Most theories of social behaviour and cooperation assume that animals can recognise other individuals, but this is rarefy tested. Using Neolamprologus brichardi, a cooperatively breeding cichlid fish, we monitored behavioural responses to (1) real fish versus video images of fish; (2) mate versus neighbour and (3) video images of mate versus video image of neighbour. All tests were controlled for size and sex. Fish reacted appropriately to the playbacks, although responses to videos were not as strong as to real fish. Both males and females fought against the images of stranger and neighbour fish and they courted images of mates. These results confirm that the cooperatively breeding fish, Neolamprologus brichardi, recognises individuals based on vision and that video playbacks contain sufficient information to facilitate recognition.
In the animal kingdom most species follow standard sex roles: males compete more intensely for mates and females exert greater mate choice. Recent theory suggests that the direction of sexual selection is the outcome of sexual differences in potential reproductive rates (PRRs): the sex with the higher PRR will compete for mates and the sex with the lower PRR will be most selective. This study tests the theory experimentally by examining competition for mates and mate choice in the black-chinned tilapia, Sarotherodon melanotheron, a paternal mouth brooding cichlid. In this species, the PRR of males is lower than that of females. In laboratory competition trials, females were more aggressive: they bit, chased and initiated mouth fights more often than males. Dominant females were also much better at monopolising potential mates compared to dominant males. A second experiment confirmed that males were choosy for size, preferring large partners over small ones, while females did not discriminate for size. Therefore, the prediction of sex role reversal (competitive females and discriminating males) is confirmed.