Hormonal changes related to paternal and alloparental care in common marmosets (Callithrix jacchus ) Maria Teresa da Silva Mota a, * , Celso Rodrigues Franci b , Maria Bernardete Cordeiro de Sousa a a Departamento de Fisiologia, Centro de Biocie ˆncias, UFRN, Caixa Postal 1511, Campus Universita ´rio, Natal, RN 59078-970, Brazil b Faculdade de Medicina de Ribeira ˜o Preto-USP, Sa ˜o Paulo, Brazil Received 6 April 2005; revised 25 July 2005; accepted 26 July 2005 Available online 26 August 2005 Abstract The physiological mechanisms of parental and alloparental care in cooperatively breeding nonhuman primate species such as the common marmoset (Callithrix jacchus ) are poorly known. In this study, we examined prolactin and cortisol plasma levels of fathers and older offspring of both sexes, with and without previous experience in infant carrying, around parturition and during infant carrying. Blood samples were collected from fathers and older offspring and prolactin and cortisol were measured by RIA and EIA, respectively. Prolactin levels of both caretakers were not influenced by infant’s birth, previous experience or proximity to parturition. However, prolactin levels increased in both caretakers while in physical contact with infants and also with the number of infants being carried in older offspring. These findings suggest that increased prolactin seems to be mainly due to physical effort rather than a physiological trigger of paternal and alloparental care in common marmosets. Cortisol levels were higher for experienced fathers shortly before parturition which could act to reinforce affiliative bonds between breeding males and females at this time or in the ability of males to detect the proximity of the parturition or both. D 2005 Elsevier Inc. All rights reserved. Keywords: Prolactin; Cortisol; Parental and alloparental behavior; Experience; Common marmoset; Callithrix jacchus Introduction The regulation of maternal care in mammals is related to hormonal (Rosenblatt, 1990) and somatosensory stimuli such as sight, sound, and odor, which contribute to contact seeking (Stern, 1997). In this sense, the hormonal correlates of maternal behavior, especially in rats (Rosenblatt, 1990; Rosenblatt et al., 1979; Bridges, 1990), are better under- stood. The close association between the young and their mothers, particularly during pregnancy and nursing, allows them to share a physiological environment that might be essential both to maintenance of the fetus and initiation of mother – infant interaction after parturition. A regulation model of maternal behavior in marmosets and tamarins was developed by Pryce (1993) and includes the hormones that control pregnancy and parturition, genital stimulation during parturition, previous experience with infants at or after it, and the synergistic interaction of these three factors at birth. Among the factors mentioned above, previous experience has an important role in establishing effective mothering (rats: Rosenblatt, 1967; Fleming and Sarker, 1990; sheep: Poindron and Le Neidren, 1980; Le ´vy and Poindron, 1987; nonhuman primates: Holman and Goy, 1995), where recognition of the infant as a familiar individual is a way of preventing avoidance behavior or even infanticide as reported for male rodents (Huck et al., 1982; Elwood and Kennedy, 1991). Thus, maternal behavior might have two different regulators: a physiological one, which is mainly related to progesterone, estradiol, prolactin, and oxytocin levels throughout pregnancy and lactation, and a non-phy- siological one related to pup stimulation for the maintenance of maternal behavior post-partum. Among mammals, paternal care is relatively uncommon and has been observed in carnivores, rodents, and primates 0018-506X/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2005.07.012 * Corresponding author. Fax: +55 84 2119206. E-mail address: mtmota@cb.ufrn.br (M.T. da Silva Mota). Hormones and Behavior 49 (2006) 293 – 302 www.elsevier.com/locate/yhbeh