Ethnobiology of snappers (Lutjanidae): target species and suggestions for management

In this study, we sought to investigate the biology (diet and reproduction) and ethnobiology (fishers knowledge and fishing spots used to catch snappers) of five species of snappers (Lutjanidae), including Lutjanus analis, Lutjanus synagris, Lutjanus vivanus, Ocyurus chrysurus, and Romboplites saliens at five sites along the northeast (Riacho Doce, Maceió in Alagoas State, and Porto do Sauípe, Entre Rios at Bahia State) and the southeast (SE) Brazilian coast (Paraty and Rio de Janeiro cities at Rio de Janeiro State, and Bertioga, at São Paulo State.). We collected 288 snappers and interviewed 86 fishermen. The stomach contents of each fish were examined and macroscopic gonad analysis was performed. Snappers are very important for the fisheries of NE Brazil, and our results indicated that some populations, such as mutton snapper (L. analis) and lane snapper (L. synagris), are being caught when they are too young, at early juvenile stages. Local knowledge has been shown to be a powerful tool for determining appropriate policies regarding management of target species, and artisanal fishermen can be included in management processes. Other suggestions for managing the fisheries are discussed, including proposals that could provide motivation for artisanal fishermen to participate in programs to conserve resources, such as co-management approaches that utilize local knowledge, the establishment of fishing seasons, and compensation of fishermen, through 'payment for environmental services'. These suggestions may enhance the participation of local artisanal fishermen in moving to a more realistic and less top-down management approach of the fish population.     

Dual Acylation Accounts for the Localization of α19-Giardin in the Ventral Flagellum Pair of Giardia lamblia

A Giardia-specific protein family denominated as α-giardins, represents the major protein component, besides tubulin, of the cytoskeleton of the human pathogenic parasite Giardia lamblia. One of its members, α19-giardin, carries an N-terminal sequence extension of MGCXXS, which in many proteins serves as a target for dual lipid conjugation: myristoylation at the glycine residue after removal of the methionine and palmitoylation at the cysteine residue. As the first experimental evidence of a lipid modification, we found α19-giardin to be associated with the membrane fraction of disrupted trophozoites. After heterologous coexpression of α19-giardin with giardial N-myristoyltransferase (NMT) in Escherichia coli, we found the protein in a myristoylated form. Additionally, after heterologous expression together with the palmitoyl transferase Pfa3 in Saccharomyces cerevisiae, α19-giardin associates with the membrane of the main vacuole. Immunocytochemical colocalization studies on wild-type Giardia trophozoites with tubulin provide evidence that α19-giardin exclusively localizes to the ventral pair of the giardial flagella. A mutant in which the putatively myristoylated N-terminal glycine residue was replaced by alanine lost this specific localization. Our findings suggest that the dual lipidation of α19-giardin is responsible for its specific flagellar localization.The human pathogenic parasite Giardia lamblia (syn. Giardia intestinalis), a phylogenetically basal eukaryote (41), is the causative agent of giardiasis, an intestinal disease most prevalent in developing countries (39). The protist has a simple life cycle consisting of two stages, a vegetative trophozoite dwelling in the host intestine and an infective cyst form. Proliferating trophozoites are distinguished by a complex cytoskeleton whose most striking feature are eight flagella and a ventral disk, by which the parasite attaches to the intestinal epithelium of the host (11). As a diplomonad protist, the parasite possesses four different pairs of flagella, of which only the ventral and posterolateral ones are replicated in the first round of the cell cycle; the other two pairs require two further cell divisions for their complete renewal (32).Besides tubulin, the Giardia-specific giardins account for the major protein components of the giardial cytoskeleton (7, 36). From these 30- to 45-kDa proteins, the α-giardins have been recognized, based on sequence similarities, as annexin homologues (28). They represent a multiple set of all-helical proteins distinguished by four annexin domains each. We have previously confirmed that some α-giardins, indeed, satisfy a criterion of annexins, i.e., Ca²⁺-dependent association with phospholipids (1, 13, 43). Hence, these giardins have been nominated as protozoan annexins E1 to E3 (9). However, in contrast to annexins of multicellular organisms, some α-giardins contain specific sequence motifs in the fourth annexin domain, and these motifs are located at the cytoplasmic face and may make contact between the plasma membrane and the cytoskeleton within the cell (35, 43).The genome of G. lamblia possesses a total of 21 α-giardin-encoding genes (27, 30, 47). The particular importance of their gene products for the parasite may be indicated by the following: the human genome contains only 12 annexin genes, and the genome of Saccharomyces cerevisiae has none at all. Phylogenetic analyses of the α-giardin genes revealed that 19 members of this family evolved from two widely ramified branches, whereby the genes coding for α14-giardin (annexin E1, according to the annexin nomenclature) and α19-giardin jointly form a single arm (47). α19-Giardin, the subject of the present study, carries a predicted N-terminal sequence extension with an MGCXXS motif known as a target for dual fatty acylation, i.e., myristoylation at the N-terminal glycine and palmitoylation at the cysteine residue (8). However, no experimental data for a lipid conjugation to this protein and any other giardin are currently available.In the present study, we provide the first evidence that α19-giardin indeed can be both myristoylated and palmitoylated. In contrast to α14-giardin, which we found to be located in all giardial flagella as well as in the median body of the trophozoites (43, 46), α19-giardin appears exclusively localized to the ventral flagella of the trophozoites and is restricted to those portions protruding outside the cell body.     

