1Department of Anthropology, University of Toronto, 2Department of Anthropology, University of Calgary, 3Department of Integrated Biosciences, University of Tokyo
March 28, 2015 2:30, Grand Ballroom E/F/G
Infants in several primates are born with a distinct natal coat. Anecdotal reports suggest that infants may transition from natal coats to the adult pelage at varying rates. We investigated whether inter-individual variation in the duration of natal coat transitions is best explained by group differences in the intensity of scramble feeding competition or infanticide pressure. From 2008-2013, we collected demographic data on nine Colobus vellerosus groups that varied in composition. We recorded the number of days infants took to transition from white to grey (N=29) and from white to black-and-white (N=35). Using GEE, we investigated whether durations varied according to group size, infant sex, and adult male group composition. Infants in larger groups transitioned from white to grey later than infants in smaller groups (p=0.013), but this effect dissipated later in development (white to black-and-white: p=0.506). Infant males transitioned earlier than females (white to grey: p=0.000; white to black-and-white: p=0.003), perhaps because infanticidal males target male infants more than female infants. Infants in multi-male groups transitioned earlier than infants in uni-male groups (white to grey: p=0.000; white to black-and-white: p=0.006), possibly due to multi-male groups containing lesser-quality males with unstable dominance relationships, which increases infanticide pressure. Lower maternal energetic net gains due to higher feeding competition in larger groups may inhibit early infant development, but variation in natal coat transitions was best explained by the infanticide pressure hypothesis. Our results suggest that the threat of infanticide ultimately shapes infant development in C. vellerosus.