Social cognition: imitation, imitation, imitation

Monkeys recognize when they are being imitated, but they seem unable to learn by imitation. These facts make sense if imitation is seen as two different capacities: social mirroring, when actions are matched and have social benefits; and learning by copying, when new behavioural routines are acquired by observation.     

Organophosphate poisoning in marmosets

Due to faulty use of a chlorpyriphos-diazinon combination as a pesticide within a laboratory animal house, 19 marmosets of 2 species (Saguinus fuscicollis and Callithrix jacchus) of 98 at risk died from organophosphorous poisoning (19%) mortality). The clinical signs were those of cholinesterase inhibitors. The morphological lesions consisted predominantly of haemorrhages in several organs, particularly the CNS, and of bone marrow necroses.     

Automatic imitation in budgerigars

A fully automated procedure, involving computer-controlled stimulus presentation and computer-recorded response measurement, was used for the first time to study imitation in non-human animals. After preliminary training to peck and step on a manipulandum, budgerigars were given a discrimination task in which they were rewarded with food for pecking during observation of pecking and for stepping during observation of stepping (Compatible group), or for pecking while observing stepping and for stepping while observing pecking (Incompatible group). The Incompatible group, which had to counter-imitate for food reward, showed weaker discrimination performance than the Compatible group. This suggests that, like humans, budgerigars are subject to 'automatic imitation'; they cannot inhibit online the tendency to imitate pecking and/or stepping, even when imitation of these behaviours interferes with the performance of an ongoing task. The difference between the two groups persisted over 10 test sessions, but the Incompatible group eventually acquired the discrimination, making more counter-imitative than imitative responses in the final sessions. These results are consistent with the associative sequence learning model, which suggests that, across species, the development of imitation and the mirror system depends on sensorimotor experience and phylogenetically ancient mechanisms of associative learning.     

Automatic imitation in dogs

After preliminary training to open a sliding door using their head and their paw, dogs were given a discrimination task in which they were rewarded with food for opening the door using the same method (head or paw) as demonstrated by their owner (compatible group), or for opening the door using the alternative method (incompatible group). The incompatible group, which had to counterimitate to receive food reward, required more trials to reach a fixed criterion of discrimination performance (85% correct) than the compatible group. This suggests that, like humans, dogs are subject to ‘automatic imitation’; they cannot inhibit online the tendency to imitate head use and/or paw use. In a subsequent transfer test, where all dogs were required to imitate their owners'' head and paw use for food reward, the incompatible group made a greater proportion of incorrect, counterimitative responses than the compatible group. These results are consistent with the associative sequence learning model, which suggests that the development of imitation depends on sensorimotor experience and phylogenetically general mechanisms of associative learning. More specifically, they suggest that the imitative behaviour of dogs is shaped more by their developmental interactions with humans than by their evolutionary history of domestication.     

Social factors determine cooperation in marmosets

We investigated which factors determine cooperative behaviour of common marmosets, Callithrix jacchus, in an instrumental task. During the approach phase each of eight individuals of a family group learned in isolation to pull a handle moving a bowl with attractive food towards its reach. In the following two experimental phases we used 16 dyads. In a dyadic training phase we assessed whether the partners were willing to manipulate the apparatus and to share food. In the subsequent cooperation test we examined whether they were willing to cooperate at a slightly modified apparatus whose solution required one individual (the producer) to pull the handle and the other (the scrounger) to grasp the bowl. Although all individuals were willing to cooperate with at least one partner, only half of the dyads solved the task in the cooperation phase. Examination of the factors that correlated with success in this phase revealed that primarily those dyads cooperated in which the dominant subject took the role of the scrounger and the subordinate took the role of the producer. However, in these successful dyads the dominant animal did not force the subordinate partner to pull the handle. Rather, the partners of cooperative dyads shared the reward and pulled equally often in both the dyadic training and the cooperation test. Thus, cooperation of marmosets in an instrumental task seems to depend on a specific distribution of roles and the tolerance of higher-ranking individuals.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Social implications of gummivory in marmosets

