Data from: Genetic versus census estimators of the opportunity for sexual selection in the wild

The existence of a direct link between intensity of sexual selection and mating system type is widely accepted. However, the quantification of sexual selection has proven problematical. Several measures of sexual selection have been proposed, including the operational sex ratio (OSR), breeding sex ratio (BSR) and opportunity for sexual selection (Imates). For a wild population of pronghorn (Antilocapra americana), we calculated OSR and BSR. We estimated Imates from census data on the spatial and temporal distribution of receptive females in rut and from a multi-generational genetic pedigree. OSR and BSR indicated weak sexual selection on males, but census and pedigree Imates suggested stronger sexual selection on males than on females. OSR and BSR correlated with census but not pedigree estimates of Imates, and census Imates did not correlate with pedigree estimates. This suggests that the behavioral mating system, as deduced from the spatial and temporal distribution of females, does not predict the genetic mating system of pronghorn. The differences we observed between estimators were primarily due to female mate sampling and choice, and the sex ratio. For most species, behavioral data is not perfectly accurate, and therefore will be an insufficient alternative to using multi-generational pedigrees to quantify sexual selection.

性选择强度与交配系统类型间存在直接关联，这一论断已获广泛认可。然而，性选择的量化工作却始终存在挑战。目前学界已提出多种性选择量化指标，包括有效性别比（operational sex ratio, OSR）、繁殖性别比（breeding sex ratio, BSR）以及性选择机会（opportunity for sexual selection, Imates）。本研究针对野生叉角羚（Antilocapra americana）种群，计算了其OSR与BSR数值；并基于发情期接受交配雌性的时空分布普查数据，结合多代遗传谱系数据，估算了性选择机会Imates。结果显示，OSR与BSR表明雄性所受性选择较弱，但普查数据与谱系数据得到的Imates则显示，雄性面临的性选择强度显著高于雌性。进一步分析发现，OSR与BSR与普查得到的Imates估算值呈显著相关，但与谱系估算的Imates并无关联；同时普查所得Imates与谱系估算值之间也不存在相关性。这表明，通过雌性时空分布推导得出的行为交配系统，无法准确预测叉角羚的遗传交配系统。不同估算方法间的结果差异，主要源于雌性的配偶取样与选择行为，以及性别比例因素。对于多数物种而言，行为数据并不完全准确，因此无法替代多代遗传谱系数据，用于性选择的量化研究。