Hair phenotype diversity across Indriidae lemurs

Objectives Hair (i.e., pelage/fur) is a salient feature of primate (including human) diversity and evolution— serving functions tied to thermoregulation, protection, camouflage, and signaling—but wild primate pelage evolution remains relatively understudied. Specifically, assessing multiple hypotheses across distinct phylogenetic scales is essential but is rarely conducted. We examine whole body hair color and density variation across Indriidae ( Avahi , Indri , Propithecus )—a lineage that, like humans, exhibits vertical posture (i.e., their whole bodies are vertical to the sun). Materials and Methods Our analyses consider multiple phylogenetic scales (family-level, genus-level) and hypotheses (e.g., Gloger’s rule, the body cooling hypotheses). We obtain hair color and density from museum and/or wild animals, opsin genotypes from wild animals, and climate data from WorldClim. To analyze our data, we use phylogenetic generalized linear mixed models (PGLMM) using Markov chain Monte Carlo algorithms. Results Our results show that across the Indriidae family, darker hair is typical in wetter regions. However, within Propithecus , dark black hair is common in colder forest regions. Results also show pelage redness increases in populations exhibiting enhanced color vision. Lastly, we find follicle density on the crown and limbs increases in dry and open environments. Discussion This study highlights how different selective pressures across distinct phylogenetic scales have likely acted on primate hair evolution. Specifically, our data across Propithecus may implicate thermoregulation and is the first empirical evidence of Bogert’s rule in mammals. Our study also provides rare empirical evidence supporting an early hypothesis on hominin hair evolution.