During lecture, we discussed how different organisms orient to various cues: light, odor, fluid motion [wind, water currents], gravity, magnetic fields, among others [see references below]. The response to each of these cues differed yet provided guidance to the organisms to reach their goal.

General texts on orientation and sensory ecology:

Schone, H. 1984. Spatial Orientation. The Spatial Control of Behavior in Animals and Man. Princeton University Press, NJ.

Dusenbery, D. 1992. Sensory Ecology. How Organisms Acquire and Respond to Information. WH Freeman and Co., NY.

Useful Text for Independent Projects:

Lehner, PH. 1996. Handbook of Ethological Methods. Second Edition. Cambridge U. Press, UK.

In this laboratory, we shall examine the response of copepods, a dominant member of the plankton, to signals of three modalities: light, odor, and fluid motion. The hypothesis we wish to test is:

Ha: The response to light is linear motion while the response to odors and fluid motion is nonlinear - corresponding to how these signals are transmitted through fluids.

[The null hypothesis that we would disprove, according to the inductive method described by Platt (1964) would be Ho: The response to light is not linear while the response to odors and fluid motion is linear motion.]

We shall visit the laboratory of Professor Yen (Discovery 154, South Campus, Marine Sciences Research Center). Using two species of copepod collected during our field trip, we will precondition half of them by overnight starvation in filtered seawater. We will test the responses as follows:

Response to light:

1. Place group of fed copepods in tank. Place fiber optic light source (no heat transmitted) in center of vessel in view of both cameras. Darken room and use only He Ne laser (632 nm red light not apparent to plankton) and ir laser for illumination, wait 3 minutes, turn on vcr with number generator. Videotape swimming movements in the dark for 3 minutes. Turn on point source of light after 3 minutes. Record for 3 minutes and repeat. Take tape upstairs for computer image analyses.

2. Repeat for group of starved copepods.

Variations: A. Change light intensity and wavelength. B. Move light source slowly and monitor behavior.

Response to prey odors:

3. Place group of fed copepods in tank and wait 3 minutes. Record initial behavior using Schlieren optics. Add phytoplankton [should be able to see them]. Record behavior. Take tape upstairs for computer image analyses.

4. Repeat for starved copepods.

Variations: Change phytoplankton type and odor concentration.

Response to predator odors:

5. Place group of fed copepods in tank and wait 3 minutes. Record initial behavior using Schlieren optics. Add fish odor. Record behavior. Take tape upstairs for computer image analyses.

Variations: Change fish type and odor concentration.

Response to mates:

6. Place group of fed male copepods in tank and wait 3 minutes. Record initial behavior using Schlieren optics. Add females. Record behavior. Take tape upstairs for computer image analyses.

Variations: Change copepod type and ratio of females to males.

Response to fluid disturbances:

7. Place group of fed copepods in tank and wait 3 minutes. Record initial behavior using Schlieren optics. Attract copepods to center using point source of light. Record behavior. Turn on fluid mechanical disturbance for 10 seconds intervals of on/off. Take tape upstairs for computer image analyses.

Variations: Change intensity and frequency.

Camera system:

A pair of cameras are oriented at right angles to each other. From each 2D image, we can get the x,z and y,z co-ordinates at time t. In other words, we can get the 3-dimensional coordinates through time (x,y,z,t). The number stamped at the corner of the video synchronizes the two images. In a newer design, a single camera captures both images so that it is easy to match movements. Here, by limiting the number of copepods to only 10 animals, we match their paired 2D images.

Temporal resolution:

A videotaped sequence records frames at 30 frames per second. Each frame consists of two interlaced fields that can be separated so that we can double our temporal resolution to 60 fields per second. (The number stamped in corner will change for each frame with each field represented as single or double dots; e.g. For a time separation of 1/30 sec, the number will change from 23: to 24: For a time separation of 1/60 sec, the number will change from 23: to 23.). For fast reactions, it may be necessary to use a camera that records images at high speeds. If this is justified, we will use it for any of the independent projects.

Computer image analysis:

Position in 3D space and velocity measurements: The videotaped sequence is digitized by streaming the images into the computer using the Perception Video Recorder that also will allow you to analyse either frames or fields. Using BioScan Optimus, we can open up a series of images and obtain their 2D co-ordinates which goes directly into an Excel spread sheet. This system will be available for independent projects. Using Scion [downloadable freeware available in computer classroom in Life Sciences, 6th floor], coordinates can be obtained and moved into your Excel spreadsheet. Place coordinates for matched pairs in your Excel spreadsheet and determine the 3D co-ordinates at time t for a selected sequence showing interesting behavior. Using the formulae of Pythagoras, we can calculate the distance between two points in 3D space. Since we know the time interval between successive frames, we can calculate the swimming velocity.

Data to collect:

A. Turning frequency = number of turns in selected time interval. Compare over similar time intervals (may need to adjust depending on speed of change: for slow transitions, need long timed intervals; for quick changes, need short timed intervals analysing many of the 60 fields per second). Determine for the untreated copepods, for the treated copepods and during the transition between treatments.

B. Swimming velocity: Determine for the untreated copepods, for the treated copepods and during the transition between treatments.

C. Trajectory analyses: Plot the 2D trajectories and examine by fractal analysis to determine the difference from linearity. (See reference Yen and Bundock 1997).

D. Time spent on different behaviors: Despite the misnomer that plankton, from the greek word 'planktos' meaning wanderer, and the usual definition that plankton are organisms that drift passively in the current, many plankters have quite a large number of responses in their behavioral repertoire. These include: upward swimming, sinking, horizontal swimming, fast swimming, slow swimming, pausing, feeding, hops, turns, attacks. Look for these differences in behavior and quantify in terms of frequency or time spent per behavior.