Data from: A method for estimating population sex ratio for sage-grouse using noninvasive genetic samples

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 feces, 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) fecal samples, examined how success and error rates for sex identification changed in response to fecal sample exposure time, and used simulation models to evaluate precision and bias of 3 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 fecal DNA for estimating the sex ratio of sage-grouse populations has great potential and, with minor adaptations, should be applicable to numerous species.

种群性比是野生动物管理与保护领域的重要指标，但性比估计往往难以获取，尤其是针对雌雄同形物种，或是雌雄个体探测概率存在差异的物种。利用聚合酶链式反应（polymerase chain reaction, PCR）开展的非损伤性遗传采样（Noninvasive genetic sampling, NGS）已成为通过毛发、羽毛或粪便等样本鉴定物种性别的常用方法，同时也是估算种群性比的潜在途径。但若聚合酶链式反应的扩增成功率存在性别偏倚，直接使用非损伤性遗传采样数据可能会导致性比估计结果出现偏差。本研究以艾草松鸡（greater sage-grouse, Centrocercus urophasianus）的粪便样本为研究对象，测定了其W和Z染色体的扩增成功率与错误率，分析了性别鉴定的成功率与错误率随粪便样本环境暴露时长的变化规律，并通过模拟模型评估了3种性别判定准则在不同样本量与聚合酶链式反应重复次数下，种群性比估计的精度与偏差。研究发现，雌性样本的聚合酶链式反应扩增成功率高于雄性，且性别判定准则的选择会显著影响对应性比估计结果的偏差与精度。本研究的模拟结果表明，在设计未来相关研究时，需综合考量聚合酶链式反应成功率的性别偏倚、基因分型重复次数、样本量、真实种群性比以及性别判定规则的准确性之间的相互作用，这一点至关重要。本研究结果显示，利用粪便DNA估算艾草松鸡种群性比具有极大应用潜力，经小幅优化后，该方法可推广应用于众多其他物种。