What is Parthenogenesis?
Parthenogenesis comes from two Greek words Parthenos meaning “virgin” and Genesis meaning “birth”. Parthenogenesis species are often mistaken for hermaphroditic (species that can reproduce by themselves) species, the difference is that hermaphrodites have reproductive organs from both sexes while the parthenogenesis only has the female reproductive organs.
Parthenogenesis is a form of asexual reproduction where the growth and development of the embryo occurs without fertilization therefore females don’t have to mate to be able to reproduce. Gynogenesis and Pseudogamy are closely related to parthenogenesis. In these two cases sperm or pollen triggers the development of the egg but doesn’t contribute to the genetic of the embryo. This basically means that parthenogenesis is a form of cloning. The offspring’s can either get half of all of the mother genes, making them “half clones” or “full clones”. They are not true clones because the offspring doesn’t have the same genetics as the parent like cloned animals do.
Some species that use parthenogenesis can also use sexual reproduction. It’s normally because of different season or lack of males. During spring and summer female’s uses parthenogenesis to produce plenty of offspring’s instead of finding a male to mate with. When the conditions are not as great (fall or winter) the females will find males to mate with in order to mix the genes, giving offspring´s the best chance of survival. This practice is used by honeybees where females are produced through sexual reproduction, while males (drones) are produced when the queen lays unfertilized eggs.
Parthenogenesis occurs naturally in plants, some invertebrates species e.g. nematodes, waters fleas, scorpions, bees and parasitic wasps also a few vertebrates e.g. fish, amphibians, reptiles and birds. For vertebrates to have asexual reproduction is rare and normally occurs when males are absent so the females can switch between sexual and asexual reproduction. First it was believed that it only happens in captivity, but it´s been recorded in approximately 70 vertebra species, e.g. Komodo dragons, Hammerhead sharks and Blacktip sharks. A theory why Komodo dragons use parthenogenesis and then change back to sexual reproduction is that when they colonies islands one single female can start producing offspring’s. If the offspring’s are male she can then reproduce with them to give the next generation a larger genetic diversity. This seems to be a common practice in the Komodo dragon since approximately 75% are males.
Parthenogenesis has never been seen in mammals. It´s believed to be due to the fact that mammals need to have a fertilized egg to attach in the uterus to create offspring’s.