Plasticity of sex-biased aggression in response to the sex of territory intruders in an African cichlid fish, Julidochromis marlieri.

Conspecific intruders represent unique threats to each sex in an established mating pair, where each member may respond differently to the intruder. We investigated how individuals from established pairs of <i>Julidochromis marlieri</i> , a biparental cichlid that forms female-larger pairs , respond to conspecific intruders of either sex. When males were the larger individual in the pair, they have increased responses to male intruders compared to female intruders; whereas when females were the larger individual, they did not change their behavior. We suggest the pressures on both sexes are different based on the natural history of the species.