Some observations of the structure of the choroid plexus and its cysts

The structure of the choroid plexus was studied in five normal human embryos, three normal fetuses and three fetuses with choroid plexus cysts. These were detected by ultrasound and the fetuses were karyotypically normal. The choroid plexus appears in the lateral cerebral ventricles at the seventh developmental week. The early structure is lobulated with vessels running in the mesenchymal stroma and forming capillary nets under the single-layered ependymal epithelium. This embryonal structure is converted into the fetal type during the ninth developmental week as the embryonal capillary net is replaced by elongated loops of wavy capillaries that lie under regular longitudinal epithelial folds. The choroid plexus cysts exhibited accumulation of fluid within distended mesenchymal stroma and did not show the wavy folds on this surface, which was smooth. Within this connective tissue of the cyst wall were distended angiomatous interconnecting thin-walled capillaries. Therefore, filled cavities were not lined by any epithelium. We suggest that fetal choroid plexuses cysts (at least in many cases) are in fact pseudocysts exhibiting angiomatous patterns of capillaries in their walls. Copyright © 2002 John Wiley & Sons, Ltd.     

Experience,but not distance,influences the recruitment precision in the stingless bee <Emphasis Type="Italic">Scaptotrigona mexicana</Emphasis>

Recruitment precision, i.e. the proportion of recruits that reach an advertised food source, is a crucial adaptation of social bees to their environment. Studies with honeybees showed that recruitment precision is not a fixed feature, but it may be enhanced by factors like experience and distance. However, little is known regarding the recruitment precision of stingless bees. Hence, in this study, we examined the effects of experience and spatial distance on the precision of the food communication system of the stingless bee Scaptotrigona mexicana. We conducted the experiments by training bees to a three-dimensional artificial patch at several distances from the colony. We recorded the choices of individual recruited foragers, either being newcomers (foragers without experience with the advertised food source) or experienced (foragers that had previously visited the feeder). We found that the average precision of newcomers (95.6 ± 2.61%) was significantly higher than that of experienced bees (80.2 ± 1.12%). While this might seem counter-intuitive on first sight, this “loss” of precision can be explained by the tendency of experienced recruits to explore nearby areas to find new rewarding food sources after they had initially learned the exact location of the food source. Increasing the distance from the colony had no significant effect on the precision of the foraging bees. Thus, our data show that experience, but not the distance of the food source, affected the patch precision of S. mexicana foragers.     

Some factors affecting the colonization of a dredged channel

Standing crop, population size, and species diversity of the macrobenthic organisms in an estuarine channel were studied before and after dredging. A new suction-corer which sampled an area 0.1 m² to a depth of 30 cm was used in order to insure the inclusion of large, deep-dwelling animals. Eleven months after dredging, biomass and number of species and specimens had not recovered to pre-dredging levels. Colonization began with relatively large, swiftly moving forms such as the errant polychaete Nereis succinea and the crab Neopanope texana sayi. Stations in silt and mud regions recovered more slowly than those in sandier sediments. Most of the dominant and subdominant species had not recovered 11 months after dredging, and the previously abundant polychaetes Notomastus latericeus and Clymenella torquata had virtually disappeared. Only relatively uncommon lamellibranchs such as Tellina agilis, Lyonsia hyalina and Mulinia lateralis increased after dredging. Distribution of sediment types changed as the result of modified tidal velocities in the channel. Mud and silt were removed by the dredge, exposing the sand underneath, and sandy stations became muddier as the result of lowered current velocities. Marked changes in species composition reflected this change in sediment character. Eleven months after dredging no evidence of succession was found, but colonization had begun. Values of all three parameters studied were reduced to small fractions of pre-dredging levels, although species diversity in sandy sediments exceeded pre-dredging levels.     

Rare royal families in honeybees, Apis mellifera

The queen is the dominant female in the honeybee colony, Apis mellifera, and controls reproduction. Queen larvae are selected by the workers and are fed a special diet (royal jelly), which determines caste. Because queens mate with many males a large number of subfamilies coexist in the colony. As a consequence, there is a considerable potential for conflict among the subfamilies over queen rearing. Here we show that honeybee queens are not reared at random but are preferentially reared from rare “royal” subfamilies, which have extremely low frequencies in the colony's worker force but a high frequency in the queens reared.