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Temperature-Dependent Sex Determination in Fish: Molecular Mechanisms, Epigenetics, Reaction Norms and Prevalence

AuthorsPiferrer, Francesc ; Blázquez, Mercedes ; Viñas, Jordi ; Navarro-Martín, Laia ; Ospina-Álvarez, Natalia
Issue DateMay-2008
CitationInternational Symposium on Sex Determination and Gametogenesis in Fish (2008)
AbstractAccumulating evidence indicates that in fish the effects of high water temperature (HT) on sex ratios are mediated by changes in gonadal aromatase gene expression. However, recent research in our laboratory suggests that rather than a generalized inhibition of aromatase in HT-exposed fish, HT reduces the number of fish that express gonadal aromatase at high levels. When HT exposure targets the critical period for sex differentiation, the net result is a progressive decrease in the number of fish with sufficient amounts of estrogen necessary for ovarian differentiation. This explains the higher proportion of males observed in many fish populations after exposure to HT. In addition, early effects of HT appear to be mediated by changes in the methylation level of the aromatase promoter. This suggests that gonadal sex is a threshold dichotomy originated in aromatase regulation and exemplifies an epigenetic mechanism by which conditions experienced during early development affect the ulterior hormonal milieu due to aromatase gene silencing. But, is this temperature-dependent sex determination (TSD)? Analyzing field and laboratory data for the 59 fish species where so far TSD has been assumed, we found that many species considered as having TSD exhibit sex chromosomes, a feature indicative of genotypic sex determination (GSD), and, further, many tested temperatures to elicit a sex ratio response are ecologically irrelevant. Thus, many cases of TSD in fish can be explained by thermal alterations of an otherwise predominately GSD mechanism and thus not all species with sex ratio responses to temperature have TSD. These species can be better referred to as GSD+TE species (GSD + thermal effects). Reaction norms of sex ratio response in these species follow a single general pattern, producing highly male-biased sex ratios after exposure to HT. Together, these results provide a unifying and testable framework where to view and study the effects of temperature -a major environmental factor- on sex ratios -a key population demographic parameter- as it applies to fish and possibly to other vertebrates with TSD or GSD+TE. (Funded by Spanish MEC grant “Sexgene” to FP)
DescriptionInternational Symposium on Sex Determination and Gametogenesis in Fish: Current Status and Future Directions, 29-31 May 2008, Honolulu, EE.UU.
Appears in Collections:(ICM) Comunicaciones congresos
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