Fish and Wildlife Sciences, University of Idaho, Moscow, ID 83844, USA.
Mol Ecol Resour. 2013 May;13(3):393-402. doi: 10.1111/1755-0998.12069. Epub 2013 Jan 25.
Population sex ratio is an important metric for wildlife management and conservation, but estimates can be difficult to obtain, particularly for sexually monomorphic species or for species that differ in detection probability between the sexes. Noninvasive genetic sampling (NGS) using polymerase chain reaction (PCR) has become a common method for identifying sex from sources such as hair, feathers or faeces, and is a potential source for estimating sex ratio. If, however, PCR success is sex-biased, naively using NGS could lead to a biased sex ratio estimator. We measured PCR success rates and error rates for amplifying the W and Z chromosomes from greater sage-grouse (Centrocercus urophasianus) faecal samples, examined how success and error rates for sex identification changed in response to faecal sample exposure time, and used simulation models to evaluate precision and bias of three sex assignment criteria for estimating population sex ratio with variable sample sizes and levels of PCR replication. We found PCR success rates were higher for females than males and that choice of sex assignment criteria influenced the bias and precision of corresponding sex ratio estimates. Our simulations demonstrate the importance of considering the interplay between the sex bias of PCR success, number of genotyping replicates, sample size, true population sex ratio and accuracy of assignment rules for designing future studies. Our results suggest that using faecal DNA for estimating the sex ratio of sage-grouse populations has great potential and, with minor adaptations and similar marker evaluations, should be applicable to numerous species.
种群性别比例是野生动物管理和保护的一个重要指标，但估计可能很困难，特别是对于性二态性物种或雌雄两性之间检测概率存在差异的物种。聚合酶链反应（PCR）的非侵入性遗传采样（NGS）已成为从毛发、羽毛或粪便等来源识别性别的常用方法，也是估计性别比例的潜在来源。然而，如果 PCR 成功率存在性别偏倚，那么简单地使用 NGS 可能会导致性别比例估计值出现偏差。我们测量了从大角羊（Centrocercus urophasianus）粪便样本中扩增 W 和 Z 染色体的 PCR 成功率和错误率，研究了性别鉴定的成功率和错误率如何随粪便样本暴露时间的变化而变化，并使用模拟模型评估了三种性别分配标准在不同样本量和 PCR 重复水平下估计种群性别比例的精度和偏差。我们发现雌性的 PCR 成功率高于雄性，并且性别分配标准的选择会影响相应性别比例估计的偏差和精度。我们的模拟结果表明，在设计未来研究时，考虑到 PCR 成功率的性别偏倚、基因分型重复次数、样本量、真实种群性别比例和分配规则的准确性之间的相互作用非常重要。我们的结果表明，使用粪便 DNA 估计大角羊种群的性别比例具有很大的潜力，并且只需进行微小的调整和类似的标记评估，就应该适用于许多物种。
