A comparative study of the function of heterospecific vocal mimicry in European passerines

Although heterospecific vocal imitation is well documented in passerines, the evolutionary correlates of this phenomenon are poorly known. Here, we studied interspecific variation in vocal mimicry in a comparative study of 241 European songbirds. We tested whether vocal mimicry is a mode of repertoire acquisition or whether it resulted from imperfect song learning. We also investigated the effect of the degree of contact with the vocal environment (with species having larger ranges, abundance, or being long lived having a higher degree of mimicry) and a possible link with cognitive capacity (an overall larger brain in species with mimicry). Finally, we determined the potential evolutionary role of vocal mimicry in different interspecific contexts, predicting that mimicry may affect the intensity of brood parasitism, predation, or degree of hybridization. While controlling for research effort and phylogenetic relationships among taxa, we found that effect sizes for intersong interval, brain size, breeding dispersal, abundance, age-dependent expression of repertoires, and predation risk reached a level that may indicate evolutionary importance. Vocal mimicry seems to be a consequence of song continuity rather than song complexity, may partially have some cognitive component but may also be dependent on the vocal environment, and may attract the attention of predators. However, estimates of sexual selection and interspecific contacts due to brood parasitism and hybridization varied independently of vocal mimicry. Therefore, mimicry may have no function in female choice for complex songs and may be weakly selected via interspecific associations. These findings provide little evidence for vocal mimicry having evolved to serve important functions in most birds

Social integration of macroparasites in ant societies: ultimate and proximate mechanisms

Ant colonies are commonly parasitized simultaneously by several species. While some parasites are recognized and attacked by their ant hosts, others have apparently cracked the ants’ recognition code and interact mainly peacefully with their hosts. Although such apparent differences in social integration among ant parasites have been described, the underlying mechanisms resulting in differential integration remain mostly unknown. Using Leptogenys army ants and their parasites, I studied ultimate mechanisms that might be responsible for differing integration levels by comparing the strength of host defence with the negative impact of parasites. In addition, I investigated proximate mechanisms of differing integration levels by evaluating the role of chemical deception by mimicry. The interactions of several parasitic beetle species with their Leptogenys hosts revealed that particular species fed on host larvae, while others did not. The hosts’ aggressiveness was enhanced towards brood-killing species, while non-predatory species received almost no aggression, resulting in social integration. Accordingly, the fitness costs of parasites likely influence the evolution of host defences against them in a multi-parasite situation. The role of chemical mimicry has been investigated in detail for two kleptoparasites, namely the silverfish Malayatelura ponerophila and the spider Gamasomorpha maschwitzi. By analyzing the transfer of a chemical label from the host ants to the parasites, I empirically demonstrated for the first time that ant parasites are able to acquire mimetic compounds from their host. Additional biosynthesis of mimetic compounds seems unlikely in both parasites, since the concentration of each cuticular hydrocarbon decreased in individuals that were isolated from the host. In addition, a high accuracy in chemical host resemblance was shown to be beneficial for the social integration of both parasites. Reduced accuracy in chemical host resemblance resulted either in aggressive host responses towards the silverfish or elevated host inspection behaviour towards the spider. The degree of dependency on chemical mimicry to achieve social integration differed considerably between the two parasites, however. Accordingly, the parasites’ level of social integration is affected by ultimate mechanisms such as the negative impact on the host as well as by proximate mechanisms such as the degree of accuracy in chemical host resemblance

Human Minds

Articl

Social attitudes modulate automatic imitation

In naturalistic interpersonal settings, mimicry or ‘automatic imitation’ generates liking, affiliation, cooperation and other positive social attitudes. The purpose of this study was to find out whether the relationship between social attitudes and mimicry is bidirectional: Do social attitudes have a direct and specific effect on mimicry? Participants were primed with pro-social, neutral or anti-social words in a scrambled sentence task. They were then tested for mimicry using a stimulus-response compatibility procedure. In this procedure, participants were required to perform a pre-specified movement (e.g. opening their hand) on presentation of a compatible (open) or incompatible (close) hand movement. Reaction time data were collected using electromyography (EMG) and the magnitude of the mimicry / automatic imitation effect was calculated by subtracting reaction times on compatible trials from those on incompatible trials. Pro-social priming produced a larger automatic imitation effect than anti-social priming, indicating that the relationship between mimicry and social attitudes is bidirectional, and that social attitudes have a direct and specific effect on the tendency to imitate behavior without intention or conscious awareness

