Multi-year survey of genotypic and phenotypic sex ratios and frequencies of genotype/phenotype mismatches in pejerrey odontesthes bonariensis from lake Chascomús

SHIOTA S ; YAMAMOTO Y; HATTORI RS; STRÜSSMANN CA; MIRANDA LA; COLAUTTI DC; BERASAIN GE

Mar del Plata

Jornada; XXV Jornadas de la Sociedad Argentina de Biología; 2023

Sociedad Argentina de Biología

In thepejerrey Odontesthes bonariensis, exposure to high and low temperaturesduring the critical period of sex determination (CPSD) induces testicular andovarian differentiation, respectively, regardless of the presence or not of thesex-determining gene amhy, which is crucial for testis formation only atintermediate, sexually neutral temperatures. Therefore, the presence/absence ofamhy serves as a marker of genotypic sex (XX/XY) and allows to monitorthe changes in genotypic and phenotypic sex ratios of wild pejerrey populationsas well as to analyze the impacts of anthropogenic and climatic factors onpejerrey resources. Nevertheless, studies on sex determination in naturalpopulations are virtually inexistent. Our group has conducted yearly biologicalmonitoring of the pejerrey population in Lake Chascomús since 2014 using the amhyas a genetic marker of genotypic sex. In this study, we performed otolithincrement analysis and growth history reconstruction (back-calculation) in representativeindividuals from different size classes collected on each year between 2014 and2019 to discriminate all possible year classes represented in the annual collections.The analysis classified individuals as born between 2012 and 2019 and as age 0,1, or 2 years old. Marked year-to-year variations in genotypic and phenotypicsex ratios were observed. Genotypic sex ratios were generally balanced, but XYfish were notably abundant in the 2013 year-class whereas the opposite was truein 2019. Genotypic female-to-phenotypic male transitions were far moreprevalent that its reciprocal, male-to-female transition, and this wasreflected in markedly male-biased phenotypic sex ratios in at least threeyear-classes. Combining otolith analysis with genotypic and phenotypic sexdiscrimination provides important insights into the ecology and reproductive healthof pejerrey populations.