The presence of a rival male affects sperm quality, according to a research study led by the University of Alicante and the University of Upsala (Sweden). The work was carried out with adult zebrafish (Danio rerio) and reveals that male spermatozoa exposed to high competition (two males and a single female) present dramatic changes in phenotype resulting in faster and more competitive spermatozoa. However, this phenotypic plasticity may incur a cost in the next generation as it has negative effects on DNA integrity.