Common wall lizards learn familiar-unfamiliar identity of conspecifics through chemical cues

Despite numerous studies on individual recognition having been carried out on lizards, a clear demonstration that lizards are able to identify conspecifics is still lacking. Individual recognition in lizards involves identifying conspecifics based on distinctive characteristics, including physical, acoustic, and chemical cues. Lizards use specialized epidermal glands for intraspecific communication, which secrete a mixture of proteins and lipids. To demonstrate individual recognition, a training period needs to be devised to establish associations between traits and memories of interactions with other individuals. We thus performed a 3-week study on the common wall lizards (Podarcis muralis) to assess whether lizards are able to associate between previous experience with conspecifics and their chemical signals. Further, we investigated whether proteins played a role in this association. We acclimated 40 males to laboratory conditions during the first week. In the second week, we trained lizards to develop familiarity with odors (feces, urine, skin, femoral gland secretion) from previously unknown individuals. During the third week, we tested lizards by exposing them to odors from familiar and unfamiliar individuals. Lizards examined unfamiliar signals for longer in terms of time and frequency compared to familiar ones. These results form the basis of showing that lizards may be capable of recognizing conspecifics as different individuals, based on their chemical signals, even if the observed discrimination remains at the level of familiarity and unfamiliarity. The experiment does, however, demonstrate evidence of learned responses in common wall lizards.