Physiological and Ecological Studies on the Effects of Global Warming on Fish Reproduction

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This project is concerned with the development of basic and applied research leading to the understanding of the mechanisms of action of high temperatures on sex differentiation and gonadal function, and the development of methods to monitor and forecast the effects of global warming on fish reproduction and natural fish populations. Research was conducted in four main areas as follows. 1) Study of the role of high temperature-induced apoptosis on the process of sex differentiation, particularly on thermolabile sex determination, and the phenomenon of germ cell degeneration and disappearance. In brief, we elucidated the molecular and cellular mechanisms of apoptosis induction in zebrafish larvae as well as the dynamics of cellular and biochemical process of apoptosis in pejerrey larvae, juveniles, and young adults. It became clear that apoptosis of gonadal cells plays an important role in gonadal sex differentiation in both species and particularly in temperature-dependent sex determin … More ation of pejerrey. We also showed that exposure to high temperatures triggers a quick apoptotic response in gonadal cells of juveniles and adults that eventually leads to germ cell degeneration, reduced fertility and even sterility during prolonged exposure. 2) Study of the effects of high temperatures on gonadal steroidogenesis and its relevance for thermolabile sex determination. We cloned and characterized the ovarian cytochrome p450 aromatase (cyp19A1) gene in pejerrey and examined the effect of high temperatures on the gene expression of this important enzyme catalyzing the conversion from male to female steroid hormones during sex differentiation in pejerrey and zebrafish. High temperature suppressed aromatase gene expression and was associated with masculinization in both species. Treatment with fadrozole, an aromatase inhibitor, also caused masculinization a result that also emphasizes the role of this enzyme in ovarian differentiation. Moreover, we determined in medaka that low and high temperatures during sex differentiation have synergistic and antagonistic effects, respectively, with estradiol, the main female steroid hormone. 3) Study of the effects of temperatures on the development and function of the brain-pituitary-gonad axis. These studies clarified the molecular structure of major brain and pituitary gonadotrophic hormones (GnRH, FSH, LH) and their receptors and evaluated their ontogeny in relation to gonadal sex differentiation at different temperatures. The results obtained suggest a role of the brain and pituitary in sex differentiation and temperature-dependent sex determination. 4) Development of methods to monitor expression of temperature-dependent sex determination and germ cell degeneration in natural fish populations. We clarified the relationship between the chemical composition of otoliths and water temperature in pejerrey and medaka and validated the technique of otolith microchemistry to reconstruct thermal history in model wild pejerrey populations from Japan and Argentina. We also developed a SNP sex-linked marker in Patagonian pejerrey and applied this marker to the study of the effects of temperature on genotypic and temperature-dependent sex determination in this species. These examples and the abundant information obtained in this study provide the basis for the study of the effects of global warming on the reproduction of natural fish populations. Less