Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5E2
Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
Proc Biol Sci. 2018 Nov 21;285(1891):20181251. doi: 10.1098/rspb.2018.1251.
Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels () that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.
费希尔原理解释了，由于负频率依赖选择，有性繁殖生物的种群性别比例维持在 1:1，即稀有性别的个体比更常见性别的个体实现更大的生殖机会，直到达到平衡。如果使后代性别比例偏向稀有性别是适应性的，那么这样做的个体应该有更多的孙代。在一个经历资源丰度和种群密度波动的北美的红松鼠（）的野生种群中，我们表明，在 26 年的时间里，总体上第二性比为 1:1；然而，在成年性别比例偏向某一性别的年份中，并没有产生偏向稀有性别的后代性别比例。使后代性别比例偏向稀有性别的雌性没有更多的孙代。至关重要的是，成年性别比例在不同年份之间没有时间自相关，因此父母经历的种群性别比例与它们在初次繁殖时经历的后代种群性别比例无关。使后代性别比例偏向某一性别的预期适应性收益可能会被多年来波动的环境所掩盖或抵消，这限制了当前性别比例的预测价值。
