Abstract

Food availability can influence the optimal allocation of time and energy among alternative behaviors such as foraging, courting, and competing for mates. If populations differ consistently in food availability, selection may cause geographic divergence in allocation strategies. At the opposite extreme, a norm of reaction may evolve such that food intake influences the allocation strategy of individuals in the same way in all populations. Between these two extremes, food intake reaction norms may diverge genetically among populations. For example, at sites where food is scarce, selection may strengthen the effect of food intake on behavior, whereas at sites with abundant food, selection may be weak or even oppose plasticity. We tested these ideas by raising male guppies from streams differing in food availability in a common laboratory environment on either low or high food levels, and then observing them in the presence of male competitors and receptive females. Males from low-food-availability streams spent more time foraging than males from high-food-availability streams, independent of food intake. Compared with males raised on the high food level, males raised on the low food level spent more time foraging and were less aggressive towards other males. Courtship display rate increased with food intake but only in males from low-food streams. In contrast, males from high-food streams showed greater plasticity with respect to male-male aggression. These results generally support the resource availability/behavioral tradeoff hypothesis while also revealing a surprising degree of ontogenetic complexity in a relatively simple system.