Odor Plumes and Animal Navigation in Turbulent Water Flow: A Field Study.

Turbulence causes chemical stimuli to be highly variable in time and space; hence the study of animal orientation in odor plumes presents a formidable challenge. Through combined chemical and physical measurements, we characterized the transport of attractant released by clam prey in a turbulent aquatic environment. Concurrently, we quantified the locomotory responses of predatory crabs successfully searching for sources of clam attractant. Our results demonstrate that both rheotaxis and chemotaxis are necessary for successful orientation. Perception of chemical cues causes crabs to move in the upstream direction, but feedback from attractant distributions directly regulates movement across-stream in the plume. Orientation mechanisms used by crabs difler from those employed by flying insects, the only other system in which navigation relative to odor plumes has been coupled with fluid dynamics. Insects respond to odors by moving upstream, but they do not use chemical distributions to determine across-stream direction, whereas crabs do. Turbulent eddy diffusivities in crab habitats are 100 to 1000 times lower than those of terrestrial grasslands and forests occupied by insects. Insects must respond to plumes consisting of highly dispersed, tiny filaments or parcels of odor. Crabs rely more heavily on spatial aspects of chemical stimulus distributions because their fluid dynamic environment creates a more stable plume structure, thus permitting chemotaxis.

Computer assisted data collection for stereology: rationale and description of point counting stereology (PCS) software.

The paper describes microcomputer software for point counting stereology. Stereology includes a collection of statistical methods that quantify the images of light and transmission electron microscopy. The methods use test grids placed over images to collect raw data, which includes counts of points, intersections, transections, and profiles. In turn, the counts are included in stereological equations that give estimates of compartmental volumes, surfaces, lengths, or numbers. These parameters describe the composition of a structure in three-dimensional space. The PCS (point counting stereology) System Software III serves as a data collection, storage, and management tool. Users set up point counting protocols without programming, enter data by pressing predefined function (MS-DOS) or alphabetic keys (UNIX), store data in files, select files for analysis, and calculate results as stereological densities. The latest version of the PCS software includes a new user interface and is designed as a research "front end" that can feed data either into the calculation tools of a stereology tutorial (Bolender, 1992, this issue) or into the analysis routines of quantitative morphology databases (Bolender and Bluhm, 1992).

PCS System I: point counting stereology programs for cell biology.

PCS System I (PCS) is a set of four software modules designed to simplify the application of stereology to problems in cell biology. It is written in BASIC for the Tektronix 4052A microcomputer (Beaverton, OR). A Counting Module collects raw data counts in either a Density Mode (points, intersections, transections, profiles) or a Boundary Mode (intersections with complete nuclear profiles). This information is stored on tape or disk data files and can also be printed. Three analysis modules use data files created with the Counting Module. The Density Module uses Density Mode data files to calculate volume, surface, length, and numerical densities. The B Numerical Density Module uses both Boundary Mode and Density Mode data to calculate the means for the boundary, diameter, and surface area of a nuclear compartment. The mean nuclear surface area is then used with the nuclear surface density to estimate the nuclear numerical density, which, in turn, is used to calculate surface areas of membrane compartments in average cells and in 10(6) cells. The Format Module reformats raw data files for analysis with Tektronix statistical software.