Inbiology,gonochorism is asexual system where there are twosexes and each individual organism is eithermale orfemale.[1] The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.[2]: 212–222
Gonochorism hasevolved independently multiple times.[8] It is very evolutionarily stable in animals.[9] Its stability and advantages have received little attention.[10]: 46 Gonochorism owes its origin to the evolution ofanisogamy,[11] but it is unclear if the evolution of anisogamy first led to hermaphroditism or gonochorism.[2]: 213
Gonochorism is thought to be the ancestral state inpolychaetes,[9]: 126 Hexacorallia,[12]: 74 nematodes,[13]: 62 and hermaphroditicfishes. Gonochorism is thought to be ancestral in hermaphroditic fishes because it is widespread inbasalclades of fish and other vertebrate lineages.[14]
Two papers from 2008 have suggested that transitions between hermaphroditism and gonochorism or vice versa have occurred in animals between 10 and 20 times.[15] In a 2017 study involving 165 taxon groups, more evolutionary transitions from gonochorism to hermaphroditism were found than the reverse.[16]
The term gonochorism is most often used for animal species, an estimated 95% of which are gonochoric.[17] It is very common invertebrate species, 99% of which are gonochoric.[18][19] Ninety-eight percent of fishes are gonochoric.[20]Mammals (includinghumans[21][22]) andbirds are solely gonochoric.[23] andTardigrades are almost always gonochoric.[24] Seventy-five percent ofsnails are gonochoric.[25] Mostarthropods including a majority ofcrustaceans are gonochoric.[26][27]
The term gonochorism is not usually applied toplants.Vascular plants which have single-sex individuals are calleddioecious,[28] whilebryophytes with single-sex individuals aredioicous.[29] Inflowering plants, individual flowers may be hermaphroditic (i.e., with both stamens and ovaries) or dioecious (unisexual), having either no stamens (i.e., no male parts) or no ovaries (i.e., no female parts). Among flowering plants with unisexual flowers, some also producehermaphrodite flowers, and the three types may occur in different arrangements on the same or separate plants. Plant species can thus be hermaphrodite,monoecious,dioecious,trioecious,polygamomonoecious,polygamodioecious,andromonoecious, orgynomonoecious.
Unlike mostflatworms,schistosomes are gonochoric. The narrow female can be seen emerging from the thicker male's gynecophoral canal below his ventral sucker.
Examples of species with gonochoric or dioeciouspollination includehollies andkiwifruit. In these plants the male plant that supplies thepollen is referred to as thepollenizer.
^Bester C."Stoplight parrotfish".Florida Museum of Natural History, Ichthyology Department. Archived fromthe original on 6 December 2009. Retrieved15 December 2009.
^Afonso P, Morato T, Santos RS (2008). "Spatial patterns in reproductive traits of the temperate parrotfish Sparisoma cretense".Fisheries Research.90 (1–3):92–99.doi:10.1016/j.fishres.2007.09.029.
