Hormonal correlates of life history characteristics in wild female Colobus vellerosus

Documenting primate life history characteristics is important because it provides information about traits that affect the timing and rate of reproduction in these long-lived species. This study describes the hormonal correlates of female reproductive events and quantifies for the first time key life history variables for Colobus vellerosus, using hormonal and observational data. This study also biologically validates that the reproductive events determined in the hormone profiles correspond to observed reproductive events for each female. We collected behavioural data on 18 females in our four study groups during 12 months (May 2012-2013) at the Boabeng-Fiema Monkey Sanctuary, using 10-min continuous focal and ad libitum sampling. We concurrently collected faecal samples (n = 1866) every 2-3 days from these 18 females (prepubescent n = 2, cycling n = 2, lactating n = 12, pregnant, n = 7, and post-reproductive n = 1) and extracted oestrogen (E2) and progesterone (P) metabolites in the field using solid-phase extraction cartridges. We created a hormone profile for each female by analyzing 1586 of our samples for E2 using radio-immuno assays, and P using enzyme-immunoassays at the Wisconsin National Primate Research Center. Mean ovarian cycle length was 24 days +/- A 1 (n = 2 cycles). Mean gestation length was 23 weeks (range = 21-25 weeks, n = 2 complete pregnancies). For females whose infants survived to nutritional independence, the mean inter-birth interval (IBI) was significantly longer than for females whose infants died prior to reaching nutritional independence (Mann-Whitney U Test; U = 14.5, p = 0.006; IBI surviving infants: 17.75 months, range = 8-20.75 months, n = 11 vs. IBI infant death: 11.89 months, range = 8-18.5 months, n = 9). The values for most life history traits reported in this study are similar to those documented in other similarly sized colobine species. Some values are on the lower end of the range for similarly sized colobines; C. vellerosus shows a cycle of 24 days and gestation length of 5.75 months vs. a range of 24-29 days for cycle length and 5.25-7.5 months for gestation length in other colobines. This may be due to C. vellerosus' smaller body size, or their limited access to higher quality food resources.