A test for the parallel co-evolution of male colour and female preference in Trinidadian guppies (Poecilia reticulata)

Question: Do male traits and female preferences co-evolve in response to divergent natural selection? Organisms: Six Trinidadian guppy (Poecilia reticulata) populations adapted to high- or low-predation environments in three separate drainages. Methods: Measurement of colour patterns on wild-caught and lab-reared males. 'No-choice' mating experiments to quantify female preference functions for male traits. Comparisons of male colour and female preference functions between predation environments. Predictions: If divergent natural selection drives parallel co-evolution, both male traits and female preferences should be similar for populations in similar environments but different for populations in different environments. Conclusions: Male traits have broadly diverged in parallel between predation environments, leading to larger body size and increased colour in low-predation sites. Female preferences also appear to be diverging because females discriminate against colourful males in high-predation sites but not in low-predation sites. Despite this general pattern, deviations from parallel co-evolution were also present, suggesting a substantial role for other selective agents.