Convergent evolution through independent rearrangements in the primate amylase locus

Structurally complex regions of the genome are increasingly recognized as engines of evolutionary convergence due to their propensity to generate recurrent gene duplications that give rise to similar gene expression patterns and traits across lineages. However the mutational mechanisms driving these duplications and the regulatory changes enabling novel expression patterns remain poorly understood. The primate amylase locus, marked by independent gene duplications, provides an ideal model to investigate these dynamics. Leveraging high-quality genome assemblies from 53 primates and multi-tissue transcriptomes from Old World monkeys, we reconstructed the evolutionary history of the recurrent gene duplications across the primate phylogeny. Our data suggest that lineage-specific LTR retrotransposon insertions are associated with initial structural instability, while subsequent duplications are primarily driven by non-allelic homologous recombination. Recurrent independent duplications in rhesus macaques, olive baboons, and great apes gave rise to distinct amylase gene copies with convergent expression in the pancreas and salivary glands. We found that these independent gene duplications are accompanied by episodic diversifying selection on lineage-specific copies, likely driving the emergence of functional divergence. Our comparative analyses in primates indicate that the gene ancestral to great ape AMY1 and AMY2A was expressed in both salivary glands and pancreas in the Catarrhini ancestor. The great ape-specific duplication of this ancestral gene likely facilitated subfunctionalization into salivary gland- and pancreas-specific expression, respectively. Comparative analysis of primate amylase promoter regions reveals regulatory rewiring, driven by motif turnover mediated by structural rearrangements, and partially explaining evolutionary shifts in expression. Together, our findings highlight how structural and regulatory modularity in complex genomic regions drives evolutionary innovation and molecular convergence, and we provide a genomic framework for dissecting these processes across diverse lineages.