Geckos (Gekkota) are a highly diversified group of lizards with an exceptional diversity in sex-determining systems. Despite this intriguing documented variability, data on sex determination in many lineages is still scarce. Here, we document the previously overlooked heteromorphic ZZ/ZW sex chromosomes in the thick-tailed gecko, Underwoodisaurus milii, a member of the ancient lineage of pygopodoid geckos. The finding of female heterogamety within pygopodoid geckos was unexpected, as until now only male heterogamety and environmental sex determination have been reported in this group, and female heterogamety was known only in distantly related gecko families separated from the pygopodoid geckos around 150 million years ago. The W chromosome in U. milii is highly heterochromatic and contains a large number of telomeric-like repeats comparable to around 50% of all telomeric-like sequences present in male genomes. The accumulation of these repeats might have been responsible for the considerable size expansion of the W chromosome in comparison to the Z chromosome. The heteromorphic ZZ/ZW sex chromosomes with accumulated telomeric-like repeats in the thick-tailed geckos further illustrate the exceptional diversity of sex-determining systems in geckos and add important information to our understanding of the evolution and phylogeny of sex-determining systems in reptiles.

Alföldi J, Di Palma F, Grabherr M, Williams C, Kong L, et al: The genome of the green anole lizard and a comparative analysis with birds and mammals. Nature 477:587-591 (2011).
Azzalin CM, Nergadze SG, Giulotto E: Human intrachromosomal telomeric-like repeats: sequence organization and mechanisms of origin. Chromosoma 110:75-82 (2001).
Cawthon RM: Telomere measurement by quantitative PCR. Nucleic Acids Res 30:e47 (2002).
Charlesworth D: Plant sex determination and sex chromosomes. Heredity 88:94-101 (2002).
Cogger HG: Reptiles and Amphibians of Australia, ed 6 (Ralph Curtis Publishing, Sanibel Island 2000).
Cole C, Gans C: The karyotype of Dibamus novaeguineae (Squamata). Herpetologica 53:229-232 (1997).
de Vosjoli P, Fast F, Repashy A: Rhacodactylus: The Complete Guide to Their Selection and Care (Advanced Visions Inc., Vista 2003).
Doughty P, Oliver PM: A new species of Underwoodisaurus (Squamata: Gekkota: Carphodactylidae) from the Pilbara region of Western Australia. Zootaxa 3010:20-30 (2011).
Ezaz T, Quinn AE, Sarre SD, O'Meally D, Georges A, Graves JAM: Molecular marker suggests rapid changes of sex determining mechanisms in Australian dragon lizards. Chromosome Res 17:91-98 (2009).
Fagundes VR, Vianna-Morgante AM, Yonenaga-Yassuda Y: Telomeric sequences localization and G-banding patterns in the identification of a polymorphic chromosomal rearrangement in the rodent Akodon cursor (2n = 14, 15 and 16). Chromosome Res 5:228-232 (1997).
Gamble T: A review of sex determining mechanisms in geckos (Gekkota: Squamata). Sex Dev 4:88-103 (2010).
Gamble T, Bauer AM, Colli GR, Greenbaum E, Jackman TR, et al: Coming to America: multiple origins of New World geckos. J Evol Biol 24:231-244 (2011).
Gauthier JA, Kearney M, Maisano JA, Rieppel O, Behlke ADB: Assembling the squamate tree of life: perspectives from the phenotype and the fossil record. Bull Peabody Mus Nat Hist 53:3-308 (2012).
Gorman GC, Gress F: Sex chromosomes of a pygopodid lizard, Lialis burtonis. Experientia 26:206-207 (1970).
Harlow PS: Temperature-dependent sex determination in lizards, in Valenzuela N, Lance VA (eds): Temperature-Dependent Sex Determination in Vertebrates, pp 42-52 (Smithsonian Books, Washington 2004).
Ijdo JW, Baldini A, Ward DC, Reeders ST, Wells RA: Origin of human chromosome 2: an ancestral telomere-telomere fusion. Proc Natl Acad Sci USA 88:9051-9055 (1991).
Jones KW, Singh L: Conserved repeated DNA sequences in vertebrate sex chromosomes. Hum Genet 58:46-53 (1981).
King M: Chromosomal evolution in the Diplodactylinae (Gekkonidae: Reptilia). I. Evolutionary relationships and patterns of change. Aust J Zool 35:507-531 (1987).
