Alternative mating tactics and acoustic behaviour in the grass goby Zosterisessor ophiocephalus: a behavioural analysis of the interaction between the parasitic and the bourgeois male

Abstract

In this study the behavioural interaction between the bourgeois and the parasitic male of the grass goby, Zosterissor ophiocephalus, is investigated during spawning in the laboratory. Large grass goby males care for the eggs (bourgeoise males), whereas small males are believed to adopt an alternative mating tactic. The behavioural interaction between one large male spawning inside an artificial nest (a large plastic box buried in the sand provided with two entrance tubes opening on the substrate) and one small male, was investigated in five small male‐large male pairs. The small male performed parasitic activity in four replicates. The main activity of the parasitic male was staying still on the substrate by one nest opening (Waiting), usually followed by one or more attempts to enter the nest. Waiting was performed repeatedly by the parasitic male at both nest openings across the spawning period. The activity of the large male inside the nest consisted mainly of switching between spawning‐related activities (e.g. Upside‐down) and standing still inside one of the two entrance tubes of the nest (Patrolling). The analysis of temporal relationship among behavioural activities showed a positive relationship between the occurrence of Waiting and Patrolling in 3 out of 4 replicates, with Patrolling occurring more frequently at the nest opening at which the parasitic male was Waiting. Only 20% of all the intrusion attempts observed in the five replicates were successful, i.e. the parasitic male entered the burrow and performed egg‐fertilization movements. A significant emission of sounds by the bourgeois male, mostly associated with Patrolling, was documented. The function of the bourgeois male sound production during spawning is discussed.