Changes in gene copy number are a critical source of variation for evolution, but new copy num- bers that alter gene dose often presents a challenge for organismal survival. The scale of copy-number change can range from the deletion or duplication of one or a few genes, to polyploidization of all genes through whole-genome duplication [1–3]. Post-duplication, genes typically have one of three fates: nonfunctionalization, in which only one of the copies retains any function; subfunctionalization, in which the copies diversify to “share” the function of the original; or neofunctionalization, in which one of the gene copies gains a novel function [2, 4, 5]. There is a strong population genetic component to the probability of these different fates, but before the fate is realized, the organism containing the duplicates faces the challenge of surviving with an over-abundance of gene product for duplicate genes or under-abundance of non-duplicated, interacting