A major goal of genomic and reproductive biology is to understand the evolution of sex determination and sex chromosomes. Species of the 2 genera of the Salamander family Proteidae - Necturus of eastern North America, and Proteus of Southern Europe - have similar-looking karyotypes with the same chromosome number (2n = 38), which differentiates them from all other salamanders. However, Necturus possesses strongly heteromorphic X and Y sex chromosomes that Proteus lacks. Since the heteromorphic sex chromosomes of Necturus were detectable only with C-banding, we hypothesized that we could use C-banding to find sex chromosomes in Proteus. We examined mitotic material from colchicine-treated intestinal epithelium, and meiotic material from testes in specimens of Proteus, representing 3 genetically distinct populations in Slovenia. We compared these results with those from Necturus. We performed FISH to visualize telomeric sequences in meiotic bivalents. Our results provide evidence that Proteus represents an example of sex chromosome turnover in which a Necturus-like Y-chromosome has become permanently translocated to another chromosome converting heteromorphic sex chromosomes to homomorphic sex chromosomes. These results may be key to understanding some unusual aspects of demographics and reproductive biology of Proteus, and are discussed in the context of models of the evolution of sex chromosomes in amphibians.

Arntzen JW, Denoël M, Miaud C, Andreone F, Vogrin M, et al: Proteus anguinus. The IUCN Red List of Threatened Species. Version 2014.3 (2009). www.iucnredlist.org.
Bachtrog D, Kirkpatrick M, Mank JE, McDaniel SF, Pires JC, et al: Are all sex chromosomes created equal? Trends Genet 27:350-357 (2011).
Bergero R, Charlesworth D: The evolution of restricted recombination in sex chromosomes. Trends Ecol Evol 24:94-102 (2009).
Blaser O, Neuenschwander S, Perrin N: Sex-chromosome turnovers: the hot-potato model. Am Nat 183:140-146 (2014).
Charlesworth B, Charlesworth D: The degeneration of Y chromosomes. Philos Trans R Soc Lond B Biol Sci 355:1563-1572 (2000).
Charlesworth D, Charlesworth B, Marais G: Steps in the evolution of heteromorphic sex chromosomes. Heredity 95:118-128 (2005).
de Oliviera RR, Feldberg E, dos Anjos MB, Zuanon J: Occurrence of multiple sexual chromosomes (XX/XY1Y2 and Z1Z1Z2Z2/Z1Z2W1W2) in catfishes of the genus Ancistrus (Siluriformes: Loricariidae) from the Amazon basin. Genetica 134:243-249 (2008).
Dufresnes C, Borzée A, Horn A, Stöck M, Ostini M, et al: Sex chromosome homomorphy in Palearctic tree frogs results from both turnovers and X-Y recombination. Mol Biol Evol 32:2328-2337 (2015).
Eggert C: Sex determination: the amphibian models. Reprod Nutr Dev 44:539-549 (2004).
Evans BJ, Pyron RA, Wiens JJ: Polyploidization and sex chromosome evolution in amphibians, in Soltis PS, Soltis DE (eds): Polyploidy and Genome Evolution, pp 385-410 (Springer-Verlag, Berlin 2012).
Ferguson-Smith M: X-Y chromosomal interchange in the aetiology of true hermaphroditism and of XX Klinefelter's syndrome. Lancet 2:475-476 (1966).
Gorički Š: Filogeografska in morfološka analiza populacij močerila (Proteus anguinus). Dokt. disertacija. Ljubljana, Univ. v Ljubljani, Biotehniška fakulteta, Odd. za biologijo (2006).
Gorički Š, Trontelj P: Structure and evolution of the mitochondrial control region and flanking sequences in the European cave salamander Proteus anguinus. Gene 378:31-41 (2006).
Graves JAM: How to evolve new vertebrate sex determining genes. Dev Dyn 242:354-359 (2013).
Green DM, Sessions SK: Amphibian Cytogenetics and Evolution, ed 1 (Academic Press, San Diego 1991).
Green DM, Zeyl CW, Sharbel TF: The evolution of hypervariable sex and supernumerary (B) chromosomes in the relict New Zealand frog, Leiopelma hochstetteri. J Evol Biol 6:417-441 (1993).
Green DM, Weir LA, Casper GS, Lannoo MJ: North American Amphibians: Distribution and Diversity (University of California Press, Berkeley 2013).
