Anuska Irene Alencar

Body weight of wild and captive common marmosets (callithrix jacchus)

Captive studies and occasional trappings of wild individuals indicate that callitrichids have small size and body weight and lack sexual dimorphism. We compared body weights of captive and wild Callithrix jacchus obtained by repeatedly weighing subjects from two populations in Brazil. We obtained captive data by routinely weighing 138 individuals from the Universidade Federal do Rio Grande do Norte colony and wild data via regular trapping of 243 individuals in 15 free-ranging groups from IBAMAs field site in Nísia Floresta. We assigned all subjects to one of four age classes—infant, juvenile, subadult, and adult—according to their birth dates or size, reproductive status, and dental development. There is no significant difference between males and females in any of the four age classes, but captive subjects were heavier than wild ones in all age classes but infant. Reproductive and nonreproductive adult females showed no statistical difference in weight. These results accord with previous reports of lack of body size sexual dimorphism in common marmosets and suggest that differences between wild and captive common marmosets are not constitutional, but are instead a consequence of diet and physical activity. The absence of weight difference between reproductive and nonreproductive females suggests that any possible advantage from high rank is outweighed by the costs of reproduction in common marmosets.

Mating Systems and Female–Female Competition in the Common Marmoset, Callithrix jacchus

Mating systems in callitrichids are flexible, but usually only one female breeds. Reproductive skew models suggest that either dominant individuals can control the incidence of subordinate reproduction, and that when subordinates breed, it represents a concession from the dominant individual (Optimal Skew Model (OSM)), or alternatively, that subordinates breed because dominants are unable to control them (Incomplete Control Model (ICM)). We present data both from a captive study and a long term field study to test which model better explains mating systems and female-female competition in Callithrix jacchus. A 10-year study of a wild population allowed us to identify three possible mating systems occurring in groups: monogyny, monogyny with breeding attempts from subordinates (pseudo-polygyny), and polygyny. Comparison of interbirth intervals and time to produce a surviving offspring indicated that polygyny is costly to females, suggesting that females should benefit from monopolization of reproduction. Data from an experimental captive study indicated that dominant females are not always able to physiologically and/or behaviorally suppress subordinate females’ reproduction. The literature suggests that helpers are necessary to ensure the survival of dominant females’ offspring; however, our field data show that not all adults help equally. A few individuals, mostly adult males, participate significantly more in infant care than other helpers, suggesting that dominant females gain little by retaining subordinate females in their groups. These results indicate that dominant females are not able to control subordinates’ reproduction, suggesting that the flexibility of C. jacchus mating systems is better explained by ICM than by OSM.

Adult criticism and vigilance diminish free riding by children in a social dilemma

In cooperative situations, individual interests can be in conflict with those of the group, creating a social dilemma in which one must choose whether to cooperate or not. Sensitivity to social stimuli is an important factor influencing cooperative behavior in such dilemmas. The current study investigated the influence of verbal feedback and vigilance by adults on childrens donating behavior in a public goods game. The participants were 739 public school children, between 5 and 12 years of age, who were divided into 34 groups. Each group was assigned to one of four experimental conditions: control, positive feedback (praise), negative feedback (criticism), or vigilance. Participants then played eight rounds of the game. The childrens donations were greater in the feedback and vigilance conditions, but the effects were mediated by age and rounds. The results are most likely related to concerns about reputation, which tend to become stronger with age. Older children are better at self-presentation and understanding social norms. Thus, compared with younger children, they seemed more concerned with appearing to be generous, but only when they could get credit for it. Nevertheless, childrens donations still decreased across the rounds. Although adult vigilance and feedback influence childrens cooperation among peers, other mechanisms are necessary to stabilize their behavior over time.

Stickers versus wafers: The value of resource in a public goods game with children

Investigamos como el tipo de recurso, alimentar (oblea) o no alimentar (pegatina), la edad y el genero influyen en la cooperacion de los ninos. 251 ninos fueron investigados en ocho partidos de un juego de bienes publicos, en dos condiciones experimentales: oblea o pegatina. Las obleas eran todas iguales, pero las pegatinas eran variadas. Los resultados indicaron que 1) los ninos mayores donaron mas pegatinas que los ninos mas pequenos, pero no difieren con respecto a las donaciones de obleas; y 2) las donaciones de pegatinas se mantuvieron altas durante las rondas, mientras que las donaciones de obleas disminuyeron. Proponemos que diferentes estrategias pueden ser adoptadas de acuerdo con la calidad, particularmente con respecto a la diversidad de los recursos utilizados, y el costo de la cooperacion puede ser superado cuando es mas ventajoso esperar por una recompensa futura mejor.

Boas e más razões para cooperar do ponto de vista de crianças: uma análise evolucionista

Good and bad reasons to cooperate from the viewpoint of children - an evolutionary analysis. Cooperation is a behavior apparently opposed to natural selection, however it is possible of comparation if we understand as a mechanism by which individuals can increase aptitude. This behavior has been investigated by the evolutionist psychologists whom identify some reasons for its existence such as the kinship election, the reciprocal altruism and the indirect reciprocal altruism. Very little evolutionist studies have been developed with children. Thus, the objective of this work was to analyze reports which corroborate with evolutionist findings, identified in adults. It was observed that, in the reports, one can identify examples of the kinship election, the reciprocal altruism and the indirect reciprocal altruism, as well as the importance of reputation to trigger cooperative behavior of the game partners.