Sneaker "jack" males outcompete dominant "hooknose" males under sperm competition in Chinook salmon (Oncorhynchus tshawytscha).
In a variety of taxa, males deploy alternative reproductive tactics to secure fertilizations. In many species, small "sneaker" males attempt to steal fertilizations while avoiding encounters with larger, more aggressive, dominant males. Sneaker males usually face a number of disadvantages, including reduced access to females and the higher likelihood that upon ejaculation, their sperm face competition from other males. Nevertheless, sneaker males represent an evolutionarily stable strategy under a wide range of conditions. Game theory suggests that sneaker males compensate for these disadvantages by investing disproportionately in spermatogenesis, by producing more sperm per unit body mass (the "fair raffle") and/or by producing higher quality sperm (the "loaded raffle"). Here, we test these models by competing sperm from sneaker "jack" males against sperm from dominant "hooknose" males in Chinook salmon. Using two complementary approaches, we reject the fair raffle in favor of the loaded raffle and estimate that jack males were ∼1.35 times as likely as hooknose males to fertilize eggs under controlled competitive conditions. Interestingly, the direction and magnitude of this skew in paternity shifted according to individual female egg donors, suggesting cryptic female choice could moderate the outcomes of sperm competition in this externally fertilizing species.
Molecular and Computational Biology, University of Southern California Ray R. Irani Building room 304A, 1050 Childs Way, Los Angeles, California, 90089.
Brent
B
Young
Department of Preventive Medicine, Keck School of Medicine, University of Southern California 2001 N. Soto Street 202S, Los Angeles, California, 90089.
David V
DV
Conti
Molecular and Computational Biology, University of Southern California Ray R. Irani Building room 304A, 1050 Childs Way, Los Angeles, California, 90089.
Matthew D
MD
Dean
Hooknose; jack; salmon; sexual selection; sneaker male; sperm competition