Kubat Z, Hobza R, Vyskot B, Kejnovsky E: Microsatellite accumulation on the Y chromosome in Silene latifolia. Genome 51:350-356 (2008).
Lee C, Sasi R, Lin CC: Interstitial localization of telomeric DNA sequences in the Indian muntjac chromosomes: further evidence for tandem chromosome fusions in the karyotypic evolution of the Asian muntjacs. Cytogenet Cell Genet 63:156-159 (1993).
Matsubara K, Knopp T, Sarre SD, Georges A, Ezaz T: Karyotypic analysis and FISH mapping of microsatellite motifs reveal highly differentiated XX/XY sex chromosomes in the pink-tailed worm-lizard (Aprasia parapulchella, Pygopodidae, Squamata). Mol Cytogenet 6:60 (2013).
Matthey R: Nouvelle contribution á l'étude des chromosomes chez les Sauriens. Rev Suisse Zool 40:281-316 (1933).
Meyne J, Baker RJ, Hobart HH, Hsu TC, Ryder OA, et al: Distribution of non-telomeric sites of the (TTAGGG)n telomeric sequence in vertebrate chromosomes. Chromosoma 99:3-10 (1990).
O'Callaghan NJ, Fenech M: A quantitative PCR method for measuring absolute telomere length. Biol Proced Online 13:3 (2011).
Pellegrino KCM, Rodrigues MT, Yonenaga-Yassuda Y: Chromosomal evolution in the Brazilian lizards of genus Leposoma (Squamata, Gymnophthalmidae) from Amazon and Atlantic rain forests: banding patterns and FISH of telomeric sequences. Hereditas 131:15-21 (1999).
Pokorná M, Kratochvíl L: Phylogeny of sex-determining mechanisms in squamate reptiles: are sex chromosomes an evolutionary trap? Zool J Linn Soc 156:168-183 (2009).
Pokorná M, Rábová M, Ráb P, Ferguson-Smith MA, Rens W, Kratochvíl L: Differentiation of sex chromosomes and karyotypic evolution in the eye-lid geckos (Squamata: Gekkota: Eublepharidae), a group with different modes of sex determination. Chromosome Res 18:809-820 (2010).
Pokorná M, Giovannotti M, Kratochvíl L, Kasai F, Trifonov VA, et al: Strong conservation of the bird Z chromosome in reptilian genomes is revealed by comparative painting despite 275 million years divergence. Chromosoma 120:455-468 (2011a).
Pokorná M, Kratochvíl L, Kejnovský E: Microsatellite distribution on sex chromosomes at different stages of heteromorphism and heterochromatinization in two lizard species (Squamata: Eublepharidae: Coleonyx elegans and Lacertidae: Eremias velox). BMC Genet 12:90 (2011b).
Rovatsos MT, Marchal JA, Romero-Fernández I, Fernández FJ, Giagia-Athanosopoulou EB, Sánchez A: Rapid, independent, and extensive amplification of telomeric repeats in pericentromeric regions in karyotypes of arvicoline rodents. Chromosome Res 19:869-882 (2011).
Ruiz-Herrera A, García F, Giulotto E, Attolini C, Egozcue J, et al: Evolutionary breakpoints are co-localized with fragile sites and intrachromosomal telomeric sequences in primates. Cytogenet Genome Res 108:234-247 (2005a).
Ruiz-Herrera A, García F, Mora L, Egozcue J, Ponsà M, Garcia M: Evolutionary conserved chromosomal segments in the human karyotype are bounded by unstable chromosome bands. Cytogenet Genome Res 108:161-174 (2005b).
Ruiz-Herrera A, Nergadze SG, Santagostino M, Giulotto E: Telomeric repeats far from the ends: mechanisms of origin and role in evolution. Cytogenet Genome Res 122:219-228 (2008).
Sarre SD, Georges A, Quinn A: The ends of a continuum: genetic and temperature-dependent sex determination in reptiles. Bioessays 26:639-645 (2004).
Seipp R, Henkel FW: Rhacodactylus: Biology, Natural History & Husbandry (Edition Chimaira, Frankfurt 2000).
Sumner AT: A simple technique for demonstrating centromeric heterochromatin. Exp Cell Res 75:304-306 (1972).
Townsend TM, Larson A, Louis E, Macey JR: Molecular phylogenetics of Squamata: the position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. Syst Biol 53:735-757 (2004).
Wiens J, Hutter C, Mulcahy D: Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biol Lett 8:1043-1046 (2012).
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.