The Snake 2-Choice apparatus is used in studying learning and choice behaviors of snakes when presented with airborne odorants. The apparatus uses a simple set-up of a chamber divided into three sections using guillotine doors. Each section of the chamber comes equipped with a shallow base covered with a wire mesh that can hold scent chips. The Snake 2-Choice chamber utilizes the basic decision-making protocol that is often seen with apparatuses such as the rodent Sociability Chamber used in the assessment of social preference in rodents.

Odors have been shown to play a role in foraging and mate-finding, among other behaviors in snakes (Clark, 2004; Richard, Tillman, Humphrey, Avery, & Parker, 2018). In addition to their well-formed olfactory system, snakes are also equipped with the vomeronasal organ that helps in detection of heavy moisture-borne odor particles. The Snake 2-Choice apparatus relies on these systems to allow evaluation of different behaviors based on odor perception. Odors in each of the 3 chambers can be provided using scented chips placed in the shallow base. The subject is tasked with choosing either of the lateral chambers based on the training given to it or its preferences. The apparatus can be applied to evaluate learning behaviors and flexibility of these behaviors under different combinations of scents and protocols. Further, the effects of different treatments such as lesions or pharmacological manipulations on learning, foraging, mating, and trail following behaviors can also be evaluated.

The Snake 2-Choice incorporates guillotine doors as well as a wire mesh flooring. The guillotine doors allow controlling of the chamber access and can also be used to introduce delays in the task. The wire mesh flooring, in addition to serving as the floor, also ensures the snakes do not have direct lingual contact with the chips. Other apparatuses used in the evaluation of behaviors include the Snake Y-Maze, the Snake T-Maze, and the Zebrafish 3 Chamber Choice.

The Snake 2 choice apparatus is made of a glass tank measuring 62.5 x 31.25 x 31.25 cm. The floor of the tank is divided into three shallow rectangular compartments each 2.9 cm deep. A removable wire mesh is rested above these compartments and serves as the floor for the animal. Guillotine doors divide the upper portion of the apparatus into three chambers. A wire mesh covers the top of the apparatus.

Rinse the apparatus thoroughly with water before starting the trial and in between trials. Appropriately light the apparatus. A tracking and recording system such as the Noldus Ethovision XT can be used to assist with observations.

Snake 2 choice task

Choose one of the lateral chambers as the correct side of the tank. Place the scent chips in the shallow compartments of the apparatus. Place the subject in the middle chamber. Raise the doors of the choice chambers after 30 seconds. Allow the subject access to all the chambers. When 2 minutes have passed offer the subject a reward if its head is in the correct chamber. Allow the subject 3 minutes to accept the reward. Push the subject into the correct chamber if its head is in the middle or incorrect chamber and offer it a smaller piece of the reward. Perform 2-3 trials a day for 5 days a week until 100 trials have been done.

Evaluation of Conditioned Discrimination of Airborne Odorants by Garter Snakes

Begun, Kubie, O’Keefe, and Halpern (1988) evaluated conditioned discrimination of airborne odorants by Garter snakes (Thamnophis radix) in a Snake 2 choice apparatus. Juvenile and adult garter snakes (2 males and 5 females) were used in the experiment. Unscented pine chips mixed with lemon extract were placed in the compartment on the correct side of the tank whereas plain, unscented pine chips were placed in the incorrect and middle compartments. For the first few trials, the snakes remained in the middle chamber, which accounted for more than 50% of their choices. However, their choice of the middle chamber decreased to less than 15% after 20 trials. It was observed that the snakes made fewer errors and performance significantly improved from the first 10 trials (55% correct choices) to the last 10 trials (74.3% correct choices). Trials were also conducted in the reverse condition. It was observed that in the first 10 trials, 37.5% correct choices were made whereas 70% correct choices were made in the last 10 trials indicating that performance significantly improved in the reversal condition as well. The results indicated that garter snakes could learn, modify, and make a discriminated response to an arbitrary odor by using one or more of their nasal chemical senses.

The following parameters can be observed on a Snake 2 choice apparatus:

• Frequency of choosing the correct chamber
• Frequency of choosing the incorrect chamber
• Frequency of choosing the middle chamber
• Time spent in the middle chamber
• Time spent in the correct chamber
• Time spent in the incorrect chamber
• Frequency of errors

Strengths

The Snake 2 choice apparatus is used to study learning and behavior in relation to airborne odorants in snakes. It can be easily modified to different investigatory needs using simple modifications such as guillotine doors or using different protocols. The Snake 2 choice apparatus can be used to test the effects of diseases and disorders associated with the nasal chemical senses in snakes. It can also be used to assess the effects of learning and behavior resulting from brain lesions and pharmacological manipulations in snakes. The Snake 2 choice apparatus allows for easy acquisition and interpretation of data.

Limitations

Presence of trailing cues from previous trials may affect the task. The behavior of the subject to perform the task may be influenced by hunger or preference for food. Factors such as age, gender, and strain of the subjects may contribute towards their task behavior. Subject’s explorative behavior influences experimental results. Unnecessary stimuli may affect the way the subject performs the task.

• The Snake 2 choice apparatus is used to study learning and behavior in relation to airborne odorants in snakes.
• The Snake 2 choice apparatus is composed of three chambers, each having three compartments underneath that can hold scent chips.
• The Snake 2 choice apparatus can be used to test the effects of diseases and disorders associated with the nasal chemical senses in snakes

1. Begun D., Kubie J.L., O’Keefe M.P., & Halpern M. (1988). Conditioned Discrimination of Airborne Odorants by Garter Snakes (Thamnophis radix and sirtalis sirtalis). Journal of Comparative Psychology, 102(1), 135-43. doi: 10.1037/0735-7036.102.1.35.
2. Clark R. W. (2004). Timber rattlesnakes (Crotalus horridus) use chemical cues to select ambush sites. Journal of Chemical Ecology, 30, 607–617. 10.1023/B:JOEC.0000018632.27010.1e
3. Richard, S. A., Tillman, E. A., Humphrey, J. S., Avery, M. L., & Parker, M. R. (2018). Male Burmese pythons follow female scent trails and show sex-specific behaviors. Integrative Zoology. doi: 10.1111/1749-4877.12376.