Rapid protamine evolution suppresses meiotic drive in .

Many animal species replace histones with protamines during spermatogenesis. Despite their importance for sperm function, protamines rapidly evolve in many species; the biological causes behind their rapid evolution remain unknown. Here, using gene replacement, we investigated the causes and consequences underlying the rapid evolution of protamine , which is essential for male fertility in . ortholog replacements led to defects in DNA compaction of X-chromosome-bearing sperm compared to Y-chromosome-bearing sperm during spermatogenesis, resulting in fewer X-bearing mature sperm and male-biased progeny. Unlike , is not essential for male fertility in but is still required to suppress sex-ratio distortion. Our results suggest that relentless pressure to suppress sex chromosomal meiotic drive drives the rapid evolution of protamines.