Diurnal cycle in salivary cortisol levels in common marmosets

A noninvasive method of saliva sampling was used to assess the diurnal cortisol rhythm from 0900 to 1700 hr in the common marmoset (Callithrix jacchus). The levels of cortisol were highest in the morning and declined significantly over the day. Individual marmosets varied in the magnitude of the cycle, and the greatest individual variability occurred in the morning levels. The decrease in cortisol levels was more rapid after than before the midday feeding period in subordinate marmosets (aged 53-63 months) compared to dominant marmosets (aged 79-80 months), and overall, the levels of cortisol were higher in the subordinate marmosets. We found no effect of sex on cortisol levels across the cycle.