Landmark maps for honeybees

Experiments by Fabre (1915), Thorpe (1950), Chmurzynski (1964), and most recently Gould (1986) suggest that insects have maps of their terrain which enable them to find their way directly to a goal when they are displaced several hundred metres from it. This paper discusses what might constitute an insect's map in terms of a two-part computational model. The first part describes how an insect reaches a goal when the insect is sufficiently close that it can see some of the landmarks which are visible from the goal. The second part considers the problem of navigating when there is no similarity between the view from the release-site and the view from the goal.We start from a model designed to explain how a bee might return to a goal using a two-dimensional snapshot of the landscape seen from the goal (Collett and Cartwright 1983). To guide its return, the model bee continuously compares its snapshot with its current retinal image and moves so as to reduce the discrepancy between the two. Bees can only be guided in the right direction by the difference between current retinal image and snapshot when there is some resemblance between the two. In a realistically cluttered world, snapshot and retinal image become very dis-similar only a short distance from the goal.To increase the distance from which a model bee can return, the bee takes two snapshots at the goal. The first snapshot excludes landmarks near to the goal and the second snapshot includes them. With close landmarks filtered from both snapshot and retinal image, the match between the two deteriorates gradually as the bee moves away from the goal. A model bee using a filtered snapshot and image finds its way back to the neighbourhood of the goal from a relatively long distance (Fig. 2). The bee then switches to the second snapshot and is guided to the precise spot by its memory of the close landmarks.For longer range guidance, the model bee is equipped with an album of snapshots, each taken at a different location within the terrain. Linked to each snapshot is a vector encoding the distance and direction from the place where the snapshot was taken to the hive. When the bee is displaced to a new position, it selects the snapshot which best matches its current image and follows the associated home-vector back to the hive (Fig. 3). Such a hive-centred map can also be used to devise novel routes to places other than the hive. For instance, a bee can reach a foraging site from anywhere in its terrain by adding the home-vector recalled at the starting position to a vector specifying the distance and direction of the foraging site from the hive. The sum of these two vectors defines a direct trajectory to the foraging site.     

Ant navigation: reading geometrical signposts

Ants often travel along complex pheromone trail systems between their nest and foraging areas. A new and surprising discovery is that Pharaoh's ants can work out from the geometry of individual branch points on the trail whether they are heading towards or away from the nest.     

Characterization of virus-specific RNA synthesized in bovine cells infected with bovine viral diarrhea virus.

Infection of bovine kidney cells with bovine viral diarrhea virus resulted in the synthesis of a single species of virus-specific RNA. Electrophoresis of this RNA on agarose-urea and agarose-formaldehyde gels indicated that it had a molecular weight of 2.9 X 10(6), corresponding to 8,200 bases (8.2 kilobases). This 8.2-kilobase RNA was resistant to RNase A treatment at 1 microgram/ml but was digested at higher concentrations of RNase (10 micrograms/ml). Sedimentation on neutral sucrose gradients indicated that the majority of this RNA (98%) sedimented at 21S, with a small amount sedimenting at 33S. Sedimentation on formaldehyde-containing sucrose gradients resulted in the conversion of all of the RNA to the faster-sedimenting form. At no time after infection were we able to detect virus-specific RNA species of lower molecular weight than the 8.2-kilobase RNA. The implications of these findings with respect to the means of replication of various togaviruses are discussed.     

Small-scale processes in desert locust swarm formation: how vegetation patterns influence gregarization

Desert locusts ( Schistocerca gregaria ) change phase in response to population density: 'solitarious' insects avoid one another, but when crowded they shift to the gregarious phase and aggregate. This individual-level process is the basis for population-level responses that may ultimately include swarm formation. We have recently developed an individual-based model of locust behavior in which contagious resource distribution leads to phase change. This model shows how population gregarization can result from simple processes operating at the individual level. In the present study, we performed a series of laboratory experiments in which vegetation pattern and locust phase state were assigned quantitative, measurable indices. The pattern of distribution of the resource was represented via fractal dimension; the phase state was evaluated using a behavioral assay based on logistic regression analysis. Locusts were exposed to different patterns of food resource in an artificial arena, after which their behavioral phase state was assayed. These experiments showed that when the distribution of the vegetation was patchy, locusts were more active, experienced higher levels of crowding, and became more gregarious. These results are consistent with simulation predictions and field observations, and demonstrate that small-scale vegetation distribution influences individual behavior and phase state and plays a role in population-level responses.     

Enzymatic characteristics of pp60v-src isolated from vanadium-treated transformed cells

The transforming protein of Rous sarcoma virus (RSV) typically appears as a single phosphorylated polypeptide designated pp60^v-src, pp60^v-src possesses a protein kinase activity specific for tyrosine residues on select protein substrates. Treatment of RSV-transformed cells with vanadium ions resulted in the appearance of an electrophoretic variant of pp60^v-src and was paralleled by a significant increase in the src kinase specific activity in purified enzyme preparations. Both the normal (standard) src kinase and the src kinase preparations obtained from vanadium-treated cells exhibited similar optimal activity profiles for MgCl₂, KCl, and pH. Furthermore, their site specificities of phosphorylation of the substrates casein and vinculin were the same. The reaction kinetic profile of the standard src kinase showed a nonlinear pattern, while the vanadium enzyme exhibited conventional linear Michaelis-Menten kinetics. These results are discussed with respect to the possible functional regulation of pp60^v-src activity by a vanadium-sensitive protein phosphatase activity.     

Does vertical disparity scale the perception of stereoscopic depth?

It has been suggested that a measure of the gradients of vertical disparity over a surface may scale the mapping between horizontal disparity and perceived depth. We have investigated this possibility by obtaining estimates of the depth within stereograms that simulated two apposed fronto-parallel planes placed at different distances from an observer. The gradients of vertical disparity in a stereogram were set to simulate those appropriate to a viewing distance of 12.5 cm, 25 cm, 50 cm or 100 cm, whereas the distance specified by vergence and accommodative cues was always fixed at 50 cm. Judgements of the perceived depth between the two planes were uninfluenced by changes in the gradients of vertical disparity. It thus seems that the human visual system does not employ vertical disparity as a scaling parameter in stereoscopic depth judgements.     

Insect navigation: measuring travel distance across ground and through air

Walking insects probably monitor leg movements to estimate how far they travel, whereas flying insects monitor optic flow.