Diurnal Variations of Plasma Testosterone in Two Prosimian Primates (Galago crassicaudatus crassicaudatus and Lemur catta)

Blood samples were collected at 3-h intervals over a 24-h period from males of two prosimian species ( Galago crassicaudatus crassicaudatus , N = 6; Lemur catta , N = 6). In the diurnal species ( L. catta ), testosterone levels determined by radioimmunoassay were significantly higher during the period of darkness (X = 13.50 ng/ml ± 3.07 SEM) than during the period of light (X = 2.83 ng/ml ± 1.25 SEM). By 0800 h of the second day, however, plasma testosterone concentrations in L. catta had returned to the low levels observed at 0800 h on the first day of sampling. The nocturnal species ( G. c. crassicaudatus ), however, showed only a nonsignificant (P>0.10