Meeting Abstract
Temperature plays an important role in regulating reproduction in many temperate fishes. The estuarine sheepshead minnow (Cyprinodon variegatus) serves as a useful model for studying temperature effects on reproduction because it exhibits one of the widest thermal tolerance ranges of any fish. Here, we examined the effects of thermal environment on reproductive function in sheepshead minnows by comparing gonadosomatic index (GSI) and relative transcript levels for genes associated with gonadal steroidogenesis in sexually-mature minnows maintained at 25°C or 35°C for 14-15 days. Both females and males maintained at 35°C exhibited a smaller GSI than fish at 25°C. In addition, females at 35°C showed lower relative levels of mRNA transcripts encoding follicle-stimulating hormone receptor (fshr) and luteinizing hormone receptor (lhr) as well as cholesterol side chain cleavage enzyme (p450scc) and steroid acute regulatory protein (star). Females kept at 35°C also exhibited lower levels of mRNAs encoding two steroidogenic enzymes: ovarian aromatase (cyp19a1a) and 3β-hydroxysteroid dehydrogenase (3βhsd). Similar to females, males kept at 35°C exhibited lower relative levels of lhr mRNAs in the testis than males kept at 25°C. However, no difference was observed in fshr mRNA levels. Males also had lower testicular levels of mRNAs encoding p450scc, but there was no difference in star mRNA levels. There was no effect of temperature on mRNA abundance for cyp19a1a or 3βhsd in the testis. Taken together our results imply that despite the phenomenal thermal range exhibited by C. variegatus, individuals experience decreased reproductive performance at 35°C even though this temperature is well within the species’ thermal tolerance range.
