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Thelytoky (from the Greek thēlys "female" and tokos "birth") is a type of parthenogenesis in which females are produced from unfertilized eggs, as for example in aphids. Thelytokous parthenogenesis is rare among animals and reported in about 1,500 species, about 1 in 1000 of described animal species, according to a 1984 study.[1] It is more common in invertebrates, like arthropods, but it can occur in vertebrates, including salamanders, fish, and reptiles such as some whiptail lizards.

Thelytoky can occur by a number of different mechanisms each of which has a different impact on the level of homozygosity. It can be induced in Hymenoptera by the bacteria Wolbachia and Cardinium,[2] and has also been described in several groups of Hymenoptera, including Cynipidae, Tenthredinidae, Aphelinidae, Ichneumonidae, Apidae and Formicidae.[3]

Thelytoky in ants, bees, and wasps[edit]

Hymenoptera (ants, bees, and wasps) have a haplodiploid sex-determination system. They produce haploid males from unfertilized eggs through arrhenotokous parthenogenesis. However, in a few social hymenopterans, queens or workers are capable of producing diploid female offspring by thelytoky.[4] The daughters produced may or may not be complete clones of their mother depending on the type of parthenogenesis that takes place.[5][6] The offspring can develop into either queens or workers. Examples of such species include the Cape bee, Apis mellifera capensis, Mycocepurus smithii and clonal raider ant, Cerapachys biroi.


The effects of central fusion and terminal fusion on heterozygosity

Automixis is a form of thelytoky. In automictic parthenogenesis, meiosis takes place and diploidy is restored by fusion of first division non-sister nuclei (central fusion) or the second division sister nuclei (terminal fusion).[7] (see diagram).

Automixis with central fusion[edit]

Automixis with central fusion tends to maintain heterozygosity in the passage of the genome from mother to daughter. This form of automixis has been observed in several ant species including the desert ant Cataglyphis cursor,[4] the clonal raider ant Cerapachys biroi,[8] the predaceous ant Platythyrea punctata,[7] and the electric ant (little fire ant) Wasmannia auropunctata.[9] Automixis with central fusion also occurs in the Cape honey bee Apis mellifera capensis,[10] the brine shrimp Artemia parthenogenetica,[11] and the termite Embiratermes neotenicus.[12]

Oocytes that undergo automixis with central fusion often display a reduced rate of crossover recombination. A low rate of recombination in automictic oocytes favors maintenance of heterozygosity, and only a slow transition from heterozygosity to homozygosity over successive generations. This allows avoidance of immediate inbreeding depression. Species that display central fusion with reduced recombination include the ants P. punctata[7] and W. auropunctata,[9] the brine shrimp A. parthenogenetica,[11] and the honey bee A. m. capensis.[10] In A. m. capensis, the recombination rate during the meiosis associated with thelytokus parthenogenesis is reduced by more than 10-fold.[10] In W. auropunctata the reduction is 45-fold.[9]

Single queen colonies of the narrow headed ant Formica exsecta provide an illustrative example of the possible deleterious effects of increased homozygosity. In this ant the level of queen homozygosity is negatively associated with colony age.[13] Reduced colony survival appears to be due to decreased queen lifespan resulting from queen homozygosity and expression of deleterious recessive mutations (inbreeding depression).

Automixis with terminal fusion[edit]

Automixis with terminal fusion tends to promote homozygosity in the passage of the genome from mother to daughter. This form of automixis has been observed in the water flea Daphnia magna[14] and the Colombian rainbow boa constrictor Epicrates maurus.[15] Parthenogenesis inE. maurus is only the third genetically confirmed case of consecutive virgin births of viable offspring from a single female within any vertebrate lineage.[15] However, survival of offspring over two successive litters was poor, suggesting that automixis with terminal fusion leads to homozygosity and expression of deleterious recessive mutations (inbreeding depression).

See also[edit]


