Sexual dimorphism and growth in Alouatta palliata based on 20+ years of field data

Alouatta palliata patterns of growth and sexual dimorphism are evaluated using 20 plus years of field data. Comparisons are made to other species of Alouatta and other New World primates.

Records of 92 A. palliata from Guanacaste Province, Costa Rica, were used to generate growth curves for body mass and linear measurements. Timing of growth for the properties was compared, and males and females were contrasted. Slopes and elevations for periods of rapid growth were evaluated. Growth allometry and proportion ratios were also explored.

Body mass growth is rapid during the first 2 years. Males and females begin to diverge around a year of age as male growth increases and female growth slows. Adult mass for both is reached about 4 years of age. Linear measurements show rapid growth the first 18 months for both sexes. Differences develop as males continue the same rate of linear growth while female growth slows. Adult size is reached for head and body length around 3 years, and for hind-foot and tail lengths around 2 years.

A. palliata males grow in mass more rapidly than females, while both grow similarly in linear dimensions, so that dimorphism is more pronounced in mass. This pattern is seen in other dimorphic New World primates. Male A. palliata may grow more rapidly than A. seniculus, reflecting earlier emigration for A. palliata males. Linear dimensions reach adult proportions earlier than body mass. For hind-foot and tail, this is probably an adaptation for gripping.