Multiple selection pressures influence Trinidadian guppy (Poecilia reticulata) antipredator behavior

Animals alter their behavior to avoid a variety of different types of predators. Trinidadian guppies (Poecilia reticulata) have been an important system for examining the evolution of antipredator behavior because geographically isolated populations experience different amounts of aquatic predation. Although the influence of aquatic predators has been well documented, selective pressures from other types of predators are less well understood. We examined the response of wild-caught individuals from upstream and downstream populations to an aquatic predator and a simulated aerial predator. As previously documented, fish from the downstream population responded more strongly to the aquatic predator than did fish from the upstream population, inspecting for longer periods of time. Guppies also exhibited a strong behavioral response to the potential aerial predator. Although both populations displayed a similar magnitude of response, they differed in the specific behaviors used. Upstream fish tended to freeze on the tank bottom, whereas downstream fish tended to hide under shelter. Field observations suggest that these strategies are related to habitat features specific to each site. The behaviors used against aerial predators differed substantially from the behaviors used against aquatic predators, suggesting that different types of predators exert conflicting selection pressures. This research demonstrates the importance of considering multiple selection pressures acting on an organism when trying to understand the evolutionary history of behavioral and morphological traits.