Kamilar, J. M. | Search bioRxiv

bioRxiv2022

Melanism in a wild sifaka population: Darker where cold and fragmented

Pigmentation is one of the most striking examples of diversity in the natural world. Mainly, pelage (hair/fur) pigmentation provides a substrate for selection (i.e., crypsis, signaling, thermoregulation) and is capable of rapid change. Thus, this trait may be the one potential early signal of adaptation (or maladaptation) in wild primate populations. However, most of our hypotheses on the forces responsible for primate pelage pigmentation are based solely on macro-evolutionary studies. Here, we characterize pelage color and pattern variation within a population of wild primates, diademed sifakas (Propithecus diadema), exhibiting striking diversity in coloration (melanic to tri-colored). Our approach jointly assesses climate and pelage variation across the region. We score pelage using a semi-quantitative methodology. We then test if pelage variation is associated with climatic or demographic factors (i.e., sex-class, age-class) across the Tsinjoarivo forest, Madagascar. We find darker bodies and less complex faces occur in colder and more fragmented forests. We explore three hypotheses that may explain this phenotypic pattern: isolation by distance, an environmental gradient, or unique local adaptation. Importantly, each scenario signals the need for enhanced conservation of diademed sifakas in the Tsinjoarivo forest. More studies on primate pigmentation in wild populations will be needed to contextualize if this pattern is exceptional or typical. It is likely that in other primate populations pigmentation may also foretell of adaptation or environmental mismatch.

evolutionary biology↗

bioRxiv2021

Hair phenotype diversity across Indriidae lemurs

ObjectivesHair (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 MethodsOur analyses consider multiple phylogenetic scales (family-level, genus-level) and hypotheses (e.g., Glogers 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. ResultsOur 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. DiscussionThis 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 Bogerts rule in mammals. Our study also provides rare empirical evidence supporting an early hypothesis on hominin hair evolution.

evolutionary biology↗