The Komodo dragon (Varanus komodoensis) is the largest lizard in the world. Surprisingly, it has not yet been cytogenetically examined. Here, we present the very first description of its karyotype and sex chromosomes. The karyotype consists of 2n = 40 chromosomes, 16 macrochromosomes and 24 microchromosomes. Although the chromosome number is constant for all species of monitor lizards (family Varanidae) with the currently reported karyotype, variability in the morphology of the macrochromosomes has been previously documented within the group. We uncovered highly differentiated ZZ/ZW sex microchromosomes with a heterochromatic W chromosome in the Komodo dragon. Sex chromosomes have so far only been described in a few species of varanids including V. varius, the sister species to Komodo dragon, whose W chromosome is notably larger than that of the Komodo dragon. Accumulations of several microsatellite sequences in the W chromosome have recently been detected in 3 species of monitor lizards; however, these accumulations are absent from the W chromosome of the Komodo dragon. In conclusion, although varanids are rather conservative in karyotypes, their W chromosomes exhibit substantial variability at the sequence level, adding further evidence that degenerated sex chromosomes may represent the most dynamic genome part.

1.
Altmanová M, Rovatsos M, Kratochvíl L, Johnson Pokorná M: Minute Y chromosomes and karyotype evolution in Madagascan iguanas (Squamata: Iguania: Opluridae). Biol J Linn Soc 118:618-633 (2016).
2.
Auffenberg W: The Behavioral Ecology of the Komodo Monitor (University Press of Florida, Gainesville 1981).
3.
Chaiprasertsri N, Uno Y, Peyachoknagul S, Prakhongcheep O, Baicharoen S, et al: Highly species-specific centromeric repetitive DNA sequences in lizards: molecular cytogenetic characterization of a novel family of satellite DNA sequences isolated from the water monitor lizard (Varanus salvator macromaculatus, Platynota). J Hered 104:798-806 (2013).
4.
Ciofi C: The Komodo dragon. Sci Am 280:84-91 (1999).
5.
Ciofi C: Conservation genetics, in Murphy JB, Ciofi C, De La Panouse C, Walsh T (eds): Komodo Dragons: Biology and Conservation, pp 129-164 (Smithsonian Institution Press, Washington 2002).
6.
Ciofi C, Beaumont MA, Swingland IR, Bruford MW: Genetic divergence and units for conservation in the Komodo dragon Varanus komodoensis. Proc Biol Sci 266:2269-2274 (1999).
7.
Ciofi C, Smith BR, Hutchins M: Conservation. In situ and ex situ contributions, in Murphy JB, Ciofi C, De La Panouse C, Walsh T (eds): Komodo Dragons: Biology and Conservation, pp 211-230 (Smithsonian Institution Press, Washington 2002).
8.
Ciofi C, Tzika AC, Natali C, Watts PC, Sulandari S, et al: Development of a multiplex PCR assay for fine-scale population genetic analysis of the Komodo monitor Varanus komodoensis based on 18 polymorphic microsatellite loci. Mol Ecol Res 11:550-556 (2011).
9.
Endow SA: Polytenization of the ribosomal genes on the X and Y chromosomes of Drosophila melanogaster. Genetics 100:375-385 (1982).
10.
Halverson J, Spelman LH: Sex determination and its role in management, in Murphy JB, Ciofi C, De La Panouse C, Walsh T (eds): Komodo Dragons: Biology and Conservation, pp 165-177 (Smithsonian Institution Press, Washington 2002).
11.
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).
12.
Hocknull SA, Piper PJ, van den Bergh GD, Morwood MJ, Kurniawan I: Dragon's paradise lost: palaeobiogeography, evolution and extinction of the largest-ever terrestrial lizards (Varanidae). PLoS One 4:e7241 (2009).
13.
IUCN: World Conservation Monitoring Centre. 1996. Varanus komodoensis. The IUCN Red List of Threatened Species 1996: e.T22884A9396736. . Downloaded on 25 January 2016.
14.
Johnson Pokorná M, Rovatsos M, Kratochvíl L: Sex determination and karyotype of the (nearly) mythical creature, the Gila monster, Heloderma suspectum (Squamata: Helodermatidae). PLoS One 9:e104716 (2014).
15.
Kasai F, O'Brien PCM, Martin S, Ferguson-Smith MA: Extensive homology of chicken macrochromosomes in the karyotypes of Trachemys scripta elegans and Crocodylus niloticus revealed by chromosome painting despite long divergence times. Cytogenet Genome Res 136:303-307 (2012).
16.
King M, King D: Chromosomal evolution in the lizard genus Varanus (Reptilia). Aust J BioI Sci 28:89-108 (1975).
17.
