Urine washing and urinary odor profiles in relation to dominance rank status in wild male capuchin monkeys (Cebus imitator)

Urine plays an essential role in mammalian olfactory communication, though
its potential role in primates has long been overlooked due to focus on
their visual adaptations for communication. Here we combined behavioral
and chemical data to test the role of urine in signaling male dominance in
white-faced capuchins (Cebus imitator). We predicted that: 1) urine
washing (i.e., depositing urine onto hands/feet and rubbing them onto
substrates) is more frequently performed by alpha than subordinate males,
and 2) the chemical composition of alpha male urine is distinct from that
of subordinates. We collected 457 hours of focal behavioral follows and
153 urine samples from 24 males in five groups at Sector Santa Rosa, Área
de Conservación Guanacaste, Costa Rica. We extracted urinary volatile
compounds into thermal desorption tubes and analyzed them by gas
chromatography-mass spectrometry. We found that alphas urine wash more
than subordinates, especially during the dry season when urinary odors can
last longer and intergroup interactions are more frequent. Additionally,
dominance rank predicted a modest fraction of overall sample chemical
dissimilarity. Our results support the hypothesis that urine may be an
olfactory signaling medium; future experimental research is needed to test
the extent to which urinary odors may be cues vs. evolved signals.