The Effects of Geotropic Excitation in Behavioural Orientation

Mechanisms in Helix aspersa

Russell Gibson, Jens Herzog, and Tony Vaillancourt

Introduction

• Helix aspersa are negatively Geotaxic

• Attempted to find re-orientation mechanism

• Rarely documented in modern studies

• Tested various levels of excitation

• Hypothesis: H. aspersa are able to determine changes in direction relative to gravity and are capable of readjusting accordingly

Test Subjects

• Helix aspersa: common garden snail

• Same individuals used in previous lab

• Found across globe• Wild individuals• Negatively geotaxic

(travel against gravity) for foraging

H. Apsersa Movement

• Many factors– Humidity– Nutritional needs– Predator evasion– Reproductive condition

(include chemoreception)

– Length of laboratory housing

• Often negative to travel upwards on plants

• Acquire as much food as possible

• Negative during day, indifferent at night

Previous Literature

• Cole 1926– First real study of gastropod

movement– Change in gravitational

force acts on foot, which alters direction

• Crozier 1935– Further detail on

movement

• Hyman 1967– Large review of many

mollucs including gastropods

• Clarke 1970– General geotactic

responses in several species

• Iglesias and Castillejo 1999– More modern field

study of Helix aspersa

Follow-Up from Previous Material

• Modification of lab design earlier in course• Used findings from earlier results to

determine study parameters– e.g. slope of board– e.g. previous literature analysis

Materials and Methods

• Limited supply of materials for geotaxis testing• Materials used– Protractors– Packing tape– Plexiglas board– String– Lab clamps and stands

• Though this apparatus was constructed crudely, it served our purpose flawlessly.

Construction of the Apparatus• This apparatus was set up so that the

surface of the Plexiglas plate remained at a constant 25° incline.– Optimal angle based on previous

experiment

• Protractors were placed on the under side of the plate and used to measure the angle of the snails path.

• Snails placed on center of plate and allowed to move freely for a maximum of 300 seconds.– A predetermined threshold of 5cm from

the origin had to be reached before the plate was rotated.

Methods• Goal to measure the angle travelled

by the snail across the surface of the plate– Keep 25° incline at the same time

• Rotate the entire surface of the Plexiglas plate clockwise without disturbing the animal.– Rotating without disturbing the animal

was crucial

• Clockwise rotation was consistent and optimal due to the fact that these snails all had dextral shells.

Methods continued...

• Ten snails per angle group• String one: measure distance

and positional angle from the origin.

• String two: plumb-line to measure the angle of plate rotation.

• 0° test served as a control to the other 9 manipulated groups.– Once the snail hit the threshold

the board was rotated 0 – 90°, measured in 10° intervals.

• All testing occurred in a climate controlled room.• Each individual snail was placed in warm shallow water

prior to testing.• To eliminate trail following behaviours we wiped down

the Plexiglas plate with paper towels and water.• No heavy disinfectants were used during wipe downs

between testing individuals.• Testing occurred over a one week duration and every

attempt was made to ensure that the same times were consistent between settings.

Methods Cont.

• We had constructed two models to double our testing to reduce our overall lab time.

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14Results

Results

0 5 10 15 20 25

-175

-125

-75

-25

25

75

125

175

Distance After Threshold (cm)

Dev

iatio

n A

fter

Thr

esho

ld (D

egre

es)

N.S.

N.S.

Significant

SignificantResults

Results

Mean Difference Control 10 20 30 40 50 60 70 80 90Control x

10 -3.058 x20 -6.159 -3.101 x30 -6.274 -3.217 -0.1158 x40 -23.574** -20.516** -17.415** -17.299** x50 -20.783** -17.725** -14.625** -14.509** 2.79 x60 -10.203* -7.146 -4.045 -3.929 13.37** 10.58* x70 -45.991** -42.933** -39.832** -39.716** -22.417** -25.207** -35.787** x80 -51.813** -48.755** -45.654** -45.538** -28.239** -31.029** -41.609** -5.822 x90 -23.46** -20.402** -17.301** -17.185** 0.114 -2.676 -13.256** 22.531** 28.353** x

