| Summary: | 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 males' sperm in freshwater spawners, but longer than bourgeois males' sperm in saltwater spawners. These results highlight a need to take spawning salinity into account in intraspecific as well as interspecies comparisons of adaptations to sperm competition in external fertilizers. Key of definitions of variable names, column headings and row labels: Species: The species of the study and for Salmo salar study location Salinity: The salinity in which sperm longevity was measured (same as male native salinity) Temperature: The temperature in which sperm longevity was measured ART_highest_longevity: which of the two alternative reprocuctive tactics which has significantly higher sperm longevity than the other. Sneaker = sneaker male and dominant = dominant male. NS = no significant difference Longevity_sneaker_s: Sperm longevity of sneaker males Longevity_dominant_s: Sperm longevity of dominant males Longevity_sneak_log10: Sperm longevity of sneaker males log10 transformed Longevity_dominant_log10: Sperm longevity of dominant ...
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