Invited review: Clonal reproduction in freshwater fish: mechanisms, systematic overview, genetic and ecological consequences

Abstract

While clonal reproduction is common in plants and not uncommon in invertebrate animals it is very rare in vertebrates. There are, however, several freshwater fish species that reproduce unisexually. All these fish are of hybrid origin and still depend on sperm from closely related sexual species for reproduction. They have long been perceived as slow to evolve and doomed to an early extinction. It has been shown, however, that some unisexual fish are much older than expected from theoretical predictions and that they are quite successful in terms of individual numbers and geographic distribution. They successfully compete with their sexual ancestors and should therefore have an important impact on their environment. Unisexual fish are also key species in understanding the evolution and maintenance of sex. This review summarizes the mechanisms of unisexual reproduction in freshwater fish, gives an overview about their systematic and geographic distribution, presents some examples of clonally reproducing fish and highlights the genetic and ecological consequences of unisexual reproduction in fish.