O efeito da composição do grupo no desenvolvimento motor de infantes de um primata de reprodução cooperativa: o papel do gênero

Abstract

The size and composition of social groups can shape behavioral patterns and the structure of relationships of the animals that make up these groups. One of the main advantages of living in social groups is the possibility for some species to develop offspring care or cooperative reproduction, a behavior that is very common in primates. Researches involving the care of offspring have already been carried out extensively, however, little is known about the consequences that the number of individuals in a group can exert on the motor development of infants. Common marmoset (Callithrix jacchus), a small Neotropical primate, are characterized by a peculiar social system in which non-breeding individuals help in the care of the offspring in a cooperative way. In view of this, we sought to assess the effect of group composition on the motor development of their infants. More specifically, we seek to investigate the relationship of helpers in the motor development of infants. For this purpose, four groups of freeliving common marmosets were monitored in an area of the Atlantic Forest in Pernambuco, northeastern Brazil. The motor behaviors of infants aged one to four months were recorded. We used the motor diversity index (Shannon Index) as an indicator of motor development. Through this we verified that the index of motor diversity of infants with two months of age revealed to be prematurely in groups with fewer adults. In groups with more females, the diversity of two-month-old infants was significantly lower when compared to three-month-old infants. However, motor diversity increases with age regardless of the number of adult males in the group. These results bring a new bias in relation to the role of females in these small primates. While males play an important role in caring for the offspring, females seem to play a key role in the infants' motor development. In the reproduction system of these animals, apparently, the absence of helpers reflects in a premature motor development regarding the infants.