OCCURRENCE OF SEX GENOTYPE / SEX PHENOTYPE MISMATCHESAND SUPER-MALES (YY) IN WILD POPULATIONS OF PEJERREY Odontesthes bonariensis

SEIYA, T.; HATTORI, R.; YAN, Z.; YAMAMOTO, J.; MIRANDA, L. A.; COLAUTTI, D. C.; BERASAIN, G. E.; STRUSSMANN, C. A.

Kona Hawaii

Simposio; Seventh International Symposium on Vertebrate Sex Determination; 2015

The pejerrey Odontesthes bonariensis is known for its strong temperature-dependent sex determination (TSD). However, recent studies have shown that this species also possess the testis-determining gene amhy(Y-chromosome-linked anti-Müllerian hormone), first described in the congeneric O. hatcheri,and that amhy plays a role insex determination of O. bonariensis at intermediate temperatures. These findings make possible to monitor wild pejerrey populations for mismatches between genotypic (XX or XY) and phenotypic (ovary or testis) sex and may prove instrumental for field studies addressing the effects of abnormal temperatures on reproduction.It is also possible that YY individualsoccur in the wild, for example, by mating ofsex-reversed (XY) femalesto normal XY males, but current assays cannot distinguish XY from YY individuals.Because of the possible impact that sex-reversed and YYindividuals might have on the sex ratios of natural populations, weartificially produced YY individuals to test their survival and fertility and developed a molecular method to discriminate fish with single (XY) and double (YY) copies of amhy. Finally, we carried out a field study in the Chascomus Lake (Argentina) to preliminarily assess the presence of sex reversals andYY individuals in wild populations. First, captive-reared broodstock were genetically screened for amhy and a sex-reversed XY female was mated to an XY male. Their progeny was reared for 18 months until reaching sexual maturity, and screened by genomic DNA PCRanalysis using amhy-specific primers. In this screening, 66% (53 out of 80) of the progeny was amhy-positive, which suggested the presence of YY fishassuming Mendelian segregation (XX 1:3 XY+YY). We then performed a quantitative PCR analysis on genomic DNAwhichdetected 16 individuals, presumably YY individuals,with amhyvalues twice higher than the other 37 amhy-positive fishes. Progeny testswith amhy-negative (XX) females showed thatthe presumedYY individualswere in fact YY as their offspring was 100% amhy-positive (XY).We then used these molecular tools to screen wild pejerrey (n=158) collected in Lake Chascomus, Argentina, on August 2014. Fish were individually labeled, and fin clipped for genotypic sex determination following the above protocols.Their phenotypic sex was determined either by dissection and visual inspection of the gonads on spot or by histological analysis.The analysis revealed the presence of 35 XX-females, 4 XY-females, 12XX-males,105XY-males, and 2 YY-males. We did not find any YY-female. The results of this study reveal that YY pejerrey are both viable and fertile and confirm the occurrence of sex reversal in both directions, probably as a result of TSD, and even YY individuals in a wild pejerrey population. This study also shows that quantitative PCR using only genomic DNA can obviate progeny test as a means to identify the genotypic sex of pejerrey and therefore may be useful for surveyingthe effects of temperature and other factors on sex determination of wild pejerrey populations.