Social environment shapes male colour development in Trinidadian guppies

Plasticity plays an important role in species persistence under environmental change. Morphological traits are well known to respond to various ecological factors such as temperature and predation, but less is known about the effect of social cues. In this study, we test the impact of both predator and social environmental cues on the development of male body colouration in Trinidadian guppies (Poecilia reticulata) adapted to different predation regimes. We raised second-generation (F2) fish adapted to either a high or low predation environment in a full-sibling experimental design under two crossed environments: a predator treatment (with or without predator cues) and a social treatment (isolated, or with adult tutors from their predation regime, or the opposite). Guppies adapted to a low-predation environment had a greater relative area of orange colour than high-predation guppies, repeating previous results indicating a genetic basis to male colouration. Surprisingly, predator cues had no effect on conspicuous colouration, yet social cues had a strong effect. Fish reared in isolation (regardless of population) showed more orange and black body colouration than fish reared with tutors. These results emphasize the importance of examining plasticity under complex environmental contexts and suggest a role of social dynamics in the development of trait diversity in nature. This information will contribute to our broader understanding of the interacting role of genetics and plasticity in species' responses to environmental change.