A nonsemen copulatory fluid influences the outcome of sperm competition in Japanese quail.

Sperm competition is a powerful and widespread evolutionary force that drives the divergence of behavioral, physiological, and morphological traits. Elucidating the mechanisms governing differential fertilization success is a fundamental question of sperm competition. Both sperm and non-sperm ejaculate components can influence sperm competition outcomes. Here, we investigate the role of a non-semen copulatory fluid in sperm competition. Male Japanese quail possess a gland that makes meringue-like foam. Males produce and store foam independent of sperm and seminal fluid, yet transfer foam to females during copulation. We tested whether foam influenced the outcome of sperm competition by varying foam state and mating order in competitive matings. We found that the presence of foam from one male decreased the relative fertilization success of a rival, and that foam from a given male increased the probability he obtained any fertilizations. Mating order also affected competitive success. Ma...