Most of the reef-building Acropora corals around Okinawa Island spawn in May and/or June. We found that two morphotypes of Acropora divaricata spawned in August and/or September. The “robust” and “slender” morphotypes differed in branch width and in the diameter of axial corallites. Histological analyses showed that the onset of gamete production/maturation occurred from June onwards. Most of the other Acropora species spawned from late May to early June. A. florida, which spawned in May/June, initiated gamete production in early April. We assumed that the two morphotypes of A. divaricata were reproductively isolated from most of the other Acropora species because of differences in the spawning seasons. We found that the spawning seasons of the two morphotypes slightly overlapped in 2015 but not in 2019, and inter-morphotype gamete compatibility was high. However, population genetics analyses and a phylogeny of the mitochondrial d-loop region showed that they were genetically distinct and rarely hybridized. Thus, the broadcast-spawning coral A. divaricata might have speciated when there might have been only a low possibility of interspecific gamete interaction.

中文翻译：

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产卵时间的差异驱动了珊瑚鹿角珊瑚的神秘物种形成

冲绳岛周围的大部分造礁鹿角珊瑚在 5 月和/或 6 月产卵。我们发现鹿角的两种形态类型在 8 月和/或 9 月产卵。“健壮”和“细长”形态型的分枝宽度和轴向珊瑚的直径不同。组织学分析表明，配子产生/成熟的开始发生在 6 月以后。大多数其他鹿角珊瑚物种在 5 月下旬至 6 月初产卵。A. florida 在 5/6 月产卵，4 月初开始配子生产。由于产卵季节的差异，我们假设 A. divaricata 的两种形态类型与大多数其他鹿角珊瑚物种在生殖上是分离的。我们发现两种形态型的产卵季节在 2015 年略有重叠，但在 2019 年没有重叠，且形态型间配子兼容性高。然而，群体遗传学分析和线粒体 d-loop 区域的系统发育表明它们在遗传上是不同的，很少杂交。因此，当种间配子相互作用的可能性很低时，广播产卵珊瑚 A. divaricata 可能已经形成物种。