QUANTIFICATION AND PHYLOGENETIC COMPARATIVE ANALYSIS OF PELAGE SEXUAL DICHROMATISM IN PRIMATES

Abstract

This study is the first to quantify pelage sexual dichromatism (PelSD) across the order Primates. The hypothesis that PelSD evolves as a consequence of sexual selection on the pelage color of male primates is considered. Color-corrected high-resolution photographs were taken of primate pelts taken from museum collections, representing primate 83 species. Two measures of color, luminance and hue, were taken for the dorsal and ventral aspects of the trunk of each specimen. These measurements are proxies for the absolute and relative concentrations of melanin(s) in primate pelage. Highly-dichromatic species were identified and the evolution of luminance and hue in males and females of those species was analyzed. Species where male luminance or hue was under selection without concomitant selection on females were considered to be under sexual selection. There was little clear evidence of sexual selection on male luminance in highly-dichromatic species. However, there was substantial evidence of sexual selection on male hue. To determine if male pelage color is an ornament that signals quality and is used by females in choosing mates, fluctuating asymmetry (FA), a proxy for mate choice, was regressed against PelSD. Evidence of trunk pelage as ornamentation (i.e., significant correlation between FA and PelSD) was only observed among platyrrhines. Sexual selection on male hue and a trend toward yellower pelage in males of highly-dichromatic species suggests a shift to phaeomelanin production in those males. Explanations for the observed shift to yellow pelage/phaeomelanin production are explored.