Discussion

Factors for H. aspersa movement

1. Humidity

2. Nutritional needs3. Predator evasion4. Reproductive condition

(include chemoreception)

5. Length of laboratory housing

Factor Control in Study

1. Climate-controlled lab, warmed snails in water prior to testing

2. All individuals well fed3. No possible predator risk4. Boards wiped down with

paper towel and water between trials*

5. Snails were all recovered from wild territory (Newfoundland)

*Not fully disinfected*

Reasons for moving

• Therefore – H. aspersa were acting normally, responding to gravity changes we imposed

• Gravitational forces act on 8 major foot muscles

• Excitation causes shell/visceral mass shift, pulling on foot – snail readjusts

• H. aspersa were able to determine changes in direction relative to gravity and readjusted accordingly

Study Errors – what possible cause?

60 degree

• Experiments conducted around 5:00pm-6:00pm in early November in New Brunswick

• Dark outside• Cole (1926): Helix aspersa are indifferent with

geotaxis at night– May have affected individual circadian rhythms

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Similar pattern

90 Degrees

• Snails are travelling in a circular pattern, travelled with gravity initially before adjusting

• Individuals departed from right side

In Conclusion

• Helix aspersa travel in negatively geotaxic patterns and have mechanisms that allow them to re-orient themselves when exposed to geotaxic excitation

• Estimate mechanisms are response of sensitivity to weight and pressure in foot musculature

• Extreme excitation = more response

Future Studies and Repeat Experimentation

• For repeating study– Keep trail testing times at same time every day– Thoroughly disinfect board between trials– Repeat change in response differences

• Future study considerations– How do the other factors explained earlier impact re-

orientation i.e. are they more influential?– Attempt same study at different incline slope angle– Analyze behaviour patterns after 90 degrees

Bean, B. (1984). Microbial geotaxis. Membranes and sensory transduction. pp. 163-198. Springer US. Boyle, P. R., & Boyle, P. R. (1981). Molluscs and man (pp. 26-35). London: Edward Arnold. Clarke, A. M. (1970), Geotactic responses in infra-human animals: A note on a new relationship between gravitational variables. Australian Jnl of Psychology, 22: 67–70. doi: 10.1080/00049537008255213 Cole, W. H. (1926). Geotropism and muscle tension in Helix. The Journal of General Physiology, 8(3), 253-263. Crozier, W. J. (1935). On the geotropic orientation of Helix. The Journal of General Physiology, 18(5), 659-667. Farkas, S. R., & Shorey, H. H. (1976). Anemotaxis and odour-trail following by the terrestrial snail Helix aspersa. Animal Behaviour, 24(3), 686-689. Gibson, R. and Herzog, J. (2013). Geotaxis observtions in H. aspersa. Unpublished. Guiller, A., Coutellec Vreto, M. A., Madec, L., & Deunff, J. (2001). Evolutionary history of the land snail Helix aspersa ‐in the Western Mediterranean: preliminary results inferred from mitochondrial DNA sequences. Molecular Ecology, 10(1), 81-87. Hoagland, H., & Crozier, W. J. (1931). Geotropic excitation in Helix. The Journal of general physiology, 15(1), 15-28. Hyman, L. H. (1967). The Invertebrates: Volume VI, Mollusca 1. Pulmonata: Habits and Behaviour (pp 627-631). McGraw-Hill, New York Ierusalimsky, V. N., Zakharov, I. S., Palikhova, T. A., & Balaban, P. M. (1994). Nervous system and neural maps in gastropodHelix lucorum L. Neuroscience and Behavioral Physiology, 24(1), 13-22. Iglesias, J., & Castillejo, J. (1999). Field observations on feeding of the land snail Helix aspersa Müller. Journal of Molluscan Studies, 65(4), 411-423. Purchon, D. R. (1968). The biology of the Mollusca. Form and Function of the Mantle Cavity: Pulmonata. (pp 29-33) Pergamon Press. London. Stephens, G. J., & McGaugh, J. L. (1972). Biological factors related to learning in the land snail Helix aspersa Müller). Animal Behaviour, 20(2), 309-315.

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