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. 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 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, and has also been described in several groups of Hymenoptera, including Cynipidae, Tenthredinidae, Aphelinidae, Ichneumonidae, Apidae and Formicidae.
In ants, bees, and wasps
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. The daughters produced may or may not be complete clones of their mother depending on the type of parthenogenesis that takes place. 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.
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). (see diagram).
With central fusion
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, the clonal raider ant Cerapachys biroi, the predaceous ant Platythyrea punctata, and the electric ant (little fire ant) Wasmannia auropunctata. Automixis with central fusion also occurs in the Cape honey bee Apis mellifera capensis, the brine shrimp Artemia parthenogenetica, and the termite Embiratermes neotenicus.
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 and W. auropunctata, the brine shrimp A. parthenogenetica, and the honey bee A. m. capensis. In A. m. capensis, the recombination rate during the meiosis associated with thelytokus parthenogenesis is reduced by more than 10-fold. In W. auropunctata the reduction is 45-fold.
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. Reduced colony survival appears to be due to decreased queen lifespan resulting from queen homozygosity and expression of deleterious recessive mutations (inbreeding depression).
With terminal fusion
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 and the Colombian rainbow boa constrictor Epicrates maurus. Parthenogenesis in E. maurus is only the third genetically confirmed case of consecutive virgin births of viable offspring from a single female within any vertebrate lineage. However, survival of offspring over two successive litters was poor, suggesting that automixis with terminal fusion leads to homozygosity and expression of deleterious recessive alleles (inbreeding depression).
|Look up thelytoky in Wiktionary, the free dictionary.|
- 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.
- 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.
- 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.
- 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.
- 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.
- 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): 243–252. doi:10.1534/genetics.167.1.243. PMC . PMID 15166151.
- Kellner, Katrin; Heinze, Jürgen (2010). "Mechanism of facultative parthenogenesis in the ant Platythyrea punctata". Evolutionary Ecology. 25 (1): 77–89. doi:10.1007/s10682-010-9382-5.
- 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". Current Biology. 24 (4): 451–8. doi:10.1016/j.cub.2014.01.018. PMC . PMID 24508170.
- 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". Molecular Biology and Evolution. 28 (9): 2591–601. doi:10.1093/molbev/msr082. PMID 21459760.
- Nougué O, Rode NO, Jabbour-Zahab R, Ségard A, Chevin LM, Haag CR, Lenormand T (2015). "Automixis in Artemia: solving a century-old controversy". Journal of Evolutionary Biology. 28 (12): 2337–48. doi:10.1111/jeb.12757. PMID 26356354.
- 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". Proceedings of the Royal Society of London B: Biological Sciences. 282 (1809): 20150260. doi:10.1098/rspb.2015.0260. PMC . PMID 26019158.
- Haag-Liautard C, Vitikainen E, Keller L, Sundström L (2009). "Fitness and the level of homozygosity in a social insect". Journal of Evolutionary Biology. 22 (1): 134–42. doi:10.1111/j.1420-9101.2008.01635.x. PMID 19127611.
- 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. PMC . PMID 26341660.
- 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". Journal of Heredity. 102 (6): 759–63. doi:10.1093/jhered/esr080. PMID 21868391.