The Persistence of Polymorphisms across Species Radiations

Studies on polymorphisms have been foundational to our understanding of evolution. The presence of different phenotypic morphs is sometimes considered a precursor to speciation in which morphs evolve into different species. While speciation should initially reduce genetic variation in daughter versus parental species, a common pattern is the recurrence of the same phenotypic polymorphism in many species of a clade. Despite the ubiquity of these persistent polymorphisms, there is little discussion of their evolutionary origins. How does the genetic variation underpinning such polymorphisms cross speciation boundaries? What selection pressures maintain the morphs in multiple daughter species? Using diverse case studies, we highlight the characteristics of polymorphisms and selection regimes influencing the likelihood of polymorphism retention across species radiations.