The few motile SPZ exhibited severely impaired swimming [average path velocity (VAP) = 42.5 vs. 137.1 μM/s for WT mice; straight-line velocity (VSL) = 25.8 vs. 115.4 μM/s; curvilinear velocity (VCL) = 77.2 vs. 232.6 μM/s; amplitude of lateral head displacement (ALH) = 5.6 vs. 11.2 μM], concluding that Ankrd31 gene deletion induced severe asthenozoospermia (Supplementary Videos 1,2). This evidence concerns the gene ANKRD31 and Reduced sperm motility.