Geckos differentiate self from other using both skin and faecal chemicals: evidence towards self-recognition?

Self-recognition is the ability to recognise stimuli originating from oneself. Humans and some non-human animals show evidence of true visual self-recognition in the mirror test. They use their reflection to inspect themselves and to remove a mark that is only visible in the mirror. Not all animals, however, rely primarily on vision. In lizards, chemical cues are crucial in social interactions, and therefore, lizards would benefit from a chemical self-other distinction. Here, we test the tokay gecko (Gekko gecko), a social species, on their ability to discriminate their own skin and faecal chemicals from those of same-sex, unfamiliar conspecifics. We predicted that individuals would show more self-directed behaviour when confronted with the chemicals from unfamiliar individuals within their home enclosure as a sign of the need for increased comparison. Geckos showed higher self-directed responses towards chemicals from unfamiliar individuals compared to self-produced chemicals and a water control. Furthermore, scat and skin chemicals (regardless of origin) elicited similar but stronger responses than peppermint oil pointing towards a possible social function of scat piles. Although further tests and controls are needed, our study provides evidence towards chemical self-recognition and for a social function of scat piling in tokay geckos. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10071-023-01751-8.