Smirnov Georgii Yu, Shkurikhin Alexey O, Davydova Yulia A, Vorobeichik Evgenii L
Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia.
J Exp Zool A Ecol Integr Physiol. 2025 Nov;343(9):1031-1048. doi: 10.1002/jez.70016. Epub 2025 Jul 24.
Despite its potential significance for male fertility, bilateral testicular asymmetry in vertebrates remains poorly understood. Fluctuating asymmetry (FA), which serves as an indicator of stochastic developmental variation, constitutes a crucial yet frequently overlooked aspect of phenotypic variability. Although FA is commonly examined in morphological traits, its measurement in functional testicular traits has not been previously conducted due to methodological constraints. We analyzed FA in epididymal sperm motility (curvilinear velocity, VCL) and sperm concentration (SEC) in reproductively mature male bank voles (Clethrionomys glareolus, n = 61) from wild populations using Computer-Aided Sperm Analysis (CASA). Parallel measurements of "soft" (testis and kidney mass) and "hard" (mandibular dimensions) morphological traits were performed for comparison. CASA showed reliable reproducibility (VCL: 0.89; SEC: 0.73), enabling accurate FA quantification and confirming the absence of directional asymmetry or antisymmetry. Functional traits exhibited remarkably high FA values: 12% of the mean trait value for VCL and 30% for SEC, which is an order of magnitude greater than that of morphological traits. FA accounted for one-quarter (VCL) to one-half (SEC) of the total variation, representing two to three times the corresponding proportions of morphological traits. These elevated FA levels suggest that within-individual left/right differences may surpass between-individual variation. Our findings underscore the importance of (1) conducting repeated bilateral measurements for accurate FA quantification in testicular function and (2) utilizing averaged data from both testes for population-level analyses. These findings have significant practical implications for physiological and ecotoxicological research using rodent models, in which epididymal sperm analysis is standard practice, highlighting the necessity of considering functional asymmetry to prevent biased conclusions.
尽管双侧睾丸不对称对雄性生育能力具有潜在重要意义，但脊椎动物中这一现象仍未得到充分了解。波动不对称性（FA）作为随机发育变异的指标，是表型变异的一个关键但常被忽视的方面。虽然FA通常在形态特征中进行检测，但由于方法上的限制，此前尚未对功能性睾丸特征进行测量。我们使用计算机辅助精子分析（CASA），分析了来自野生种群的生殖成熟雄性林姬鼠（Clethrionomys glareolus，n = 61）附睾精子活力（曲线速度，VCL）和精子浓度（SEC）中的FA。同时对“软”（睾丸和肾脏质量）和“硬”（下颌尺寸）形态特征进行平行测量以作比较。CASA显示出可靠的可重复性（VCL：0.89；SEC：0.73），能够准确量化FA，并确认不存在方向不对称或反不对称。功能特征表现出非常高的FA值：VCL为平均特征值的12%，SEC为30%，这比形态特征高一个数量级。FA占总变异的四分之一（VCL）到二分之一（SEC），是形态特征相应比例的两到三倍。这些升高的FA水平表明个体内左右差异可能超过个体间差异。我们的研究结果强调了（1）进行重复双侧测量以准确量化睾丸功能中的FA，以及（2）使用来自两个睾丸的平均数据进行种群水平分析的重要性。这些发现对使用啮齿动物模型的生理和生态毒理学研究具有重要的实际意义，在这些研究中附睾精子分析是标准做法，突出了考虑功能不对称以防止得出有偏差结论的必要性。
