Age at first reproduction in philopatric female muriquis (Brachyteles arachnoides hypoxanthus)

Female northern muriquis (Brachyteles arachnoides hypoxanthus or B. hypoxanthus) at the Estacao Biologica de Caratinga/RPPN-FMA, Minas Gerais, Brazil typically disperse from their natal groups at an average age of 6.1 +/- 0.6 years (median= 6.0 years, range = 5.3-7.8 years, n = 22), prior to the onset of puberty and sexual activity. Immigrants do not conceive until at least their second mating season, and the minimum interval from immigration to first reproduction has been 2.0 years. Age at first reproduction in dispersing females, previously estimated at 8.9 years, has now been documented at 9.0 and 9.25 years for two females whose birth dates are known. This is older than the 7.5 years at which the only female previously known to have reproduced in her natal group gave birth. Here, we present new data from a second female that reproduced in her natal group. This female (BA) was first observed to copulate at 5.5 years, and gave birth to her first infant at 7.25 years of age. Her 1.75-year cycling-to-first conception delay was only slightly shorter than the minimum recorded for immigrant females, and thus was not responsible for her young age at first reproduction compared to dispersing females. Although our sample size is small, our findings suggest that early puberty may permit females to reproduce in their natal group, implying a possible link between life history trade-offs and dispersal patterns. Because the only two females that have reproduced in their natal group were maternal sisters, it is also possible that maternal effects on age at puberty can impact dispersal patterns, particularly in small populations of primates.