Kitanobo Seiya, Isomura Naoko, Fukami Hironobu, Iwao Kenji, Morita Masaya
Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Sesoko, Motobu, Okinawa 905-0227, Japan.
Department of Bioresources Engineering, Okinawa National College of Technology, 905 Henoko, Nago-City, Okinawa 905-2192, Japan.
Biol Lett. 2016 Aug;12(8). doi: 10.1098/rsbl.2016.0511.
Multi-specific synchronous spawning risks both sperm limitation, which reduces fertilization success, and hybridization with other species. If available sperm of conspecifics are limited, hybridization with heterospecific sperm could be an alternative. Some species of the reef-building coral Acropora produce hybrid offspring in vitro, and therefore hybridization between such species does sometimes occur in nature. Here, we report that the interbreeding species Acropora florida and A. intermedia preferentially bred with conspecifics at optimal gamete concentrations (10(6) cells ml(-1)), but when sperm concentration was low (10(4) cells ml(-1)), A florida eggs displayed an increased incidence of fertilization by sperm of A intermedia However, A intermedia eggs never crossed with heterospecific sperm, regardless of gamete concentrations. It appears that A florida eggs conditionally hybridize with heterospecific sperm; in nature, this would allow A florida to cross with later-spawning species such as A intermedia These results indicate that hybridization between some Acropora species could occur in nature according to the number of available sperm, and the choice of heterospecific sperm for fertilization could be one of the fertilization strategies in the sperm-limited condition.
多特异性同步产卵既存在精子限制风险（这会降低受精成功率），也存在与其他物种杂交的风险。如果同种的可用精子有限，与异种精子杂交可能是一种替代方式。造礁珊瑚鹿角珊瑚属的一些物种在体外产生杂交后代，因此此类物种之间的杂交在自然界中有时确实会发生。在此，我们报告杂交物种佛罗里达鹿角珊瑚和中间鹿角珊瑚在最佳配子浓度（10⁶个细胞/毫升）时优先与同种进行繁殖，但当精子浓度较低（10⁴个细胞/毫升）时，佛罗里达鹿角珊瑚的卵子被中间鹿角珊瑚的精子受精的发生率增加。然而，无论配子浓度如何，中间鹿角珊瑚的卵子从未与异种精子杂交。看来佛罗里达鹿角珊瑚的卵子会有条件地与异种精子杂交；在自然界中，这会使佛罗里达鹿角珊瑚能够与诸如中间鹿角珊瑚等晚产卵的物种杂交。这些结果表明，一些鹿角珊瑚物种之间的杂交可能会根据可用精子数量在自然界中发生，并且在精子受限的情况下选择异种精子进行受精可能是受精策略之一。
