Levitan Don R, Fukami Hironobu, Jara Javier, Kline David, McGovern Tamara M, McGhee Katie E, Swanson Cheryl A, Knowlton Nancy
Department of Biological Science, Florida State University, Tallahassee, Florida 32306-1100, USA.
Evolution. 2004 Feb;58(2):308-23.
Many coral species spawn simultaneously and have compatible gametes, leading to controversy over the nature of species boundaries and the frequency with which hybridization occurs. Three western Atlantic corals, Montastraea annularis, M. faveolata, and M. franksi, typify this controversy; they all spawn sympatrically on the same evenings after the fall full moons. Here we show, in both Panama and the Bahamas for multiple years, how a variety of mechanisms may act in concert to reproductively isolate all three species. Field studies indicate that M. franksi spawns two hours earlier than the other two species, and the eggs released during this earlier period disperse an average of 500 m by the time the other species spawn. Field measures of fertilization indicate that peak fertilization occurs when spawning synchrony is high and that corals that spawn at the tails of the spawning distributions have greatly reduced fertilization success. Laboratory studies indicate that there is a gametic incompatibility between M. faveolata and the other two species. There are regional differences in the gametic compatibility of M. franksi and M. annularis. In Panama, the two species are completely compatible, whereas in the Bahamas, M. franksi sperm can fertilize M. annularis eggs but the reciprocal cross often fails. Gamete age influences patterns of fertilization, such that very young eggs seem resistant to fertilization and old sperm lose viability after two hours. In sum, the combination of temporal differences in spawning, sperm aging, gamete dispersal and dilution, and gametic incompatibility act in various combinations among the three species, making it unlikely that hybrid fertilization would occur.
许多珊瑚物种会同时产卵且配子具有兼容性，这引发了关于物种界限的本质以及杂交发生频率的争议。西大西洋的三种珊瑚，即环纹菊珊瑚（Montastraea annularis）、蜂巢菊珊瑚（M. faveolata）和弗朗氏菊珊瑚（M. franksi），就是这场争议的典型代表；它们都在秋季满月后的同一个晚上同域产卵。在此，我们在巴拿马和巴哈马群岛进行了多年研究，展示了多种机制如何协同作用，在生殖上隔离这三个物种。野外研究表明，弗朗氏菊珊瑚比其他两个物种早两小时产卵，在其他物种产卵时，在此较早时期释放的卵平均已扩散500米。受精的野外测量结果表明，当产卵同步性高时受精高峰出现，而在产卵分布尾部产卵的珊瑚受精成功率大幅降低。实验室研究表明，蜂巢菊珊瑚与其他两个物种之间存在配子不兼容性。弗朗氏菊珊瑚和环纹菊珊瑚的配子兼容性存在区域差异。在巴拿马，这两个物种完全兼容，而在巴哈马群岛，弗朗氏菊珊瑚的精子能使环纹菊珊瑚的卵受精，但反向杂交往往失败。配子年龄会影响受精模式，非常年轻的卵似乎对受精有抗性，而老化的精子在两小时后会失去活力。总之，产卵时间差异、精子老化、配子扩散与稀释以及配子不兼容性等多种因素以不同组合方式作用于这三个物种之间，使得杂交受精不太可能发生。
