Dominance rank, age, and parasitism predict male vervet monkey (Chlorocebus pygerythrus) genital skin colouration


SOCIETY FOR INTEGRATIVE AND COMPARATIVE BIOLOGY
2021 VIRTUAL ANNUAL MEETING (VAM)
January 3 – Febuary 28, 2021

Meeting Abstract


P6-3  Sun Jan 3  Dominance rank, age, and parasitism predict male vervet monkey (Chlorocebus pygerythrus) genital skin colouration Snyder, KP*; Greenberg, D; Mastromonaco, G; Schoof, VAM; Dept. of Biology, York University, Toronto, Canada; Div. of Experimental Medicine, McGill University, Montreal, Canda; Reproductive Sciences, Toronto Zoo, Toronto, Canada; Bilingual Biology Program, Dept. of Multidisciplinary Studies, Glendon, York University, Toronto, Canada snyderk@yorku.ca

Male secondary sexual characteristics may convey important information about the signaller. The red penis and blue scrotum of male vervet monkeys makes them a good species to examine variation in signal expression. We quantified colour variation (i.e., hue, saturation, luminance, contrast) in vervets at Lake Nabugabo, Uganda from standardized photos taken in May-June 2016 and Jan-June 2019. We collected agonistic data to determine male dominance rank and fecal samples for parasite and hormone analyses (n=174). Using a linear model search, we identified the ‘best’ models (lowest AICc, highest R2) to describe interindividual variation in genital color in relation to rank, mean fecal hormone metabolites, and parasite species richness (species count) and prevalence (% infected samples). Blue scrotal hue of higher-ranking males (β=5.687, F=14.096, p<0.05) and those with higher parasite prevalence (β=34.480, F=1.162, p<0.05) was teal-blue compared to true-blue in lower-ranking males and those with lower parasite prevalence, but the interaction was not significant. In contrast to blue scrotal hue, red penile saturation was predicted by the interaction of rank and prevalence (β=-2.057, F=6.761, p<0.05), with higher-ranking males with high parasite prevalence having more saturated penile coloration. Younger males had more luminant (i.e., pinker) penises than older males (β=-0.102, F=11.380, p<0.05). These results suggest that the multi-component genital signal conveys information about male age, health, and competitive ability.

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