King M, Mengden GA, King D: A pericentric-inversion polymorphism and a ZZ/ZW sex-chromosome system in Varanus acanthurus Boulenger analysed by G- and C-banding and Ag staining. Genetica 58:39-45 (1982).
18.
Matsubara K, Tarui H, Toriba M, Yamada K, Nishida-Umehara C, et al: Evidence for different origin of sex chromosomes in snakes, birds, and mammals and step-wise differentiation of snake sex chromosomes. Proc Natl Acad Sci USA 103:18190-18195 (2006).
19.
Matsubara K, Sarre SD, Georges A, Matsuda Y, Graves JAM, Ezaz T: Highly differentiated ZW sex microchromosomes in the Australian Varanus species evolved through rapid amplification of repetitive sequences. PLoS One 9:e95226 (2014).
20.
Olmo E, Signorino GG: Chromorep: a reptiles chromosomes database. http://chromorep.univpm.it/ (2016).
21.
O'Meally D, Patel HR, Stiglec R, Sarre SD, Geordes A, et al: Non-homologous sex chromosomes of birds and snakes share repetitive sequences. Chromosome Res 18:787-800 (2010).
22.
Pianka ER, King D, King RA: Varanoid Lizards of the World (Indiana University Press, Bloomington 2004).
23.
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).
24.
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).
25.
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 Genetics 12:91 (2011b).
26.
Pokorná M, Giovannotti M, Kratochvíl L, Caputo V, Olmo E, et al: Conservation of chromosomes syntenic with avian autosomes in squamate reptiles revealed by comparative chromosome painting. Chromosoma 121:409-418 (2012).
27.
Pokorná M, Rens W, Rovatsos M, Kratochvíl L: A ZZ/ZW sex chromosome system in the thick-tailed gecko (Underwoodisaurus milii; Squamata: Gekkota: Carphodactylidae), a member of the ancient gecko lineage. Cytogenet Genome Res 142:190-196 (2014).
28.
Pyron RA, Burbrink FT, Wiens JJ: A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evol Biol 13:93 (2013).
29.
Rovatsos M, Kratochvíl L, Altmanová M, Johnson Pokorná M: Interstitial telomeric motifs in squamate reptiles: when the exceptions outnumber the rule. PLoS One 10:e0134985 (2015).
30.
Rovatsos M, Johnson Pokorná, Altmanová M, Kratochvíl L, Velenský P, et al: Sexing of Komodo Dragons, Varanus komodoensis. Gazella (Zoo Praha) 42, in press.
31.
Rutkowska J, Lagisz M, Nakagawa S: The long and the short of avian W chromosomes: no evidence for gradual W shortening. Biol Lett 8:636-638 (2012).
32.
Sastrawan P, Ciofi C: Population distribution and home range, in Murphy JB, Ciofi C, De La Panouse C, Walsh T (eds): Komodo Dragons: Biology and Conservation, pp 42-77 (Smithsonian Institution Press, Washington 2002).
33.
Singh L: Evolution of karyotypes in snakes. Chromosoma 38:185-236 (1972).
34.
Sola L, Rossi AR, Iaselli V, Rasch EM, Monaco PJ: Cytogenetics of bisexual/unisexual species of Poecilia. II. Analysis of heterochromatin and nucleolar organizer regions in Poeciliamexicanamexicana by C-banding and DAPI, quinacrine, chromomycin A3, and silver staining. Cytogenet Cell Genet 60:229-235 (1992).
35.
Srikulnath K, Uno Y, Nishida C, Matsuda Y: Karyotype evolution in monitor lizards: cross-species chromosome mapping of cDNA reveals highly conserved synteny and gene order in the Toxicofera clade. Chromosome Res 21:805-819 (2013).
36.
Sulandari S, Zein MSA, Arida EA, Hamidy A: Molecular sex determination of captive Komodo dragons (Varanus komodoensis) at Gembira Loka Zoo, Surabaya Zoo, and Ragunan Zoo, Indonesia. Hayti J Biosci 21:65-75 (2014).
37.
Sumner AT: A simple technique for demonstrating centromeric heterochromatin. Exp Cell Res 75:304-306 (1972).
38.
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).
39.
Uetz P, Hošek J (eds): The reptile database (2016). http://www.reptile-database.org, accessed January 1, 2016.
40.
Vidal N, Hedges SB: The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes. C R Biol 328:1000-1008 (2005).
41.
Watts PC, Buley KR, Sanderson S, Boardman W, Ciofi C, Gibson R: Parthenogenesis in Komodo dragons. Nature 444:1021-1022 (2006).
42.
Wiens JJ, Hutter CR, Mulcahy DG, Noonan BP, Townsend TM, et al: Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biol Lett 8:1043-1046 (2012).
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