The role of visual and olfactory cues in social decisions of guppies and zebrafish

Vision and olfaction are expensive to maintain, and in many taxa there appears to be a trade-off in investment between the two sensory systems. Previous work has suggested that guppies (Poecilia reticulata) and zebrafish (Danio rerio) may differ in the relative importance they place on these two senses in social interactions. In this study, we directly examined this issue by experimentally contrasting olfactory and visual information in social situations. In the first experiment, we found that guppies spent more time where conspecifics were visible than where they could smell them. On the contrary, zebrafish spent significantly more time in an empty compartment containing smell of conspecifics than in a compartment in which they only saw them. The difference was not large, suggesting that both species integrate various types of information to locate a nearby shoal. In two subsequent experiments, we studied the role of vision and smell in the discrimination of the quality of the social group, namely the number and the familiarity of its members. Zebrafish and guppies were confirmed to rely on different senses to estimate the size of a social group, whereas they did not differ in the discrimination of familiar and non-familiar conspecifics which appears to be based equally on the two senses. Similarly to what happens in other vertebrate clades, we suggest that, among teleosts, there are large differences in the relative importance of the different senses in the perception of the external world.