Sperm longevity and salinity – the overlooked importance of spawning environment for alternative reproductive tactics

Studies on adaptive responses to sperm competition have focused on mating modes and mating roles. The main mating modes studied are external and internal fertilization and spermcasting. The focus of male mating roles assumes one advantageous ‘bourgeois’ role and another disadvantageous ‘parasitic’ role regarding the probability of fertilization. However, sperm longevity between teleost fishes spawning in hypoosmotic freshwater and species spawning in hyperosmotic saltwater differs markedly. We argue that this can have major impacts on sperm adaptations in relation to sperm competition, due to physiological constraints and different outcomes of trade-offs. To test this hypothesis, we extracted sperm longevity data from studies on species with alternative reproductive tactics. We show that spawning salinity affects sperm longevity by orders of magnitudes and that this affects the direction in which male tactics differ in sperm longevity: parasitic males’ sperm lived shorter than bourgeois...