Data from: Testing the phenotype-linked fertility hypothesis in the presence and absence of inbreeding

The phenotype-linked fertility hypothesis suggests that females can judge male fertility by inspecting male phenotypic traits. This is because male sexually selected traits might correlate with sperm quality if both are sensitive to factors that influence male condition. A recent meta-analysis found little support for this hypothesis, suggesting little or no shared condition dependence. However, we recently reported that in captive zebra finches (Taeniopygia guttata) inbreeding had detrimental effects both on phenotypic traits and on measures of sperm quality, implying that variation in inbreeding could induce positive covariance between indicator traits and sperm quality. Therefore, we here assess empirically the average strength of correlations between phenotypic traits (courtship rate, beak colour, tarsus length) and measures of sperm quality (proportion of functional sperm, sperm velocity, sperm length) in populations of only outbred individuals and in mixed populations consisting of inbreds (F=0.25) and outbreds (F=0). As expected, phenotype sperm-trait correlations were stronger when the population contained a mix of inbred and outbred individuals. We also found unexpected heterogeneity between our two study populations, with correlations being considerably stronger in a domesticated population than in a recently wild-derived population. Correlations ranged from essentially zero among outbred-only wild-derived birds (mean Fisher's Zr±SE=0.03±0.10) to moderately strong among domesticated birds of mixed inbreeding status (Zr±SE=0.38±0.08). Our results suggest that, under some conditions, the phenotype-linked fertility hypothesis might apply.

表型关联生育力假说（phenotype-linked fertility hypothesis）认为，雌性可通过观察雄性的表型特征判断其生育能力。这是因为若雄性性选择特征与精子质量均对影响雄性自身状态的因素敏感，则二者可能存在相关性。近期一项元分析（meta-analysis）未为本假说提供多少支持，表明二者几乎不存在共同的状态依赖性。不过，我们此前的研究发现，圈养斑胸草雀（Taeniopygia guttata）的近交对其表型特征与精子质量指标均存在不利影响，这意味着近交程度的差异可诱导指示特征与精子质量之间产生正协方差。因此，本研究通过实验评估了两类种群中表型特征（求偶率、喙色、跗跖长度）与精子质量指标（功能性精子占比、精子活力、精子长度）之间相关性的平均强度：一类为仅包含远交个体的种群，另一类为包含近交个体（F=0.25）与远交个体（F=0）的混合种群。正如预期，当种群包含近交与远交混合个体时，表型与精子特征间的相关性更强。我们还发现两个研究种群间存在未预期的异质性：驯化种群中的相关性显著强于近期源自野生的种群。相关性范围从仅含远交个体的野生源种群中几乎为零（平均费舍尔Zr转换值±标准误=0.03±0.10），到近交状态混合的驯化种群中达到中等强度（Zr±SE=0.38±0.08）。本研究结果表明，在部分条件下，表型关联生育力假说或许成立。