Ecology & Evolutionary Biology
University of Kansas
Flip the script: evolutionary insights from “reversed” sex chromosomes in moths and butterflies

Most genetic and genomic research involves animals where females have two copies of the same sex chromosome while males have differentiated sex chromosomes. In other words, females are XX and males are XY, where the Y is a degenerate and gene-poor chromosome. However, some groups of organisms have this situation reversed, where males have two of the same chromosomes and females have the differentiated pair. This is the case in Lepidoptera (moths and butterflies), where males are ZZ and females are ZW; the W is degenerate and gene-poor like the Y. This reversal of sex chromosomes presents novel opportunities to test hypothesis about sex chromosome evolution because it reverses the relationship between sex-specific selection and carrying a degenerate sex chromosome. As will be discussed, this has important implications for sex chromosome dosage compensation, the outcome of sexual antagonism, and the rapid evolution of sex chromosomes. Additionally, Lepidoptera present other strikingly unique and enigmatic phenomena related to sex, including several examples of neo-sex chromosomes and sperm without DNA.