Meeting Abstract
Gonadal sex differentiation in fishes can be influenced by environmental temperature, and prolonged exposure to high temperatures can impair gametogenesis or, in extreme cases, trigger gonadal sex reversal. Recently, we identified a population of Cyprinodon nevadensis amargosae pupfish that occupies a high temperature freshwater spring (Tecopa Bore) and exhibits reduced sexual dimorphism in morphology compared to C. n. amargosae in the nearby Amargosa River, a stream in the Death Valley region of California. Temperatures in this desert stream vary widely both diurnally and seasonally, but average nearly 15°C less than in Tecopa Bore. We hypothesize that exposure of fish to the consistently elevated temperatures of Tecopa Bore impacts gonadal steroid production to alter sexual differentiation of morphology in that population. To begin to test that idea, we examined how exposure to high temperatures under laboratory conditions influences gonadal steroidogenic gene expression. Adult male and female pupfish from both Tecopa Bore and the Amargosa River were collected from the wild and maintained in captivity under either 24°C or 34°C temperature conditions for 88 days. In males and females from both populations, gene transcripts encoding receptors for the gonadotropin hormones (GtH) follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were depressed in fish of both sexes at 34°C. Tecopa Bore females exposed to 34°C also exhibited reduced transcript abundance for cytochrome P450 aromatase (cyp19a1) in the ovary. These findings suggest that exposure of pupfish to high temperatures may impair gonadal steroidogenic activity in pupfish both by reducing gonadotropin hormone (GtH) receptor abundance in both the testis and ovary, and also by depressing aromatase estrogen synthesis in the ovary.