Gregory TR: Animal Genome Size Database. http://www.genomesize.com (2005).
Grossen C, Neuenschwander S, Perrin N: The balanced lethal system of crested newts: a ghost of sex chromosomes past? Am Nat 180:E174-E183 (2012).
Hayes T: Sex determination and primary sex differentiation in amphibians: genetic and developmental mechanisms. J Exp Zool 281:373-399 (1998).
Hayman D, Sharp P: Verification of the structure of the complex sex chromosome system in Lagorchestes conspicillatus Gould (Marsupialia: Mammalia). Chromosoma 83:263-274 (1981).
Hillis D, Green DM: Evolutionary changes of heterogametic sex in the phylogenetic history of amphibians. J Evol Biol 3:49-64 (1990).
Hughes JF, Skaletsky H, Koutseva N, Pyntikova T, Page DC: Sex chromosome-to-autosome transposition events counter Y-chromosome gene loss in mammals. Genome Biol 16:104 (2015).
Ijdo JW, Wells RA, Baldini A, Reeders ST: Improved telomere detection using a telomere repeat probe (TTAGGG)n generated by PCR. Nucleic Acids Res 19:4780 (1991).
Juberthie C, Durand J, Dupuy M: Là reproduction des protées (Proteus anguinus): bilan de 35 ans d'élevage dans les grottes-laboratoires de moulis et d'aulignac. Mémoires de Biospéologie, Tome XXIII:53-56 (1996).
Kezer J, Sessions SK: Chromosome variation in the plethodontid salamander, Aneides ferreus. Chromosoma 71:65-80 (1979).
Kezer J, Seto T, Pomerat CM: Cytological evidence against parallel evolution of Necturus and Proteus. Am Nat 99:153-158 (1965).
Landeen EL, Presgraves DC: Evolution: from autosomes to sex chromosomes - and back. Curr Biol 23:R848-R850 (2013).
Leaché AD, Sites JW Jr: Chromosome evolution and diversification in North American spiny lizards (genus Sceloporus). Cytogenet Genome Res 127:166-181 (2009).
Macgregor HC, Horner H: Heteromorphism for chromosome 1, a requirement for normal development in crested newts. Chromosoma 76:111-122 (1980).
Macgregor HC, Sessions SK, Arntzen JW: An integrative analysis of phylogenetic relationships among newts of the genus Triturus (family Salamandridae), using comparative biochemistry, cytogenetics and reproductive interactions. J Evol Biol 3:329-373 (1990).
Malcolm JW, Kudra RS, Malone JH: The sex chromosomes of frogs: variability and tolerance offer clues to genome evolution and function. J Genomics 2:68-76 (2014).
McElreavey K, Cortes LS: X-Y translocations and sex differentiation. Semin Reprod Med 19:133-139 (2001).
Miura I, Ogata M: Change of heterogametic sex from male to female: why so easy in the frog? Chromosome Sci 16:3-9 (2013).
Morescalchi A: Chromosome evolution in the caudate Amphibia. Evol Biol 8:339-387 (1975).
Muller HJ: The relation of recombination to mutational advance. Mutat Res 106:2-9 (1964).
Oguiura N, Ferrarezzi H, Batistic RF: Cytogenetics and molecular data in snakes: a phylogenetic approach. Cytogenet Genome Res 127:128-142 (2009).
Ohno S: Sex Chromosomes and Sex-Linked Genes (Springer-Verlag, New York 1967).
Pennell MW, Kirkpatrick M, Otto SP, Vamosi JC, Peichel CL, et al: Y fuse? Sex chromosome fusions in fishes and reptiles. PLoS Genet 11: e1005237 (2015).
Perrin N: Sex reversal: a fountain of youth for sex chromosomes? Evolution 63:3043-3049 (2009).
Rao L, Turlapati R, Patel M, Panda B, Tosh D, et al: Cytogenetic characterization and fluorescence in situ hybridization of (GATA)10 repeats on established primary cell cultures from Indian water snake (Natrix piscator) and Indian mugger (Crocodylus palustris) embryos. Cytogenet Genome Res 127:287-296 (2009).
Rice WR: Genetic hitchhiking and the evolution of reduced genetic activity of the Y sex chromosome. Genetics 116:161-167 (1987).
Schmid M: Chromosome banding in Amphibia. V. Highly differentiated ZW/ZZ sex chromosomes and exceptional genome size in Pyxicephalus adspersus (Anura, Randidae). Chromosoma 80:69-96 (1980).
