Determinants of male fitness: disentangling intra‐ and inter‐sexual selection

Both intra‐ and inter‐sexual selection may crucially determine a male’s fitness. Their interplay, which has rarely been experimentally investigated, determines a male’s optimal reproductive strategy and thus is of fundamental importance to the understanding of a male’s behaviour. Here we investigated the relative importance of intra‐ and inter‐sexual selection for male fitness in the common lizard. We investigated which male traits predict a male’s access to reproduction allowing for both selective pressures and comparing it with a staged mating experiment excluding all types of intra‐sexual selection. We found that qualitatively better males were more likely to reproduce and that sexual selection was two times stronger when allowing for both selective pressures, suggesting that inter‐ and intra‐sexual selection determines male fitness and confirming the existence of multi‐factorial sexual selection. Consequently, to optimize fitness, males should trade their investment between the traits, which are important for inter‐ and intra‐sexual selection.