Understanding the genetic basis of biodiversity: Sexual selection, gene expression and primate pigmentation.

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Humans and chimpanzees share nearly 99% of their genomes, yet show striking differences in appearance and cognition. In some butterfly species, genetically identical individuals developing in different environments can have remarkably different wing coloration. Such examples illustrate how high levels of biological diversity can arise from very little genetic diversity. To understand how this occurs, biologists are shifting the focus from studying gene sequences to studying how and when genes are expressed. Taking advantage of recent technical advances developed in biomedical science, gene expression research now provides unprecedented opportunities to understand how closely related and genetically similar animal species can be so different in appearance and behaviour. My research examines gene expression in the hair follicles of primates to understand the genetic basis of variation in hair pigmentation. Understanding animal pigmentation is crucial to understanding many aspects of animal biology, including speciation events (are pigmentation differences between closely-related species a cause or a consequence of the species split?), the trade-offs between natural and sexual selection (conspicuous colours can attract mates and warn rivals but also increase the risk of predation), and the evolution of cooperative behaviours (unique coloration may allow individuals to recognize each other and identify their relatives). Primate pigmentation is especially interesting as primates are arguably the most colourful mammalian order, often showing marked colour differences between closely-related species, between individuals within populations, between males and females, and between infants and adults. Although Darwin recognized the evolutionary importance of primate colour diversity over a century ago, the topic has received surprisingly little research attention since. I am examining hairs from a range of primates (humans, apes, New and Old World monkeys, and prosimians) to identify where in the pigmentation pathway hairs of different colours diverge in their patterns of gene expression. I am taking a candidate gene approach focusing on about 20 pigment-related genes, selected because of their known involvement in determining coat colour in mice, and two reference genes to serve as controls. By measuring and comparing the relative amounts of gene product (RNA) specific for each gene in hair follicles of various colours from numerous individuals, I can identify associations between gene expression and hair colour. Results should provide insights into how evolution tinkers with a limited amount of genetic variation to produce such a great diversity of forms. Ultimately, I plan to compare the genetic basis of hair coloration across primates to assess how consistent or variable this 'tinkering' is across taxa. For example, I plan to compare red and black hair in red-headed vs. brunette humans, in chimpanzees vs. orangutans, in black howler monkeys vs. red howler monkeys, and in black ruffed lemurs vs. red ruffed lemurs. Identifying which pigmentation genes are flexible (vary across taxa) and which are conserved (similar across taxa) in their expression patterns is an obvious first step to understanding how pigmentation influences and is influenced by natural and sexual selection.