Stereotypy and variability in the mating call of the Lusitanian toadfish, Halobatrachus didactylus.

Abstract

During the breeding season, Lusitanian toadfish males become territorial and emit a tonal advertisement call (the boatwhistle) to attract mates to their nests. We recorded 16 males in the Tagus River estuary (Portugal) during the breeding season and studied boatwhistle variability in a short (minutes) and long time scale (days). We also related boatwhistle acoustic features with male physical characteristics. The recorded males were inside closed artificial nests in groups of eight individuals. Boatwhistles showed individuality in short periods of time but some males showed significant intraindividual variability in a longer time scale. Both social interactions (number of calling males) and tide level changed significantly male calling rate and acoustic characteristics of boatwhistles. The fundamental frequency of boatwhistles (equivalent to the sonic muscle contraction frequency) and boatwhistle emission rate were correlated with male condition (somatic and lipid content). Sound emission rate was also correlated with sonic muscle index. These results suggest that different toadfish males produce distinct boatwhistles, and that they have the ability to modulate the acoustic characteristics of their sounds with the level of social interactions, which increase during rising and high tide. Moreover, boatwhistles characteristics and acoustic activity seems dependent on male condition and sonic muscle index.