Gummivory or exudate feeding is a major dietary specialization which has received relatively little attention in the literature. While plant exudates contribute to the diet of many primate species, we suggest that the callitrichid species Cebuella pygmaea and Callithrix jacchus are obligate exudate feeders under free-ranging conditions. Callithrix jacchus provides an excellent model for examining the effects of exudate feeding and foraging upon social behavior, since other callitrichid species of similar body size do not share this dietary specialization. We review the effects of exudate foraging on specific social behaviors observed both in field and laboratory populations of C. jacchus. By comparing this species to closely related species, exudate foraging is seen to (1) be retained under laboratory conditions, (2) increase the frequency of territorial marking behavior while decreasing the frequency of overt aggression in males, (3) decrease the duration of infant care, and (4) increase the number of nonadults in social groups but not affect group size. The evidence presented supports the hypothesis that the consequences of exudate foraging in C. jacchus are fundamental and socially complex. © 1994 Wiley-Liss, Inc.     

Selective imitation in domestic dogs

The transmission of cultural knowledge requires learners to identify what relevant information to retain and selectively imitate when observing others' skills. Young human infants--without relying on language or theory of mind--already show evidence of this ability. If, for example, in a communicative context, a model demonstrates a head action instead of a more efficient hand action, infants imitate the head action only if the demonstrator had no good reason to do so, suggesting that their imitation is a selective, interpretative process [1]. Early sensitivity to ostensive-communicative cues and to the efficiency of goal-directed actions is thought to be a crucial prerequisite for such relevance-guided selective imitation [2]. Although this competence is thought to be human specific [2], here we show an analog capacity in the dog. In our experiment, subjects watched a demonstrator dog pulling a rod with the paw instead of the preferred mouth action. In the first group, using the "inefficient" action was justified by the model's carrying of a ball in her mouth, whereas in the second group, no constraints could explain the demonstrator's choice. In the first trial after observation, dogs imitated the nonpreferred action only in the second group. Consequently, dogs, like children, demonstrated inferential selective imitation.     

Cerebellar imitation synkineses

Imitation synkineses had not been described in cerebellar ataxia and were not known in cerebellar experimental neurophysiology. We describe here imitation synkineses when alternate movements of foot or hand were performed, in 2 cases of pure genetic cerebellar ataxia. The phenomenon was observed in other types of cerebellar ataxia (8 cases of anterior lobe cortical atrophy, 2 cases of surgical injury of the vermis). More imitation synkineses occurred on the right side in right-handed subjects, suggesting that the cerebellum physiologically inhibits a contralateral transfer of the copy of the movement. This inhibition would be particularly effective on the dominant side.     

Infanticide and cannibalism in wild common marmosets

Infanticide has been observed in many different species [1], including common marmosets [2-4], due to sexual selection, reproductive strategies or resource competition [3, 5, 6], which may ultimately lead to exploitation (cannibalism) [1, 7]. Wild callithrichids have a very flexible mating system, including monogamy, polygynandry, polyandry and polygyny [4, 8, 9], with Monteiro da Cruz [10] finding all these patterns within the same population. This results from the high degree of deforestation of their habitat [4], but non-monogamous groups cannot ensure successful rearing of infants, since helpers are crucial and should be present in high numbers [11]. In this study, we show for the first time that cannibalism can follow infanticide, and we hypothesise that it is a result of both competition for scarce resources and the need for animal protein, exacerbated by forest degradation.     

Environmental enrichment for laboratory marmosets

The authors report on using two environmental enrichment devices for marmosets, and suggest the design of five other devices that may be more successful in stimulating foraging or grooming behavior than the devices tested.     

Neural mechanisms of imitation

Recent advances in our knowledge of the neural mechanisms of imitation suggest that there is a core circuitry of imitation comprising the superior temporal sulcus and the 'mirror neuron system', which consists of the posterior inferior frontal gyrus and adjacent ventral premotor cortex, as well as the rostral inferior parietal lobule. This core circuitry communicates with other neural systems according to the type of imitation performed. Imitative learning is supported by interaction of the core circuitry of imitation with the dorsolateral prefrontal cortex and perhaps motor preparation areas--namely, the mesial frontal, dorsal premotor and superior parietal areas. By contrast, imitation as a form of social mirroring is supported by interaction of the core circuitry of imitation with the limbic system.     

