OTOLITH-BASED APPROACH TO STUDY THE EFFECTS OF WATER TEMPERATURE ON THE SEX DETERMINATION OF PEJERREY ODONTESTHES BONARIENSIS IN LAKE CHASCOMÚS

Yokochi, H.¹, Okajima, H. ¹, Kakuta, N. ¹, Yamamoto, Y.¹, Strüssmann, C.A ¹, Miranda, L.A.², Colautti, D.C.³, Berasain, G.E.^4.

¹Laboratory of Population Biology, TUMSAT,

²Laboratorio de Ictiofisiología y Acuicultura, IIB-INTECH,

³Instituto de Limnología Dr. Raúl A. Ringuelet, UNLP.,

⁴ Estación Hidrobiologica de Chascomús, MAAGBA

carlos@kaiyodai.ac.jp

The pejerrey is known for its strong temperature-dependent sex determination (TSD). In laboratory experiments, low temperatures favor the formation of females and high temperatures that of males. However, the extent that TSD affects the sex ratios of natural populations is still unknown. We have recently shown that this species has the XY system of sex determination and a genotypic testicular determinant, the Y-chromosome-linked anti-Müllerian hormone (amhy) gene. This gene provides a strong push towards testicular differentiation and its presence/absence serves therefore as a marker of genotypic sex, making possible to survey the changes in genotypic sex ratios and the presence of phenotypic/genotypic sex mismatches in wild pejerrey populations as well as to analyze the impacts of environmental factors on pejerrey resources. We have been monitoring the pejerrey population in Lake Chascomús since 2014 and have uncovered highly skewed sex ratios, several sex-reversed XX males and XY females, and even YY (supermales) that are likely the offspring from crosses between normal XY males and sex-reversed XY females. In this study, we extended the analysis to 150 fish captured in Lake Chascomús in 2016 and conducted an investigation of the usefulness of otolith daily-increment analysis to discriminate between fish from different year-classes and between fish born in different seasons (e.g. spring vs autumn). The samples were ascribed to the 2016 and the 2015 year-classes based on the birth date. Sex-reversed XX males were found in both year-classes whereas XY females were found only in the 2015 year-class. Sex-reversed XY females were born predominantly in the second half of autumn whereas sex-reversed XX males were born in early autumn and in spring. Monitoring wild pejerrey populations with a combination of otolith analysis and molecular tools may provide crucial insight on the reproductive ecology of this species.

Palabras clave: PEJERREY, SEX DETERMINATION, TSD, OTOLITH