Schmid M, Olert J, Klett C: Chromosome banding in Amphibia. III. Sex chromosomes in Triturus. Chromosoma 71:29-55 (1979).
Schmid M, Nanda I, Steinlein C, Kausch K, Haaf T, Epplen JT: Sex determining mechanisms and sex chromosomes in Amphibia, in Green DM, Sessions SK, (eds): Amphibian Cytogenetics and Evolution, pp 393-430 (Academic Press, San Diego 1991).
Schmid M, Feichtinger W, Steinlein C, Haaf T, Schartl M, et al: Chromosome banding in Amphibia. XXVI. Coexistence of homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus maussi (Anura, Leptodactylidae). Cytogenet Genome Res 99:330-343 (2002).
Schmid M, Feichtinger W, Steinlein C, Visbal García R, Fernández Badillo A: Chromosome banding in Amphibia. XXVIII. Homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus riveroi (Anura, Leptodactylidae). Cytogenet Genome Res 101:62-73 (2003).
Schmid M, Steinlein C, Bogart JP, Feichtinger W, León P, et al: The chromosomes of terraranan frogs. Insights into vertebrate cytogenetics. Cytogenet Genome Res 130-131:1-568 (2010).
Sessions SK: Evidence for a highly differentiated sex chromosome heteromorphism in the salamander Necturus maculosus (Rafinesque). Chromosoma 77:157-168 (1980).
Sessions SK: Cytogenetics of diploid and triploid salamanders of the Ambystoma jeffersonianum complex. Chromosoma 84:599-621 (1982).
Sessions SK: Chromosomes: molecular cytogenetics, in Hillis DM, Moritz C, Mable BK (eds): Molecular Systematics, ed 2, pp 121-168 (Sinauer Associates, Sunderland 1996).
Sessions SK: Evolutionary cytogenetics in salamanders. Chromosome Res 16:183-201 (2008).
Sessions SK, Wiley JE: Chromosome evolution in salamanders of the genus Necturus. Brimleyana 10:37-52 (1985).
Sessions SK, Macgregor HC, Schmid M, Haaf T: Cytology, embryology, and evolution of the developmental arrest syndrome in newts of the genus Triturus (Caudata: Salamandridae). J Exp Zool 248:321-334 (1988).
Sharp A, Kusz K, Jaruzelska J, Szarras-Czapnik M, Wolski J, Jacobs P: Familial X/Y translocations associated with variable sexual phenotype. J Med Genet 41:440-444 (2004).
Sims SH, Macgregor HC, Pellatt PS, Horner HA: Chromosome 1 in crested and marbled newts (Triturus): an extraordinary case of heteromorphism and independent chromosome evolution. Chromosoma 89:169-185 (1984).
Sket B: Distribution of Proteus (Amphibia: Urodela: Proteidae) and its possible explanation. J Biogeogr 24:263-280 (1997).
Sket B, Arntzen JW: A black, non-troglomorphic amphibian from the karst of Slovenia: Proteus anguinus parkelj n. ssp. (Urodela: Proteidae). Contrib Zool 64:33-53 (1994).
Stanković D, Lužnik M, Poboljšaj K: Conservation and declines of amphibians in Slovenia, in Heatwole H, Wilkinson JH (eds): Amphibian Biology, vol 11, part 4. Status of Conservation and Decline of Amphibians: Eastern Hemisphere, Southern Europe and Turkey, pp 32-44 (Pelagic Publishing, Exeter 2015).
Stöck M, Horn A, Grossen C, Lindtke D, Sermier R, et al: Ever-young sex chromosomes in European tree frogs. PLoS Biol 9:e1001062 (2011).
van Doorn GS: Patterns and mechanisms of evolutionary transitions between genetic sex-determining systems. Cold Spring Harb Perspect Biol 6:a017681 (2014).
van Doorn GS, Kirkpatrick M: Transitions between male and female heterogamety caused by sex-antagonistic selection. Genetics 186:629-645 (2010).
Viegas-Péquignot E, Benazzou T, Dutrillaux B, Petter F: Complex evolution of sex chromosomes in Gerbillidae (Rodentia). Cytogenet Genome Res 34:158-167 (1982).
Wallace H: Chromosome 1 and sex determination of crested newts. Caryologia 37:3-8 (1984).
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