Effect of Predation on Shaping Parental Brood Defense and Larval Ontogeny of Convict Cichlids Leading to Population Divergence

(1) Predation selects for antipredator competence in prey. For fishes with parental care, brood predators exert selection on the morphological phenotype of offspring, and also exert strong selection pressure to promote parental care behavior of adults. (2) This review summarizes field and lab studies on the ontogeny of antipredator competence in convict cichlids, a freshwater fish with extended biparental care of their free-swimming young. (3) Here, data show that differences in swimming performance between small and large young are exploited by parents when they adopt (smaller) young. Velocity and acceleration of startle responses improves nonlinearly with body size, increasing rapidly at a point when the skeleton rapidly ossifies from cartilage to bone, at the size at which discrimination by adopting parents shifts, and the timing of change in the rate of change in area protected by parents. Convict cichlids in a Nicaraguan lake population showed a similar correlation among these traits, but these traits are delayed relative to Costa Rican fish. (4) Population divergence is likely explained by relatively more intense brood predation in the lake, which selects for different optima of larval antipredator competence and parental brood defense.

Interactions of natural and sexual selection: damselfish prioritize brood defense with male–male competition or courtship

Natural and sexual selection often act in opposing directions, forcing individuals to prioritize activities necessary for survival with those required for reproduction. We examined the interaction of natural and sexual selection pressures on the behaviour of beaugregory damselfish, Stegastes leucostictus, by presenting territorial males with an egg predator and either a male or female conspecific, requiring males to prioritize brood defense with either courtship or intra-sexual competition. By measuring the time spent near stimuli, we examined the influence of several factors, including stimuli type, variation in predator number, and the presence of eggs in a nest site. Generally, males spent more time with conspecific stimuli than egg predators, suggesting that the sexual selection pressures of deterring rivals and attracting mates outweigh the natural selection pressure to engage in brood defense. This decision was affected by the sex of the conspecific presented, the presence of eggs in a male's territory, and a number of interactions of these factors, indicating that male damselfish consider multiple factors before investing in certain types and intensities of behaviours. Furthermore, observations of behaviours associated with courtship and intrasexual aggression show that a natural selection pressure impacts intra- and inter-sexually selected behaviours differently in this system.

The Effects of a Trade-Off Between Foraging and Brood Defense On Parental Behaviour in the Convict Cichlid Fish, Cichlasoma Nigrofasciatum

Parental convict cichlids, Cichlasoma nigrofasciatum, responded to the presence of a potential brood predator by decreasing net energy gains (food intake decreased and energy expenditure increased) while increasing parental effort (large allocation of time to brood defense). These behaviours are important factors in the life-history trade-off between current and future reproductive investments. The allocation of energy into defense behaviours and elevated activity levels, combined with a voluntary reduction of food consumption, represent an investment in the current brood which could (in nature) reduce future reproduction. Contrary to parental investment theory predictions, consistent increases in parental effort with brood age were not evident.