Predictable adaptive trajectories of sexual coloration in the wild: evidence from replicate experimental guppy populations

The question of whether populations evolve predictably and consistently under similar selective regimes is fundamental to understanding how adaptation proceeds in the wild. We address this question with a replicated evolution experiment focused upon male sexual coloration in guppies (Poecilia reticulata). Fish were transplanted from a single high predation population in the Guanapo River to four replicate, guppy-free low predation headwater streams. Two streams had their canopies thinned to adjust the setting under which male coloration is displayed and perceived. We assessed evolutionary divergence using second-generation lab-bred offspring of fish sampled four to six years following translocation. A prior experiment of the same design, performed in an adjacent drainage, resulted in the evolution of more extensive orange, black, and iridescent markings. We however found evidence for expansion only in structural coloration (iridescent blue/green), no change in orange, and a reduction in black. This response amplifies earlier findings for Guanapo fish, revealing that trajectories of color elaboration differ among drainages. We also found that color phenotypes evolved more greatly at the thinned-canopy sites. Our findings support the predictability of sexual trait evolution in the wild, and underscore the importance of signaling conditions and ornamental starting points in shaping adaptive trajectories.