Defense of a Predator's Young by a Herbivorous Fish: An Unusual Strategy

Abstract

One species of cichlid fish Cichlasoma nicaraguense was observed defending the young of the largest cichlid in the lake, the predator C. dovii. The behavior of these fish was analogous to that of cichlid parents defending young to which they were genetically related. With this added help, C. dovii parents were not required to attack predators upon their own young as often as conspecific parents without helpers. Survivorship of C. dovii young was increased by the added protection afforded by these nonrelated individuals. A model is given to explain this unusual behavior in terms of individual natural selection. The arguments presented account for this behavior in terms of delayed return benefit (Trivers 1971) in that the individual (or his close kin) who defends the predator''s young will later be repaid. This repayment is derived from the predator feeding on the main competitors of the altruist.