Pillbugs

Experiment set up and data

Each group was given an orientation arena and told to set 0 towards the front of the room. They were then assigned a location to place their lamp at. For example, groups assigned 0 set their lamps at the top of the arena, while groups assigned 180 set their lamps at the bottom of the arena. This was done to try and eliminate any directional bias in the room.

The groups’ lamp assignment:

Group	Lamp.Location
One	0
Two	50
Three	90
Four	140
Five	0
Six	230
Seven	270
Eight	320

The groups then each released the isopods individually in the center of the arena. They collected data on three “experimental” animals which were run with the lamp turned on, and two “control” animals with the lamp turned off. They measured the angle at which the animals crossed the edge of the arena, with respect to the front of the room. To get the angle with respect to the lamp, the students subtracted the angle where they measured the animals cross the arena from the angle position of their lamp. The numbers shown below are the student’s adjusted results, corrected to be with respect to the lamp position. To get the uncorrected version, simply add the group’s lamp location to the reported measurement.

The data:

Group	Lamp.Location	Exp.1	Exp.2	Exp.3	Cntrl.1	Cntrl.2
One	0	180	100	180	120	90
Two	50	130	210	70	120	170
Three	90	130	230	170	60	50
Four	140	160	-145	90	100	70
Five	0	170	130	-90	90	100
Six	230	20	120	80	30	10
Seven	270	-240	-95	-50	-270	60
Eight	320	-220	-290	NA	-100	-300

Experiment Analysis

Here we show the class’s data plotted, with the corresponding statistical tests for their experimental group (with respect to the lamp, and then again with respect to the front of the room), and the control group (with respect to the lamp, and then again with respect to the front of the room). We end with a watson’s two test comparing the experimental and control group.

The Experimental group, Relative to the lamp

If the animals had phototaxis, they would be oriented relative to the light here (where the light is at 0)

## $`Rayleigh Test P-value`
## [1] 0.0064683
## 
## $`Mean Angle`
## [1] 2.544426
## 
## $`Mean Resultant Vector Length`
## [1] 0.4601774

The Experimental group, relative to the front of the room

This orientation should be random. If not, it indicates there is a directional bias in the room itself

## $`Rayleigh Test P-value`
## [1] 0.3125656
## 
## $`Mean Angle`
## [1] -2.366986
## 
## $`Mean Resultant Vector Length`
## [1] 0.2259028

Control Group, Relative to the lamp

If the animals were not being influenced by the presence of the lamp itself, this orientation should be random. If not, it indicates the animals had a prefered direction they liked to move relative to the lamp, regardless of whether it was turned on. The lamp is at 0.

## $`Rayleigh Test P-value`
## [1] 0.0001978523
## 
## $`Mean Angle`
## [1] 1.403986
## 
## $`Mean Resultant Vector Length`
## [1] 0.6888091

The Control group, relative to the front of the room

This orientation should be random. If not, it indicates there is a directional bias in the room itself

## $`Rayleigh Test P-value`
## [1] 0.3575454
## 
## $`Mean Angle`
## [1] 3.01729
## 
## $`Mean Resultant Vector Length`
## [1] 0.255507

A Watson two-test to see if the direction of orientation for the experimental group and the control group (relative to the lamp) are the same

See slides for more details on what a watson two-test is.

watson.two.test(Experimental.Corrected,Control.Corrected)

## 
##       Watson's Two-Sample Test of Homogeneity 
## 
## Test Statistic: 0.214 
## 0.01 < P-value < 0.05 
##