Behavioral coordination is a fundamental element of human cooperation. It is facilitated when individuals represent not only their own actions but also those of their partner. Identifying whether action corepresentation is unique to humans or also present in other species is therefore necessary to fully understand the evolution of human cooperation. We used the auditory joint Simon task to assess whether action corepresentation occurs in common marmosets, a monkey species that engages extensively in coordinated action during cooperative infant care. We found that marmosets indeed show a joint Simon effect. Furthermore, when coordinating their behavior in the joint task, they were more likely to look at their partner than in a joint control condition. Corepresentation is thus not unique to humans but also present in the cooperatively breeding marmosets. Since marmosets are small-brained monkeys, our results suggest that routine coordination in space and time, rather than complex cognitive abilities, plays a role in the evolution of corepresentation. Research ArticleHumans are a hyper-cooperative species, and the evolution of human cooperation and its underlying mechanisms continue to be a matter of debate (Richerson et al., 2016;Tomasello & Gonzalez-Cabrera, 2017). Our goal was therefore to investigate whether one such mechanism, namely action corepresentation during joint action, may be present in another highly cooperative primate species, the common marmoset monkey (Callithrix jacchus).When human social partners are jointly engaged in a cooperative task, they corepresent each other's actions-for instance, in the joint Simon task (Sebanz, Knoblich, & Prinz, 2003). This task is based on the individual Simon effect (Simon & Rudell, 1967), which is the compatibility effect arising when an irrelevant feature of a test stimulus interferes with the response, as when a stimulus is played back from one side, whereas the required response is on the opposite side. For instance, in the auditory version (Ruys & Aarts, 2010) of the Simon task (full task), subjects have to learn to discriminate between two sound stimuli, "L" and "R," and choose the corresponding left-or righthand response option. If the stimuli are played back from either the left-hand or the right-hand side of the subject, the task is easier in compatible trials (i.e., when stimulus "L," requiring a left-hand response, is played back from the left-hand side, and stimulus "R," requiring a right-hand response, is played back from the righthand side) than in incompatible trials (i.e., when stimulus "L" is played back from the right-hand side, and stimulus "R" is played back from the left-hand side). This compatibility effect is referred to as the Simon effect. However, when subjects have to solve only half of the task because one response option is not available (i.e., the half task), the corresponding stimulus can be ignored, and the compatibility or Simon effect disappears. Thus, when only one response option is available (e.g., on the right-hand ...

Many prey taxa use kairomones or alarm pheromones to assess the risk of predation in aquatic environments, and the rate at which these cues attenuate determines how precisely they indicate the local density of predators. We estimated the rate of degradation of chemical cues generated by Aeshna dragonfly larvae feeding on Rana temporaria tadpoles. The half-life of the cue was 35 h and was not influenced by whether it was aged in pond water or tap water or whether other tadpoles were present in the container in which cue-aging occurred. A review of other published estimates of predator cue half-life revealed values of 0.2-126 h, and variation among studies was unrelated to the type of aging water, the venue in which water was aged or prey behavior observed (laboratory, field), or the type of behavior that was recorded. We conclude that factors affecting the persistence of predator cues remain uncertain in spite of their importance for understanding the evolution of induced defenses. AbstractMany prey taxa use kairomones or alarm pheromones to assess the risk of predation in aquatic environments, and the rate at which these cues attenuate determines how precisely they indicate the local density of predators. We estimated the rate of degradation of chemical cues generated by Aeshna dragonfly larvae feeding on Rana temporaria tadpoles. The halflife of the cue was 35 h and was not influenced by whether it was aged in pond water or tap water or whether other tadpoles were present in the container in which cue-aging occurred. A review of other published estimates of predator cue half-life revealed values of 0.2-126 h, and variation among studies was unrelated to the type of aging water, the venue in which water was aged or prey behavior observed (laboratory, field), or the type of behavior that was recorded. We conclude that factors affecting the persistence of predator cues remain uncertain in spite of their importance for understanding the evolution of induced defenses.