Recognition of familiar objects in tortoise hatchlings (Testudo spp.)

Abstract

Tortoises do not show parental care and live solitary except for the context of reproduction. Despite their limited need to interact with conspecifics, we previously observed that young tortoises, at their first experiences with conspecifics, can discriminate between familiar and unfamiliar conspecifics after just one encounter with another tortoise. Tortoise hatchlings ignored familiar conspecifics, while they first explored and then actively avoided unfamiliar conspecifics. It remains to be established whether the different reactions to unfamiliar and familiar individuals in tortoise hatchlings are reactions to novelty, or whether they are specific to the interactions with living animals. To test this, we familiarized one-month-old tortoise hatchlings with an object (a brown cone vs. a blue sphere) and then tested them in a novel arena once with the familiar object and once with an unfamiliar one. To measure the reactions toward familiar and unfamiliar objects, we measured the distance between the tortoise and the object throughout the test. Differently from what happened with unfamiliar and familiar conspecifics, we found no difference in behavior toward familiar and unfamiliar objects. This shows that the different reactions toward familiar and unfamiliar conspecifics previously observed are specific for social interactions and are not a mere reaction to the novelty effect. The behavioral responses displayed by young tortoises for unfamiliar conspecifics, but not for unfamiliar objects, show the relevance of social behavior from the beginning of life, even for solitary species.