Male-male behavioral interactions drive social-dominance mediated differences in ejaculate traits

Higher social status is expected to result in fitness benefits as it secures access to potential mates. In promiscuous species, male reproductive success is also determined by an individual’s ability to compete for fertilization after mating by producing high quality ejaculates. However, the complex relationship between a male’s investment in social status and ejaculates remains unclear. Here we examine how male social status influences ejaculate quality under a range of social contexts in the pygmy halfbeak Dermogenys cf. collettei, a small, group-living, internally fertilizing freshwater fish. We show that male social status influences ejaculate traits, both in the presence and absence of females. Dominant males produced faster swimming and more viable sperm, two key determinants of ejaculate quality, but only under conditions with frequent male-male behavioral interactions. When male-male interactions were experimentally reduced through the addition of a refuge, differences in ejacul...