Evidence for stronger sexual selection in males than females using an adapted method of Bateman's classic study of Drosophila melanogaster

Bateman’s principle, originally a test of Darwin’s theoretical ideas, has since become fundamental to sexual selection theory and vital to contextualising the role of anisogamy and the operational sex ratio in sex differences in both reproductive competition and precopulatory sexual selection. Despite this, Bateman’s principle has received substantial criticism, and researchers have highlighted both statistical and methodological errors, suggesting that Bateman’s original experiment contains too much sampling bias for there to be any evidence of sexual selection. This study uses Bateman’s original method as a template, accounting for two fundamental flaws in his original experiments, (i) viability effects and (ii) a lack of mating behaviour observation. Experimental populations of Drosophila melanogaster consisted of wild-type focal individuals and non-focal individuals established by backcrossing the brown eye (bw-) eye-colour marker. Mating assays included direct observation of mating behaviour and subsequently, total number of offspring were counted, to obtain measures of mating success, reproductive success, and standardised variance measures based on Bateman’s principle. The results provide observational support for Bateman’s principle, particularly that (i) males had significantly more variation in number of mates compared to females and (ii) males had significantly more individual variation in total number of offspring. We also find significantly steeper Bateman gradient for males compared to females, suggesting that sexual selection is operating more intensely in males. However, female remating was limited, providing the opportunity for future study to further explore female reproductive success in correlation with higher levels of remating.