The functional basis for variable antipredatory behavioral strategies in the chameleon Chamaeleo calyptratus.

To counterbalance demands of different selective pressures, many species possess morphological, physiological and behavioral specializations that increase survival in their environments. Predation is one such pressure that can elicit multiple adaptive responses, and the effectiveness of antipredator behaviors likely vary both by environment and individual across time. Chameleons use multiple antipredator strategies, many of which vary with body size and habitat type. Although their unique morphological and physiological traits produce relatively slow locomotion, which is poorly suited for fleeing, chameleons can also use crypsis or aggression to avoid predation. To examine the functional basis for variable antipredator behavioral responses, we subjected chameleons to a series of mock predation trials and determined how often individuals adopted each antipredator strategy, and then quantified the performance capacities underlying each strategy. In particular, we measured bite force as a determinant for aggression, sprint velocity for fleeing, and degree of color change for crypsis. We found that aggression was predicted by traits associated with higher absolute and relative bite force, as well as habitat type; fleeing was predicted by higher normalized sprint velocity and habitat type; and crypsis was predicted by habitat type, color change capacity in bird color space and the interaction between the two. These results illustrate the importance of considering both functional capacity and environmental context in antipredator behavior decision-making.

Effects of striatal lesions on components of choice: Reward discrimination, preference, and relative valuation.

The striatum is a key structure involved in reward processing and choice. Recently, we have developed a paradigm to explore how components of reward processing work together or independently during choice behavior. These components include reward discrimination, preference and relative valuation, and the goal of the present study was to determine how the striatum is involved in these dissociable components during this novel free choice paradigm. We tested choice utilizing two different outcome series with one being a more straightforward single-option discrimination anchored by a 0 reward outcome, and the other as a multi-option outcome discrimination of greater difficulty. We compared the free choice reward task to a sequential reward task and an extinction task. Striatal lesions impaired responding only in the free choice version with alterations in both appetitive and consummatory measures. Ventral striatal lesions had greater impact altering discrimination, preference and relative valuation in both the single and multi-option week studies. A major factor involved in these deficits was a significant aversion to the multi-option that contained a larger outcome option but with a longer delay to reward. Dorsal striatal lesions caused less impairment even leading to enhanced choice behavior compared to control animals during the more difficult multi-option free choice series. Overall, the results suggest that the context of action is crucial when linking striatal function to choice behavior and its diverse components. The implications include the idea that striatal involvement in decision-making is increased when responses are self-paced and diverse in a more naturalistic environment.