Seasonal variations of fecal progesterone and 17beta-estradiol in captive female black-handed spider monkeys (Ateles geoffroyi).

A number of studies in free-ranging and captive spider monkeys (Ateles spp.) have shown that this genus is able to reproduce throughout the entire year. Nonetheless, it is still controversial whether births, and therefore conceptions, tend to be more frequent during certain seasons. In the present study, we monitored changes in fecal 17beta-estradiol and progesterone for approximately 1 years in five female black-handed spider monkeys (Ateles geoffroyi) kept in captivity in Mexico City. The objective was to determine whether hormone concentrations and menstrual cycles of summer and autumn accounted for a greater chance of conception than those of winter and spring, consistent with birth patterns previously reported. We collected fecal samples from the five monkeys almost daily for 1 year (March 2004 to February 2005) and used radioimmunoassay of fecal extracts to determine concentrations of 17beta-estradiol and progesterone. Concurrently, menstrual cycle phases were determined by cytological evaluation of vaginal swabs. Periovulatory 17beta-estradiol concentrations were significantly higher in autumn than in winter, spring or summer. Moreover, as evidenced by progesterone peaks, most of the summer-autumn menstrual cycles were ovulatory; in contrast, most of the winter and spring cycles were anovulatory. In conclusion, our data supported the notion that, although not a strictly seasonal reproducer, the black-handed spider monkey is more likely to conceive at the end of the rainy season and throughout autumn.