Ottolini B, Hornsby MJ, Abujaber R, Macarthur JA, Badge RM, Schwarzacher T, Albertson DG, Bevins CL, Solnick JV, Hollox EJ. 2014. Evidence of convergent evolution in humans and macaques supports an adaptive role for copy number variation of the β-defensin-2 gene. Genome Biology and Evolution 6(11): 3025-3038. DOI: 10.1093/gbe/evu236

β-defensins are a family of important peptides of innate immunity, involved in host defense, immunomodulation, reproduction and pigmentation. Genes encoding β-defensins show evidence of birth-and-death evolution, adaptation by amino acid sequence changes and extensive copy number variation (CNV) within humans and other species. The role of CNV in the adaptation of β-defensins to new functions remains unclear, as does the adaptive role of copy number variation in general. Here, we fine-map CNV of a cluster of β-defensins in humans and rhesus macaques. Remarkably, we found that the structure of the CNV is different between primates, with distinct mutational origins and CNV boundaries defined by retroviral long terminal repeat elements. While the human β-defensin CNV region is 322 kb and encompasses several genes, including β-defensins, a long non-coding RNA gene and testes-specific zinc-finger transcription factors, the orthologous region in the rhesus macaque shows CNV of a 20 kb region, containing only a single gene, the orthologue of the human β-defensin-2 gene. Despite its independent origins, the range of gene copy numbers in the rhesus macaque is similar to humans. In addition, the rhesus macaque gene has been subject to divergent positive selection at the amino acid level following its initial duplication event between 3 and 9.5 million years ago, suggesting adaptation of this gene as the macaque successfully colonised novel environments outside Africa. Therefore, the molecular phenotype of β-defensin-2 copy number variation has undergone convergent evolution, and this gene shows evidence of adaptation at the amino acid level in both primates.

Ottolini B, Hornsby MJ, Abujaber R, Macarthur JA, Badge RM, Schwarzacher T, Albertson DG, Bevins CL, Solnick JV, Hollox EJ. 2014. Evidence of convergent evolution in humans and macaques supports an adaptive role for copy number variation of the β-defensin-2 gene. Genome Biology and Evolution 6(11): 3025-3038. DOI: 10.1093/gbe/evu236