Sexually selected lip colour indicates male group-holding status in the mating season in a multi-level primate society.
Level 5 - mechanism / opinion, no new human data
Animal observational study (Level 5 by CEBM rules)
PubMed 27019735 · doi:10.1098/rsos.150490
What was done
The authors quantified lower lip redness in 15 male black-and-white snub-nosed monkeys (Rhinopithecus bieti)—comprising eight bachelors and seven one-male unit (OMU) holders—in a group at Xiangguqing, China. Mixed models were used to analyze the effects of age, group-holding status, and mating season on lip redness.
What was found
The abstract reports no numerical values, effect sizes, or test statistics. It reports that lip redness increased with age, and that a significant interaction existed between group-holding status and mating season: lip colour of OMU-holding males underwent reddening in the mating season, whereas lips of subadult and juvenile bachelors became paler.
Why it matters
This study provides the first documentation of facial coloration correlates in this species, suggesting seasonal lip reddening functions as a badge of group-holding status in a multi-level primate society.
Limits
The sample size is small (n = 15 males) and restricted to a single group. No exact quantitative values or statistical metrics are reported in the abstract. The observational design cannot differentiate between male-male competition and female mate choice mechanisms.
Cited by
- supports In non-human animal species, facial reddening is associated with physical robustness.