Arrhenotoky (fromGreek ἄρρηνárrhēn "male" and τόκοςtókos "birth"), also known asarrhenotokous parthenogenesis, is a form ofparthenogenesis in which unfertilizedeggs develop into males. In most cases,parthenogenesis produces exclusively female offspring, hence the distinction.
The set of processes included under the term arrhenotoky depends on the author:[1] arrhenotoky may be restricted to the production of males that arehaploid (haplodiploidy); may includediploid males that permanently inactivate one set ofchromosomes (parahaploidy); or may be used to cover all cases of males being produced by parthenogenesis (including such cases asaphids, where the males are XO diploids).[1] The form of parthenogenesis in which females develop from unfertilized eggs is known asthelytoky; when both males and females develop from unfertilized eggs, the term "deuterotoky" is used.[2]
In the most commonly used sense of the term, arrhenotoky is synonymous with haploid arrhenotoky or haplodiploidy: the production of haploid males from unfertilized eggs ininsects having ahaplodiploid sex-determination system. Males are produced parthenogenetically, whilediploid females are usually[a] produced biparentally from fertilized eggs. In a similar phenomenon, parthenogenetic diploid eggs develop into males by converting one set of their chromosomes toheterochromatin, thereby inactivating those chromosomes.[4] This is referred to as diploid arrhenotoky or parahaploidy.[5]
Arrhenotoky occurs in members of the insect orderHymenoptera (bees,ants, andwasps)[6] and theThysanoptera (thrips).[7] The system also occurs sporadically in somespider mites,Hemiptera,Coleoptera (bark beetles),Scorpiones (Tityus metuendus) androtifers.