Multiple male reproductive morphs in the invasive round goby (Apollonia melanostoma)

Alternative male reproductive tactics are taxonomically widespread. In such species, parental, or conventional, males express secondary sexual characteristics, court females and guard offspring, while smaller parasitic or sneaker males avoid the costs of courtship and parental care by performing sneak fertilizations. Theory predicts that sneakers will invest more in testes mass and produce more competitive ejaculates than parentals because …