Meeting Abstract
Temperature-dependent sex change (TSC) is common in fishes and reptiles but the physiological mechanisms are not fully understood. Mangrove rivulus fish (Kryptolebias marmoratus) is an ideal model for exploring the physiological mechanisms governing TSC. Adult rivulus exist predominantly as self-fertilizing hermaphrodites and change sex into secondary males in response to high temperature (≥28°C). Androgenic and estrogenic hormones play important roles in regulating sex change, and most studies have focused on the aromatase gene (Aro), which encodes an enzyme that converts testosterone to estradiol. However, other steroid biosynthesis enzymes such as 11β-hydroxylase (11βH) and 17β-hydroxysteroid dehydrogenase (17βHSD), which drive androgen synthesis, have received relatively little attention. We hypothesized that high temperature would decrease Aro expression but increase 11βH and 17βHSD expression to establish an androgenic environment that would promote sex change. To test this hypothesis, adult hermaphroditic rivulus were maintained at three temperatures (high: 30°C, normal: 25°C, low: 20°C) for 21 days. Expression of brain and gonad Aro, 11βH and 17βHSD were quantified using quantitative-PCR. Pre- and post-treatment testosterone (T), 11-ketotestosterone (11KT) and estradiol (E2) levels were also quantified using enzyme immunoassay. The results showed increases in all three hormones at high temperature and decreases in E2 and 11KT at low temperature. Low temperature also decreased the E2/T ratio, suggesting suppression of aromatase function. Temperature did not affect expression of brain Aro, 11βH or 17βHSD. However, low temperature significantly decreased gonad Aro expression, while high temperature significantly increased gonad 11βH and 17βHSD expression. This study demonstrates that high temperatures establish an androgenic environment conducive to initiating sex change.
