathopods were able to copulate. We also show that females require a full copulation of several bouts to extrude eggs. We conclude that the function of the posterior gnathopods is to facilitate copulation and suggest future studies focus on the selective pressures acting on copulating males.

Robust face recognition using posterior union model based neural networks

Face recognition with unknown, partial distortion and occlusion is a practical problem, and has a wide range of applications, including security and multimedia information retrieval. The authors present a new approach to face recognition subject to unknown, partial distortion and occlusion. The new approach is based on a probabilistic decision-based neural network, enhanced by a statistical method called the posterior union model (PUM). PUM is an approach for ignoring severely mismatched local features and focusing the recognition mainly on the reliable local features. It thereby improves the robustness while assuming no prior information about the corruption. We call the new approach the posterior union decision-based neural network (PUDBNN). The new PUDBNN model has been evaluated on three face image databases (XM2VTS, AT&T and AR) using testing images subjected to various types of simulated and realistic partial distortion and occlusion. The new system has been compared to other approaches and has demonstrated improved performance.

Effect of pooling samples on the efficiency of comparative studies using microarrays

Motivation: Many biomedical experiments are carried out by pooling individual biological samples. However, pooling samples can potentially hide biological variance and give false confidence concerning the data significance. In the context of microarray experiments for detecting differentially expressed genes, recent publications have addressed the problem of the efficiency of sample pooling, and some approximate formulas were provided for the power and sample size calculations. It is desirable to have exact formulas for these calculations and have the approximate results checked against the exact ones. We show that the difference between the approximate and the exact results can be large.

Effect of short-term macrophage depletion in the development of posterior capsule opacification in rodents

Aim: To evaluate the role of macrophages in the development of posterior capsule opacification (PCO). Methods: For this purpose, an extracapsular lens extraction was performed in 18 consecutive Sprague-Dawley rats. Animals were treated with liposomal clodronate (Cl MDP-lip-treated group, n = 10) or phosphate-buffered saline (PBS) (control group, n = 8) 1 day preoperatively and on the first day postoperatively, and sacrificed 3 days postoperatively. Masked clinical, light microscopy and immunohistochemistry studies were conducted. The Fisher exact test and randomisation test were used to assess statistically differences between groups. Results: A statistically significant reduction in the number of macrophages (ED1+, ED7+, ED8+) was found in the Cl MDP-lip-treated group compared with the PBS-lip-treated group (p = 0.048, p = 0.004, p = 0.027, respectively). There were no statistically significant differences with regards to the presence/absence of central opacification (p = 0.29) and capsular wrinkling (p = 0.21) as detected clinically between groups. Similarly, a qualitative evaluation of the degree of PCO with regards to lens epithelial cell (LEC) proliferation, capsular wrinkling and Soemmerring ring formation showed no statistically significance between groups (p = 0.27, p = 0.061, p = 1.0, respectively). However, a statistically significant reduction in the number of lens epithelial cells (LEC) counted in the centre of the posterior capsule was found in the Cl MDP-lip- treated group (p = 0.009). Conclusion: Depletion of macrophages was accompanied by a reduction in LEC in the centre of the posterior capsule in rodents.