Unisexual reproduction among vertebrates.

The past decade has seen a remarkable revision of perspectives on unisexual reproduction in vertebrates. One can no longer view it as a rare curiosity far outside the mainstream of evolution. More than 80 taxa of fish, amphibians, and reptiles are now known to reproduce by parthenogenesis (Greek for 'virgin birth') or its variants, and they persist in nature as all-female lineages. Other lower vertebrates that ordinarily rely on sexual reproduction can resort to facultative parthenogenesis under extenuating circumstances that isolate females from males. Molecular tools have now been applied to the study of unisexual organisms, and fascinating insights have emerged regarding the molecular mechanisms that preserve heterozygosity and increase genetic diversity in all-female populations. A deeper understanding of the underlying genetics increasingly calls into question the assumption that unisexuality in vertebrates is an evolutionary dead-end.