The role of familiarity in grouping decisions of Trinidadian guppies

Social grouping is widely observed in numerous taxa, providing individuals with a variety of benefits including efficient information exchange and predator protection. However, grouping can also carry costs such as increased competition for resources, which means that individuals must often make decisions regarding joining or leaving a group. These decisions to leave or stay might in turn depend on prior experience with potential groupmates. Past work has shown that many fish distinguish between familiar and unfamiliar conspecifics and use these distinctions in their grouping choices. Trinidadian guppies (Poecilia reticulata), well known for their diversity in shoaling preferences, are an excellent system in which to investigate the role of familiarity in grouping decisions. We examined preferences for familiar individuals following both a 15-day and 55-day cohabitation period in two different guppy populations. Utilizing two binary-choice designs, we found no evidence for a familiarity preference in either population, despite observing a high preference to group with conspecifics in both populations. These results suggest that various contextual- and population-level differences may impact familiarity preferences, in turn contributing to the growing body of work on the evolution of social organization and grouping decisions in teleost species and beyond.