Interactions among paternal behavior, steroid hormones, and parental experience in male marmosets (Callithrix kuhlii)

Male black tufted-ear marmosets (Callithrix kuhlii) contribute to the reari ng of their offspring. Here we evaluated predictions of hypotheses suggesti ng that (1) T and E-2 influence infant-care behavior in male marmosets, (2) levels of T and E-2 are modulated by paternal experience, and (3) paternal behavior and levels of T and E-2 in male marmosets covary with stress. We observed the behavior of marmosets in their family groups following the bir th of infants and evaluated urinary concentrations of T, E-2, and the stres s hormone cortisol (CORT) among fathers before and after the birth of young . Urinary levels of T, E-2, and CORT were lower among males who carried inf ants at high rates than males who carried at low rates, and T and CORT leve ls were negatively correlated with carrying rates across all males. Males h ad significantly lower T levels while carrying the second compared to the f irst litter and slightly lower rates of infant-carrying, possibly due to as sistance provided by offspring of the first litter. There were increases in CORT revels of fathers after the birth of the first litter, but decreases in CORT after the birth of the second. Our results suggest a relationship i n C. kuhlii between paternal behavior, hormones, and paternal experience. R ates of infant-carrying appear to be linked to hormone levels, and hormone levels in turn are affected by experience caring for young. Our data also s uggest that T, E-2, and CORT have synergistic influences on infant-carrying behavior or alternatively that associations between T and E-2 and rates of infant-carrying are influenced by stress or other glucocorticoid-related v ariables. Finally, we propose a hypothesis suggesting that experience-relat ed changes in hormones reinforce the commitment of males to successful bree ding partnerships. (C) 2001 Academic Press.