Complementary hemispheric functions during spontaneous exploration in Hermann's tortoises

Brain lateralization is a widespread feature of vertebrate nervous systems, yet evidence from reptiles remains limited. We investigated behavioural lateralization in Hermann's tortoises (Testudo hermanni) during spontaneous exploration of a novel environment. Forty-six adult tortoises were observed in a rectangular arena allowing free exploration of two lateral end-zones connected by a central corridor, over three sessions, revealing a dissociation in the direction of lateralization across different behavioural measures. Tortoises showed a rightward bias in gaze direction. Automated tracking of animals' position also revealed that males alternated more often between the neutral zone and the right side, suggesting a more cautious or monitoring-type exploration in that direction. In contrast, measures associated with active exploration showed a leftward tendency: animals spent longer touching the left corner and, in males, entered the left end-zone more frequently. The dissociation between rightward attentional biases and leftward exploratory behaviour is consistent with models proposing complementary hemispheric functions, in which the left hemisphere contributes to sustained visuomotor control whereas the right hemisphere supports rapid responses to salient stimuli. Overall, these findings provide new evidence for functional lateralization in chelonians and contribute to a comparative understanding of hemispheric specialization across vertebrates.