Cameron Elissa Z, Linklater Wayne L
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
Biol Lett. 2007 Aug 22;3(4):395-7. doi: 10.1098/rsbl.2007.0089.
Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. Studies investigating sex ratio variation in mammals have produced notoriously inconsistent results, although recent studies suggest more consistency if sex ratio variation is related to maternal condition at conception, potentially mediated by changes in circulating glucose level. Consequently, we hypothesized that change in condition might better predict sex ratio variation than condition per se. Here, we investigate sex ratio variation in feral horses (Equus caballus), where sex ratio variation was previously shown to be related to maternal condition at conception. We used condition measures before and after conception to measure the change in condition around conception in individual mothers. The relationship with sex ratio was substantially more extreme than previously reported: 3% of females losing condition gave birth to a son, whereas 80% of those females that were gaining condition gave birth to a son. Change in condition is more predictive of sex ratio than actual condition, supporting previous studies, and shows the most extreme variation in mammals ever reported.
适应性理论预测，母亲若能根据后代未来的繁殖成功率来调整后代的性别比例，将更具优势。尽管近期研究表明，如果性别比例的变化与受孕时的母体状况相关，且可能由循环葡萄糖水平的变化介导，那么这种变化会更具一致性，但调查哺乳动物性别比例变化的研究结果一直以来都极不一致。因此，我们推测，状况的变化可能比状况本身更能预测性别比例的变化。在此，我们研究了野马（Equus caballus）的性别比例变化，此前已表明其性别比例变化与受孕时的母体状况有关。我们使用受孕前后的状况指标来衡量个体母亲受孕前后的状况变化。与性别比例的关系比之前报道的更为极端：状况变差的雌性中有3%生下了雄性后代，而状况变好的雌性中有80%生下了雄性后代。与实际状况相比，状况变化更能预测性别比例，这支持了之前的研究，并且显示出哺乳动物中迄今报道的最极端的变化。
