Spatial learning in red swamp crayfish (procambarus clarkii)

Spatial learning, or the process by which animals gather and use information within their environment to navigate and remember the location of stimuli, is of significant ecological importance. Spatial learning is commonly studied in vertebrates using various types of mazes. In this experiment two types of mazes (multiple-turn maze, consecutive T-maze) were used to determine if aquatic arthropods exhibit spatial learning. Three cohorts of red swamp crayfish (Procambarus clarkii) were given the opportunity to learn two mazes using food as a motivator over two consecutive six-week periods. The crayfish were exposed to the multiple turn maze first and then to the consecutive T-maze. The prediction was that exposure to the multiple turn maze would improve crayfish performance in the consecutive T-maze. Time to completion was measured and the number of wrong turns was counted for each individual in the conditioned group in each maze type; a control or unconditioned crayfish was placed in a maze start gate so that all crayfish were handled in the same way but was not allowed to try to learn the maze. After the 4-week conditioning period, all crayfish underwent a 1-week latency period and conditioned and unconditioned crayfish were then tested in the maze without the motivator to determine if spatial learning had taken place. Crayfish then were conditioned in the T-maze in the same fashion. Although there was a great deal of variability, conditioned crayfish showed some improvement in completion time in both the multiple- turn maze as well as the consecutive T maze, and the number of wrong turns decreased slightly, but they did not show improvement when compared to the control group. The starting mean completion time for the multiple turn maze conditioned group was 1745.81 sec and by week 6 was 1653.29 sec compared to the unconditioned mean of 1082.41 sec. The starting mean for the consecutive T-maze conditioned group was 831.62 sec and by week 6 was 397.44 sec compared to the unconditioned 834 sec. The starting mean number of wrong turns for the multiple turn maze conditioned group was 2.5 and by week 6 was 1.9 compared to the unconditioned mean of 1.76. The starting mean for the consecutive T-maze conditioned group was 1.62 and by week 6 was 1.67 compared to the unconditioned 2.25. There were also no notable differences in the mean completion time 1653.29 sec vs 1082.41 sec (df = 38.527, t=1.497, p=0.143) between the conditioned and unconditioned crayfish in the multiple-turn maze. A repeated-measures ANOVA with all cohorts combined showed that there was a difference between weeks in mean completion time (df = 4, F = 2.806, p = 0.031), with mean times in week 3, 1548.89 sec, being lower than those in week 2, 2202.82 sec, (mean difference= -1048.7; p = 0.032). Although the mean number of wrong turns for all cohorts combined showed a slight downward trend, there was no statistical difference between weeks (df = 4; F = 0.099; p = 0.983). The mean number of wrong turns, was similar, 1.9 vs 1.76 (df = 33.644, t=0.281, p=0.780) between the conditioned and control groups. In the T-maze for completion times, a repeated-measures ANOVA, with Greenhouse-Geisser correction, showed similar completion times between weeks with mean completion times from week 1 through 6 being, 831.62 sec, 1052.86 sec, 601.5 sec, 917 sec, and 397.44 sec (df = 4, F = 1.115, p = 0.353). After the latency period, the mean completion time of the conditioned group dropped to about half that of the unconditioned individuals, 397.44 sec vs 834 sec, but there was no statistical difference (df = 26.853, t=-1.674, p=0.106). The number of wrong turns was similar between weeks for the T-bar maze with mean number of wrong turns from week 1 to week 6 being, 1.62, 2.14, 1.6, 2, and 1.67 (df = 4, F = 1.611; p = 0.195). Although the number of wrong turns in conditioned individuals, 1.67, was slightly less than that of the control group, 2.25, there was no statistical difference (df = 21.180, t=-1.146, p=0.265). This experiment was marked by a great deal of variability in the results due factors such as high mortality, molting, and aspects of the experimental set up, such as training crayfish on mazes in bright light. Additional research is warranted using larger sample sizes to evaluate responses with greater statistical power. This experiment failed to provide evidence for spatial learning in Procambarus clarkii, but did not eliminate the possibility for spatial learning to occur in this species. Crayfish are model organisms for neurological studies due to their large easily accessible neurons, further studies are needed to determine if spatial learning can be found in this species.