Am Nat. 2020 Aug;196(2):180-196. doi: 10.1086/709547. Epub 2020 Jun 16.
Sexual selection studies widely estimate several metrics, but values may be inaccurate because standard field methods for studying wild populations produce limited data (e.g., incomplete sampling, inability to observe copulations directly). We compared four selection metrics (Bateman gradient, opportunity for sexual selection, opportunity for selection, and ) estimated with simulated complete and simulated limited data for 15 socially monogamous songbird species with extrapair paternity (4%-54% extrapair offspring). Inferring copulation success from offspring parentage creates nonindependence between these variables and systematically underestimates copulation success. We found that this introduces substantial bias for the Bateman gradient, opportunity for sexual selection, and . Notably, 47.5% of detected Bateman gradients were significantly positive for females, suggesting selection on females to copulate with multiple males, although the true Bateman gradient was zero. Bias generally increased with the extent of other sources of data limitations tested (nest predation, male infertility, and unsampled floater males). Incomplete offspring sampling introduced bias for all of the metrics except the Bateman gradient, while incomplete sampling of extrapair sires did not introduce additional bias when sires were a random subset of breeding males. Overall, our findings demonstrate how biases due to field data limitations can strongly impact the study of sexual selection.
性选择研究广泛估计了几种指标，但由于研究野生种群的标准野外方法产生的数据有限（例如，采样不完整，无法直接观察交配），因此数值可能不准确。我们比较了四种选择指标（Bateman 梯度、性选择机会、选择机会和），这些指标是根据 15 种具有婚外配的社会性一夫一妻制鸣禽物种的模拟完整数据和模拟有限数据估计的，这些物种的婚外后代比例为 4%-54%。从后代的亲代推断交配成功率会导致这些变量之间的非独立性，并系统地低估交配成功率。我们发现，这对 Bateman 梯度、性选择机会和 都产生了很大的偏差。值得注意的是，47.5%的雌性 Bateman 梯度显著为正，表明雌性有选择与多个雄性交配的倾向，尽管真正的 Bateman 梯度为零。随着测试的其他数据限制来源（巢捕食、雄性不育和未采样的游荡雄性）的严重程度增加，偏差通常会增加。除了 Bateman 梯度外，所有指标的不完全后代采样都会引入偏差，而当雄性是繁殖雄性的随机子集时，对婚外雄性的不完全采样不会引入额外的偏差。总的来说，我们的研究结果表明，由于野外数据限制引起的偏差会如何强烈影响性选择的研究。
