Male-Mediated Maturation in Wild Geladas

Reproductive endocrinology of wild female woolly monkeys (Lagothrix lagotricha poeppigii) during puberty, ovarian cyclicity, and pregnancy

“…Moreover, woolly monkey males are often observed scent marking during intergroup encounters (Camargo-Peña, 2020;Di Fiore et al, 2006), and, therefore, predispersal subadult females may be exposed to chemical signals from extra-group males, which may also help trigger the onset of puberty (Petrulis, 2013) before females emigrate from their natal groups. Similar observations have been recorded in wild geladas (Theropithecus gelada), where subadult females were found to be three times more likely to mature after exposed to a nonresident male in the context of a male takeover (Lu et al, 2021), and therefore, exposure of novel males may trigger the process of sexual maturation in subadult females. However, given the small sample size for subadult females in our study, this suggestion should be considered as preliminary and must be taken with caution.…”

“…Additionally, social and environmental conditions can also influence the onset of female puberty in primates (Coe et al, 1981; Ziegler et al, 1987). For example, in both primates and other mammals, female exposure to novel males can trigger the process of sexual maturation (e.g., Baddaloo & Clulow, 1981; Bronson & Maruniak, 1975; Carter et al, 1980; Lu et al, 2021; Vandenbergh, 1969; Ziegler et al, 1987). The home ranges of woolly monkey social groups overlap substantially, and, therefore, intergroup encounters are more common than in the related muriquis or spider monkeys (Di Fiore et al, 2011).…”

The Goldilocks effect: female geladas in mid-sized groups have higher fitness

“…This analysis, however, did not consider whether unit size interacts with other metrics that might track ecological advantages, such as reproductive ageing, age at maturation or age at first birth. Based on a recent analysis on female maturations for this population [ 65 ], we expect that females in small units will have later ages at maturation and first birth to avoid inbreeding (since their fathers have longer tenures), and we expect that females in large units will have earlier ages at maturation and first birth due to the ‘Vandenbergh effect’ that accompanies male takeovers. However, even if these predictions are supported in future analyses, we do not expect these unit size differences to significantly alter our reproductive success estimates for two reasons: first, the observed range in age at first birth in this population is narrow [ 57 ], and second, in similarly long-lived primates, age at first birth had a very modest impact on variation in lifetime fitness [ 66 , 67 ].…”

How long‐term studies reveal otherwise hidden phenomena: The Long‐Term Animal Research Seminar Series

“…Jacinta Beehner described her work regarding male takeovers in gelada monkeys ( Theropithecus gelada ), which occur every ~2 to 4 years. Following male takeovers, males kill infants (accounting for ~50% of all infant deaths 12 ), immature females are more likely to sexually mature and begin cycling (the “Vandenbergh effect” 13 ), and nearly all pregnant females terminate their pregnancies (the “Bruce effect” 14 ). Fernando Campos and Matthew Zipple discussed the killing of immature individuals by males following takeover or aggressive immigration in populations of white‐faced capuchins ( Cebus capucinus imitator ) and yellow baboons ( P. cynocephalus ).…”