Scene content selected by active vision

The primate visual system actively selects visual information from the environment for detailed processing through mechanisms of visual attention and saccadic eye movements. This study examines the statistical properties of the scene content selected by active vision. Eye movements were recorded while participants free-viewed digitized images of natural and artificial scenes. Fixation locations were determined for each image and image patches were extracted around the observed fixation locations. Measures of local contrast, local spatial correlation and spatial frequency content were calculated on the extracted image patches. Replicating previous results, local contrast was found to be greater at the points of fixation when compared to either the contrast for image patches extracted at random locations or at the observed fixation locations using an image-shuffled database. Contrary to some results and in agreement with other results in the literature, a significant decorrelation of image intensity is observed between the locations of fixation and other neighboring locations. A discussion and analysis of methodological techniques is given that provides an explanation for the discrepancy in results. The results of our analyses indicate that both the local contrast and correlation at the points of fixation are a function of image type and, furthermore, that the magnitude of these effects depend on the levels of contrast and correlation present overall in the images. Finally, the largest effect sizes in local contrast and correlation are found at distances of approximately 1 deg of visual angle, which agrees well with measures of optimal spatial scale selectivity in the visual periphery where visual information for potential saccade targets is processed.     

Electrophysiological correlates of synchronous neural activity and attention: a short review

Attentional selection implies preferential treatment of some sensory stimuli over others. This requires differential representation of attended and unattended stimuli. Most previous research has focused on pure rate codes for this representation but recent evidence indicates that a mixed code, involving both mean firing rate and temporal codes, may be employed. Of particular interest is a distinction of attended from unattended stimuli based on synchrony within neural populations. I review electrophysiological evidence at macroscopic, mesoscopic and microscopic spatial scales showing that the degree of synchronous activity varies with the attentional state of the perceiving organism.     

Axial-shear interaction effects on microdamage in bovine tibial trabecular bone

Because many osteoporotic fractures occur during a fall, understanding the effect of off-axis loads on initiation and propagation of microdamage in trabecular bone should provide further insight into the biomechanics of age-related fractures. Fourteen on-axis cylindrical specimens were prepared from 12 bovine tibiae. Fluorescent stains were used to label the microdamage due to a sequence of compressive and torsional damaging loads. The mean decrease in Young's modulus was over four times greater than that in the shear modulus after the compressive overload, while there was no difference between the decrease in the axial and torsional stiffnesses after the torsional overload. The total microcrack density due to compression was uniform across the radius of the cylindrical specimens, while the mean density of microcracks due to torsional overloading increased from the axis of the cylindrical specimen to the circumference. The high density of microcracks near the axis of the specimen following torsional overloading was unexpected because of the low strains. Nearly 40% of the microcracks due to torsion propagated from pre-existing microcracks caused by axial compression, indicating that existing microcracks may extend at relatively low strain if the loading mode changes. The propagating microcracks were, on average, longer than the initiating microcracks due to either compressive or torsional loading. Damage due to axial compression appears to increase the susceptibility of trabecular bone to damage propagation during subsequent torsional loads, but it has little effect on the elastic properties in shear.     

Effects of damage on the orthotropic material symmetry of bovine tibial trabecular bone

The macroscopic mechanical properties of trabecular bone can be predicted by its architecture using theoretical relationships between the elastic and architectural properties. Microdamage caused by overloading or fatigue decreases the apparent elastic moduli of trabecular bone requiring these relationships to be modified to predict the damaged elastic properties. In the case of isotropic damage, the apparent level elastic properties could be determined by multiplying all of the elastic constants by a single scalar factor. If the damage is anisotropic, the elastic constants may change by differing factors and the material coordinate system could become misaligned with the fabric coordinate system. High-resolution finite element models were used to simulate damage overloading on seven trabecular bone specimens subjected to pure shear strain in two planes. Comparison of the apparent elastic moduli of the specimens before and after damage showed that the reduction of the elastic moduli was anisotropic. This suggests that the microdamage within the specimens was inhomogeneous. However, after damage the specimens exhibited nearly orthotropic material symmetry as they did before damage. Changes in the orientation of the orthotropic material coordinate system were also small and occurred primarily in the transverse plane. Thus, while damage in trabecular bone is anisotropic, the material coordinate system remains aligned with the fabric tensor.     

Feasibility of using a magnetic tracking device for measuring carpal kinematics

While several different methods have been used to measure carpal kinematics, biplanar radiography is generally considered to be the most accurate and popular one. However, biplanar radiography is tedious and so only pseudo-dynamic kinematics can be measured. Recently, magnetic tracking system has been developed for the measurement of joint kinematics which is versatile and easy to use and so the possibility of measuring motions dynamically. In this study, the capability of a magnetic tracking device to accurately measure carpal kinematics was investigated by comparing it with biplanar radiography. The kinematics of the third metacarpal, scaphoid, and lunate in five fresh cadaveric specimens were measured using both methods as the wrists were placed in eight positions. The finite screw rotation of each bone with respect to the distal radius during selecting the seven wrist motions was calculated for both measuring techniques and compared. In general, the kinematics for all three bones measured by using either magnetic tracking device or biplanar radiography was identical and showed no statistical difference. The averaged differences ranged from 0.0 to 2.0°. These differences were due to the potential effect of the weight of the sensors and the interference of the attaching rod to the surrounding tissue. It is concluded that the application of the magnetic tracking device to carpal kinematics is warranted, if proper technical procedures as suggested are followed.