Extreme Y chromosome polymorphism corresponds to five male reproductive morphs of a freshwater fish

Loss of recombination between sex chromosomes often depletes Y chromosomes of functional content and genetic variation, which might limit their potential to generate adaptive diversity. Males of the freshwater fish Poecilia parae occur as one of five discrete morphs, all of which shoal together in natural populations where morph frequency has been stable for over 50 years. Each morph uses a different complex reproductive strategy and morphs...