Morita Masaya, Nishikawa Akira, Nakajima Ayako, Iguchi Akira, Sakai Kazuhiko, Takemura Akihiro, Okuno Makoto
Department of Chemistry, Biology and Marine Sciences, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan.
J Exp Biol. 2006 Nov;209(Pt 22):4574-9. doi: 10.1242/jeb.02500.
Corals perform simultaneous mass spawning around the full moon. Most Acropora species release gamete bundles, which are a complex of eggs and sperm, into the seawater. Then, gamete bundles are separated into eggs and sperm. Eggs are fertilized when sperm and eggs come in contact with each other. However, it is still unclear how sperm meet the eggs of the same species in the presence of many eggs of different species and how eggs guard against the fertilization attempts by sperm of different species. In this study, we observed that A. digitifera, A. gemmifera and A. tenuis sperm showed motility initiation/attraction close to eggs. Sperm were completely immotile in seawater, but they began to swim in circular motion when they came in close proximity to eggs, and then approached the eggs in straightforward paths. Sperm flagellar motility was not activated by an egg from different species, suggesting that motility initiation by the egg is species specific. In addition, hybridization among these species did not occur under observed conditions. Furthermore, motility-activated sperm became quiescent when many sperm approached the eggs. This study is the first report to show that the egg secretes immobilization factor(s). Our results suggest that the flagellar motility regulation has evolved to avoid hybridization among different species during the mass spawning.
珊瑚在满月前后同时进行大规模产卵。大多数鹿角珊瑚物种会将包含卵子和精子的配子束释放到海水中。然后，配子束会分离成卵子和精子。当精子和卵子相互接触时，卵子受精。然而，在存在许多不同物种卵子的情况下，精子如何找到同一物种的卵子，以及卵子如何防止不同物种的精子进行受精尝试，目前仍不清楚。在这项研究中，我们观察到指状鹿角珊瑚、宝石鹿角珊瑚和细枝鹿角珊瑚的精子在靠近卵子时会启动运动/产生吸引力。精子在海水中完全不活动，但当它们靠近卵子时，会开始做圆周运动，然后直接靠近卵子。来自不同物种的卵子不会激活精子的鞭毛运动，这表明卵子引发的运动具有物种特异性。此外，在观察到的条件下，这些物种之间没有发生杂交。此外，当许多精子靠近卵子时，被激活运动的精子会变得静止。本研究首次报道了卵子会分泌固定因子。我们的结果表明，鞭毛运动调节的进化是为了避免在大规模产卵期间不同物种之间发生杂交。