A kinematic study on (un)intentional imitation in bottlenose dolphins

The aim of the present study was to investigate the effect of observing other's movements on subsequent performance in bottlenose dolphins. The imitative ability of non-human animals has intrigued a number of researchers. So far, however, studies in dolphins have been confined to intentional imitation concerned with the explicit request to imitate other agents. In the absence of instruction to imitate, do dolphins (un)intentionally replicate other's movement features? To test this, dolphins were filmed while reaching and touching a stimulus before and after observing another dolphin (i.e., model) performing the same action. All videos were reviewed and segmented in order to extract the relevant movements. A marker was inserted post hoc via software on the videos upon the anatomical landmark of interest (i.e., rostrum) and was tracked throughout the time course of the movement sequence. The movement was analyzed using an in-house software developed to perform two-dimensional (2D) post hoc kinematic analysis. The results indicate that dolphins' kinematics is sensitive to other's movement features. Movements performed for the "visuomotor priming" condition were characterized by a kinematic pattern similar to that performed by the observed dolphin (i.e., model). Addressing the issue of spontaneous imitation in bottlenose dolphins might allow ascertaining whether the potential or impulse to produce an imitative action is generated, not just when they intend to imitate, but whenever they watch another conspecific's behavior. In closing, this will clarify whether motor representational capacity is a by-product of factors specific to humans or whether more general characteristics such as processes of associative learning prompted by high level of encephalization could help to explain the evolution of this ability

The role of social cognition in decision making

Successful decision making in a social setting depends on our ability to understand the intentions, emotions and beliefs of others. The mirror system allows us to understand other people's motor actions and action intentions. ‘Empathy’ allows us to understand and share emotions and sensations with others. ‘Theory of mind’ allows us to understand more abstract concepts such as beliefs or wishes in others. In all these cases, evidence has accumulated that we use the specific neural networks engaged in processing mental states in ourselves to understand the same mental states in others. However, the magnitude of the brain activity in these shared networks is modulated by contextual appraisal of the situation or the other person. An important feature of decision making in a social setting concerns the interaction of reason and emotion. We consider four domains where such interactions occur: our sense of fairness, altruistic punishment, trust and framing effects. In these cases, social motivations and emotions compete with each other, while higher-level control processes modulate the interactions of these low-level biases

Vengefulness Evolves in Small Groups

We discuss how small group interactions overcome evolutionary problems that might otherwise erode vengefulness as a preference trait. The basic viability problem is that the fitness benefits of vengeance often do not cover its personal cost. Even when a sufficiently high level of vengefulness brings increased fitness, at lower levels, vengefulness has a negative fitness gradient. This leads to the threshold problem: how can vengefulness become established in the first place? If it somehow becomes established at a high level, vengefulness creates an attractive niche for cheap imitators, those who look like highly vengeful types but do not bear the costs. This is the mimicry problem, and unchecked it could eliminate vengeful traits. We show how within-group social norms can solve these problems even when encounters with outsiders are also important.

Smile asymmetries and reputation as reliable indicators of likelihood to cooperate: An evolutionary analysis

Cooperating with individuals whose altruism is not motivated by genuine prosocial emotions could have been costly in ancestral division of labour partnerships. How do humans ‘know’ whether or not an individual has the prosocial emotions committing future cooperation? Frank (1988) has hypothesized two pathways for altruist-detection: (a) facial expressions of emotions signalling character; and (b) gossip regarding the target individual’s reputation. Detecting non-verbal cues signalling commitment to cooperate may be one way to avoid the costs of exploitation. Spontaneous smiles while cooperating may be reliable index cues because of the physiological constraints controlling the neural pathways mediating involuntary emotional expressions. Specifically, it is hypothesized that individuals whose help is mediated by a genuine sympathy will express involuntary smiles (which are observably different from posed smiles). To investigate this idea, 38 participants played dictator games (i.e. a unilateral resource allocation task) against cartoon faces with a benevolent emotional expression (i.e. concern furrows and smile). The faces were presented with information regarding reputation (e.g. descriptions of an altruistic character vs. a non-altruistic character). Half of the sample played against icons with symmetrical smiles (representing a spontaneous smile) while the other half played against asymmetrically smiling icons (representing a posed smile). Icons described as having altruistic motives received more resources than icons described as self-interested helpers. Faces with symmetrical smiles received more resources than faces with asymmetrical smiles. These results suggest that reputation and smile asymmetry influence the likelihood of cooperation and thus may be reliable cues to altruism. These cues may allow for altruists to garner more resources in division of labour situations