Morning and Afternoon Patterns of Fecal Cortisol Excretion among Reproductive and Non-Reproductive Male and Female Common Marmosets, Callithrix jacchus

Abstract

Adult female common marmosets show diurnal variation in the pattern of fecal cortisol excretion, with low levels in the morning and higher levels in the afternoon. In this species females compete to reproduce, the subordinate ones have their fertility suppressed, and cortisol levels tend to be higher in reproductive (dominant) than in non-reproductive females. To determine if males show the same diurnal variation and the influence of reproductive condition on the pattern of fecal cortisol excretion, we collected fecal samples from 10 captive adult (5 male and 5 female) common marmosets (Callithrix jacchus) living in 3 family groups in outdoor cages in the Núcleo de Primatologia, Natal, RN, Brazil. All fecal samples were collected from 05:00 a.m. to 05:00 p.m. (a light phase of approximately 12 hours), twice a week for 4 consecutive weeks for each family. We standardized as morning the period from 05:00 to 11:00 a.m. and as afternoon 11:00 a.m. to 05:00 p.m. Fecal cortisol was measured in the samples after extraction procedures (hydrolysis and solvolysis) followed by enzyme-immunoassay. The MANOVA post hoc Tukey test showed that the diurnal excreted cortisol did not vary among males and was significantly lower than in females. When the reproductive condition of males and females was taken into account, statistical analysis showed that fecal cortisol did not differ within reproductive and non-reproductive males and females. Baseline values for cortisol in feces were higher in females than in males, even among those that were not reproducing. This probably reflects the fact that the relationship between females is more tense within the social group since they have to dispute and maintain their reproductive status. Besides reflecting different reproductive strategies for males and females of common marmosets, the low excretion of cortisol in males may be the consequence of low cortisol levels in blood or may be due to different mechanisms involved in its excretion in this gender.