生物時計と潮汐によるサンゴ礁棲ベラ類の産卵時刻あわせ

珊瑚礁中的许多贝类每天都会产卵，产卵高峰在日间涨潮前后。在这项研究中，我们研究了印度-太平洋珊瑚礁中的常见物种--三斑鱼的卵巢发育与潮汐有关。早晨在不同潮位采集时，性腺指数(GSI)和卵巢组织学发生变化，随着GSI的升高而进入高潮，一批最高级的卵母细胞从卵黄发生期发育到成熟期。多数卵巢在涨潮前后存在排卵卵和排卵后卵泡(POF)，落潮前后仅有POF残留，提示产卵发生在涨潮期间或涨潮后。我们注意到，与潮汐相关的产卵在上午显着，大部分卵巢在下午涨潮时采集，表现出产卵后的特征。有人认为，某些敏感物种对它们的产卵时间具有可塑性，并利用强有力的环境线索来获得繁殖成功。与前体类固醇孵育的卵巢组织，在涨潮和落潮时，睾酮转化为17β-雌二醇的速率较高，而在低潮和大潮时，17α-羟孕酮转化为17α，20β-二羟基-4-孕烯-3-酮和17-α，20-β，21-三羟基-4-孕烯-3-酮的转化率较高。卵巢切片与人绒毛膜促性腺激素孵育后，类固醇激素的波动与潮汐相似。这些类固醇激素的产生与卵巢中卵母细胞的发育有关，可能受促性腺激素的调节。这些结果表明，日周期是卵母细胞发育的基础，潮汐周期叠加在这一过程之上。

Many wrasses in coral reefs exhibit daily spawning that peaks around daytime high tide. In this study, we examined tidal-related ovarian development in the threespot wrasse Halichoeres trimaculatus, which is a common species in coral reefs of the Indo-Pacific Ocean. When the fish were collected in the morning at different tidal phases, the gonadosomatic index (GSI) and ovarian histology changed; concomitant with increases in GSI towards high tide, a clutch of the most advanced oocytes developed from vitellogenic to maturation stages. Ovulated eggs and post-ovulated follicles (POF) existed in most ovaries around high tide, but only POF remained around ebb tide, suggesting that spawning occurred during or after high tide. We noticed that tidal-related spawning was remarkable in the morning and that most ovaries collected at afternoon high tide exhibited post-spawning features. It was suggested that certain labrid species possess plasticity with regard to their spawning time and utilize potent environmental cues for their reproductive success. When the ovarian pieces were incubated with precursor steroids, high conversion of testosterone to 17β-estradiol occurred during high and ebb tides, while that of 17α-hydroxyprogesterone to 17α,20β-dihydroxy-4-pregnen-3-one and 17α,20β,21-trihydroxy-4-pregnen-3-one was observed during low and flood tides. Incubation of the ovarian pieces with human chorionic gonadotropin resulted in similar fluctuations of the steroid hormones with tide. Production of these steroid hormones correlated with oocyte development in the ovaries and was probably regulated by gonadotropin. These results demonstrate that the daily cycle is fundamental for oocyte development, and the tidal cycle is superimposed on this process.