• dominance;
  • macaque;
  • species comparisons


Whole blood serotonin (WBS) determinations were made in 56 pigtailed macaques (Macaca nemestrina) with approximately equal numbers in three age groups: young-adult (4–5 years), middle-aged (13–14 years), and old (over 18 years). The animals were housed in ten living groups with one female and male of each age group in each living group. Half of the groups were fed a diet high in lipid, cholesterol, simple sugars, and sodium; the other half received a restricted diet. Three determinations per animal showed WBS levels to be stable at two times of day and at a 1-week interval, and individual differences were stable over several months' time. The mean WBS concentrations in M. nemestrina were found to be considerably higher than those reported for other species. The mean levels in females were almost 25% higher than in males. No significant effects of age, diet, or dominance status were detected.