Thermal influences on fish sexual development

Abstract

Temperature is the main abiotic factor that affects multiple biological functions at different organization levels by changing the rates of physiological processes and chemical reactions. This is especially relevant for poikilothermic animals such as fish and of particular interest in processes like the sexual development. Sex in fishis very plastic since fish exhibit several types of reproduction, including gonochorism, various forms of hermaphroditism, and unisexuality. Further, sex determination can range from genetic sex determination (GSD)to environmental sex determination (ESD). Temperature-dependent sex determination (TSD) has been identified in several species but now is recognized that even species with GSD may have populations with sex ratio response to temperature which, under certain environmental conditions, can produce skewed sex ratios. Here, we used data from many species to show type of reproduction-related differences in thermal preferences and, using a cold water species (turbot, Scophthalmus maximus), a temperate water species (sea bass, Dicentrarchus labrax) and a tropical species (zebrafish, Danio rerio), we investigated common patterns of gene expression in response to heat. We focus not only in the analysis of genes and signaling pathways related to the endocrinology of testis and ovarian differentiation, but also consider genes related to the stress response and to epigenetic regulatory mechanisms. Further, we compared effects of temperature during early development at both the time of sex differentiation and in juveniles and adults. We describe the appearance of new phenotypes (neomales and pseudofemales) as a result of elevated temperature, suggest the existence of transgenerational transmission of epigenetic marks related to sexual development and discuss the possible consequences for natural populations in a global warming scenario