Female preference function related to precedence effect in an amphibian anuran (Alytes cisternasii):: tests with non-overlapping calls

We quantified precedence effect (measured as female preference for the leading calls in an acoustic interaction between two males) with non-overlapping, simulated male calls presented with various phase relationships to female Iberian midwife toads (Alytes cisternasii) in two-speaker phonotaxis playback tests. The resulting information determines the shape of the female preference function for intercall delays. Females preferentially approached leading callers for most tested phase angles. We found a gradation in the degree to which females selected the leader. They tended to exert a strong preference for the leader in 30 test, and at higher phase angles, the overall preference was weaker and graded (the higher the phase angle, the lower the preference). Other parameters of female preference (latency acid repeatability) also had a graded relationship with phase angle value. The sharp difference in probability of approach between 30 and 60 is consistent with a mechanism of male calling inhibition immediately after hearing a competitor's call previously described in other taxa. In natural interactions, male A. cisternasii adjust the timing of their calls to a phase angle that provides a slight but significant advantage to the leading caller.