Tolerated mouth-to-mouth food transfers in common marmosets

In this paper we describe tolerated mouth-to-mouth food transfers in captive adult common marmosets, where an animal approached a conspecific that has recently received a piece of food, opened the other’s mouth forcefully, and picked food pieces out of it. Tolerated mouth-to-mouth food transfers occurred between animals of both sexes. They were observed when the possessor was subordinate as well as when it was dominant, and in four dyads they were observed in both directions. We argue that this behaviour might have a social function and that the cooperative breeding system of marmosets might have facilitated its evolution.     

Dissecting the imitation faculty: The multiple imitation mechanisms (MIM) hypothesis

Is the imitation faculty one self-contained domain-general mechanism or an amalgamation of multiple content-specific systems? The multiple imitation mechanisms (MIM) hypothesis posits that the imitation faculty consists of distinct content-specific psychological systems that are dissociable both structurally and functionally. This hypothesis is supported by research in the developmental, cognitive, comparative and neural sciences. This body of work suggests that there are dissociable imitation systems that may be distinguished by unique behavioral and neurobiological profiles. The distribution of these different imitation skills in the animal kingdom further suggests a phylogenetic dissociation, whereby some animals specialized in some (but not all possible) imitation types; a reflection of specific selection pressures favoring certain imitation systems. The MIM hypothesis attempts to bring together these different areas of research into one theoretical framework that defines imitation both functionally and structurally.     

Post-conception reproductive competition in cooperatively breeding common marmosets

Common marmosets are cooperatively breeding monkeys that exhibit high female reproductive skew. Subordinate females usually fail to breed as a consequence of ovulation suppression and inhibition of sexual behavior, and, even when they do breed, typically rear fewer infants than dominants. We evaluated possible mechanisms of post-conception reproductive competition by comparing hormonal profiles across pregnancy, pregnancy outcomes, infant survivorship, and behavior in laboratory-housed families containing one (N=9) or two (N=7) breeding females. Breeding females in plurally breeding groups did not exhibit well-defined dominance relationships and rarely engaged in escalated aggression with one another. No significant differences were found among singly breeding mothers, plurally breeding mothers, and plurally breeding daughters in urinary chorionic gonadotropin or estradiol sulfate concentrations during pregnancy, fetal biparietal diameter, frequency of spontaneous abortion, frequency of stillbirths, number of live-born infants per litter, or infant mortality rates. When females gave birth while another female in the family was pregnant, however, their infants were highly likely to be killed. The perpetrator was definitively identified in only one family, in which a pregnant female killed her daughter's infant. These results are consistent with observations of free-living common marmosets and suggest that breeding females do not regularly influence one another's pregnancy outcomes, but that they may commonly kill each other's infants, especially during their own pregnancy. Our findings further suggest that infanticide by breeding females may have selected for the evolution of reproductive restraint in subordinate female marmosets.     

Pentatrichomonas hominis in laboratory-bred common marmosets

Trichomonadid protozoa have been found in the intestinal tracts of common marmosets(Callithrix jacchus). However, there is little information available onspecies identification and the pathogenicity of these trichomonads. In this study, weconducted a fecal survey of a common marmoset colony maintained as laboratory animals inJapan and identified the trichomonad species. Screening using a fecal smear examinationrevealed that 66% (58/88) of the marmosets had trichomonadid trophozoites in their feces.The trichomonads were found in both normal feces (31/49, 63%) and diarrhea (27/39, 69%),with no significant difference in frequency. The protozoa were identified asPentatrichomonas hominis using morphological characters and the 100%identity of the nucleotide sequence of the partial 18S rRNA gene (297 bp). Theintraspecific genetic variability between P. hominisfrom the marmosets in this study and P. hominis fromother reported mammal hosts was ≤1% in the nucleotide sequence, including the internaltranscribed spacer (ITS)-1, 5.8S rRNA gene, and ITS-2 (293 bp). P.hominis inhabits the large intestine of various mammalian hosts,including primates, and is considered nonpathogenic. These results suggest thatP. hominis is transmitted among marmosets and othermammals but is not a primary cause of bowel disease in marmosets.