Iwata Eri, Mikami Kyohei, Manbo Jun, Moriya-Ito Keiko, Sasaki Hideaki
College of Science and Engineering, Iwaki Meisei University, Iwaki 970-8551, Japan.
Zoolog Sci. 2012 Dec;29(12):849-55. doi: 10.2108/zsj.29.849.
Anemonefish, Amphiprion spp., are socially controlled, protandrous sex changers with a monogamous mating system. Under certain conditions, sexually immature anemonefish with ambisexual gonads differentiate directly into males or females. Formation and maintenance of social rank in a group are considered key requirements for the induction of sex change or differentiation. Generally, each animal living in a social group experiences a different level of social stress in accordance with its social rank, and we hypothesize that the stress situation of individual anemonefish influences its sex determination. Groups of three sexually immature anemonefish were placed into each of five experimental tanks and kept for 10 days to allow for social rank formation and behavioral observation. The fish were then euthanized, and blood and brain samples were collected from each fish. The social rank of each individual was distinguishable from day 1 of the experiment. Aggressive behaviors were most frequent and blood Cortisol values were higher in dominant individuals. The transcription of mRNA for stress-related genes, i.e., those encoding for glucocorticoid and arginine vasotocin receptors, was higher in the brains of dominant individuals than in other social ranks. Furthermore, we detected higher transcription levels of gonad and brain aromatase genes, which encode the enzyme that converts androgens into estrogens, in the brains of dominant individuals. These results suggest that social rank reflects the blood Cortisol value, which in turn leads to sex differentiation by manipulating transcription of genes, including aromatase genes, in the brain.
小丑鱼，双锯鱼属，是具有一夫一妻制交配系统的受社会控制的雄性先熟的性逆转鱼类。在某些条件下，具有两性性腺的性未成熟小丑鱼可直接分化为雄性或雌性。群体中社会等级的形成和维持被认为是诱导性逆转或分化的关键条件。一般来说，生活在社会群体中的每只动物根据其社会等级会经历不同程度的社会压力，我们推测个体小丑鱼的压力状况会影响其性别决定。将三组性未成熟的小丑鱼放入五个实验水箱中的每个水箱中，并饲养10天，以形成社会等级并进行行为观察。然后对鱼实施安乐死，并从每条鱼身上采集血液和大脑样本。从实验第一天起，每个个体的社会等级就可区分。攻击行为在占主导地位的个体中最频繁，且血液皮质醇值更高。与压力相关基因（即编码糖皮质激素和精氨酸血管加压素受体的基因）的mRNA转录在占主导地位个体的大脑中高于其他社会等级。此外，我们在占主导地位个体的大脑中检测到性腺和脑芳香化酶基因的转录水平更高，这些基因编码将雄激素转化为雌激素的酶。这些结果表明，社会等级反映血液皮质醇值，进而通过操纵大脑中包括芳香化酶基因在内的基因转录导致性别分化。
