TASHIRO S, HATTORI RS, ZHANG Y, YAMAMOTO Y, MI Occurrence of sex genotype / sex phenotype mismatches and yy super-males (yy) in wild populations of pejerrey Odontesthes bonariensis.

TASHIRO S; HATTORI RS; ZHANG Y; YAMAMOTO Y; MIRANDA LA; COLAUTTI DC; BERASAIN E; STRUSSMANN CA

Kona

Simposio; 7th 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 in sex 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 individuals occur in the wild, for example, by mating of sex-reversed (XY) females to normal XY males, but current assays cannot distinguish XY from YY individuals. Because of the possible impact that sex-reversed and YY individuals might have on the sex ratios of natural populations, we artificially 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 and YY 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 PCR analysis using amhy-specific primers. In this screening, 66% (53 out of 80) of the progeny was amhy-positive, which suggested the presence of YY fish assuming Mendelian segregation (XX 1:3 XY+YY). We then performed a quantitative PCR analysis on genomic DNA which detected 16 individuals, presumably YY individuals, with amhy values twice higher than the other 37 amhy-positive fishes. Progeny tests with amhy-negative (XX) females showed that the presumed YY individuals were 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, 12 XX-males, 105 XY-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 surveying the effects of temperature and other factors on sex determination of wild pejerrey populations.