Exploratory decisions of Trinidadian guppies when uncertain about predation risk.

Animals can reduce their uncertainty of predation risk by gathering new information via exploration behaviour. However, a decision to explore may also be costly due to increased predator exposure. Here, we found contextual effects of predation risk on the exploratory activity of Trinidadian guppies Poecilia reticulata in a novel environment. First, guppies were exposed to a 3-day period of either high or low background predation risk in the form of repeated exposure to either injured conspecific cues (i.e. alarm cues) or control water, respectively. A day later, guppies were moved into a testing arena with limited visual information due to structural barriers and were then presented with an acute chemical stimulus, either alarm cues (a known and reliable indicator of risk), a novel odour (an ambiguous cue), or control water. In the presence of control water, guppies from high and low background risk showed a similar willingness to explore the arena. However, high-risk individuals significantly reduced their spatial evenness, although not their movement latency, in the presence of both the alarm and novel cues. When these high-risk individuals were a member of a shoal, they became willing to explore the environment more evenly in the presence of alarm cues while remaining cautious toward the novel cue, indicating an effect of the greater uncertainty associated with the novel cue. In contrast, low-risk guppies showed a willingness to explore the arena regardless of acute threat or social context. Such contextual effects of background risk and social context highlight the complexity of exploratory decisions when uncertain.