J effrey sachs is an economist, not an evangelist. But give the man 10 minutes behind a microphone, and a scholarly symposium starts to feel like a revival meeting. “Ladies and gentlemen,” he tells a hushed hall after describing how AIDS sufferers die in Malawi for want of $1-a-day drugs, “this plague is exploding. Its consequences will make the world quake. Rich countries could stop the devast...

Life experiences can alter cognitive abilities and subsequent behavior. Here we asked whether differences in experience could affect social status. In hierarchical animal societies, high-ranking males that typically win aggressive encounters gain territories and hence access to mates. To understand the relative contributions of social experience and physical environment on status, we used a hig...

Behavioural laterality (e.g., during social interactions) is often observed at the individual level in lower vertebrates such as fish, whereas population-level laterality is observed in many higher vertebrates. Population-level laterality can be explained mainly by internal factors (e.g., cerebral lateralization), whereas little is known about the behavioural mechanisms underlying individual-le...

Reversible changes in how readily animals fight can be explained in terms of adaptive responses to differences in the costs and benefits of fighting. In contrast, long-term differences in aggressiveness raise a number of questions, including why animals are consistent with respect to this trait, why aggressiveness is often linked to general risk taking, and why aggressive and nonaggressive anim...

Carotenoid pigments are responsible for many examples of sexually attractive red, orange, and yellow coloration in animals and play an important role in antioxidant and immune defenses. Because vertebrates cannot synthesize carotenoids, limited dietary availability may impose a trade-off between maintaining ornamental coloration and health. We used an experimental approach to test the carotenoi...

Fighting fish species in the genus Betta are found in several Southeast Asian countries. Depending on the mode of paternal care for fertilized eggs and hatchlings, various species of the betta fish are classified as mouth brooders or nest builders whose members in turn have been grouped according to their similarities mainly in morphology. The mouth brooders as well as some nest builders involv...

Investigations of communication networks in animals have focused primarily on determining whether animals extract information from peripheral contests (eavesdropping) or respond to the presence of bystanders (audience effect). The possibility that an animal’s response to being watched might be context dependent, however, has been explored in far less detail. This study investigated the influenc...