Although domestic ducks have been important poultry species throughout human history, their origin remains enigmatic, with mallards and/or Chinese spot-billed ducks being proposed as the direct wild ancestor(s) of domestic ducks. Here, we analyzed 118 whole genomes from mallard, Chinese spot-billed, and domestic ducks to reconstruct their evolutionary history. We found pervasive introgression patterns among these duck populations. Furthermore, we showed that domestic ducks separated from mallard and Chinese spot-billed ducks nearly 38 thousand years ago (kya) and 54 kya, respectively, which is considerably outside the time period of presumed duck domestication. Thus, our results suggest that domestic ducks may have originated from another wild duck population that is currently undefined or unsampled, rather than from present-day mallard and/or Chinese spot-billed ducks, as previously thought. Overall, this study provides new insight into the complex evolution of ducks.

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The comb is a naked head appendage of chickens that consists of layers of epidermis, dermis, and central connective tissue. The major chemical constituents of this tissue include collagen, hyaluronic acid, and galactosaminoglycans (Nakano & Sim, 1992). As a secondary sexual ornament, comb variations in shape and structure are an attractive topic in evolutionary biology. Additionally, the comb is associated with health status, mate choice, social ranking, and body temperature regulation (