Ito Lauro Satoru, Yamashita Michiaki, Takashima Fumio, Strüssmann Carlos Augusto
Department of Marine Biosciences, Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan.
J Exp Zool A Comp Exp Biol. 2005 Jun 1;303(6):504-14. doi: 10.1002/jez.a.159.
This study evaluated the effects of different temperatures on the histological process of sex differentiation in the pejerrey Odontesthes bonariensis, a fish with marked temperature-dependent sex determination (TSD), at feminizing, neutral, and masculinizing temperatures. Fish reared at three temperatures (17 degrees C, 24 degrees C, and 29 degrees C) from hatching were sampled weekly until 11 weeks and their gonads were examined by histology. The percentages of females at 17 degrees C, 24 degrees C, and 29 degrees C were 100%, 73%, and 0%, respectively. Sex differentiation occurred earlier and at a smaller body size at higher temperatures in both sexes. The first signs of ovarian differentiation were observed at 4 and 7 weeks at 24 degrees C and 17 degrees C, respectively, and those of testicular differentiation at 4 and 7 weeks at 29 degrees C and 24 degrees C, respectively. Body or gonadal growth rates before sex differentiation were not proportional to temperature and showed no sexual dimorphism at 24 degrees C, where both sexes were present. Thus, differential growth rate is probably not a factor in TSD or histological sex differentiation in pejerrey. Blood vessels were formed before sex differentiation in both sexes and at all temperatures, and may be important for sex differentiation. No signs of intersexuality were found in any of the groups, and this characterizes pejerrey as the differentiated type of gonochorist even at feminizing and masculinizing temperatures. Ovaries were formed by the same histological processes at feminizing (17 degrees C) and neutral (24 degrees C) temperatures and without any pathological features such as germ cell degeneration. The process of testicular formation was generally similar at 24 degrees C and 29 degrees C, but some fish at 29 degrees C had widespread germ cell degeneration before sex differentiation. This suggests that pathological processes leading to germ cell death, such as heat-induced dysfunction of the supporting somatic cells, could be involved in masculinization of the genetic females at high temperatures.
本研究评估了不同温度对银汉鱼（Odontesthes bonariensis）性别分化组织学过程的影响。银汉鱼是一种具有明显温度依赖型性别决定（TSD）的鱼类，实验设置了雌性化温度、中性温度和雄性化温度。将孵化后的鱼苗在三种温度（17摄氏度、24摄氏度和29摄氏度）下饲养，每周取样直至第11周，通过组织学方法检查其性腺。在17摄氏度、24摄氏度和29摄氏度下，雌性的比例分别为100%、73%和0%。两性在较高温度下性别分化更早且鱼体尺寸更小。分别在24摄氏度和17摄氏度下，于4周和7周观察到卵巢分化的最初迹象；在29摄氏度和24摄氏度下，分别于4周和7周观察到睾丸分化的最初迹象。性别分化前的鱼体或性腺生长速率与温度不成比例，在24摄氏度（两性均存在）时未表现出性别二态性。因此，生长速率差异可能不是银汉鱼TSD或组织学性别分化的一个因素。在所有温度下，两性在性别分化前均已形成血管，血管可能对性别分化很重要。在任何组中均未发现雌雄同体的迹象，这表明即使在雌性化和雄性化温度下，银汉鱼也是典型的雌雄异体类型。在雌性化温度（17摄氏度）和中性温度（24摄氏度）下，卵巢通过相同的组织学过程形成，且没有任何病理特征，如生殖细胞退化。在24摄氏度和29摄氏度下，睾丸形成过程总体相似，但在29摄氏度下，一些鱼在性别分化前存在广泛的生殖细胞退化。这表明导致生殖细胞死亡的病理过程，如高温诱导的支持性体细胞功能障碍，可能参与了高温下遗传雌性的雄性化过程。
