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

Abstract

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.

Sex-specific discrimination of familiar and unfamiliar mates in the Tokay gecko

“…We also predicted that geckos would show greater responses toward social stimuli, rather than towards the controls, and among social stimuli, less responses towards their own odour, all of which is supported by our results, but most prominently in males. This is likely linked to the information content of the different stimuli, with controls providing the least information, their own odour being very familiar as part of their environment providing no new information (Szabo and Ringler 2023), and the social stimuli giving the most information about potential mating partners. The low response rate towards the peppermint oil control also rules out that novelty was a factor influencing response rates but rather social information encoded in the different social pheromone stimuli.…”

“…Using the tongue flick quantification method, studies have shown that some lizards species can discriminate their own odour from that of their conspecifics (e.g. Alberts 1992;Aragón et al 2001;Cooper et al 1999;Mangiacotti et al 2020;Moreira et al 2006;Szabo and Ringler 2023), familiar from unfamiliar conspecifics (e.g. Aragón et al 2001;Font and Desfilis 2002), kin from non-kin (e.g.…”

Olfactory self-recognition in two species of snake

“…Evidence for self-recognition has been sought in species that are not primarily visual, such as dogs [10], wolves [22] and reptiles [23–27], using chemosensory-based self-recognition tests. In these paradigms, subjects are presented with the odour of a substance that originated from themselves (e.g.…”

“…Broadly, olfactory self-recognition studies have found that scent-reliant animals will investigate their marked odour more than their unmarked odour [10,22] or discriminate between self-originating and other-originating skin lipids [25,27]. Burghardt et al .…”

Multiple Chemical Signals in Male Rock Lizards: Femoral Gland Secretions and Feces May Provide Information on Body Size but Using Different Compounds

“…For example, fecal chemicals may proportionate similar or complementary information to femoral gland secretions to female Psammodromus algirus lizards, which can discriminate between young (subadult sneakers) and old (territorial) males based on chemical cues from either femoral secretions or from the feces of males [18]. Tokay geckos (Gekko gecko) can discriminate between their own skin and fecal chemicals, and those of unfamiliar conspecifics of the same sex [19]. However, self-recognition in male Lioalemus tenuis lizards is based on fecal chemicals, but not on precloacal secretions [6].…”