Thuman Katherine A, Widemo Fredrik, Griffith Simon C
Department of Animal Ecology, EBC, Uppsala University, Norbyvägen 18d, SE-752 36, Uppsala, Sweden.
Mol Ecol. 2003 Jan;12(1):213-8. doi: 10.1046/j.1365-294x.2003.01717.x.
Sex allocation theory predicts that females should bias the production of offspring towards the sex that will maximize maternal fitness. Here we demonstrate evidence for nonrandom sex allocation by female ruffs (Philomachus pugnax), at both the individual and population level in relation to female condition. At the population level, female condition varies significantly across 3 years and is mirrored by population sex ratio, such that in years when females are in poor condition the population offspring sex ratio is female-biased, while in years when females are in better condition there was little or no bias. In the year when females were in overall poor condition, females in better condition produced more daughters. The same relationship is also revealed by comparing the sex ratios of individual females breeding in two consecutive years in different condition. As the condition of an individual female improves (across years) she tends to produce more female offspring. Although we have shown that, as in other birds, female condition is an important determinant of sex allocation, our results also suggest that such nonrandom allocation does not occur in every year, being particularly strong in a year when females, on average, are in poorer condition. We suggest that our results are consistent with the idea that skewing the sex ratio is likely to carry a cost to females and that it is adaptive only when the fitness differential between sons and daughters is sufficient to outweigh probable costs.
性分配理论预测，雌性应该将后代的生产偏向于能使母体适应性最大化的性别。在此，我们展示了雌性流苏鹬（Philomachus pugnax）在个体和种群水平上与雌性身体状况相关的非随机性别分配的证据。在种群水平上，雌性身体状况在3年中差异显著，且与种群性别比相对应，即当雌性身体状况较差时，种群后代性别比偏向雌性，而当雌性身体状况较好时，几乎没有或不存在偏向。在雌性总体身体状况较差的年份，身体状况较好的雌性会生育更多的雌性后代。通过比较处于不同身体状况的雌性连续两年繁殖的性别比，也揭示了同样的关系。随着个体雌性身体状况的改善（跨年度），她往往会生育更多的雌性后代。尽管我们已经表明，与其他鸟类一样，雌性身体状况是性别分配的一个重要决定因素，但我们的结果也表明，这种非随机分配并非每年都会发生，在雌性平均身体状况较差的年份尤其明显。我们认为，我们的结果与这样一种观点一致，即偏向性别比可能会给雌性带来代价，并且只有当儿子和女儿之间的适应性差异足以超过可能的代价时，这种偏向才是适应性的。
