Martín-Coello Juan, Benavent-Corai Jose, Roldan Eduardo R S, Gomendio Montserrat
Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), c/José Gutiérrez Abascal 2, 28006-Madrid, Spain.
Evolution. 2009 Mar;63(3):613-23. doi: 10.1111/j.1558-5646.2008.00585.x. Epub 2008 Dec 12.
Reproductive barriers between closely related species are often incomplete and asymmetric, but the evolutionary significance of these well-known phenomena remains unsolved. We test the hypothesis that the degree of gametic incompatibility in reciprocal crosses is associated to levels of sperm competition because this selective force favors both increased sperm competitiveness and ovum defensiveness. Using three species of Mus with high, intermediate, and low levels of sperm competition, we examined fertilization rates in competitive and noncompetitive contexts. We found that the influence of sperm competition upon sperm competitiveness is as strong as it is upon ovum defensiveness, revealing an effect upon female gametes so far overlooked. As a result, fertilization success was strongly related to differences in sperm competition levels between species providing sperm and ova, thus generating major asymmetries in reciprocal crosses. When placed in competition, conspecific sperm maintained levels of fertilization success similar to those found in noncompetitive contexts, at the expense of the success of heterospecific sperm. When only heterospecific sperm competed, species with highest levels of sperm competition outcompeted others and asymmetries were exacerbated. We conclude that sperm competition explains both the degree of gametic isolation and the degree of asymmetries between closely related species.
亲缘关系较近的物种之间的生殖隔离往往是不完全且不对称的，但这些众所周知的现象的进化意义仍未得到解决。我们检验了这样一个假说：相互杂交中配子不相容的程度与精子竞争水平相关，因为这种选择压力既有利于提高精子竞争力，也有利于增强卵子防御能力。我们利用三种精子竞争水平分别为高、中、低的小家鼠属物种，研究了在竞争和非竞争环境下的受精率。我们发现，精子竞争对精子竞争力的影响与对卵子防御能力的影响一样强烈，这揭示了一种迄今为止被忽视的对雌配子的影响。因此，受精成功率与提供精子和卵子的物种之间精子竞争水平的差异密切相关，从而在正反交中产生了主要的不对称性。当处于竞争状态时，同种精子维持的受精成功率水平与在非竞争环境中相似，但以异种精子的受精成功率为代价。当只有异种精子竞争时，精子竞争水平最高的物种胜过其他物种，不对称性加剧。我们得出结论，精子竞争既解释了配子隔离的程度，也解释了亲缘关系较近的物种之间不对称的程度。
