Slowly walking down to the more food: Relative “number” discrimination in African spurred tortoises (Centrochelys sulcata)

Abstract

Abstract Numerical discrimination is thought to be highly adaptive as it allows an organism to select greater amounts of food or larger social groups. The processes underlying this ability are well understood in mammals with two systems being posited to control behavior, the approximate number system, which uses the ratios between numbers and the object file system which tracks individual small numbers. Much less in known in reptiles, the work that is available suggests that chelonia may use the ratios between the numbers to discriminate numerical values. This experiment examined the effect of ratio and number size on relative numerical discrimination in African spurred tortoises (Centrochelys XXXulcate). To assess this, tortoises were presented with trays containing favored food in all possible number combinations between 1 and 7. The tortoise had to approach the tray it perceived as having the larger number, if correct, the tortoise received one piece of reinforcement. Each tortoise received 36 pairings of each stimulus combination. The results revealed that numerical discrimination was influenced by the ratio between the numbers, with performance improving as the ratio between the numbers increased. This suggests that the approximate number system may be controlling their behavior. However, the opposite tendency was observed for the larger numbers, suggesting that an object-file system may also be involved in numerical discrimination.