Male antagonistic behaviour after spawning suggests paternal care in brown trout, Salmo trutta

The evolution of parental care depends on the sex-dependent resolution of a trade-off between present and future reproduction. In salmonids, the mating systems are often characterised by fierce male-male competition, and the absence of paternal care is widely admitted in these species. However, the fact that brown trout eggs can be cannibalised by peripheral individuals just after spawning suggests that dominant males would benefit from protecting their offspring by keeping cannibals away from the nest. We used 77 field observations of brown trout spawning to document the defensive behaviour of dominant males towards peripheral individuals before and after spawning, and test whether this behaviour was related to the probability of the clutch being cannibalised. We showed that dominant males stayed on the nest and chased peripherals even after the eggs were laid and fertilised. The number of chases performed by dominant males during the 2 min following spawning was negatively correlated to the probability of egg cannibalism. This result indicates that brown trout males can provide direct benefits to females through protection against egg cannibalism by peripheral individuals.