Sex-Linked Chromosomal Heterozygosity in the Scorpion Tityus confluens Borelli, 1899 (Buthidae)

OJANGUREN-AFFILASTRO AA; OJANGUREN-AFFILASTRO AA; ADILARDI RS; ADILARDI RS; MOLA LM; MOLA LM

Foz do Iguaçu

Congreso; 21st International Chromosome Conference; 2016

Tityus shows holokinetic chromosomes, achiasmatic male meiosis and absence ofheteromorphic sex chromosomes, as all Buthidae. Previous studies of males froma population of Tityus confluens Borelli,1899 from Reserva Natural Formosa (Argentina) revealed a numerical and structuralpolymorphism, comprising four cytotypes: A) 2n=6, II+IV at meiosis I; B) 2n=5, Vtype 1; C) 2n=5, V type 2; D) 2n=6, VI. In this work we analyzed thecytogenetic differences between males and females and discuss its possiblerelation with sex chromosomes. Thirteen males, 6 females and a litter of 15 embryos (of one of these females) from the same population were analyzed by C-bandingand FISH with 28S rDNA probe. All the females presented 2n=6 with two large andfour medium chromosomes, rDNA signals were detected at one terminal region oftwo medium chromosomes and C-banding pattern allowed us to distinguish threechromosome pairs. Within the litter, eight embryos presented 2n=6 and sevenembryos presented 2n=5. Males of cytotype A showed rDNA signals at one terminalregion of the bivalent. Cytotypes B and D showed terminal signals at twochromosomes of different size, while cytotype C showed signals at one terminalregion of a medium chromosome and at an interstitial region of the largestchromosome. The fact that all the analyzed males were structural heterozygotesand all the females were homozygotes could indicate a case of sex-linkedchromosomal heterozygosity, being the male the heterogametic sex. We proposethat the ancestral karyotype of this species could have had homomorphic sexchromosome pairs XY/XX (male/female) and a fusion between the Y chromosome andan autosome could have occurred. Rearrangements involving the autosomes and theY chromosome could have given rise to meiotic multivalents in males andbivalents in females. The different karyotypes observed in the litter ofembryos support this model.Fundingwas provided by grants from the Consejo Nacional de Investigaciones Científicasy Técnicas (CONICET PIP 00342), Universidad de Buenos Aires (UBACYT20020130100694BA) and Agencia Nacional de Producción Científica yTecnológica-SECyT (PICT 2010-1665).