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Recent signaling resolution models of parent-offspring conflict have provided an important framework for theoretical and empirical studies of communication and parental care. According to these models, signaling of need is stabilized by its cost. However, our computer simulations of the evolutionary dynamics of chick begging and parental investment show that in Godfray's model the signaling equilibrium is evolutionarily unstable: populations that start at the signaling equilibrium quickly depart from it. Furthermore, the signaling and nonsignaling equilibria are linked by a continuum of equilibria where chicks above a certain condition do not signal and we show that, contrary to intuition, fitness increases monotonically as the proportion of young that signal decreases. This result forces us to reconsider much of the current literature on signaling of need and highlights the need to investigate the evolutionary stability of signaling equilibria based on the handicap principle.

The idea that sensitivity to self-produced motion could lie at the foundations of the clear-cut divide that the brain operates between the two basic domains of inanimate and animate objects dates back to Aristotle. Sensitivity to self-propelled objects is apparent in human infants from around the fifth month of age, which leaves undetermined whether it is acquired by experience with animate objects or whether it is innately predisposed in the brain. Here, we report that newly hatched, visually naive domestic chicks presented with objects exhibiting motion either self-produced or caused by physical contact prefer to associate with self-propelled objects. This finding supports the idea of an evolutionarily ancient, predisposed neural mechanism in the vertebrate brain for the detection of animacy. animated object | self-propelled motion | filial imprinting | predisposition doi/10.1073/pnas.0908792107

The warning signals of toxic insects often combine pyrazine odors with conspicuous colorations, such as red or yellow. An investigation of these warning signals in prey choice experiments with birds shows that pyrazine interacts with red and yellow to trigger strong aversions to these typical aposematic colors that are not shown in the absence of the odor. Pyrazine is not inherently aversive and does not produce aversion when combined with a less conspicuous color. These provide the first proof that the purpose of multicomponent signals lies in the psychological responses produced by the interaction of different sensory components.