Direct benefits of familiarity and grouping: a cross cichlid species comparison.

Cooperation is a highly complex social interaction that often requires coordination and communication between two individuals. Reciprocity is one explanation for how cooperation evolves and is maintained; help now will eventually be repaid in kind. For reciprocity to work, individuals must be able to differentiate between those who helped previously versus those who cheated. However, there is little empirical evidence that cooperative species have an enhanced recognition capacity compared to non-cooperative species. Here we conducted a comparative study to address this question using three cooperatively breeding cichlids and three of their close relatives that are not cooperative breeders, all from Lake Tanganyika. In a first experiment, we offered fish a choice between spending time with a familiar versus an unfamiliar conspecific and found that while cooperative cichlids spent more time with familiar individuals, the non-cooperative cichlids spent more time with unfamiliar individuals. In a second experiment, we provided a choice between affiliating with one versus three individuals (all unfamiliar) and found that 2/3 cooperative and 3/3 non-cooperative cichlids strongly preferred to affiliate with larger groups. The strength of the grouping preference was negatively correlated with an overall activity level but did not relate to measures of boldness. Our results suggest that both cooperative and non-cooperative cichlids have evolved the ability to recognize familiar individuals and have affiliative preferences; however, the nature of these preferences differ.