Changes in agonistic, courtship and parental displays of the male brook stickleback, Culaea inconstans, across the breeding cycle

Although the individual elements of stickleback behaviour are well known, to date a robust investigation of the temporal cycling of aggressive, courtship and parental behaviour during the breeding cycle has been undertaken in only one species, the threespine stickleback, Gasterosteus aculeatus. In order to understand the evolution of behaviour in this fascinating group of fishes, comparative studies conducted upon other members of the Gasterosteidae are necessary. We thus documented the cyclic changes and structure of sixteen agonistic, parental and courtship displays across the breeding cycle for a population of brook sticklebacks, Culaea inconstans, from Nebraska and compared it to the temporal cycling of reproductive behaviour in the threespine. Our results indicate that in the brook stickleback: (1) aggressive behaviour varies temporally in response to a male, but not a female, intruder. (2) During those phases wherein the young are nest bound, aggressive and parental elements are negatively correlated. (3) The location of the focal fish within the tank during the trial is an accurate indicator of his primary motivation and (4), a sex specific differential response to intruding fish is apparent only during the courtship interval.The temporal structure of reproductive behaviour in the brook stickleback mirrors that of the threespine stickleback in three respects: (1) aggressive motivation across the breeding cycle exhibits a U-shaped distribution, with peak levels of aggression occurring in the nest-building stage and final days of parental care. (2) During the courtship phase sexual motivation supercedes aggression in response to the presence of a nuptially coloured female and (3), the pattern of parental fanning shows an inverted U-shaped distribution with peak frequencies coinciding with the hatching of the eggs.