Ellegren H, Gustafsson L, Sheldon B C
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala Biomedical Centre, Uppsala, Sweden.
Proc Natl Acad Sci U S A. 1996 Oct 15;93(21):11723-8. doi: 10.1073/pnas.93.21.11723.
When the relative fitness of sons and daughters differs, sex-allocation theory predicts that it would be adaptive for individuals to adjust their investment in different sexes of offspring. Sex ratio adjustment by females in response to the sexual attractiveness of their mate would be an example of this. In vertebrates the existence of this form of sex ratio adjustment is controversial and may be confounded with sex-biased mortality, particularly in sexually size-dimorphic species. Here we use PCR amplification of a conserved W-chromosome-linked gene to show that the sex ratio within broods of a natural population of sexually size-monomorphic collared flycatchers Ficedula albicollis is related to the size of their father's forehead patch, a heritable secondary sexual character implicated in female choice. Experimental manipulations of paternal investment, which influence the size of his character in future breeding attempts, result in corresponding changes in the sex ratio of offspring born to males in those breeding attempts. In contrast, manipulations of maternal investment have no effect on future sex ratios, and there is no relationship between variables predicting the reproductive value of the brood and nestling sex ratio. Analysis of recruitment of offspring reveals similar patterns of sex ratio bias. The results suggest that female collared flycatchers be able to adjust the sex ratio of eggs ovulated in response to the phenotype of their mate. This finding is most consistent with "genetic quality" models of sexual selection.
当儿子和女儿的相对适合度不同时，性分配理论预测，个体调整对不同性别的后代投资将是一种适应性行为。雌性根据配偶的性吸引力来调整性别比例就是一个例子。在脊椎动物中，这种性别比例调整形式的存在存在争议，并且可能与性别偏向的死亡率混淆，特别是在两性体型二态性物种中。在这里，我们通过对一个保守的W染色体连锁基因进行PCR扩增，表明性体型单态的白领姬鹟自然种群的窝内性别比例与其父亲前额斑块的大小有关，前额斑块是一种与雌性选择有关的可遗传的第二性征。对父本投资的实验性操作会影响其在未来繁殖尝试中的性状大小，从而导致这些繁殖尝试中雄性所产后代的性别比例发生相应变化。相比之下，对母本投资的操作对未来的性别比例没有影响，并且预测窝的繁殖价值的变量与雏鸟性别比例之间没有关系。对后代招募情况的分析揭示了类似的性别比例偏差模式。结果表明，白领姬鹟雌性能够根据配偶的表型来调整排卵的性别比例。这一发现与性选择的“遗传质量”模型最为一致。
