Independent Estimates of Population History Help Unlock the Genetic Signatures in Duck Populations

Genetic signatures can reveal species’ evolutionary and demographic pasts influenced by ancient environmental and geologic changes. The utility of DNA for making these inferences depends on the relationship between effective population size, mutation, and genetic drift (and in some cases immigration and emigration). More mutations and less genetic drift lead to higher levels of genetic diversity in larger populations than in smaller populations resulting in a linear positive relationship between effective population size and genetic diversity. However, the diversity of DNA polymorphisms can also be influenced by natural selection, complicating relationships between effective population size, mutation and drift; natural selection is more efficient in larger populations and can have different effects depending on the type of selection (balancing vs. stabilizing and directional). Disentangling the influences of selection and demographic histories on genetic structure requires additional data independent of the genome. We investigate the importance of demographic history and natural selection on genetic signatures in populations of Anas ducks around the world using a natural experiment. In this experiment, differing climate histories of five continents are the treatments, and 23 species serve as replicates (4-6 per continent). We estimate effective population sizes and long-term changes in demographic histories (i.e., growth rates) using coalescent models of six independent loci. We estimate population histories independently using species distribution models, backcasting based on palaeoclimate reconstructions.