Artificial selection on walking distance suggests a mobility-sperm competitiveness trade-off

Securing matings is a key determinant of fitness and in many species males are the sex that engages in mate searching. Searching for mates is often associated with increased mobility. This elevated investment in movement is predicted to trade-off with sperm competitiveness, but few studies have directly tested whether this trade-off occurs. Here, we assessed whether artificial selection on mobility affected sperm competitiveness and mating behavior, and if increased mobility was due to increased leg length in red flour beetles (Tribolium castaneum). We found that in general, males selected for decreased mobility copulated for longer, stimulated females more during mating and tended to be better sperm competitors. Surprisingly, they also had longer legs. However, how well males performed in sperm competition depended on females. Males with reduced mobility always copulated for longer than males with high mobility, but this only translated into greater fertilization success in females fr...成功交配是决定个体适合度（fitness）的关键因素，在多数物种中，雄性是开展配偶搜寻的性别。配偶搜寻通常与移动能力的提升相关联。学界普遍预测，这种对运动投入的增加，会与精子竞争力（sperm competitiveness）存在权衡关系，但目前鲜有研究直接验证该权衡是否真实存在。本研究以赤拟谷盗（Tribolium castaneum）为实验材料，探究了针对移动能力的人工选择是否会影响精子竞争力与交配行为，以及移动能力的提升是否由腿长增加所致。研究结果显示，总体而言，经人工选择降低移动能力的雄性，其交配时长更长，交配过程中对雌性的刺激更强，且往往具备更优的精子竞争力。令人意外的是，这类雄性的腿长同样更长。不过，雄性在精子竞争中的表现优劣取决于雌性个体：移动能力降低的雄性，其交配时长始终长于高移动能力雄性，但该优势仅能在雌性……中转化为更高的受精成功率。