Chemical information can have a direct or indirect influence beyond dyadic interactions. How
chemical cues can alter communicating interactions where the transmitters of chemical cues
do not participate is poorly understood. Chemical information plays an important role in
the sexual behaviour of urodeles. Previous studies of the newt Lissotriton boscai and other
salamandrids showed that males modify their courtship in presence of competitors to avoid
courtship interferences. The aim of this study was to test whether L. boscai males assess the
level of competition through chemical cues and adjust their courtship accordingly. In a first
experiment, male courtship displays were recorded in aquaria containing their own chemical
stimuli, or from another male. The duration and/or the number of several courtship displays
were scored, and found that males decreased their courtship effort when the water contained
chemical stimuli from another male. This experiment showed that semiochemicals can be suf-
ficient to modify courtship displays without visual contact with transmitters of the chemical
information, suggesting that males may adjust their courtship display to reduce reproductive
costs. An additional experiment resembling chemically mediated residence asymmetries was
then performed to examine whether territoriality is compatible with results of experiment 1,
and found no evidence.