Individual variation in risk taking: the effect of a predatory threat on fighting behavior in Nannacara anomala

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Abstract
The nature of fights in a species depends on the asymmetry in fighting ability of the contestants and the value of the contested resource. Animals of a population may also differ in their assessment of how dangerous it is to fight in relation to the risk of predation. To address this issue, we classified 36 males of the small South American cichlid fish, Nannacara anomala, according to how much each individual inspected a model predator in the presence of its own mirror image. We assigned each fish to either of two groups: bold (prone to inspecting) or cautious (averse to inspecting). We allowed bold and cautious dyads, matched for equal body weight within each dyad, to fight in the presence of the model predator. During these fights, there was no significant difference between the groups in inspection of the model predator, but bold dyads escalated significantly faster to mouth wrestling than cautious dyads. Bold dyads also performed significantly more low-intensity behavior (i.e., visual assessment and tail beating) compared to cautious dyads. Only two fights (22%) in the bold group and one fight (11%) in the cautious group had a clear winner. About 3 months later, the same dyads fought again without the model predator present. Both groups then decreased the time to reach mouth wrestling, but bold dyads still escalated significantly faster than cautious dyads to mouth wrestling. There was no significant difference in the use of low-intensity behaviors between groups. The results suggest that there are individual differences in the response toward predators among male N. anomala, which also correlates with the performance of fighting behavior when the animals' perceived risk of predation increases.

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