Sexual selection and sperm competition in the guppy ( Poecilia reticulata)

When differences among individuals in the ability to acquire mates result in evolutionary change, this is known as sexual selection. My goal was to investigate sexual selection on male traits in the guppy (Poecilia reticulata). I assessed reproductive skew and correlates of male reproductive success in a wild population and found that male reproductive success was strongly skewed and correlated with gonopodium length, but not with the relative area of coloured spots, body length, or sperm velocity. I then determined the role of sperm competition in shaping sperm form and function by comparing sperm traits across populations. I found that males in high predation populations, which presumably experience more intense sperm competition, had significantly faster sperm with longer midpieces than males in low predation populations, which experience less intense sperm competition. These results suggest that gonopodium length is a sexually selected trait and that sperm competition selects for sperm velocity