Proteins from femoral gland secretions of male rock lizards Iberolacerta cyreni allow self—but not individual—recognition of unfamiliar males

Individual recognition (IR) plays an important role in modulating social interactions of several animal species. IR may work at two fundamental levels: at class-level (CIR), if it allows group membership identification (e.g. familiar/unfamiliar), or at individual-level (true IR; TIR), if it allows uniquely recognizing conspecifics. Direct and indirect evidences suggest that many lizards are able to recognize conspecifics, notably using the secretions from femoral glands, specialized epidermal structures located in the cloacal region. Such secretions are made of a mix of lipids and proteins, the latter having been poorly studied but hypothesised to convey identity-related information. Using male Iberian Rock lizards, we set up bioassays to test the role of the protein fraction in IR, and specifically whether lizards: (1) can detect proteins from femoral glands, (2) can recognize their own proteins from those of an unfamiliar male (CIR) and (3) can distinguish between two unfamiliar protein signals (TIR). We found that femoral proteins can be actually detected, and the protein signal was enough to allow self-recognition, but not to distinguish between two unfamiliar males. These outcomes support the hypothesis that proteins from lizard femoral glands are used in intraspecific communication, at least at CIR level. The lack of TIR detection has three possible explanations: (1) finer IR abilities are actually absent in this species; (2) TIR requires a more complex and complete chemical signal or (3) a more prolonged and complete set of previous interactions among individuals is needed to lead to familiarity and TIR