Visual constraints in foraging bumblebees: Flower size and color affect search time and flight behavior

In optimal foraging theory, search time is a key variable defining the value of a prey type. But the sensory-perceptual processes that constrain the search for food have rarely been considered. Here we evaluate the flight behavior of bumblebees (Bombus terrestris) searching for artificial flowers of various sizes and colors. When flowers were large, search times correlated well with the color contrast of the targets with their green foliage-type background, as predicted by a model of color opponent coding using inputs from the bees' UV, blue, and green receptors. Targets that made poor color contrast with their backdrop, such as white, UV-reflecting ones, or red flowers, took longest to detect, even though brightness contrast with the background was pronounced. When searching for small targets, bees changed their strategy in several ways. They flew significantly slower and closer to the ground, so increasing the minimum detectable area subtended by an object on the ground. In addition, they used a different neuronal channel for flower detection. Instead of color contrast, they used only the green receptor signal for detection. We relate these findings to temporal and spatial limitations of different neuronal channels involved in stimulus detection and recognition. Thus, foraging speed may not be limited only by factors such as prey density, flight energetics, and scramble competition. Our results show that understanding the behavioral ecology of foraging can substantially gain from knowledge about mechanisms of visual information processing.

Migration of keratinocytes through tunnels of digested fibrin

We report here a hitherto undescribed form of cell migration. When a suspension of human keratinocytes is plated on a fibrin matrix, single cells invade the matrix and progress through it as rounded cells by dissolving the fibrin and thereby creating tunnels. These tunnels are cylindrical or helical, the latter being the result of constant change in the path of cellular advance around the helical axis. Helical tunnel formation is strongly promoted by epidermal growth factor. The rate of migration of the cell through the track of a helical tunnel (up to 2.1 mm per day) is about 7-fold greater than through a cylindrical tunnel. Pericellular fibrinolysis leading to tunnel formation depends on the presence of plasminogen in the medium and its conversion to plasmin by a cellular activator. Formation of tunnels requires that plasminogen activator be localized on the advancing surface of the keratinocyte; we propose that the tunnel is cylindrical when the site of release of plasmin is located at a fixed point on the cell surface and helical when the site of release precesses.

Aggregation dynamics and foraging behaviour of striped red mullet Mullus surmuletus in the western Mediterranean Sea

Habitat-related heterogeneity of striped red mullet Mullus surmuletus heterospecific foraging assemblages was examined off the coast of Spain. Video-based focal-follows conducted on 122 M. surmuletus assemblages (446 total individuals) revealed an array of attendant species (n = 7) with composition linked to benthic habitat complexity; bare sandy substrata were characterized by homospecific groups of M. surmuletus, while habitats with rock and vegetation attracted a variety of scrounging labrids and sparids. Although the nature of the relationship between M. surmuletus and attendants requires further exploration, the present study indicates that substratum composition can be a driving factor explaining the dynamics of this heterospecific assemblage.

Underground insulated piping systems : excluding walk-in tunnels.

"Prepared under Contract No. CST 263 between the National Academy of Sciences and the National Bureau of Standards."

Toll facilities in the United States: bridges, roads, tunnels, ferries.

Mode of access: Internet.

Behavior of the Bay Area Rapid Transit tunnels through the Hayward Fault : final report /

"Performing organization: San Francisco Bay Area Rapid Transit District"--Technical report documentation page.

Toll facilities in the United States : bridges, roads, tunnels, ferries /

"February 1995."

Aerodynamics and air quality management of highway tunnels : R. N. Schlaug, T. J. Carlin.

Mode of access: Internet.

Analysis of ground-liner interaction for tunnels /

Mode of access: Internet.

Les tunnels des Alpes. Mont Cenis--Saint Gothard--Simplon--Loetschbert--Jura--Faucille--Mont Blanc.

Mode of access: Internet.

Management of air quality in and near highway tunnels /

Mode of access: Internet.

Performance improvement of arc heaters for aerodynamic wind tunnels

Mode of access: Internet.

Characteristics of six research wind tunnels of the Ames Aeronautical Laboratory.

Mode of access: Internet.

The Odd fellow, or, The secret association, and Foraging Peter.

Mode of access: Internet.

Captain Jackman; or, A tale of two tunnels.

Mode of access: Internet.