PLASTICITY IN SPAWNING VISITS OF FEMALE DAMSELFISH, STEGASTES NIGRICANS - EFFECT OF DISTANCE TO MATES

Both sexes of the damselfish Stegastes nigricans hold individual terri tories in which they feed on filamentous algae. At dawn, females visit males' territories to spawn, and the males guard the eggs until hatch ing. We examined how females' spawning behavior varied according to th e distances to their mates. Females usually mated with a single male p er morning. The distance to the territory of a mate (0.7-12.8 m) did n ot affect a female's total spawning time per morning, but affected the number of her spawning visits with that male. Females made many repea ted spawning visits when spawning with males at short distances, while they spawned the entire clutch in one visit when spawning with males at long distances. This plasticity in female behavior appears to be re lated to two costs during the spawning visits: (1) intrusions by other fish to feed on algae in the female's territory during her absence, w hich may cause the female to return repeatedly to her territory for de fense, and (2) attacks on the female by other territorial fish, which increased with the distance to their mates' territories. To minimize t he sum of both costs, females should change the number of spawning vis its depending on the distance to the males' territories.