  1. ^ White, Michael J.D. (1984). "Chromosomal Mechanisms in Animal Reproduction" (PDF). Bolletino di zoologia 51 (1-2): 1–23. doi:10.1080/11250008409439455. ISSN 0373-4137. 
  2. ^ Jeong, G; R Stouthamer (2004-11-03). "Genetics of female functional virginity in the Parthenogenesis-Wolbachia infected parasitoid wasp Telenomus nawai (Hymenoptera: Scelionidae)" (PDF). Heredity 94 (4): 402–407. doi:10.1038/sj.hdy.6800617. ISSN 0018-067X. Retrieved 2012-01-12. 
  3. ^ Suomalainen, Esko; Anssi Saura; Juhani Lokki (1987-08-31). Cytology and evolution in parthenogenesis. CRC Press. pp. 29–31, 51. ISBN 978-0-8493-5981-1. 
  4. ^ a b Pearcy, M. (2004). "Conditional Use of Sex and Parthenogenesis for Worker and Queen Production in Ants" (PDF). Science 306 (5702): 1780–1783. doi:10.1126/science.1105453. ISSN 0036-8075. PMID 15576621. 
  5. ^ Fournier, Denis; Estoup, Arnaud; Orivel, Jérôme; Foucaud, Julien; Jourdan, Hervé; Breton, Julien Le; Keller, Laurent (2005). "Clonal reproduction by males and females in the little fire ant" (PDF). Nature 435 (7046): 1230–1234. doi:10.1038/nature03705. ISSN 0028-0836. PMID 15988525. 
  6. ^ Baudry, Emmanuelle; Per Kryger; Mike Allsopp; Nikolaus Koeniger; Dominique Vautrin; Florence Mougel; Jean-Marie Cornuet; Michel Solignac (2004-05-01). "Whole-Genome Scan in Thelytokous-Laying Workers of the Cape Honeybee (Apis mellifera capensis): Central Fusion, Reduced Recombination Rates and Centromere Mapping Using Half-Tetrad Analysis". Genetics 167 (1): 243–252. doi:10.1534/genetics.167.1.243. Retrieved 2012-01-12. 
  7. ^ a b c Katrin Kellner, Jurgen Heinze (2011). Mechanism of facultative parthenogenesis in the ant Platythyrea punctata. Evol. Ecol. 25: 77-89. DOI 10.1007/s10682-010-9382-5
  8. ^ Oxley PR, Ji L, Fetter-Pruneda I, McKenzie SK, Li C, Hu H, Zhang G, Kronauer DJ (2014). "The genome of the clonal raider ant Cerapachys biroi". Curr. Biol. 24 (4): 451–8. doi:10.1016/j.cub.2014.01.018. PMC 3961065. PMID 24508170. 
  9. ^ a b c Rey O, Loiseau A, Facon B, Foucaud J, Orivel J, Cornuet JM, Robert S, Dobigny G, Delabie JH, Mariano Cdos S, Estoup A (2011). "Meiotic recombination dramatically decreased in thelytokous queens of the little fire ant and their sexually produced workers". Mol. Biol. Evol. 28 (9): 2591–601. doi:10.1093/molbev/msr082. PMID 21459760. 
  10. ^ a b c Baudry E, Kryger P, Allsopp M, Koeniger N, Vautrin D, Mougel F, Cornuet JM, Solignac M (2004). "Whole-genome scan in thelytokous-laying workers of the Cape honeybee (Apis mellifera capensis): central fusion, reduced recombination rates and centromere mapping using half-tetrad analysis". Genetics 167 (1): 243–52. PMC 1470879. PMID 15166151. 
  11. ^ a b Nougué O, Rode NO, Jabbour-Zahab R, Ségard A, Chevin LM, Haag CR, Lenormand T (2015). "Automixis in Artemia: solving a century-old controversy". J. Evol. Biol. 28 (12): 2337–48. doi:10.1111/jeb.12757. PMID 26356354. 
  12. ^ Fougeyrollas R, Dolejšová K, Sillam-Dussès D, Roy V, Poteaux C, Hanus R, Roisin Y (2015). "Asexual queen succession in the higher termite Embiratermes neotenicus". Proc. Biol. Sci. 282 (1809): 20150260. doi:10.1098/rspb.2015.0260. PMID 26019158. 
  13. ^ Haag-Liautard C, Vitikainen E, Keller L, Sundström L (2009). "Fitness and the level of homozygosity in a social insect". J. Evol. Biol. 22 (1): 134–42. PMID 19127611. 
  14. ^ Svendsen N, Reisser CM, Dukić M, Thuillier V, Ségard A, Liautard-Haag C, Fasel D, Hürlimann E, Lenormand T, Galimov Y, Haag CR (2015). "Uncovering Cryptic Asexuality in Daphnia magna by RAD Sequencing". Genetics 201 (3): 1143–55. doi:10.1534/genetics.115.179879. PMID 26341660. 
  15. ^ a b Booth W, Million L, Reynolds RG, Burghardt GM, Vargo EL, Schal C, Tzika AC, Schuett GW (2011). "Consecutive virgin births in the new world boid snake, the Colombian rainbow Boa, Epicrates maurus". J. Hered. 102 (6): 759–63. doi:10.1093/jhered/esr080. PMID 21868391.