University College, London, UK.
The Natural History Museum, London, UK.
BMC Ecol Evol. 2022 Sep 11;22(1):107. doi: 10.1186/s12862-022-02060-3.
Sexual selection is thought to be an important driver of adaptation, speciation and extinction. Empirically testing these predictions across macroevolutionary timescales first requires an understanding of the morphology of secondary sexual traits in extant taxa. We used three-dimensional geometric morphometrics to analyse a large sample of the skull of the blue wildebeest, Connochaetes taurinus, in which horns are found in both sexes but only used in intrasexual competition in males. We show that the horns fit several predictions of secondary sexual traits; overall skull shape is significantly correlated with size (R = 0.38, p = 0.001), and the sexually selected horns show drastically higher growth rates and variation than any other skull element, supporting previous findings. We also find that despite showing significant sexual dimorphism in shape and size (R = 0.21, p = 0.001), allometric growth trajectories of sexes are identical (R = 0.01, p = 0.635) and dimorphism is not readily detectable without prior knowledge of sex, and is not possible when shape is corrected for size. Our results show that even with strong sexual selection operating in only one sex, the expression of secondary sexual traits may show characteristic and indistinguishable patterns of growth and variance in both sexes.
性选择被认为是适应、物种形成和灭绝的重要驱动因素。要在宏观进化时间尺度上验证这些预测，首先需要了解现存分类单元中次要性征的形态。我们使用三维几何形态测量法分析了大量蓝角马（Connochaetes taurinus）的头骨样本，其中雌雄两性都有角，但只有雄性在同性竞争中使用角。我们发现，这些角符合几个次要性征的预测；整体头骨形状与大小显著相关（R=0.38，p=0.001），而性选择的角比任何其他头骨元素都表现出更高的生长率和变异，这与之前的研究结果一致。我们还发现，尽管在形状和大小上表现出显著的性别二态性（R=0.21，p=0.001），但两性的生长轨迹完全相同（R=0.01，p=0.635），如果没有事先了解性别，就无法轻易检测到二态性，而且在大小校正后，二态性也无法检测到。我们的研究结果表明，即使在只有一种性别受到强烈性选择的情况下，次要性征的表达也可能在两性中表现出特征性且难以区分的生长和变异模式。
