Evolution to increase ejaculate volume in the presence of sperm competition has a consequence on testis size. Large testes can produce more sperm required for larger ejaculates, and can be found across the animal kingdom when sperm competition occurs. Males with larger testes have been documented to achieve higher reproductive success rates than males with smaller testes in male yellow pine chipmunks. In chichlid fish, it has been found that increased sperm competition can lead to evolved larger sperm numbers, sperm cell sizes, and sperm swimming speeds.